Analysis of Harms from Fishing with Insecticide-Treated Nets

Published: March 2025

Summary

Basics

There is a concern that insecticide-treated nets (ITNs) distributed for malaria prevention are sometimes used for fishing instead. This could be problematic for several reasons:

• It may lead to fewer nets being used for malaria protection.
• Using ITNs for fishing may contribute to reduced fish stocks, which could lead to harms to household nutrition or negative economic impacts.
• Fishing with ITNs may contaminate fish with insecticides, posing risks to human health.
• Discarding used ITNs in waterways could pollute aquatic ecosystems.

Understanding these potential harms is important because they could affect the overall cost-effectiveness of ITN distributions. We have looked into this issue previously2 but decided to conduct a deeper investigation, partly in response to recent criticism3 and in light of our plans to make large grants for ITN campaigns in DRC and Nigeria.

How big is this issue?

We think harms from ITN fishing have very little impact on the overall cost-effectiveness of our net campaign grants (reducing cost-effectiveness by under a percent). However, we think there are some rare “hot spots” where the use of ITNs for fishing may be more harmful and can potentially reduce cost-effectiveness by about 60%.

We’re moderately confident that overall, any potential harms of fishing are far outweighed by the effect of ITNs on mortality from mosquito-borne malaria. However, for hot spots, we're much less certain. Our estimates rely on extrapolations from limited surveys in fishing communities, mathematical models of fish population dynamics, and arguments from first principles, rather than direct evidence of worse outcomes in areas with high ITN fishing rates. This makes us particularly uncertain about the magnitude of effects in these areas.

Intuitively, we think this is unlikely to be a major issue in the average area because: (more)

• We think the harms from fishing with ITNs are likely to be limited. That’s because:
  • We estimate a small reduction in fishing yields due to overfishing with ITNs. Our best guess is that each ITN campaign causes a small (~2%) reduction in fish stocks over ~5 years, which we expect will decrease future fishing yields by a similar amount. This is primarily due to increased fishing intensity (more) and ecosystem disruption from small mesh sizes (more). We assume that while ~25% of fishers use distributed ITNs for fishing (more), ITN fishing is more common among smaller-scale fishers (more), some fishers would use other gears if ITNs weren’t available (more), and not all fisheries are overfished and vulnerable to an impact of ITNs on fish stocks (more). These estimates are based on 9 likely non-representative and highly variable4 surveys of how many people use ITNs to fish in areas where nets are distributed5 , fish stock assessments in 16 large marine fishing areas from a single source (the FAO), and several qualitative research studies, including a non-random online survey of fishery experts, interviews and focus group discussions about ITN fishing in sub-Saharan African countries, and descriptions of common fishing gears used in Madagascar from a research presentation. (more)
  • We estimate a small share (<5%) of total protein consumption across sub-Saharan Africa comes from fish, limiting the impact that reduced yields have on malnutrition. This is based on estimates of total food consumption by source from the FAO’s food balance sheets. (more). We guess other harms of reduced fish yield, such as economic harms, are also limited for similar reasons (more).
  • We think other harms of ITN fishing are likely smaller than the harms from reduced fishing yields. (more) We investigated two other harms, but consider them to be less impactful:
    • Consumption of pyrethroids (a family of insecticides used to treat ITNs) from drinking or eating fish from ITN-fished water. (more)
    • Pollution from ITNs lost in bodies of water from fishing. (more)
• We believe, with high confidence based on strong evidence, that the benefits of ITNs are large (more). We estimate that sleeping under an ITN reduces malaria mortality by approximately 40 to 55%, (varying by location), based on results from a meta-analysis by Cochrane6 , Pryce et al. 2018, which summarizes 23 randomized controlled trials of ITN distributions7 . Malaria is a major driver of child mortality in locations where GiveWell funds campaigns. Importantly, these estimates incorporate estimates of the share of ITNs delivered to households that are used, and how long they’re used, which should account for nets lost due to use for fishing. We estimate roughly 70%8 of nets are used, providing around 2 years of protection from malaria. based on multiple sources of data. (more)

We use these considerations to quantify the impact of using nets for fishing on the cost-effectiveness of nets. But there are additional, outside-the-model considerations that also inform our view: (more)

• We think few people who receive ITNs through campaigns use them to fish. We estimate that 0.1 - 0.5% of people targeted for a given ITN campaign will use distributed ITNs for fishing at some point after distribution, potentially after their use for malaria protection, and that they’re used for fishing for about 2 years. This is because we believe most people across the countries where we distribute nets are not engaged in fishing (even at a subsistence level), most people who fish don’t use ITNs, ITNs are mostly destroyed or thrown out when no longer used for protection from malaria, and among nets used for alternative purposes, most are not used for fishing. (more)
  • The low overall rate of net use for fishing makes it more plausible to us that the harms we’ve modeled above are small relative to the benefits, since we think many more nets are used for malaria protection than fishing.
• Our impression is that net campaigns have widespread support, and even researchers focused on the harms of ITN fishing do not recommend stopping net campaigns. This is based on high net use for malaria protection, expressions of support for campaigns from local leaders in a “hot spot” area that experienced higher-than-typical ITN fishing, and statements from fisheries and ecology researchers emphasizing the need to weigh benefits of campaigns against potential harms. (more)
• It feels wrong to forego the clear benefits of ITNs based on harms we see as highly uncertain. The evidence on the effects of ITN fishing is limited and based on mathematical models of fish population dynamics and arguments from first principles, rather than direct evidence that areas with ITN distributions have worse fish yields or worse outcomes, which as far as we can tell does not exist. (more) On the other hand, benefits of ITNs are based on several RCTs showing meaningful reductions in mortality (though we note limitations of this evidence in our intervention report).

• Some surveys in particular fishing areas show extremely high rates of ITNs being used for fishing. For example, a survey on Lake Tanganyika in Tanzania found that over 80% of households had used ITNs to fish at some point.9 In Benin, around two-thirds of volunteer interviewees living near a particular lake reported using ITNs to fish.10 We haven’t closely examined the methodology of these studies, but they align with anecdotes we’ve heard from malaria experts and local residents that suggest that ITN fishing is very common in some areas. (more)
• In areas where nets are more widely used for fishing, we think attrition of nets from households is likely to occur more quickly, reducing total benefits from campaigns. We estimate nets are used for 60% as long in areas where ITN fishing is common, compared to typical areas. This is primarily based on rough extrapolations from two published studies we found, one on Lake Tanganyika11 and one on Mida Creek12 in Kenya, which suggested net retention of around 40% to 80% as long as we might otherwise expect after adjusting for self-report bias. (more)
• Economic and nutritional harm from depleting a fishery is more likely in areas with widespread ITN fishing. We roughly estimate harms would be about 90 times as large in an area with highly prevalent ITN fishing than in areas with typical ITN fishing. That’s based on an intuitive sense that a high prevalence of ITN fishing would have a larger impact on depletion of the fishery and that fish serve a larger nutritional and economic role in some waterside communities, as well as anecdotal conversations in which people described the harms of ITN fishing as potentially significant in those areas where it is more common.

We’ve built a back-of-the-envelope calculation (BOTEC) to try to quantify these concerns in both “typical” areas and hot spots.

We define a “hot spot” in the BOTEC as an area which experiences universal ITN fishing and is unsustainably fished at baseline, even before accounting for ITN fishing. The hot spot estimate is highly uncertain and meant to be illustrative of our reasoning. While our best guess is that lower net use and harms from ITN fishing reduce cost-effectiveness by about half in hot spots, we think it’s plausible both that ITN fishing has a negligible impact on cost-effectiveness even in hot spots or that it leads campaigns to be a net negative in these areas.

	Overall estimate	25th-75th percentiles	Hot spot estimate
Reduction in fish yields (more)
Fraction of fishers using distributed ITNs to fish (more)	25%	3-40%	100%
Adjustment for ITNs accounting for smaller share of fish catch (more)	40%	20%-80%	60%
Fraction of this catch that would be replaced by other gears if campaigns did not occur (more)	60%	20%-80%	50%
Intermediate calc: increase in fishing intensity due to ITN fishing	4%	1%-10%	43%
Fraction of fisheries unsustainably fished at baseline (more)	65%	20%-100%	100%
Decrease in fish yields per 100% increase in fishing intensity (more)	50%	0%-125%	50%
Adjustment for decrease in fish yields due to small mesh size and toxic chemical leaching (more)	+65%	0%-200%	+65%
Subtotal: Decrease in total fish stocks due to ITN fishing	~2%	0%-10%	-35%
Duration of reduction in yield of fish (more)
Duration of ITN use for fishing (more)	2 years	0.5 - 5 years	2 years
Years of decreased fish yield per year of ITN use (more)	2.5	1-5	2.5
Subtotal: Duration of decrease in fish stocks due to ITN	5 years	2-10	5
Harms from reduction in yield of fish (more)
Percent of protein consumption coming from fish (more)	4%	2%-6%	20%
Change in fish consumption per 100% decrease in fish yield (more)	-100%	-50% - -150%	-100%
Fraction of decrease in fish protein consumption replaced by other foods (more)	50%	25% - 75%	50%
Increase in acute malnutrition per 100% decrease in protein consumption (more)	50%	25% - 75%	50%
Increase in acute malnutrition per 100% reduction in fish yield	1%	0.5 - 1.5%	5%
Total harms from ITN fishing
Population targeted (arbitrary)	1,000,000		1,000,000
Fraction of targeted population under age 5 (more)	16.5%	12%-20%	16.5%
Annual probability of death from acute malnutrition (more)	0.5%	0.1% - 1%	0.5%
Deaths caused by increased acute malnutrition	1	0-8	72
Adjustment for other harms from fishery depletion (economic harms, harms to other age groups) (more)	+100%	25% - 200%	+100%
Adjustment for harms of ITN fishing other than fishery depletion (more)	+25%	0%-100%	+25%
Subtotal: Total harm equivalent to death of a child under 5 from ITN fishing with nets from a given campaign	2	0-16	182
Benefits from ITN campaign (more)
Population targeted (same as above)	1,000,000		1,000,000
Fraction of targeted population under age 5 (more)	16.5%	12%-20%	16.5%
Annual probability of death from malaria (more)	0.54%	0.2% - 1%	0.54%
Reduction in malaria deaths from nets (more)	45%	25%-65%	45%
Years of effective net coverage per targeted child (more)	1.1	0.75-1.5	0.66
Adjustment for other benefits from net campaigns (more)	+100%	50-200%	+100%
Adjustment for benefits from ITN fishing or net repurposing (more)	+0%		+0%
Subtotal: Total benefits equivalent to death of a child under 5 from a net campaign	882	400-1200	529
Total (overall adjustment for harms due to ITN fishing)	~0 to -1%	~0% to -2%	-60%

What do we plan to do next?

We contributed over $100 million to support ITN campaigns in DRC, Nigeria, and elsewhere in 2024,13 and we plan to continue supporting future cost-effective ITN campaigns. This is based on our best guess that the benefits of ITNs still significantly outweigh the harms on average in these areas and the outside-the-model considerations we discuss above.

We’re most uncertain about how to deal with concerns about hot spots. We plan to proceed with large grants despite potential hot spots because:

• We think hot spots are rare. We think less than 1% of areas where nets are distributed are likely to fit the characteristics of a “hot spot” described above, where ITN fishing is locally widespread and may significantly reduce cost-effectiveness. (more)
• Our best guess is that campaigns still do more good than harm, even in hot spots. While we think accounting for potential harms of ITN fishing and lower net use could reduce cost-effectiveness by around 60% in hot spots, this would still mean that a campaign at our 10x-cash-transfers bar would be around 4x in a hot spot. While this is below our bar, it still represents an extremely cost-effective charitable intervention, and this doesn’t account for any potential benefits from ITN fishing (more).
• In areas where ITN fishing is known to be common, local governments already engage in mitigation, though we are uncertain of its effectiveness. Against Malaria Foundation (AMF) has said that ITN fishing is addressed via specific education and messaging from local government agencies in areas where it is thought to be an issue.14 This messaging can include radio spots or posters in advance of campaigns,15 as well as civic denouncements of net misuse or fines16 . While we aren’t sure how common or effective these practices are (more), we think it is plausible that this would reduce ITN fishing rates.
• We’re not sure how to identify hot spots in advance. Our impression is that widespread ITN fishing has been observed in some fishing areas, but not all (more). We are not aware of any systematic analysis of which areas are most at risk of high rates of ITN fishing.

We view these areas as concerning and think there are some steps we can take immediately. In areas where we plan to make grants going forward, we aim to discuss with local partners and experts any areas where they have observed or suspect ITN fishing to screen for hot spots, as well as what mitigation measures they plan to implement in these areas.
Alongside these continued campaigns, we may consider funding additional research on ITN fishing. Some projects we may consider:

• Identifying potential hot spots via extra monitoring. This would let us find hot spots in advance and understand how harmful net fishing is (e.g., how much lower net use for malaria protection is). (more)
  
• Piloting mitigation efforts or alternative vector control approaches. In areas where ITN fishing is an issue, we’d prefer to find a way to prevent it without ceasing support for ITN campaigns and losing the benefits that they provide. However, we’re not sure how effective various mitigation strategies would be. (more)
• Tracking fish stocks and chemical residues from ITNs in key bodies of water near ITN distributions. We are highly uncertain in our estimates of how ITN distribution campaigns impact both fish stocks and levels of chemical residues from ITNs. Funding additional monitoring of either would provide more certainty to our model. (more)

How could we be wrong?

This is a complex research topic, and the evidence on the prevalence and harms of ITNs for fishing is limited. As a result, we have several uncertainties that we think could change our conclusions. Several of these could be addressed by the follow-up research we describe above.

• How long are nets used for malaria protection in hot spots? Reduced duration of net usage for malaria protection in hot spots is one of the main determinants of lower ITN campaign effectiveness in those areas. We estimate that nets are used for malaria protection for about 60% as long in hot spots as they are in a typical (non-hot spot) area (more).
  • Incorporating reduced protection against malaria in hot spots due to ITN fishing in our model implies a much larger reduction (~60%) in the effectiveness of ITN campaigns than if we were to only account for the direct negative effects of ITN fishing, e.g. fishery depletion (~20%).
  • We are highly uncertain of this estimate and think additional monitoring in potential hot spots could help us update on this. We estimate that the reduction in cost-effectiveness due to use of ITNs for fishing might be ~-30% to ~ -100% in a hot spot depending on plausible updates to this parameter.17

• Where are the hotspots? We suspect that there are some areas where ITN fishing is common, but we aren’t sure how to identify these areas in advance. We think we can make progress on this by talking to partners in advance about potential hot spots and potentially supporting additional monitoring in these areas to understand where nets are being used for fishing instead of (or after) malaria protection (more).

• How can we mitigate this problem? We aren’t sure what would work best to mitigate the possible consequences of net fishing. To learn about this, we may consider piloting different approaches to mitigating ITN fishing in areas where fishing with nets is more common (discouragement of fishing, simultaneous distribution of proper fishing nets, increased monitoring/enforcement) and comparing impacts on ITN-fishing prevalence and fish stocks. We may also explore alternative approaches to mitigate damages, e.g., more surveillance to identify areas where risk is higher, supporting indoor residual spraying instead of ITNs in higher-risk areas, or distributing nets that are less suitable for fishing in waterside communities (more).
• Does ITN fishing provide significant livelihood benefits that we are not modeling? We haven’t modeled the potential benefits of ITN fishing (more). Overall, we think these benefits are likely to be small because we think most people don’t fish with ITNs, but in fishing communities, particularly near fisheries that are not overexploited (and where the practice is not illegal), ITNs could support livelihoods of subsistence fishers. These benefits may counterbalance the potential harms.
• How much does ITN fishing affect fish stocks? Our model of how ITN fishing affects stocks is crude and depends on a number of guesses about how long ITNs are used for fishing (more), how long the effects of fishing last (more), and the consequences of small mesh size and chemical leaching (more). We aren’t aware of much reliable data to refine our estimates of the status of fish stocks (more). We could be wrong in either direction: some experts argue that ITNs harvest primarily smaller fish which are more easily replaced and provide a more efficient energy source for consumption.18 If this is the case, then ITN fishing may lead to increased fishing yields without damaging sustainability. On the other hand, other authors argue that ITNs catch fish indiscriminately, cause toxicity to small aquatic organisms, and contribute to overexploitation.19
  • We are especially uncertain about how much ITN fishing affects fish stocks in hot spots and think fish stock monitoring in areas with ITN fishing might offer guidance on how much to invest in mitigation. As a lighter touch step, we may also engage with additional fishing ecologists. We’re not sure if either is likely to significantly resolve our uncertainty because we think fish population dynamics are very complicated, but both may help us triangulate some of our estimates. For example, if we saw evidence that overall fish stocks (or stocks of specific fish species) saw sudden and large declines shortly after ITNs were introduced in an area, it would increase our concern about this issue. If we learned that fish stocks were stable or increasing, we would have less concern, though we would still worry if nets were not being used for malaria protection in some areas.

• Are the effects of ITN fishing beyond malnutrition from fishery depletion more important than we think? We explicitly model the impacts of ITNs being used for fishing on fish stocks, and then estimate health impacts of increased acute malnutrition due to reductions in fish yield. To account for additional potential harms, we make two adjustments:
  • We double the estimate of harm from fishery depletion to account for other potential impacts beyond acute malnutrition (such as economic harms from reduced fish sales). (more)
  • We make an additional 25% upwards adjustment to account for potential harms of ITN fishing that are not related to fishery depletion (such as exposure to toxic chemicals). (more)

Both of these adjustments are highly subjective. We focused on fishery depletion and malnutrition because:

• We had a high-level impression that fishery depletion from ITN usage was a commonly discussed concern in academic literature, and because we thought there were a number of intuitive reasons to be concerned about ITNs depleting fisheries: ITNs could increase the number of people fishing, small mesh sizes of ITNs could catch small and juvenile fish, and toxic chemicals leaching from ITNs could disrupt the aquatic ecosystem.
• We think even small increases in acute malnutrition could be very harmful, and a lack of fish for capture could lead to increases in acute malnutrition, especially in fishing-dependent communities.
• When we looked into possible harms of ITN fishing not related to fishery depletion, like increased consumption of toxic chemicals, our tentative impression of the available evidence was that the harms were smaller than fishery depletion (more).

However, we could be wrong not to focus on other potential harms of ITN fishing. We are especially unsure about whether piperonyl butoxide or dual-active-ingredient nets could lead to more chemical leaching, as we were only able to find evidence on pyrethroid leaching. We think we could learn more about this by measuring chemical residues in bodies of water and fish where we know or suspect ITN fishing is more common.

• Are we significantly wrong about the prevalence of ITN fishing? Our overall estimate that 0.1 to 0.5% of people might fish with a distributed insecticide-treated net at some point after distribution, including after use for malaria protection, is fairly uncertain and based on a mix of non-representative surveys, self-reports, and subjective adjustments (more). Our 25th-75th percentile estimates are 0.01 to 1%.
  • Both of our partners that implement ITN distributions think that the practice is significantly rarer than our best guess in distributions they’ve supported (more). Against Malaria Foundation stated that based on their experience, including post distribution monitoring of AMF-funded nets, the number of nets used for fishing from AMF distributions is many orders of magnitude less than the general estimates we have proposed. Their estimate is less than 0.01%.
  • On the other hand, since studies and news reports occasionally show widespread fishing with ITNs in particular villages (more), and it’s difficult to establish precise prevalence estimates of a rare and sometimes illegal activity, we also think it’s possible that our estimates could be too low.
• What do local communities think about ITN fishing? Our conclusions would likely be more robust if we had engaged with a wider range of experts and local officials, particularly in hot spots. To date, our discussions with external experts and local community members on this topic have been relatively limited.20
• How should we account for harm to aquatic organisms? Since ITNs likely disproportionately catch small and juvenile fish (more), it’s possible that they lead to increased animal suffering. We haven’t investigated this issue in detail and don’t account for it in our estimates.

Rough quantitative estimates of the effect of harms of ITNs for fishing on cost-effectiveness

This section describes our model for quantifying the effect of nets for fishing on cost-effectiveness.

	Overall estimate	25th-75th percentiles	Hot spot estimate
Reduction in fish yields (more)
Fraction of fishers using distributed ITNs to fish (more)	25%	3-40%	100%
Adjustment for ITNs accounting for smaller share of fish catch (more)	40%	20%-80%	60%
Fraction of this catch that would be replaced by other gears if campaigns did not occur (more)	60%	20%-80%	50%
Intermediate calc: increase in fishing intensity due to ITN fishing	4%		43%
Fraction of fisheries unsustainably fished at baseline (more)	65%	20%-100%	100%
Decrease in fish stocks per 100% increase in fishing intensity (more)	50%	0%-125%	50%
Adjustment for decrease in fish yields due to small mesh size and toxic chemical leaching (more)	+65%	0%-200%	+65%
Subtotal: Decrease in total fish stocks due to ITN fishing	~2%	0%-10%	-35%
Duration of reduction in yield of fish (more)
Duration of ITN use for fishing (more)	2 years	0.5 - 5 years	2 years
Years of decreased fish yields per year of ITN use (more)	2.5	1-5	2.5
Subtotal: Duration of decrease in fish yields due to ITN	5 years	2-10	5
Harms from reduction in yield of fish (more)
Percent of protein consumption coming from fish (more)	4%	2%-6%	20%
Change in fish consumption per 100% decrease in fish yield (more)	-100%	-50% - -150%	-100%
Fraction of decrease in fish protein consumption replaced by other foods (more)	50%	25% - 75%	50%
Increase in acute malnutrition per 100% decrease in protein consumption (more)	50%	25% - 75%	50%
Increase in acute malnutrition per 100% reduction in fish yield	1%	0.5 - 1.5%	5%
Population targeted (arbitrary)	1,000,000		1,000,000
Fraction of targeted population under age 5 (more)	16.5%	12%-20%	16.5%
Annual probability of death from acute malnutrition (more)	0.5%	0.1% - 1%	0.5%
Deaths caused by increased acute malnutrition	1	0-8	72
Adjustment for other harms from fishery depletion (economic harms, harms to other age groups) (more)	+100%	25% - 200%	+100%
Adjustment for harms of ITN fishing other than fishery depletion (more)	+25%	0%-100%	+25%
Subtotal: Total harm equivalent to death of a child under 5 from ITN fishing with nets from a given campaign	2	0-16	182
Benefits from ITN campaign (more)
Population targeted (same as above)	1,000,000		1,000,000
Fraction of targeted population under age 5 (more)	16.5%	12%-20%	16.5%
Annual probability of death from malaria (more)	0.54%	0.2% - 1%	0.54%
Reduction in malaria deaths from nets (more)	45%	25%-65%	45%
Years of effective net coverage per targeted child (more)	1.1	0.75-1.5	0.66
Adjustment for other benefits from net campaigns (more)	+100%	50-200%	+100%
Adjustment for benefits from ITN fishing or net repurposing (more)	+0%		+0%
Subtotal: Total benefits equivalent to death of a child under 5 from a net campaign	882	400-1200	529
Total (overall adjustment for harms due to ITN fishing)	~0 to -1%	~0% to -2%	-60%

How much do nets reduce fishing yields?

We guess that a given campaign leads to a 2% decrease in fish stocks in unsustainably fished fisheries relative to the counterfactual with no net distribution, lasting 5 years. We assume that this causes a similar decline in future fishing yields. This leads to a fraction of a percent decline in cost-effectiveness on average.

Percentage of fishing population using insecticide-treated nets to fish

We estimate 25% of people who fish (for subsistence or employment) use ITNs to fish. In a hot spot, we think this number would be 100%. This is a rough guess based on reviewing several surveys and reports of ITN fishing in areas where fishing is common, including two studies from DRC, where we expect to support campaigns conducted over the next 2 years.

We did not identify any large-scale, representative surveys of how many fishers use ITNs. Instead, we found two types of sources:

• We found six studies estimating the fraction of fishers or people/households using ITNs to fish:
  • Rethink Priorities shared three studies with estimates of the fraction of fishers using mosquito nets based on either household surveys or surveys of fishers, which they reported suggested a prevalence of ~2%, 27% and 66% of fishers using mosquito nets.21
  • We also found three additional household surveys in areas of Kenya, Tanzania, and Papua New Guinea where fishing is very common (e.g. coastal areas / fishing villages) that we think suggest percentages of fishers using nets of ~1%, 60%, and ~100%.22 A simple average of these six estimates gives an estimate that around 40% to 45% of fishers use ITNs.
• We identified three additional surveys which measured the fraction of mosquito nets among fishing gears in areas of DRC and Madagascar, generally finding ~25% of fishing gears involved mosquito nets.23 While the fraction of gear used for fishing may not perfectly correspond perfectly to the fraction of fishers using these gears (e.g. if fishers are using multiple types of gears, or if some fishers are using many of one type of gear), we’d guess this roughly corresponds to 25% of fishers using ITNs.

If we took an average of the gear based-estimate and the household/fisher-based estimate, we’d estimate around 30% to 35% of fishers use ITNs. We adjust this downward by about 25% to 30% because we think it’s somewhat likely that some studies of ITN focus on areas known to have especially high rates of ITN fishing.

We didn’t review the methodologies of these studies in detail, and we don’t think that we can draw confident inferences about the rates of ITN fishing from them. We are uncertain whether our downward adjustment for sites with higher rates of ITN fishing being especially likely to have been studies/captured in our review is insufficient. We also worry about reporting bias in studies finding especially low estimates of ITN fishing.

We think additional monitoring in areas where fishing is common may help update our beliefs about this number, and we plan to consider funding this.

Adjustment for ITNs accounting for smaller share of fish catch

We guess that the percentage of fish caught with ITNs is 40% of the number of fishers using campaign ITNs at some point. That’s a guess based on two intuitive considerations:

• We identified one study from Benin where voluntary interviews suggested about half of full-time professional fishers used ITNs for fishing, but virtually all seasonal fishermen interviewed used ITNs.24 While we haven’t reviewed the methodology of this study closely and are unsure of its reliability, it aligns with our intuitive sense that ITN are more likely to be used by less professional fishers who catch fewer fish.
• We’d guess some people also use other fishing gear in addition to ITNs. In a brief review, we found one thesis which included perspectives on ITN fishing from an online survey of local fisheries and malaria experts across the world.25 This survey found that 41/54 respondents reported that ITNs were used in addition to other gears in their area.26 We didn’t review the survey construction or the background of the surveyed individuals in detail, and we aren’t sure how many ITNs are used relative to other gears in these areas.
• We also identified a report describing fishing methods used in southwest Madagascar which includes pictures and descriptions of ITN being used with other small mesh nets like the jahoto net27 or the feripe net.28 The ITN is described as the cod end, which is a pocket/pouch at the back of a larger net. We include a diagram of a cod end as Figure 1 below.

Figure 1: The cod end of a fishing net.29 ITNs may be used as part of the cod end in a larger net.

A rough attempt to quantify these considerations: we might guess ITN fishers catch around two thirds as much fish as non-ITN fishers, and that about 60% of ITN fishers’ catch is from ITNs (with the rest being attributable to other gears).30 Multiplying these together yields our 40% overall estimate.

In hotspots, where nearly all fishers are using ITNs, we don’t adjust for ITN fishers catching less than non-ITN fishers (because we assume there are no non-ITN fishers). Therefore, we simply estimate 60% of the total catch is from ITNs based on the ITN fishers using other gears in conjunction with ITNs.

Fraction of this catch that would be replaced by other gears if campaigns did not occur

We guess that around 60% of the ITN catch would be replaced by other gears if campaigns did not occur.31 In a hot spot, we guess slightly less, 50%, of the catch would be replaced. This is a rough guess based on a couple of qualitative research papers and informal conversations with experts. We rely on these studies because we did not find any quantitative studies estimating catch by the same fishers before and after they started using ITNs to fish in our brief review.

We think some of the catch from ITNs would be replaced by other gears based on two surveys in Kenya and Tanzania and a qualitative study in Mozambique that we found in a brief review, which describe ITN fishing as crowding out other forms of fishing, particularly fishing with cloth:

• A qualitative investigation of fishing with mosquito nets in Mozambique describes women using ITNs to engage in “kutanda” fishing which previously involved using cloth.32
• A Tanzanian respondent to an online survey of fishery and malaria experts reported that fishing with small mesh nets (like ITNs) had replaced fishing with cloth.33
• In a survey of 24 households engaged in fishing with mosquito nets in Mida Creek, Kenya, 15 reported previously fishing with other gears, and only 3 households said they did not fish previously.34 We are uncertain whether these households continued using old gear in combination with ITNs, but our best guess is that ITNs crowded out at least some portion of the gear previously used.

That said, we don’t think 100% of the catch would be replaced by other gears. That’s because:

• We don’t think all ITN fishing is crowding out other forms of fishing. In the survey evidence from Mida Creek, we think mosquito nets likely added to the total fishing gear of both the 3 households who reported they didn’t fish before using mosquito nets and some of the 15 households who were using other nets previously.
• A brief review of relevant literature suggests to us that ITNs are likely more effective at catching small fish than many other nets (more), so even if they were replaced with other forms of fishing, those forms might not lead to as many fish being caught.

We struggle to quantify the precise fraction of catch that would be replaced by other fishing gears. On the whole, we find the geographic variation in areas where mosquito net fishing has apparently replaced some form of cloth fishing to be suggestive that other fishing methods would prevail in absence of ITNs, so we tentatively guess most of the catch could be replaced, but we are not very confident about that, so we only estimate 60% overall.

We guess slightly less catch (50%) would be replaced in a hot spot because we think ITNs might be more commonly used in areas where other gears are harder to come by. We haven’t identified any research that supports this notion.

We might be able to improve this estimate by speaking with more experts about this issue, or by observing changes in fishing behavior and catch before and after ITNs are distributed in an area.

Fraction of fisheries unsustainably fished at baseline

We guess that, in areas where we would support net campaigns, around 65% of fisheries are overfished, or close enough to being overfished that ITN fishing would cause them to be overfished. By overfished, we mean the mass of fish caught exceeds a maximum sustainable level, such that the mass of fish available for catch will decrease.

That’s based on global estimates of overfishing rates ranging from 13-67%, and an uncertain guess that parts of Africa where we’re likely to support campaigns are likely to skew towards the higher end of this range.

Our understanding based on a very brief review of an article on overfishing from Our World in Data,35 is that there is generally not much evidence on fishing intensity across the African continent. A concern is that this lack of evidence stems from a lack of monitoring which increases the likelihood of overfishing.

We found an estimate from the United Nations Food and Agriculture Organization that across the 16 Major Fishing Areas in the world, 13-67 percent of fisheries are overfished.36 The same source notes that 15% of inland African basins are under “high pressure” and another ~60% are under “medium pressure.”37 We haven’t looked into the methodology underpinning these estimates, but we generally believe the United Nations to be a relatively high-quality source of information.

• One study in Madagascar in 2018 and 2019 suggested that the mass of fish caught per unit of area in the Bay of Toliara declined by nearly 60% since 1990.38 The authors attribute part of that decline to increased fishing intensity from mosquito net trawls.39
• A study off the coasts of Kenya and Tanzania found standing stock biomass in 2012 found standing stock biomass of around 0.15 to 0.3 t/nm^2, over 90% lower than studies from the 1980s in a similar area, though the estimates may not be directly comparable due to differences in the fish and geographic area included. The authors attribute the low standing stock biomass to exploitation by trawlers and artisanal fishers.40
• An analysis of the Usipa fishery in the southeast arm of Lake Malawi, published in 2019, suggested that it was being fished beyond maximum sustainable yields and suggested that fishing intensity should be reduced by over half to attain maximum economic benefits.41

Our estimate of nearly 65% skews toward the higher end of the 13-67% range across Major Fishing Areas because of the lack of monitoring and the concerning location-specific estimates.

This is highly uncertain; we think we could improve our guess in a particular area by speaking to local experts or commissioning monitoring. Some key uncertainties we have are:

• The 16 Major Fishing Areas referenced by the FAO are marine (saltwater) fisheries; while many of the areas we would support net campaigns are likely to be inland, away from saltwater seas and nearer to freshwater lakes and rivers. We were not able to find as much information about these stocks. The FAO reports a long-term increase, but cautions that the data is unreliable and reporting has changed over time.42
• We think there is disagreement and uncertainty about what constitutes an “overfished” stock.43 Fishing rates categorized as unsustainable may in fact be sustainable, and vice versa.
• Different methods of fishing probably capture different types of fish; for example, ITNs probably catch smaller fish than other nets (more). In the short run, this might mean that smaller species are overfished, but larger fish are not; however, it may also reduce long run sustainability by leading to higher juvenile catch. We currently make an additional adjustment for small mesh size disrupting ecosystems (more), but we aren’t sure how these dynamics play out.

Ratio of decrease in yield of overfished fisheries per % increase in fraction of available fish caught

We estimate that in overfished or nearly overfished fisheries, fish yields are reduced by half of the amount that the fraction of available fish caught increases, for a period lasting 2.5 times as long (more). For example, if there is a 1% increase in the fraction of available fish caught lasting 2 years due to ITNs, then we guess yields of overfished fisheries will be 0.5% lower on average44 for 5 years relative to if the ITNs had not been distributed.

We think increasing the fishing intensity will eventually lead to lower catch because overfished populations will be unable to reproduce at needed rates to maintain their population. We think this is in line with a simple “maximum sustainable yield” (MSY) model of fish populations, where increases in fishing intensity beyond the MSY eventually cause declines in fish populations. A depiction of such a model from Our World in Data is included as Figure 2 below. In Figure 2, overfished fisheries would be located to the right of the MSY point, so the model suggests increased fishing pressure would lead to decreases in fish catch in the long run.

Figure 2: A simple maximum sustainable yield model.45

The estimate of a 0.5:1 ratio of decline in fish yields per increase in fraction of available fish caught is a crude guess. We have not reviewed models of maximum sustainable fishery yields and how quickly fisheries are depleted by overfishing in detail, and our impression is that they are relatively complicated and uncertain. We think our model is highly simplified and the true relationship between the percent of available fish caught and how much fisheries are depleted in the future varies significantly by context.46 One key uncertainty is the timeline over which catch declines. Intuitively, we expect increased fishing effort would lead to (unsustainable) short-term gains, even in overfished fisheries, but we are uncertain how long the short term lasts. Our assumption of a 0.5% decline in yields per 1% increase in intensity reflects a belief that the increase in intensity likely doesn’t translate 1:1 to a decrease in yields, especially for larger increases in intensity. For example, we don’t think fish yields would decrease by 100% if fishing intensity doubled, even if the area was overfished at baseline.

We could likely improve our guess somewhat by speaking with ecologists, though we are not sure whether it is tractable to significantly reduce our uncertainty about the average impact on fishing yields, especially since ITN fishing may lead to very different effects on stocks of different species of fish47 . We are unsure how tractable it would be to create a model that accounts for these complexities.

Adjustment for decrease in fish stocks due to small mesh size and toxic chemical leaching

We adjust our estimate of fishery depletion caused by ITN fishing upward by 65% to account for ecosystem disruption due to small mesh sizes and toxic chemical leaching from ITNs. That’s because our overall estimate is a ~1.4 percent decrease in fish yields due to increased fishing intensity from ITNs, and we estimate around 0.9 percentage point additional decrease per year due to small mesh sizes (more) and chemical leaching (more):

What we are estimating	Value
Depletion due to increased fishing intensity48	1.35%
Depletion due to small mesh sizes of ITNs (more)	0.6%
Depletion due to toxic effects of insecticides (more)	0.3%
Adjustment for depletion due to small mesh and toxicity	65%

Those estimates are based on a number of rough guesses informed by data from a survey of fish catch in Madagascar, one unpublished dissertation chapter describing laboratory studies of chemicals leaching from nets, and a couple of informal conversations with malaria or water experts. We use the same 65% adjustment in a hotspot based on a rough assumption that harms would scale with fishing intensity.

We have not conducted a thorough literature review or spoken with fish ecologists or toxicologists. We expect doing so would improve our estimates, but we think that even with more research, we would remain uncertain about how much fishery depletion is attributable to mesh size and insecticide leaching due to variation across contexts.

Ecosystem Disruption due to Small Mesh Size

For each ITN campaign, we tentatively guess that small mesh sizes of ITNs reduce fish yields by around 1%, lasting for around 5 years.

While we believe it is likely that ITNs disproportionately catch small and juvenile fish due to their small mesh size (more), we think the effect size is small in expectation because we don’t think ITNs are used by all fishers (more), we are not sure that catching small or juvenile fish would lead to fishery depletion (more), and even if it does, we think the expected decrease in yields from this would be relatively small (more). A rough quantification of these considerations is below:

What we are estimating49	Value	25th/75th percentiles
Fraction of fishers using ITNs (more)	25%	10% - 90%
Percentage of ITNs that disproportionately catch small or juvenile fish (more)	90%	90% - 100%
Probability that this causes fishery depletion (more)	50%	15-85%
Reduction in fish yields caused per fisher using ITNs, if small mesh causes depletion (more)	5%	0%-25%
Total: depletion due to small mesh size	~0.6%	0-2%

We think we could update our beliefs about the probability that small mesh nets cause fishery depletion by talking to more experts, but we believe the amount of depletion attributable to small mesh size in real-world settings is likely to remain relatively uncertain because of variation in ITN fishing methods and species of fish available.

Percentage of ITNs that disproportionately catch small or juvenile fish

We estimate that 90% of ITNs catch more small and juvenile fish than other nets. We think it’s pretty likely that this occurs because an observational survey in Madagascar showed the average size of fish caught by mosquito net trawls was about 6.3 cm, compared to 15 cm for other common forms of fishing gear,50 because a survey from Short et al (2018) identified a number of experts who reported juvenile capture of fish from ITN fishing, and because we find it intuitively plausible that a net with mesh small enough to block mosquitoes would be more likely to catch small fish.

We don’t estimate a 100% chance of catching smaller fish because we think that ITNs may sometimes be used in place of cloth51 or other small mesh nets, so that ITNs don’t disproportionately target small fish relative to the counterfactual.

Probability that catching small and juvenile fish causes fishery depletion

We tentatively guess that ITN fishing in a given fishery has roughly a 50% chance of causing some fishery depletion (25-75th percentile 15-85%) via small-fish removal.

We are unsure about the impact of catching smaller fish on fishery depletion. Ideally, we would be able to randomize ITN distribution across fisheries and compare fishery health and small-fish populations over time to study these dynamics, but we are not aware of any such studies.

Our understanding from our brief review of the literature and a conversation with Jeppe Kolding, a fisheries scientist, is that there is disagreement among experts on whether removal of small and juvenile fish harms fishery health, as well as whether ITN fishing is occurring with sufficient intensity to cause harm via this channel.52 50% is a very rough guess, and we may be able to improve it by speaking with more experts and improving our understanding of fishery management.

Depletion by small mesh size, caused per fisher using ITNs

If small mesh size does cause fishery depletion, our guess is that the expected depletion is 5% (25th-75th percentile 0%-7.5%) of the total fish stock, leading to a 5% reduction in yields. We aren’t aware of any research on this topic, but intuitively, we guess that the depletion due to small mesh sizes would be well under 100% because in many fisheries, small mesh ITNs are just one source of fishing gear (more) and one cause of depletion (in addition to other factors like population growth and changes in climate53 ).

However, we think it’s plausible that the small mesh sizes of ITNs may lead to a dramatic decrease in the population of particular species, like the gerres oyena in Mozambique.54

We may be able to improve our guess by speaking with more experts and improving our understanding of fishery management, but we suspect variation across settings and species of fish will make it challenging to infer an average amount of depletion to this cause.

Ecosystem Disruption due to Toxicity

ITN fishing could deplete fisheries because of toxic chemicals leaching from nets into water and killing fish. We guess that this would lead to around 0.6% reduction in fish catch. Our understanding of this issue is based primarily on extremely limited laboratory evidence (Love 2023, a non-peer-reviewed study) of pyrethroid ITNs leaching and killing water fleas and some minnows. We made some rough extrapolations from this study regarding likely concentrations of chemicals leaching into the water and potential effects on fish.

We quantify the considerations leading to our estimate as follows:

What we are estimating55	Value	25th/75th percentiles
Fraction of fishers using ITNs (more)	25%	10% - 90%
Fraction of fishing occurring in bodies of water where ITN leaching causes significant toxicity (more)	5%	0% - 20%
Reduction in fish yields due to chemical leaching in such areas (more)	25%	0-100%
Total: depletion due to toxic effects	0.3%	0-1%

Fraction of ITN fishing occurring in settings where significant toxicity is likely

We guess around 5% of ITN fishing occurs in bodies of water where chemical leaching from nets would cause significant toxicity. This is a guess based on intuitive considerations and extrapolations from a study in an unpublished dissertation chapter.

• We are not aware of any evidence on toxic effects of ITN fishing in field settings, nor of measurements of pyrethroid, pyrrole, or other net-related chemical concentrations in lakes or streams in Africa, and our understanding from informal conversation with a water engineer is that determining the particular “dose” received by a fish in a field setting is not straightforward.
• We think this issue would mostly impact small and juvenile fish, and mostly smaller bodies of water. We think this because the only direct evidence we found of toxicity in fish exposed to ITNs comes from the laboratory study of Love (2023), in which 40-100% of water fleas exposed to nets over the course of a week were killed, and 0-80% of fathead minnows were killed.56
  • Our understanding is that the exposure of nets per unit water in this experiment would be roughly equivalent to the use of 20-500 nets in a 1000-liter pond57 (roughly half the size of an Olympic swimming pool), which we believe represents a fairly high concentration of nets,58 though we are uncertain about this. We also believe fathead minnows and water fleas are relatively small fish.59
• We are unsure what percentage of fishing activity occurs in small ponds in countries like DRC and Nigeria relative to large lakes or the ocean. We have seen estimates that inland sources (including large lakes) account for anywhere from 30-75% of total fish capture across Africa.60

We tentatively guess that small ponds, stagnant pools, floodplains, and oxbow lakes where toxicity is more likely to lead to fishery depletion account for 10% of this total (and with high uncertainty–25th-75th percentile: 1% - 25%), to get a total of 3-7.5% of fishing activity affected by this issue. This is an intuitive guess, based on the idea that larger fisheries probably account for a larger proportion of total catch, but we have not identified any evidence to help us quantify this intuition.

Depletion due to ITN fishing in areas where leaching is harmful

We are uncertain how much depletion of fisheries to estimate from toxic effects in small bodies of water; we use a larger estimate of 25% expected depletion (compared to 10% for mesh size) because we expect small fish to make up a relatively larger proportion of the fish in small bodies of water, and we expect that smaller ecosystems may be more fragile, so the killing of small fish might be propagate through the food chain more quickly.

This is a guess, and we haven’t identified any information to help us refine this estimate.

How long does the reduction in stock of fish last?

How long are ITNs used for fishing?

Our best guess is that ITNs used for fishing are used for around 2 years on average (25th-75th percentiles: 6 months - 5 years). This is based on limited and indirect evidence on ITN fishing, and a couple of surveys of durability of commercial fishing nets.

We are not aware of much evidence on how long ITNs are used for fishing. What we’ve found suggests that:

• Some ITNs are not suitable for fishing, but others are more durable. Reports from experts surveyed by Gurung et al (2015) reported that some (polyester) nets break immediately upon use, while other (polyethylene) nets are considered more suitable for fishing. Unfortunately, this doesn’t help us update very much: we’d guess that nets used for fishing are disproportionately likely to be the more durable nets.
• In one area, ITNs from a campaign may have been used for fishing 2 years after a campaign. A survey in Papua New Guinea asked households for “other uses of bed nets in this house” 2 years after a mass campaign, and 30.4% of households reported fishing.61 We aren’t totally sure what to infer from this because we don’t know when the households started using the nets for fishing (e.g. right after the campaign, or after they perceived it lost efficacy against malaria), and we have some uncertainty about how the households would have interpreted the question.62
• Commercial fishing nets probably last somewhere from 1 to 4 years. We found a couple of sources including a published primary research study of fishing nets commonly used in Bangladesh63 which described net life spans of 1-4 years and a single case study of uncertain reliability64 which stated commercial fishing vessels use polyethylene nets for 1-3 years.

Combining all this information, we guess that ITNs used for fishing are used for about 2 years. That’s about how long the commercial nets are used, we think it’s consistent with finding nets still in use for fishing a couple years after a campaign in Papua New Guinea, and we think it’s not so long as to be obviously implausible.

We’re very unsure about this estimate. It could be too low: We could imagine ITNs might be used for longer than commercial fishing nets, since they are likely used at lower intensity. However it could also be too high: ITNs typically wear out with around 3 years of intended use; since fishing is not the intended use, we might expect they would wear out faster when used for fishing, or if they are used for malaria protection for some time before fishing. We suspect there is high variability depending on intensity and method of use (e.g. ITNs drug along rocky reefs may not last as long).

Since distribution campaigns occur around every three years, this would suggest that the number of nets used for fishing due to distributions in a given year is around two-thirds of the number of nets distributed on average (more closer to a distribution). If our estimate of how long nets are used for fishing is correct, we wouldn’t expect this number to increase over time, since we think nets are used for a shorter period of time than the distribution interval.

We think we could learn more about the length of time ITNs are used for fishing by talking to local fishermen or through more conversations with experts.

Years of decrease in fish yields per year ITNs are used for fishing

We estimate that the decline in fish yields due to ITN fishing lasts 2.5 times as long as ITNs are used for fishing. This is a crude guess. We think declines in fish yields due to a particular set of ITNs are likely to last beyond the time period they are used based on an intuitive understanding of population dynamics:

• As an example, suppose that with ITN fishing from a particular distribution caused fish stocks in an area to decline from 1 million fish in 2020 to 950,000 fish in 2022, when otherwise they would have remained at 1 million fish.
• Even if these nets were no longer used in 2023, the fish stock would now be 950,000 fish instead of 1,000,000 in 2022. That means there are fewer fish available to reproduce and replenish stocks, so we’d expect the fish yields to be lower than the counterfactual in 2023 as well.

In the extreme case, we might estimate that this decline would persist indefinitely, so in the example above, fish yields would always be 5% lower than if the distribution hadn’t happened. But we don’t think that’s likely the typical outcome because:

• We think that fish stocks have potential to recover when underlying causes of overfishing are removed. That’s based on an analysis of fish stock recovery after areas bottom trawling was stopped, which we read a brief summary of from Our World in Data. While bottom trawling removed 6 to 41% of organisms, fisheries returned to 95% of pre-trawling biomass within around 2 to 6 years.65
• In the long run, we expect there to be some behavioral adjustments in response to decreases in fish catch. For example, areas with larger decreases in fish catch may respond with increased monitoring of illegal fishing, and by shifting more aggressively toward aquaculture could dull the impact of lower freshwater fish catch in the medium to long term. We have not reviewed evidence about impacts of monitoring or agriculture, this is based solely on an intuitive guess about behavioral responses, and we are uncertain how likely this is to occur or on what timeline.

Altogether, our estimate that 2 years of fishing with ITNs leads to 5 years of decreased fish yields is a rough guess balancing the above factors. We think we may be able to improve our guess by talking to experts or looking more deeply into fish stocks before and after ITN campaigns, but we think we are likely to remain quite uncertain about this.

Possibility of Compounding/Diminishing Effects

Given that net campaigns happen every 3 years, but our estimate is that depletion of fisheries below counterfactual levels lasts 5 years, we expect that effects from consecutive campaigns would overlap somewhat. For example, a campaign happened in 2024 and caused 3% lower fish yield from 2024-2028, and a campaign happened in 2027 caused 3% lower fish yield from 2027-2031, then we’d model fish yields in 2027 and 2028 to be around 6% lower than if neither campaign had happened.66

In the long run, if campaigns happened every 3 years and had effects lasting around 5 years, we’d expect the average annual decrease in fish yield to be around 5/3 ~= 1.67 times as large as the decrease in annual yield from any particular campaign. Since we consider campaigns one at a time, and not in general, we don’t make a separate adjustment for this in our back-of-the-envelope calculation, but we include this number to benchmark our best guess at the cumulative effects of net campaigns on fishing yields.

How do harms from reduced fish stocks due to ITN fishing reduce cost-effectiveness?

Percent of protein consumption coming from fish

We guess that fish accounts for about 4% of total protein consumption across sub-Saharan Africa.

That’s based on data from the Food and Agriculture Organization (FAO) of the United Nations.67 They estimate that 4% of protein consumption in Africa in 2021 was from fish. We assume that sub-Saharan Africa is similar to the continental average, and data from 2021 is relatively predictive of future fish consumption in areas where we might fund ITN campaigns.

We used this data because we believe that the FAO is a reputable organization, and they had the most thorough data we could find in a brief review. We have not reviewed their methodology or searched for other sources of information.

We’d estimate fish consumption is higher in potential “hot spot” areas where more fishing occurs; 20% is a rough guess. We observed estimates of around 10% in African countries which we expected to have high rates of fishing, but we scaled this up by a factor of 2 since even those countries are likely to have some areas with less fishing.

We’re uncertain about whether we should expect increases or decreases in fish consumption and the quality of this data, and we assume fish consumption varies heavily by location.

Change in fish consumption per 100% decrease in fish yield

We assume that fish consumption declines 1:1 with changes in fish yield. For example, if fish yields decline by 5%, we assume fish consumption also decreases by 5%. This is a guess.

Fish consumption could decrease by more than the decline in fish yield if increased stress on the fishery leads to substitution into other forms of food production (e.g. shifts from fishing to agriculture). It could decrease by less than the decline in fish yields if innovation or trade dampens the impact (e.g., if more fish can be imported or farmed via aquaculture).

We haven’t looked into this closely and may be able to improve our guess by speaking with fishery management experts.

Fraction of decrease in fish protein consumption replaced by other foods

We guess that 50% of the protein consumption lost from fish consumption could be replaced by other foods. We haven’t investigated this, and this guess is based on intuitive considerations: we think it makes sense that people would replace some of their fish consumption by eating more of other food sources. However, we don’t think this replacement would be 1:1 in areas where incomes and consumption are already very low–if food were readily available for substitution, we suspect people might already be eating it.

50% is a highly uncertain guess; we think we may be able to improve this guess with a more thorough literature review of evidence on how people respond to changes in food supply.

Increase in acute malnutrition per 100% decrease in protein consumption

We assume acute malnutrition increases by 50% of the decrease in protein consumption. For example, if protein consumption decreases by 1%, then we guess that acute malnutrition would increase by 0.5%. That’s based on a rough guess that about half of malnutrition is attributable to nutritional causes, and that this “diet-based” malnutrition increases by 1% for every 1% decrease in protein consumption.

We think half of malnutrition is attributable to non-nutritional causes based on a brief conversation with a nutrition expert who suggested that some malnutrition is caused by non-nutritional factors, like infectious disease, especially enteric infectious disease, as opposed to diet. We expect that this malnutrition may not be as directly affected by changes in consumption, though we think this is complicated and we aren’t sure.

The relationship between changes in protein consumption and changes in diet-based malnutrition in countries like DRC and Nigeria is highly uncertain. Our assumption of a 1:1 link is a guess. We haven’t reviewed evidence on changes in malnutrition in response to fixed decreases in protein or calorie consumption, and we expect it would depend heavily on situational factors, such that additional research may not lead to large updates.

Malnutrition could increase by more than 1% in response to a 1% decrease in protein consumption if there is significant clustering of children just above the minimal subsistence level of consumption who are all thrown into malnutrition by a small decrease in consumption, or it could decrease by less than 1% if few children are near this threshold level of consumption.

Fraction of targeted population under age 5

We took an average across locations in our cost-effectiveness analysis for ITNs, which gave a value of 16.5%68 .

Annual probability of death from acute malnutrition for children under 5

We estimate that the annual probability of death from acute malnutrition is around 0.5%. We estimate that because we think around 10% of children under 5 have acute malnutrition, and this increases their risk of death by around 5%. Multiplying these gives our estimate of 0.5%.

We estimate that around 10% of children under 5 targeted for net campaigns would be acutely malnourished (and untreated). This is based on three estimates of acute malnutrition rates in Niger, Nigeria, and DRC:

• We estimated 9% acute malnutrition in two departments of Niger and 16% in Katsina state, Nigeria, for children aged 6-59 months in our cost-effectiveness analysis for community-based management of acute malnutrition (CMAM), based on an unpublished internal analysis of data provided to us by a non-governmental organization operating in those areas.
• We also identified an estimate of 6.5% acute malnutrition rate from ReliefWeb in DRC,69 although it is unclear what percentage of those children received treatment.

Roughly averaging70 These measurements yields an estimate of around 10% acute malnutrition in children under age 5. This is a crude estimate which we could likely improve with more research.

We estimate that acute malnutrition increases all-cause mortality by around 5 percentage points. This is based on a crude extrapolation from our CMAM cost-effectiveness analysis for children aged 6-59 months in 2 departments in Niger:

• That analysis estimates annual all-cause mortality is 6% for untreated children with acute malnutrition in 2 departments in Niger. This is based on a detailed analysis of data from the Institute for Health Metrics and Evaluation along with “a ceiling analysis” and several subjective adjustments (see this section of our intervention report for more)
• We think this is about 5 percentage points higher than for children without acute malnutrition. That’s based on an estimate that children without acute malnutrition are around 20% as likely to die on average within a one-year period compared to children with acute malnutrition, roughly averaging across risk ratios estimated for moderate and acute malnutrition.71 That means the difference across groups is approximately 6%*(100%-20%) ~= 5%.

We have several uncertainties with this estimate:

• The differences in mortality between acutely malnourished and non-acutely malnourished children are not necessarily causal. There could be other factors which are correlated with malnutrition status and lead to higher mortality, which would mean we are overestimating the causal impact of malnutrition.
• We think this model of changes in all-cause mortality from changes in malnutrition is a highly incomplete model of the consequences of the loss of a food source across a large area which relies on rough categories of malnutrition and mortality risk. We think a likelier model is that most children losing access to fish become somewhat less well-nourished, which leads some of them to have a higher risk of death. We are unsure how to apply a model like that and whether it would lead us to a higher or lower estimate of the effect size.
• The estimates in our CMAM analysis apply only to children ages 6-59 months, but here we apply them to all children under age 5. Very young children (i.e. infants) are probably differentially affected by malnutrition for a variety of reasons (e.g. breastfeeding rates, susceptibility to various infectious diseases); we have not tried to account for this in the shallow analysis here.
• The locations in the CMAM cost-effectiveness analysis may not be representative of areas where we are likely to fund ITN campaigns and where ITN fishing occurs. This was done for convenience; we are unsure whether these areas would have higher or lower baseline mortality and malnutrition rates than campaign areas with ITN fishing.

Adjustment for other harms of fishery depletion

We similarly make a 100% upward adjustment (25th-75th percentiles: 25% - 200%, 95th percentile 500%) to the harms of ITN-induced fishery depletion to account for harms other than increased mortality among children under the age of 5 due to malnutrition.

We expect these other harms could include economic hardship and negative impacts of malnutrition among older people, but we have not modeled these in detail, and our estimate of 100% is a highly subjective guess. We may be able to improve this guess by modeling the economic impacts explicitly, but we are unsure how tractable this would be.

Adjustment for other harms of ITN fishing beyond fishery depletion

We make a 25% upward adjustment to the harms of ITN fishing to account for harms caused by ITN fishing other than fishery depletion. We think these harms are smaller than the reduction in fishing yields because we briefly investigated two possible harms and found little evidence of harm:

• We investigated increased consumption of pyrethroids due to consumption of contaminated water or fish. Our best guess is that, even in hot spots, the increased consumption of pyrethroids would be within the acceptable daily intake proposed by the World Health Organization. (more)
• We briefly looked into increased waste in waterways. We are not sure that nets used for fishing are especially likely to be discarded in waterways, our guess is that ITNs accumulating in waterways account for a very small proportion of total waste in waterways, and we are not sure this is more harmful than other common methods of ITN disposal or destruction. (more)

However, we still make a subjective adjustment because:

• We only identified evidence on leaching of pyrethroids from standard ITNs, but it’s possible that ITN fishing could lead to increased human consumption of other chemicals present in modern nets (e.g. chlorfenapyr, or piperonyl butoxide), which could lead to harm. We’re not aware of evidence on this, but we find it intuitively plausible.
• It’s possible we’ve missed other harms induced by ITN fishing in our review.72

The 25% adjustment is highly subjective. If we thought there was no harm, we’d set this to 0%. If we thought the harm was likely to be equal in expected magnitude to malnutrition due to fishery depletion, we’d set it to 100%. 25% is meant to capture our belief that this harm is likely smaller than the harm from depleted fisheries, but not zero in expectation..

We think we could update on this harm with more research into chemical leaching and additional expert conversations.

Harm from increased consumption of pyrethroids

Summary

As discussed above, chemicals can leach into water from ITNs. We believe there are two ways pyrethroids or other chemicals could be consumed by humans after ITNs are used for fishing: they could accumulate in fish tissues and then be eaten by humans, or they could concentrate in water and be drunk.

Our best guess is that total human consumption of pyrethroids from nets used for fishing is relatively low, around 0.0025mg/kg of body weight per day on average in populations whose entire fish consumption comes from ITN-caught fish, and entire water consumption comes from water sources in which ITNs are used. This is based on data from a review of a couple dozen studies of pyrethroid accumulation in fish and water in various settings across the world. None of these studies occurred in areas where ITNs are known to be used for fishing (the pyrethroid contamination comes from other sources, like agricultural runoff), so our extrapolation is relatively uncertain.

This is 5-25% of the WHO’s acceptable daily intake for these substances, and while we haven’t reviewed the methodology to generate this guideline, we believe WHO is generally a reputable source. Based on this, our best guess is that this level of pyrethroid consumption is not particularly harmful, even in areas where ITN fishing is common, so we don’t currently plan to make an adjustment for increased pyrethroid consumption due to ITN fishing.

However, we have several uncertainties, and we think more research on this topic may be warranted (more). Our uncertainties include:

• As mentioned above, we did not identify any measurements of pyrethroid content in fish or water in areas where fishing with ITNs is known to occur. This means our guesses rely on uncertain extrapolations from lab evidence and areas with agricultural runoff or other sources of pyrethroid exposure.
• We found limited evidence of harms from consumption of other chemicals used in newer ITNs, like chlorfenapyr and piperonyl butoxide, or from consumption of metabolites that form as pyrethroids or other chemicals used on nets decay.73 These chemicals could accumulate more in fish or water than pyrethroids, or be more harmful than pyrethroids. This contributes to our decision to include a 25% adjustment for harms due to causes other than fishery depletion (see above)
• We think it is possible that ITN fishing in small, stagnant bodies of water could cause higher concentrations of chemicals to concentrate in the fish and water, and that groups consuming very high amounts of fish per body weight may be at elevated risk.

To address these uncertainties, we may look into funding monitoring of chemical residues in waterways near ITN distributions, or studies of biomarkers of exposure to these chemicals in people living near areas where ITN fishing is relatively common. (more)

How much might ITN fishing increase pesticide consumption?

Pesticides can leach into water from ITNs (more). We believe there are two ways pyrethroids or other chemicals leaching from nets could be consumed by humans after ITNs are used for fishing: they could accumulate in fish tissues and then be eaten by humans, or they could concentrate in water and be drunk. Our best guess is that total human consumption of pyrethroids from nets used for fishing is relatively low, around 0.0025mg/kg of body weight per day on average in populations whose entire fish consumption comes from ITN-caught fish, and entire water consumption comes from water sources in which ITNs are used.

We were not able to identify evidence on pyrethroid metabolites or other chemicals leaching from nets (e.g. chlorfenapyr, or coatings like per- and polyfluoroalkyl substances) in a brief review. We tentatively guess that their leaching would result in similarly small quantities being consumed, but we are uncertain about this given the lack of evidence.

Consumption of contaminated fish

First, pesticides or other chemicals leaching from nets could be consumed by fish (at low enough concentrations that that the fish do not immediately die) and accumulate in the fish’s tissues over time, then be consumed by people when consuming fish.

Our rough guess is that this would likely lead to pyrethroid consumption in the range of 0.0016mg/kg of body weight per day for a 50kg adult consuming an around four times the average amount of fish (25th-75th percentiles ~0 - 0.01 mg/kg). Our reasoning is summarized in the following table:

What we are estimating	Overall estimate
Pyrethroid concentration in fish swimming in waters with significant ITN fishing (more)	1 mg/kg
Average daily fish consumption in sub-Saharan fishing communities (more)	.08 kg/day
Weight per person (more)	50kg
Total: Daily intake of pyrethroids from eating fish	.0016 mg/kg/day

Pyrethroid concentration in fish

We guess pyrethroids would concentrate in fish at a level of around 1mg/kg (25th-75th percentile 0.1 - 10 mg/kg) in areas with ITN fishing, based on a 2018 review of studies74 measuring pyrethroid accumulation in fish exposed to ITNs in a lab setting. We didn’t closely examine these studies, but our impression from a quick review was that both were consistent with concentrations of about 1mg of pyrethroid per 1kg of fish.75 We have significant uncertainty about how to extrapolate this data to real-world net distributions:

• None of the 17 settings in the review, nor the lab setting of Love et al,76 closely match settings like DRC or Nigeria, or measure pyrethroid residues in fish caught in bodies of water where ITN fishing occurs. The actual concentration could be higher or lower in different fish and different settings.
• These estimates could be too high: the lab study exposed fish in relatively small (5L) tanks to bednets, and our impression is that some of the studies in the measurements in the review of field studies were done because of a hypothesis that fish were being exposed to high concentrations of pyrethroids. We might expect the prevailing concentrations of pesticide to be somewhat higher in these settings than in a typical body of water fished with ITNs, especially if the body of water is large, though we haven’t analyzed this in detail.
• These estimates could be too low: fish exposed to ITNs day after day for many years may accumulate higher concentrations, or certain areas with ITN fishing could have higher concentrations of pyrethroids. One study from the Indus River77 suggests that fish found in an area with heavy agricultural runoff do not have higher concentrations than 1mg/kg per day, but we are uncertain how long fish were exposed to this runoff or if ITN fishing could generate a higher concentration of pyrethroids.

Average daily fish consumption in sub-Saharan fishing communities

We estimate daily fish consumption of around 80g per person per day for a 50kg person. That’s a rough extrapolation from daily fish consumption in Nigeria:

• We think that the average fish consumption per day in Nigeria is around 20 grams per person per day, based on estimates from the FAO. We think consumption in fishing communities might be higher, though the factor of 4 is a guess.
• We use 50kg (~110 pounds) as our weight for this example calculation. We didn’t put significant thought into this, other than that it seemed like a relatively light adult. We suspect children would weigh less, but also consume less fish. We aren’t sure whether their diet would consist of more or less fish per kilogram of body weight than adults, and we haven’t looked into this issue closely.

Drinking contaminated water

Pyrethroids or other chemicals could also leach into the water column and be consumed by humans. Our guess is that people drinking water from areas fished with ITNs consume less than 0.0008 mg/kg of body weight via this channel. That’s a very rough guess, based on the following calculation:

What we are estimating	Overall estimate
Pyrethroid concentration in water with significant ITN fishing (more)	.01 mg/kg
Average daily water consumption (more)	4 kg/day
Weight per person (more)	50kg
Total: Daily intake of pyrethroids from eating fish	0.0008 mg/kg/day

Pyrethroid concentration in water

We guess that the pyrethroid concentration in water with significant ITN fishing is around .01 mg/kg of water. We aren’t aware of any measurements of pyrethroid concentration in areas where ITN fishing is known to occur. Instead, our estimate is a guess informed by a systematic review containing around 50 pyrethroid residue measurements in water across the world.78 We rely on this review because it was the most thorough collection of pyrethroid residue measurements that we could find in a short review. We haven’t reviewed its methodology closely.

Around 80% of sites in the review had all measurements of pyrethroid concentration under 5000ng/L = .005 mg/kg of water,79 though there were exceptions, including an outlier measurement of 13000000 ng/L = 13 mg/kg following an accident.80 We aren’t sure how to translate this range of measurements into a guess at the concentration of pyrethroids in water from ITN fishing. From briefly reviewing some of the underlying studies, we think the measurements were often conducted and reported because of a suspected high pyrethroid content, usually due to runoff from heavy agricultural use of pesticides, and some of the measurements were taken of wastewater instead of drinking water. We think wastewater may have higher sediment content leading to stronger retention of pyrethroids, though we aren’t sure about this.

We subjectively guess ITN fishing might cause concentrations around 10000ng/L = 10ug/L = .01mg/kg. This is higher than most of the measurements observed in the review, but the cases of extremely high pyrethroid concentrations over 1 mg/kg lead us to guess somewhat higher than the rest of the evidence would suggest.

Average daily water consumption

We use 4L as an estimate of daily water consumption. This is a guess, and we didn’t review any data on average water consumption.

Our calculation also assumes that all water consumed is from a body of water contaminated with pyrethroids, but this may not be the case, for example, if some water comes from other sources. We are also unsure whether treatment or filtration could mitigate pesticide contamination in water.

How harmful is increased pesticide consumption due to ITN fishing?

Pyrethroids, their metabolites, or other chemicals leaching from nets may cause toxic effects in humans. Pyrethroids, for example, are a neurotoxin, and can cause acute “dizziness, headache, nausea, muscle twitching, reduced energy, changes in awareness, convulsions and loss of consciousness” at high doses. It is also possible that exposure at a lower dose for a long period of time could cause long-term negative effects. We are aware of various studies showing correlations between pesticide exposure and negative health outcomes, but we are uncertain how to interpret or weigh this evidence (more).

Above we estimated that pyrethroid consumption due to ITN fishing might be around .0024 mg/kg/day in fishing areas (.0016 mg/kg from eating fish and .0008 mg/kg from drinking water). This is around 5-25% of the WHO’s acceptable daily intake for common pyrethroids.81 We haven’t reviewed how this limit value is set, but we believe that the WHO is a reputable organization, and we tentatively guess that consumption at this level is unlikely to cause significant harm.

That said, we think it is possible that exposure to pyrethroids may be higher in small bodies of water that are densely fished with ITNs and where fish is a disproportionately high part of the local diet, and we may conduct additional research on this topic. (more)

Uncertainties and Future Research

We have several uncertainties about our conclusions:

• Does ITN fishing lead to especially high concentrations of pyrethroids? We did not identify any measurements of pyrethroid content in fish or water in areas where fishing with ITNs is known to occur. This means our guesses rely on uncertain extrapolations from lab evidence and areas with agricultural runoff or other sources of pyrethroid exposure.
• Does ITN fishing lead to especially high concentrations of pyrethroids or other chemicals in very small bodies of water, among people eating very large amounts of fish? How common are such scenarios? We think it is possible that ITN fishing in small, stagnant bodies of water could cause higher concentrations of chemicals to concentrate in the fish and water, and that groups consuming very high amounts of fish per body weight may be at elevated risk. We are unsure how to identify such potential trouble spots at scale.
• Does ITN fishing lead to unsafe consumption of other chemicals besides pyrethroids? We didn’t identify or examine evidence on harms from consumption of other chemicals used in newer ITNs, like chlorfenapyr and piperonyl butoxide, or from consumption of metabolites that form as pyrethroids or other chemicals used on nets decay. These chemicals could accumulate more in fish or water than pyrethroids, be more harmful than pyrethroids, or heighten the impact of pyrethroids.
• Are WHO acceptable daily intake standards safe? We rely on the WHO’s acceptable daily intake to benchmark “safe” levels of pyrethroid consumption. We have not reviewed the methodology used to generate these numbers, and we are unsure whether these levels of consumption are truly safe.
  
• Should we be more concerned about observational studies showing people with higher levels of pyrethroid exposure have worse health outcomes? We have identified several observational studies showing higher rates of negative health outcomes for people with higher levels of pyrethroid exposure.82 We suspect these estimates may exceed the causal impact of pyrethroid exposure because people with higher levels of pyrethroid exposure are different than people with lower levels of pyrethroid exposure, but we haven’t reviewed the underlying analyses closely, and we aren’t confident about this assessment.
• Are we interpreting the existing evidence correctly? For the increase in pyrethroid consumption, we rely on a number of studies showing pyrethroid concentrations in fish generally around or below 1mg/kg. We then scale this up by the expected amount of fish that a person might eat in a year. Love 2023 describes a similar calculation, but finds significantly higher estimates of daily pyrethroid consumption,83 exceeding the WHO acceptable daily intake levels even at consumption of less than 10g of fish per day. We spent about an hour trying to replicate Love’s calculations, but were unable to do so, which makes us worried we may be making a calculation error or misinterpreting the relevant data.

We will consider conducting additional research on this topic. In particular, we would be interested in:

• Talking to additional experts about which chemicals leaching from nets would be most harmful, how much exposure to these chemicals would be required to cause harm, and to sense-check our conclusions above.
• Measuring the concentrations of high-risk chemicals present in fish and water in areas where ITN fishing is known to be common. We would be particularly interested in concentrations in very small or shallow ponds that are densely fished with ITNs.
• Measuring human biomarkers of pyrethroid exposure in areas where ITN fishing is common relative to areas where it isn’t, as well as in areas where pyrethroids are commonly used in agriculture. This would help us better understand the magnitude of exposure generated by ITN fishing.

Harm from Waste in Waterways

How could ITN fishing lead to increased waste?

If ITNs are discarded in waterways, they could end up polluting large oceans or lakes. If 235 million nets are distributed in Sub-Saharan Africa in a given year, and ~1% of them are used to fish at some point84 , that would amount to around 2.35 million nets used for fishing. Some portion of these would likely be lost or discarded into the water, and we are uncertain how to quantify this number (25th-75th percentile 2%-75%).

We conducted a brief investigation into this and did not see evidence to make an additional adjustment to account for it.

How harmful is increased waste in waterways due to ITN fishing?

The accumulation of derelict fishing gear, including but limited to ITNs, can cause a number of problems over time. A review from NOAA lists several:

• “Damaging sensitive seafloor habitats, such as coral reefs and seagrass beds,
• Causing problems for vessels by wrapping around rudders and propellers,
• Ruining the gear of other fisheries, and
• Competing with active fishing gear by trapping economically important species.”

We have not looked into any of these harms in detail, and we are unsure how to weigh them relative to potential harms from other (more common) forms of ITN disposal or destruction (e.g. burning85 or littering). We think ITNs account for a very small portion of total aquatic waste; a rough guess is that, if all ITNs used for fishing were eventually lost in water, they would account for less than .05% of the total surface area of netting lost in the ocean alone per year.86 Based on the small scale relative to other oceanic waste, we tentatively guess that this is not a major channel of harm.

Uncertainties and Shortcomings

We are not aware of any detailed analysis of harms due to ITN waste in general, or ITN waste in waterways in particular. We could be wrong that waste in waterways is not more harmful than other forms of waste since ITNs are not biodegradable and waste accumulating in water over time could be especially harmful. We think harms could be higher for smaller inland fisheries or in areas where ITNs are more commonly used for fishing.

What are the benefits of ITN campaigns?

Annual probability of death from malaria

We estimate that the annual probability of death from malaria is 0.54%. That’s based on a simple average of estimated mortality across countries included in our cost-effectiveness analysis for insecticide-treated nets.87 The estimates in that cost-effectiveness analysis come from the Institute for Health Metrics and Evaluation Global Burden of Disease study, along with adjustments for other interventions that we think may reduce malaria burden without being reflected in our estimates. For more information, see this section of our intervention report on insecticide-treated nets.

Reduction in malaria deaths from nets

We estimate that ITNs that are used reduce malaria mortality by 45%. That’s based on the average effect across locations in our cost-effectiveness analysis for ITNs. That estimate is based on a Cochrane meta-analysis, Pryce et al., 2018, which summarizes 23 randomized controlled trials of ITN distributions, along with some subjective adjustments. See this section of our intervention report on insecticide-treated nets for more detail. While we have some uncertainties about our adjustments, we view this as relatively high-quality evidence.

Years of effective net coverage per targeted child

We estimate that a net campaign provides about 1.7 years of effective protection per net used.88 We define "effective protection" as protection at the same level provided by the nets in the studies we rely on to measure the impact of nets on malaria.89 We adjust this estimate downwards based on the number of nets per person targeted, factions of nets delivered and used, and the number of people sleeping under each used net to calculate 1.1 years of effective protection per targeted child on average, and around 0.55 years in a hot spot. The following table summarizes our reasoning:

What we are estimating	Overall estimate	Hot spot estimate
Years of effective coverage per net used (more)	1.7	1
Nets procured per person targeted90	0.55	0.55
Fraction of procured nets that are delivered91	95%	95%
Fraction of delivered nets that are used (more)	63%	63%
Number of people sleeping under each net that is used (more)	1.9	1.9
Total: Person-years of effective coverage per child targeted	1.1	0.66

Years of effective coverage per net used

We estimate that nets provide about 1.7 years of effective protection per net used. This is based on a simple average across locations in our cost-effectiveness analysis for insecticide-treated nets.92 Those estimates are based on studies that tracked, in real-life conditions, the retention and physical integrity of two common net brands. We then compare these results with data and best guesses about net durability in the meta-analysis that measured nets' impact on mortality. We discuss this in more detail in this section of our intervention report for insecticide-treated nets.

We adjust this downward by 40% in an area with higher ITN fishing to get an estimate of ~1 year of coverage. We haven’t investigated this in detail, our adjustment is based on two rough calculations from limited data in east Africa:

• One study in an area on Lake Tanganyika with extremely high prevalence of ITN fishing appeared to report that people typically kept nets for 6-12 months.93 This is about half as long as our typical assumption of 1.2 to 2 years of effective coverage,94 so it would suggest a 50% adjustment. We have several uncertainties about this extrapolation, but they are roughly balanced (discussion in footnote).95
• A survey in Mida Creek, Kenya (where around half of households fished with mosquito nets) reported that 92% of households used old nets to fish.96 If we took this at face value, and assumed that these nets were used for a normal amount of time before being used to fish, and the other ~10% of nets are new or not used for malaria protection, it would suggest a ~10% adjustment.

We arrive at a 40% adjustment by roughly averaging these two adjustments, which yields a 30% adjustment,97 then applying a subjective 10% upwards adjustment for self-reporting bias. We make the self-reporting bias adjustment because we think households may be hesitant to report using nets for purposes other than malaria protection.

This is very uncertain, and we think we could refine this estimate with additional research and expert conversations.

Adjustments for other benefits of campaigns

We make a 100% upward adjustment to cost-effectiveness for other benefits of net campaigns which are included in our cost-effectiveness analysis of nets. On average, around half (52%) of benefits are from under-5 deaths averted,98 and the other half are from lives saved among older children and long-term income benefits. We don’t include benefits from ITN fishing or net repurposing in that analysis, or this one (more)

Adjustment for benefits of ITN fishing and net repurposing

We don’t include any adjustment for benefits from ITN fishing or beneficial net repurposing (e.g., use for covering crops). We think there are likely benefits from both because:

• We don’t think people would use ITNs for fishing if they didn’t get some nutritional or economic benefit, at least in the short run. They probably catch more fish in the short-run than they would otherwise.
• Our best guess is that 90% of net repurposing is not for fishing (more). Many other forms of repurposing, like use for covering crops, hanging as curtains, or as fencing, likely improve quality of life and do not seem obviously harmful.

We haven’t attempted to quantify this because:

• We don’t think it would change our bottom line. We already don’t think ITN fishing is highly common (0.1-0.5% of people), and we don’t think the harms significantly counterbalance the benefits overall (around a 0.5% adjustment), so we plan to continue supporting otherwise cost-effective campaigns. Additionally, in areas where the practice is common and fisheries are overfished at baseline, we think we’d remain worried about ITN fishing even after accounting for benefits. That’s because we worry about decreases in nets being used for protection in areas with high ITN fishing, and our guess is that the externalities from a long-run decrease in fish yields outweigh the private benefits of ITN use for fishing.
• We think it would be difficult to estimate these benefits, but our guess is that they are small relative to the malaria prevention benefits overall. We aren’t sure how long we should expect consumption to increase for households using ITNs to fish, or by how much, nor how much weight to put on other uses of ITNs. However, given that we think ~90% of discarded nets are thrown away or destroyed rather than repurposed (more), and that the malaria prevention benefits of nets are very high, our best guess is that these benefits would be relatively small relative to the malaria prevention benefits, though this is relatively uncertain, and we haven’t investigated this.
• With respect to the benefits of ITN fishing, we also put some weight on the decision of many local communities to make fishing with ITNs illegal. Specifically, this makes us think it’s more likely that the benefits of people being able to fish with ITNs are outweighed by the harms, since community leaders have made the practice illegal, though we give this perspective somewhat less weight as we believe these policy decisions are complicated and reflect a variety of considerations.

This could be wrong. If we identify any hot spots and consider ways to mitigate ITN fishing, we’d like to talk to more local experts on this issue and understand their view on the benefits of ITN fishing and net repurposing.

Outside-the-model considerations

We’ve created a rough, back-of-the-envelope model to quantify the harms of nets for fishing, discussed above.

This section describes several outside-the-model factors that inform our view:

• We think few people who receive ITNs through campaigns use them to fish. (more)
• Our impression is that net campaigns have widespread support, and even researchers focused on the harms of ITN fishing stop short of recommending totally stopping net campaigns. (more)
• It feels wrong to forego the clear benefits of ITNs based on harms we see as highly uncertain. (more)

How many people use ITNs for fishing?

Summary

We estimate that around 0.1-0.5% of people receiving insecticide-treated nets (ITNs) procured for a typical campaign by AMF or Malaria Consortium (25th-75th percentile: 0.01%-1%) in a sub-Saharan African country like DRC or Nigeria use them for fishing, either immediately upon distribution or after some use for malaria prevention.99

We are uncertain how often and how long a given ITN is likely to be used for fishing, and suspect it varies considerably, but our best guess is that ITNs from a given distribution are used for fishing for about 2 years (more).

We think there is significant variation across areas, including many where no people use ITNs to fish, and a small number of areas where at least one member of virtually all households use distributed ITNs to fish at some point. We’d guess these areas account for less than 1% of total areas where nets are distributed (more).

Our estimate is based on two approaches, both of which end up at a similar value.

Estimate 1: Back-of-the-envelope calculation based on total fishing population

We first estimated the percentage of people using nets to fish based on guesses at the percentage of recipients of nets who are engaged in fishing and the share of those people who use insecticide-treated nets to fish. This was inspired by an estimate provided by Rethink Priorities100 , though we’ve modified their calculations slightly.

We come to an estimate of around 0.2-0.3% of people using nets for fishing:

What we are estimating	Value	25th/75th percentiles	“Hot spot”
Percentage of people targeted for a distribution who engage in small-scale commercial or subsistence fishing (more)	1.1%	0.5%-3%	38%101
Percentage of these people who ever use an insecticide-treated net to fish (more)	25%	3%-25%	100%
Total fraction of people using nets for fishing	~0.3%	0.01% - ~1%	38%

We think the advantages of this estimate are:

• It is probably less vulnerable to self-report bias compared to our other estimate. That’s because we start with a survey-based estimate of the total number of people fishing for subsistence or commercial purposes. Since people are not asked if they use ITNs to fish, but instead if they have fished at all, we think they are less likely to misreport fishing. Our other estimate relies on surveys of net use and repurposing, which we think are more vulnerable to self-report bias.
• It is simpler. It requires fewer intermediate calculations, and the logic is relatively straightforward. This also makes us a bit less uncertain about this estimate than our other estimate.

The disadvantages of this estimate are:

• Estimating the total number of people engaged in fishing is challenging. We rely on two studies that suggest a range of 0.4-1.1% of people fishing, but we don’t fully understand their methodologies, nor the difference between the two, which makes us worry that they may not capture all people engaged in fishing.
• We are very uncertain how many people engaged in fishing use nets. 25% is a guess based on limited and variable evidence.
• It doesn’t provide a legible explanation of how the nets come to be used for fishing. This estimate doesn’t explain our best guess as to when nets are being used for fishing, i.e. whether they are leaking from distribution before reaching households, being repurposed by households after distribution, or being pulled out of the trash. Our other estimate provides rough guesses at answers to these questions that we could potentially refine through monitoring. (more)

We think talking to more fishing and fishery management experts could help us better understand how reliable the estimate of people fishing is, and how many people engaged in fishing use nets.

Percentage of population engaged in fishing

We estimate that about 1% of people are engaged in small-scale fishing in sub-Saharan Africa where we might conduct net campaigns. That’s based primarily on a recent study from Virdin et al. (2023), which estimates that in 2016 about 8.7 million people102 were involved in subsistence or commercial fishing at least once per year across all of Africa. This is approximately 0.7% of the total population in Africa at the time.103 We then adjust this up by 50% to account for potential under-measurement.

Another estimate we found from the Fishing and Agriculture Organization (FAO) of the United Nations showed fishery and aquaculture employment of around 5.5 million across Africa in 2020,104 which would imply an estimate of around 0.4- 0.5%.105 We are unsure of the full reason for this difference and use the number from the Virdin study for two reasons:

• Our impression from a superficial review was that Virdin et al.’s estimate was more exhaustive, as it explicitly attempts to account for all people engaged in fishing activities for at least one hour in the last year using survey evidence,106 rather than focusing on commercial employment. We’re unsure, but we think some of these subsistence fishers may be especially likely to use ITNs.
• The estimate from Virdin et al is larger. Since we think undercounting this difficult-to-measure group is a bigger concern, we’re inclined to trust the higher estimate slightly more.

We then adjust this upward by 50% to account for potential underreporting. That’s because we have not closely reviewed the methodology used to generate Virdin et al.’s estimate, and though they mention attempting to adjust for non-response bias107 , we think it might be difficult to capture all people fishing for subsistence:

• Some people fish illegally, and they might be missed by such estimates. This includes some ITN fishers.
• Some areas where people may be fishing for subsistence at higher rates are likely to be difficult to survey effectively.

We assign a 33% upwards adjustment to the first concern and 17% to the second (details in footnote108 ) to arrive at a 50% adjustment. This is a rough guess; it would imply that estimates fail to capture one-third of people engaged in fishing.109

We have significant uncertainty about this number; our 25th percentile is 0.5% of people engaged in fishing; our 75th percentile is 3%. In addition to our uncertainty about the possibility of underreporting, we could also be wrong to use these estimates if the fraction of people engaged in fishing has changed significantly since 2016.110

We think talking to the authors of the Virdin paper or other fishing experts could help us refine this estimate; we also think attaining an estimate of the percentage of the population that lives within 1 kilometer or fishable water might help us sense-check the fishing population.

Percentage of fishing population using insecticide-treated nets to fish

We estimate 25% of people who fish (for subsistence or employment) use ITNs to fish. In a hot spot, we think this number would be 100%. This is a rough guess based on reviewing several surveys and reports of ITN fishing in areas where fishing is common, including two studies from DRC, where we expect to support campaigns conducted over the next 2 years.

We did not identify any large-scale, representative surveys of how many fishers use ITNs. Instead, we found two types of sources:

• We found six studies estimating the fraction of fishers or people/households using ITNs to fish:
  • Rethink Priorities shared three studies with estimates of the fraction of fishers using mosquito nets based on either household surveys or surveys of fishers, which they reported suggested a prevalence of ~2%, 27% and 66% of fishers using mosquito nets.111
  • We also found three additional household surveys in areas of Kenya, Tanzania, and Papua New Guinea where fishing is very common (e.g. coastal areas / fishing villages) that we think suggest percentages of fishers using nets of ~1%, 60%, and ~100%.112 A simple average of these six estimates gives an estimate that around 40% to 45% of fishers use ITNs.
• We identified three additional surveys which measured the fraction of mosquito nets among fishing gears in areas of DRC and Madagascar, generally finding ~25% of fishing gears involved mosquito nets.113 While the fraction of gear used for fishing may not perfectly correspond perfectly to the fraction of fishers using these gears (e.g. if fishers are using multiple types of gears, or if some fishers are using many of one type of gear), we’d guess this roughly corresponds to 25% of fishers using ITNs.

If we took an average of the gear based-estimate and the household/fisher-based estimate, we’d estimate around 30% to 35% of fishers use ITNs. We adjust this downward by about 25% to 30% because we think it’s somewhat likely that some studies of ITN focus on areas known to have especially high rates of ITN fishing.

We didn’t review the methodologies of these studies in detail, and we don’t think that we can draw confident inferences about the rates of ITN fishing from them. We are uncertain whether our downward adjustment for sites with higher rates of ITN fishing being especially likely to have been studies/captured in our review is insufficient. We also worry about reporting bias in studies finding especially low estimates of ITN fishing.

We think additional monitoring in areas where fishing is common may help update our beliefs about this number, and we plan to consider funding this.

Estimate 2: Explicit accounting of nets used for fishing based on survey data

We also estimate the number of nets used for fishing based on survey and administrative data on net use, attrition, and repurposing. We reach an estimate of around 0.4% of people using nets for fishing. We think this is driven by a roughly equal mix114 of people repurposing nets themselves, and nets being lost/stolen/sold and then used for fishing. We quantify this estimate as follows:

What we are estimating	Value	25th-75th percentiles	Hot spot estimate
Nets procured	1,000,000
Fraction of procured nets delivered to households115	95%	90-99.5%
Nets used for fishing while available for malaria protection
Percentage of nets which are slept under while in households116 (more)	70%	60-80%
Percentage of nets slept under at night which are also used for fishing during the day (more)	0.01%	0-0.01%
Percentage of nets available for sleeping under but unused which are used for fishing (more)	0.1%	0-0.1%
Subtotal: Nets used for fishing while in households and available for sleeping under (more)	~350	0-500
Nets used for fishing after repurposing or discarding
Percentage of nets which are eventually sold, repurposed or misused when discarded (as opposed to being destroyed or thrown away) (more)	10%	5%-20%	~100%
Of sold/repurposed/misused nets, percentage used for fishing (more)	10%	5%-20%	~100%
Percentage of nets which are eventually thrown away when discarded (as opposed to being destroyed or repurposed) (more)	~50%	25-75%	0%
Of thrown-away nets, percentage used for fishing by others (more)	0.1%	0.01%-0.3%	n/a
Subtotal: Nets delivered to households that are eventually used for fishing when discarded	~10,000
Nets used for fishing after being lost, stolen, or sold
Percentage of nets not distributed to households that are lost or stolen (more)	50%	10%-75%
Percentage of nets distributed to households that are lost, stolen, sold (more)	6%	2%-12%
Percentage of lost, stolen, or sold nets used for fishing (more)	10%	3%-30%
Subtotal: Nets lost, stolen, or sold eventually used for fishing	~8,200
People using these nets
Number of nets used per person fishing with nets (more)	2.5	1-10
Number of people targeted per net procured117	1.8	1.7-1.9
Total (fraction of people fishing with ITNs)	~0.4%	0.01%-2%

The advantages of this estimate are:

• It provides an explicit accounting for how nets might go from a factory to being used for fishing. Our first estimate relies on an estimate of how many people fish, and then some subjective guesses about how many of those people might use nets, but it doesn’t describe the various pathways by which fishers attain ITNs.
• It allows us to use monitoring data to sense check some of our calculations in the first estimate. For example, we are relatively confident that most nets reach households, and that most nets that reach households are hung, and we feel relatively confident that hung nets are not being used for fishing; this calculation allows us to quantify that.

The disadvantages of this estimate are:

• It partially relies on survey data that we think have a somewhat high risk of self-report bias. We use surveys of net repurposing to estimate the fraction of households that use nets for fishing. We think people may not always report repurposing nets for fishing honestly. We interpret the existing evidence skeptically to account for this, but we could be wrong.
• It is more uncertain.118 That’s because we have more difficult-to-estimate parameters feeding into the final estimate. For example, we think most lost or stolen nets aren’t going to be used for fishing (more). We estimate 10%. But we don’t have much data or intuition to refine this guess, and either 3% or 30% feel plausible, so our bottom line guess could easily be off by a factor of 3 in either direction.
• We make somewhat tenuous assumptions about how many nets a given person uses to fish. In order to compare to our first estimate, we want to know how many people are fishing with ITNs; but it’s more straightforward to aggregate monitoring data at the level of a net rather than a person (e.g. how many nets are used by households, how many nets are lost). Thus we have to make uncertain adjustments at the end to account for the number of ITNs used for fishing per person that uses nets for fishing.

Percentage of nets used for fishing while remaining in households available for sleeping

Our best guess is that a very low fraction (350 per million distributed) of nets in households and available for sleeping under are used for fishing. That’s because we believe households are unlikely to include nets being used for fishing when asked to report any nets “in the house that can be used while sleeping.”119

We think this because using nets for fishing would make them wet and smelly and would often involve cutting and/or re-sewing the nets, and our impression is that such nets would not suitable for sleeping, and most would not be kept in the household at all, but instead would be kept with fishing gear. We have verified this understanding with an expert.120

Of nets recorded as present in households for sleeping under, we estimate that most (70%) are used for malaria prevention, based on a variety of large surveys conducted across many countries over the past 15 years, with adjustments for self-report bias. Based on the above, we think it’s very unlikely (around .01%) that these nets would simultaneously be used for fishing and then hung at night.121 Among the 30% of nets in households not being used for malaria protection, we also think the percentage used for fishing is likely to be very low, but perhaps slightly higher (.1%).

Percentage of discarded nets that are repurposed or misused

We estimate that about 10% of nets are repurposed or misused in some way after being discarded. We base this estimate on Koenker et al’s (2014) analysis of data from 14 post-campaign surveys conducted from 2009-2012 across parts of Senegal, Nigeria, Uganda, and Ghana which found that among nets discarded by households (i.e. no longer available in the household for sleeping under and not given away) within 2-16 months of a distribution, about 10% were repurposed or misused in some way, around 50% thrown away, and around 40% were destroyed.122

We use this study because it includes data from a variety of countries including Nigeria (where we plan to consider funding net campaigns in the future), because it focuses on what happens to nets distributed in mass campaigns (which are the main way we have supported net access in the past), and because it was the most legible and comprehensive collection of data we were able to find in a brief search.

Our estimate could be too low if households are afraid to report using nets for other purposes than intended. In our brief review, we were not able to identify a good way to estimate the magnitude of this reporting bias. On the other hand, this estimate could be too high since it looked at nets discarded relatively quickly after a distribution, and we might intuitively expect nets discarded earlier to be more intact and useful for repurposing. Again, we didn’t find any evidence to quantify this effect. We tentatively assume that the two effects are balanced.

We are also uncertain because this data is somewhat old; though we are unsure whether this would lead to the estimate of repurposing being too high or too low.

Percentage of repurposed/misused nets used for fishing

We estimate that 10% of repurposed/misused nets are used for fishing. That is a guess based on very limited data which may not be representative. We have seen studies which suggest both much lower (0-2%) and much higher rates (~100%) of fishing as a fraction of total alternative use of nets. We aren’t sure how to weigh these different pieces of evidence.

• Two surveys we reviewed suggested that use for fishing accounted for 0-2% of total net repurposing.123 We think there are likely many areas where nets are distributed and fishing is not a major activity, though we are unsure how to quantify this.

• However, these surveys may miss people who are unwilling to admit to using mosquito nets for fishing, so we could be underestimating the prevalence. Moreover, we have seen evidence from some—but not all—specific areas where fishing is common that we believe would suggest much higher rates of nets being repurposed in those areas, from 50% to ~100%.124

10% is a rough guess balancing these considerations. We aren’t confident in how to improve this estimate with desk research, but talking to ITN fishing or malaria prevention experts might help.

Percentage of discarded nets thrown away

We estimate around half of nets discarded are thrown away. We rely on the same survey from Koenker et al 2014 discussed above.

Percentage of nets thrown away that are then used for fishing by others

We estimate that 0.1% of nets thrown away when discarded are then taken from the trash and used for fishing by others. We have read one report of fishermen in Malawi taking ITN scraps from the trash and using them to patch their nets.125 We think the percentage of thrown-out nets that are repurposed for fishing is low because we have not heard of it happening elsewhere and we think many nets that are thrown away are damaged or torn126 , which would make them less suitable for fishing than more intact nets.

Percentage of nets not distributed to households which are lost or stolen

We estimate that 50% of procured nets that are not distributed to households are lost or stolen. This is a rough guess. Other possibilities would be that the nets are damaged or destroyed, or that the nets are routed to other uses, like routine distribution channels. Against Malaria Foundation has provided us with monitoring data describing reasons nets may not reach households during distribution, but we haven’t conducted a detailed analysis of this data to estimate how many nets are lost, stolen, or meet other fates.

Percentage of nets distributed to households which are lost, stolen, or sold

We estimate that about 6% of nets distributed to households are eventually lost, stolen, or sold. This is based on the same analysis of national surveys from Koenker et al (2014) that is discussed above. They report that, out of 3,947 nets lost from households, 207 are stolen, sold, or have “unknown” status. 207/3,947 is around 5%. We then subjectively adjust this upward by 20% to account for the potential that households might underreport selling or losing nets, and instead report that they threw the net away. This adjustment is a guess, and we haven’t identified data that would help us refine it.

Percentage of lost or stolen nets that are used for fishing

We guess that 10% (25th-75th percentile 0.2%-10%) of lost or stolen nets are used for fishing. We are not aware of any quantitative evidence on this topic, and 10% is a very rough guess. Anecdotally, we’ve heard that some nets stolen leak to a black market; we suspect some of those nets may be used for fishing, though others are likely used for protection from malaria or other alternative uses.

We think 10% could be too high because:

• Some lost nets are probably just lost or otherwise temporarily unaccounted for, and not used for any particular purpose. In the Koenker study, around ⅔ of the nets that were lost, sold, or categorized as unknown were categorized as “unknown status”. We think there are lots of ways nets could end up in that category without fishing being a particularly likely outcome (e.g., surveyor error, or the person being surveyed truly didn’t know where the net was).
• Nets that are sold or stolen may still be used for malaria prevention. We think about 1% of nets eventually thrown away or repurposed by the household receiving them.127 A 10% estimate means that we think lost/sold/stolen nets are 10 times more likely to be used for fishing. That could be too high.

We also think it could be too low because:

• It’s possible that people who use their nets for fishing are especially likely to report their nets were stolen or have “unknown” status.
• A qualitative study describes nets being sold post-distribution in waterside communities in Malawi.128 We aren’t sure how many were used for fishing, but it’s plausible that fishing was a common outcome for those nets, and that resale is more common in fishing communities where nets are more economically valuable.
• Another qualitative study describes nets being sold in an internally displaced persons camp in DRC.129 We’re uncertain whether fishing was a likely outcome for these nets (we didn’t see any discussion of the nets being used to fish in the article), but it makes us think nets are generally more likely to be re-sold in economically precarious situations, where misuse for fishing may be more likely.

We aren’t sure how to improve the quality of this estimate.

Number of nets used per person using insecticide-treated nets to fish

We estimate a person using ITNs to fish will use 2.5 ITNs per distribution on average (25-75th percentile 1-10). This is an extremely rough guess based on our expectation that around 2-3 nets would be distributed to an average household, and an assumption that fishers using ITNs would eventually (i.e., perhaps after some use for protection from malaria) use most of the nets distributed to their household to fish.130

We are not aware of any studies which provide a representative estimate of this number. Short et al 2018 surveyed experts across areas where ITNs are distributed and found that 53% observations of ITN fishing were of fishers using single nets, 34% of fishers were using multiple nets sewn together, and 10% were using ITNs as part of other gears.131 We haven’t reviewed the methodology of this study and detail, and we are not sure how representative these expert observations are of ITN fishing in areas where we might support net campaigns.

We suspect this could vary significantly across households and net distributions. That’s because:

• Limited images of ITN fishing we’ve seen in qualitative surveys suggest large heterogeneity. We have seen images of massive fishing gears using over 50 ITNs from Western Zambia,132 though we are unsure over what time frame or how many fishers contributed ITNs to these gears. We have also observed images of groups of 3-4 women in Cabo Delgado, Mozambique apparently using a single ITN to fish kutanda-style.133 If a single person created the large fishing gears in Zambia, these two images would imply estimates of 0.25 to 50+ ITNs per person. We think the average likely lies in between these extremes (25-75th percentile 1-10), but we are especially uncertain about this parameter.
• We are relatively uncertain how long nets last when they are used for fishing and think it probably varies depending on the material of the net. If the nets break faster than the ~2 year average we estimate here, then each household using them for fishing is probably going through more nets. This would make us think that our estimates of how many nets are used per household are a bit too low, but it might also make us worry more about nets being pulled from the trash or sold to be used for fishing.

We think the estimate of 2.5 nets used for fishing per person could be too high an estimate if households use some nets they receive for protection for malaria and some for fishing or if there are often multiple fishers in the same household, but it could also be too low an estimate if people using insecticide-treated nets for fishing also attempt to gather ITNs from other households in order to build larger fishing gears (as may be occurring in western Zambia–though as stated above we are uncertain how many fishers share a given large gear).

How many hot spots are there?

We estimate that less than half a percent of nets are distributed to households in areas where ITN fishing is locally widespread, with at least one member of most households fishing and most fishers using ITNs, and fisheries are overfished at baseline (as in our hot spot example). That’s based on the above estimate of 0.1-0.5% of people using nets to fish, surveys showing some areas where ITNs are used to fish but not universally so, and a belief that not all fisheries are likely to be overfished at baseline. A rough quantification is below:

What we are estimating	Value
Total fraction of people using nets for fishing134	0.3%
Fraction of these people that live in an area where over 75% of households use ITNs to fish (more)	50%
Number of people per household (more)	5.3
Number of people fishing with ITNs per household where at least one person fishes with ITNs in a hot spot (more)	2
Fraction of these households that live near fisheries unsustainably fished at baseline (more)	65%
Fraction of households living in an area where ITN fishing is nearly universal and fisheries are unsustainably fished	0.3%

Both the fraction of households living in areas where fishing is common and the fraction of households living near fisheries unsustainably fished at baseline are highly uncertain. We haven’t spent significant time refining those estimates because we think the number of hot spots depends largely on the overall prevalence of people fishing with ITNs, which we think is low. (more)

Total fraction of people using ITNs for fishing

Based on our estimates above of 0.2-0.3% (more) and 0.4% (more) of people using distributed ITNs to fish, we’d estimate around 0.3% of people use nets to fish at some point. More detail on these estimates is provided above.

Fraction of these people that live in an area where ITN fishing is locally widespread

We estimate half of people engaged in ITN fishing live in an area where such activities are locally widespread, i.e. most households use distributed nets to fish at some point. This is a guess that we haven’t spent much time refining. We think it’s less than 100% because:

• In some places where ITN fishing occurs, we think only a portion of households fish. We haven’t looked into this in detail, but we roughly guess 30% of ITN fishers live in communities where less than 75% of households fish.
• In communities where everyone fishes, and some people use ITNs, we still think there are likely other fishers that don’t use ITNs. We’d guess another 20% of ITN fishers live in communities where only some people use ITNs to fish. That’s a guess based on survey evidence from Benin, where researchers reported professional fishers were less likely to use ITNs to fish than seasonal fishers.135

Average household size

We estimate an average household size of around 5. This is based on average household sizes across several countries136 in DHS/MIS surveys, which we believe to be reasonably high-quality, nationally representative surveys, though we haven’t reviewed the survey methodology in detail.

ITN fishers per household with at least one ITN fisher

In a hot spot where nearly all able-bodied adults fish, we estimate 2 people per household with an ITN fisher use ITNs to fish. This is a guess based on the number of people per household, age distributions, and intuition:

• A typical household contains around 5 people, and around half of the population137 is under age 15. We’d guess children are unlikely to fish at high rates, though they might do so occasionally.
• That leaves around 2.5 people per household who might plausibly fish. In a hot spot village that depends heavily on fishing, we’d guess most of these people fish, so we use an estimate of 2.

We could likely refine this estimate by talking to more experts or more closely reviewing data on the demographics of fishers.

Fraction of these households that live near fisheries unsustainably fished at baseline

We think 65% of ITN fishers live near overfished fisheries. That’s based on our estimate that around 65% of fisheries near potential ITN distributions are overfished at baseline (more). We guess that these are evenly distributed among potential ITN fishers, i.e. that ITN fishers are not more or less likely to live near overfished fisheries compared to other fishers. We are unsure about this; we’d guess ITN fishers might be more likely to live in areas with poor fishery management (which could lead to more overfishing), but also may have less access to other fishing gear (which could lead to less overfishing). We could learn more about this by reaching out to malaria or fishing experts.

How could we be wrong about the number of people using nets to fish?

Our analysis of the fraction of people using ITNs to fish has a number of uncertainties and shortcomings that make us uncertain about our conclusions, including:

• How confident can we be in survey data on uses of nets, or of people fishing? In many areas, fishing with ITNs is illegal,138 so we worry that households may not honestly report if they are using ITNs for fishing. We consider self-report bias when making our estimates, but we are very unsure of the likely magnitude of such bias.
• How generalizable are local estimates of ITN fishing prevalence? As discussed above, much of the evidence on ITN fishing consists of household surveys, interviews with expert witnesses and local officials, and anecdotal reports in small villages. We think it’s likely that ITN fishing is studied in these areas particularly because of concerns that it is common, and we worry that it may lead us to overestimate the frequency with which nets are repurposed for fishing (10% best guess, 5-20% 25th/75th percentiles), and the fraction of fishers using ITNs (25% best guess, 3-25% 25th/75th percentiles).
  
• How common is ITN fishing in the areas where we are likely to make grants? As discussed above, our best guess is that the areas that we are likely to make grants in places like DRC and Nigeria have rates of ITN fishing similar to the national average, but this is uncertain, given our sense that there is significant variability in prevalence from area to area. Both of our partners that implement ITN distributions expressed skepticism about our estimate of the prevalence of ITN fishing in a previous draft of this page (this estimate was framed slightly differently–details in footnote)139 :
  • Malaria Consortium shared that, based on feedback from local staff, they believe our estimate of the prevalence of ITN fishing is too high in Nigeria’s Ondo state and Anambra state, places where we’ve supported campaigns through their organization in the past.140
  • Against Malaria Foundation stated that based on their experience, including post distribution monitoring of AMF funded nets, the number of nets used for fishing from AMF distributions is many orders of magnitude less than the general estimates we have proposed. Their estimate is less than 0.01%.
• Is ITN fishing becoming more or less common over time? We use data from the last 15 years, and we don’t assume any kind of time trend in the prevalence of ITN fishing. This could be wrong: ITN fishing could become more common as households observe other households doing it, or less common as legal enforcement and education about the hazards of ITN fishing increases over time.

• How reliable are estimates of the number of people engaging in any kind of fishing? We use a recent estimate of the total number of people engaging in small-scale commercial or subsistence fishing that comes from combining 78 surveys on the prevalence of fishing. We did not review the methodology used to generate these estimates in detail, and we are unsure if it may be likely to over or underestimate the number of people employed or engaged in fishing.
• How long and how often are ITNs used for fishing, if they are used for fishing? We roughly estimate that ITNs used for fishing are used for 2 years. This is based primarily on two studies of uncertain quality or generalizability which described lifespans of 1-3 or 1-4 years for regular fishing nets of various types, as well as a rough rule of thumb that ITNs used as intended typically wear out within 3 years.
• How plausible is our bottom line estimate? Beyond the specifics of our calculations, we find it hard to triangulate our bottom-line estimate that 0.1-0.5% of people fish with nets against other data points.
• What do other experts think about this? Beyond a conversation with Rebecca Short several years ago141 , and a few recent informal conversations with malaria researchers and residents of countries receiving net distributions, we’ve not engaged with many experts. We aren’t certain what other implementing organizations, local malaria control programs, or other experts think about ITN fishing.
• What should we make of various news reports about fishing with ITNs? We’ve found that searching “mosquito net fishing + [large body of water]” often turns up at least one result describing the practice.142 We aren’t sure whether this should make us think the practice is very common and more than 0.1-0.5% people would engage in the practice, or whether the newsworthiness should make us think that the practice is relatively uncommon, and 25% of fishers using ITNs is too high an estimate.

We think more research can address some of these uncertainties and shortcomings and update us significantly on the prevalence of ITN fishing. We plan to consider the following steps:

• Funding a study to track the lifecycle of procured nets in a given large-scale distribution without relying on surveys. We are unsure what such a study would look like, but we would like to measure the prevalence of ITN fishing in a representative sample of nets distributed in a large area without concerns of large reporting bias. One way to estimate how many ITNs are used for fishing might involve additional monitoring (for example, transects or beach walks to count the number of ITNs observed) or geolocation tracking of a sample of nets to be distributed over time to see if any enter bodies of water. We are uncertain of how scalable and practical these options would be; we plan to look into this more.
• Conducting more research into how to identify areas with elevated levels of ITN fishing in advance of distributions. Based on the evidence described above, we think it’s likely that there are some areas with highly elevated levels of ITN fishing, but we are not sure what characteristics pre-dispose an area to higher levels of ITN fishing beyond access to fishable bodies of water. We think conducting additional studies of prevalence in a few different areas or talking to more experts and program implementers could help us identify characteristics of areas with high prevalence of ITN fishing.
• Fish stock monitoring in potential ITN fishing hot spots, as well as sampling of water/sediment/fish to measure chemical residues after distributions. In areas where we think ITN fishing may be occurring, we will consider measuring fish stocks and pyrethroid residues. Elevations in pyrethroid residues in fish and water or short term increases in fish catch after a distribution (potentially followed by a longer-term decline) would make us more concerned about ITN fishing in an area.

How do policymakers, experts, and members of local communities feel about ITN campaigns?

Our impression is that local communities, experts, and policymakers in malaria-endemic countries generally support ITN campaigns, and we are hesitant to override this without better evidence. We discuss this in our intervention report on insecticide-treated nets:

• We have not investigated this question systematically, e.g., by analyzing or conducting polls of global health experts or national malaria program representatives.
• Through our work on nets, we have built up an impression over time that mass net campaigns are widely supported by the global health community. Evidence feeding into this impression includes:
  • WHO recommends insecticide-treated net distribution as one of only two main recommended strategies for malaria vector control.143
  • Nets have been by far the most widely used malaria prevention tool in recent decades. WHO estimates that 2.5 billion ITNs were supplied globally between 2004 and 2021, and the proportion of people in sub-Saharan Africa with access to at least one ITN rose from 5% to 68% between 2000 and 2021. This compares with 2.4% of the population in sub-Saharan Africa being protected with indoor residual spraying (IRS) in 2021.144 We interpret this as evidence of widespread support for nets.
  • We have heard feedback from conversations with malaria stakeholders over time that net distributions are typically among the highest priority malaria prevention programs for national malaria programs.145

Some other factors that affect our impression are:

• We think most people who receive ITNs use them.146 We think this reflects that they value the protection they provide from mosquitoes.
• Even in an area with widespread ITN fishing in Zambia, local leaders were opposed to stopping distribution. Larsen et al (2018) write (emphasis added):
  • “Despite the number of problems raised with the use of ITNs, both traditional leaders and agency personnel were opposed to stopping their distribution. Perceived dramatic reductions in malaria infections across the region are attributed to the aggressive distribution of ITNs. Rather than stopping ITN distribution traditional leaders suggested various interventions including: increased education, enforcement of laws and rules through closer cooperation between the BRE and the central government agencies against misuse of ITNs and the use of small mesh nets in general, as well as increased monitoring and a program to remove older or extra nets from the population were cited.”
• We found at least two cases in which researchers focused on the harms of ITN fishing stopped short of recommending ceasing of distribution campaigns. We’d suspect there are others, though we’re not sure.
  • Larsen et al (2018) recommend that harms be weighted against benefits.147
  • Bush et al (2017) describe their goal as creating a starting point for building evidence to improve decision-making, rather than a basis for blanket bans on the practice.148

That said, we also think experts and stakeholders believe locally tailored vector control interventions beyond ITN campaigns alone should be considered. These may be particularly important in contexts where low net use or retention generate gaps in protection. Evidence influencing this view includes:

• In 2023, we received feedback on our ITN research from David McGuire, Director of Access and Market Shaping at the Innovative Vector Control Consortium (IVCC), highlighting some concerns about ITN distribution. While emphasizing that ITNs are a good investment overall, he told us:
  • External donors have been focused on ITNs as the primary intervention for vector control, and continue to shift resources away from other effective interventions such as Indoor Residual Spraying (IRS), despite evidence that removal of IRS often leads to increased malaria incidence.
  • Funders of ITNs have historically relied too little on advice from malaria experts in Africa when making decisions about how to best tailor vector control strategies using a broader mix of targeted interventions based on local context.
• In 2024, we spoke to Neil Lobo, a medical entomologist at the University of Notre Dame, who emphasized the importance of identifying gaps in coverage and layering to support populations in high-risk areas with lower net use.149

We also received reports from one of our partners, AMF, on social stigma, local policy, and global health organizations’ views on fishing with ITNs. Examples include:

• In Zambia, the Fisheries Act prohibits the use of mosquito nets for fishing, with penalties including fines and imprisonment, though enforcement was reported to be inconsistent.
• Several countries have implemented formal penalties for ITN fishing - for example, in North Kivu, DRC, penalties include 15-30 days imprisonment and fines of 50,000 to 100,000 Congolese Francs.
• A member of the malaria team at The Global Fund reported that fishing with ITNs is not considered a widespread concern by the The Global Fund, noting that most households use nets as intended and that in many countries fishing is well-regulated with fines for fishing with ITNs.
• Roll Back Malaria has published a Consensus Statement on Repurposing ITNs categorizing fishing with ITNs as "misuse" that is "never acceptable," while recognizing other forms of net repurposing can be beneficial or neutral.
• Local fishermen's associations have themselves spoken out against ITN fishing, citing concerns about juvenile fish being caught due to the small mesh size.

How certain are we about the harms of ITN fishing relative to the benefits?

We think the evidence in favor of ITN campaigns is quite strong: it consists of evidence from a meta-analysis of 23 randomized controlled trials (more) of ITN distributions. Our estimate from these trials is that ITNs lead to a 45% reduction in clinical malaria cases (more). We think this evidence is particularly strong because the random assignment of ITNs makes us confident that differences in outcomes are driven by ITN use rather than any other confounding factors.

In contrast, we are not aware of any randomized trials measuring impacts of ITN distribution on fishery health or potential harms related to ITN fishing. We’re also not aware of observational surveys comparing fish stocks in areas that introduced ITN campaigns relative to otherwise similar areas that didn’t. The evidence on the topic is based on a few household surveys and observational studies of fisheries suggesting that ITNs are sometimes used for fishing (more), combined with theoretical arguments about how this could be harmful, examples of particular fisheries which show signs of being overexploited in which ITNs are used (more), and a lab experiment on chemical leaching which suggests chemicals leached from ITNs and killed fish in a relatively small container (more).

This does not imply that ITNs used for fishing aren’t harmful; indeed, our best guess is that there are some areas where ITN fishing leads to harms that significantly reduce cost-effectiveness. But the lack of strong evidence makes us more hesitant to cut funding for net campaigns, especially when our best guess is that they are small relative to benefits.

What could we do to learn more?

While our best guess is that net-distribution campaigns are still very cost effective despite the use of ITNs for fishing, we are highly uncertain of both the precise prevalence of ITN fishing (which is likely to vary greatly by country or regions within a country) and the impact that fishing with ITNs has and are considering funding additional research. Some projects we may consider include:

• Identifying potential hot spots via extra monitoring. This would let us find hot spots in advance and understand how harmful net fishing is (e.g., how much lower net use is).

Monitoring we’ve seen from Against Malaria Foundation (AMF) and Malaria Consortium doesn’t suggest widespread ITN fishing. For example, in DRC, AMF assesses that most nets (71%) are present 18 months after distribution, and ~90% of nets not present 27 months after distribution are worn out and discarded rather than used for any other purpose.150 If ITN fishing were more widespread, we would expect lower net retention (more) and a higher rate of net repurposing.

However, we also don’t think ITN fishing in a few hotspot areas would automatically be captured in typical monitoring approaches. That’s because fishing isn’t specifically asked about in AMF’s post-distribution monitoring, we guess that some people are unlikely to admit to fishing with ITNs given social stigma or fear of retribution, and lower retention/higher repurposing in a small number of areas may not be obvious in aggregate data.

We think if we were worried about this in a particular area, we would have to support targeted additional monitoring to detect it. This could include:

• Oversampling, i.e., including more waterside communities in post-campaign monitoring in order to build up a larger sample of such areas in order to look for variations in use and retention in these areas.
• Commissioning focus group discussions or transect walks in communities of interest to assess the prevalence of ITN fishing and community views on the practice.
  
• Piloting mitigation efforts or alternative vector control approaches. We want to understand how promising various approaches to reducing the levels of ITN fishing are. In areas where ITN fishing is an issue, we’d prefer to find a way to prevent it without ceasing support for ITN campaigns and losing the benefits that they provide. But we’re not sure how to mitigate damages, and we haven’t seen randomized evidence on the effectiveness of different techniques.
  • We’d be interested in a randomized study trying different approaches to mitigating ITN fishing (discouragement of fishing, simultaneous distribution of other fishing nets, increased monitoring/enforcement) and comparing impacts on ITN-fishing prevalence and fish stocks.
  • We may also explore alternative approaches to mitigate damages, e.g., supporting spatial repellents or indoor residual spraying instead of ITNs in higher-risk areas, or distributing ITNs that are less suitable for fishing in waterside communities.
• Tracking fish stocks in key bodies of water near ITN distributions. Our model of how ITN distributions affect fishing yield is quite uncertain. We think we might gain from triangulating it against trends in fish stocks/yields in areas near ITN distributions, but our impression is that there are not great assessments of fish stocks across sub-Saharan Africa,151 so we think supporting better stock assessments could help us understand the effects of ITN fishing. We also think better data on fish stocks could aid in effective fishery management, regardless of how ITNs affect these stocks.
• Measuring chemical residues from ITNs in bodies of water, fish, and people near ITN distributions. Our best guess is that increased consumption of pyrethroids and other chemicals by humans is not a major channel of ITN fishing harm (more), but this is based on extrapolating from one lab study on one type of ITN and some field measurements of pyrethroids in water and fish due to other forms of pollution. We haven’t seen much evidence on other chemicals used to treat ITNs, or on metabolites of pyrethroids. We think additional data collection could be a cost-effective way to update on the importance of this harm.

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FAO, The State of World Fisheries And Aquaculture 2022, Employment in fisheries and aquaculture	Source (archive)
GiveWell - Community-Based Management of Acute Malnutrition (CMAM)	Source
GiveWell - ITNs for fishing BOTEC	Source
GiveWell, Against Malaria Foundation	Source
GiveWell, Conversation with Rebecca Short, August, 2017	Source (archive)
GiveWell, Conversation with researcher Neil Lobo, University of Notre Dame (unpublished)	Source
GiveWell, GiveWell's CEA of insecticide-treated net (ITN) distributions	Source
GiveWell, GW's analysis of ITN usage following mass campaigns, December 2024	Source
GiveWell, Mass Distribution of Insecticide-Treated Nets (ITNs)	Source
GiveWell, PDMs-Reasons for nets missing	Source
GiveWell, Putting the problem of bed nets used for fishing in perspective	Source
GiveWell, Pyrethroid Concentrations in Fish from Tang et al 2018	Source
GiveWell's CEA of insecticide-treated net (ITN) distributions	Source
Gough et al, 2009	Source (archive)
Gumulira, Forrester & Lazar, (2019)	Source
Gurung et al (2015)	Source
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Hondo et al 2023	Source
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Jones and Unsworth (2019)	Source
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Koenker et al (2014)	Source
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• 1

  You can see our list of all grants made supporting ITN distribution here. Details on our 2024 grants are not publicly available at the time of publishing this page, but we plan to make them available soon.

• 2

  We previously wrote about the topic here. We also commissioned Rethink Priorities to spend 2 days reviewing the literature to better understand the prevalence of mosquito-net fishing, possible links to overfishing, and the harm caused by fishery depletion. Their report is published here.

• 3

  We’ve seen this issue raised in a few places over the years, most recently in WIRED magazine.

• 4

  The implied frequency of ITN use for fishing in these surveys varies between 0.2% of households and as high as 87% of households using ITNs to fish. (more)

• 5
  • This includes six studies based on household surveys estimating the fraction of fishers or people/households using ITNs to fish and three additional surveys which measured the fraction of mosquito nets among fishing gears in areas of DRC and Madagascar.
  • While we see these studies as instructive, they have relatively small sample sizes, varying methods of accounting for bias, and uncertain representativeness. Therefore, we have a high level of uncertainty in these estimates.

• 6

  Cochrane, formerly known as the Cochrane Collaboration, is a not-for-profit research organization which synthesizes health research in systematic reviews.
  “Cochrane is an international network with headquarters in the UK, a registered not-for-profit organization, and a member of the UK National Council for Voluntary Organizations.
  …There are now over 7,500 Cochrane Systematic Reviews which we publish in the Cochrane Library. We also play a key role in developing new methods in evidence synthesis.” Cochrane, "About us"

• 7

  Pryce et al. 2018 is an update to an earlier Cochrane meta-analysis, Lengeler 2004a, and assesses the impact of insecticide resistance on ITN effectiveness since Lengeler 2004a was published. It incorporates three RCTs that were not included in Lengeler 2004a and excludes two RCTs which were previously included.
  “A previous version of this Cochrane Review identified that insecticide-treated nets (ITNs) are effective at reducing child mortality, parasite prevalence, and uncomplicated and severe malaria episodes. Insecticide-treated nets have since become a core intervention for malaria control and have contributed greatly to the dramatic decline in disease incidence and malaria-related deaths seen since the turn of the millennium. However, this time period has also seen a rise in resistance to pyrethroids (the insecticide used in ITNs), raising questions over whether the evidence from trials conducted before resistance became widespread can be applied to estimate the impact of ITNs on malaria transmission today.” Pryce et al. 2018, p. 1.
  "After searching for relevant trials up to 18 April 2018, we identified three new randomized controlled trials (studies in which participants are assigned to a treatment group using a random method). In total, we included 23 trials, enrolling more than 275,000 adults and children, to evaluate the effectiveness of ITNs for reducing the burden of malaria." Pryce et al. 2018, pp. 2-3.
  "We also screened the full texts of the 22 trials included in the previous version of the review against the inclusion criteria of the review update. Of these, we identified 20 trials for inclusion in the updated review." Pryce et al. 2018, p. 11.
  "A previous version of this Cochrane Review [Lengeler 2004a] identified that insecticide-treated nets (ITNs) are effective at reducing child mortality, parasite prevalence, and uncomplicated and severe malaria episodes." Pryce et al. 2018, p. 1.
  After revising the review, the authors concluded that the evidence continues to support the main conclusions from Lengeler 2004a: "ITNs, whether compared to no nets or to untreated nets, continue to be effective at reducing child mortality and malaria-related illness in affected areas." Pryce et al. 2018, p. 3

• 8

  While we previously cited a figure of 63% of ITNs being slept under in our intervention report for mass distributions of ITNs, we are using a figure of 70% here based on the results of an updated analysis.

• 9

  “A total of 196 surveys were administered over a four-week period with a 100% response rate. Over 87% of households surveyed have used a mosquito bed net for fishing at some point. The majority of respondents reported receiving their bed net for free (96.4%), observing “many” residents of their village using bed nets for fishing (97.4%), and noticing a subjective decrease in the fish supply over time (64.9%)." - McLean et al, 2014.

• 10

  “Around 67% of the population reported using impregnated mosquito nets as fishing tools and 33% exclusively for malaria.” - Hondo et al 2023

• 11

  “All households reported owning a bed net at some point in time, with the median ownership duration of six to 12 months (minimum less than six months, maximum over five years). “ - McLean et al, 2014.

• 12

  See how we arrived at this figure here.

• 13

  You can see our list of all grants made supporting ITN distribution here. Details on our 2024 grants are not publicly available at the time of publishing this page, but we plan to make them available soon.

• 14

  “Partners, particularly local health facilities, malaria control coordinators and village leaders, do address the issue of anti-malaria nets and fishing where relevant i.e. where there is a relevant body of water or water course nearby and there is some knowledge or feedback that nets are or may be being used for fishing. Nets being used for fishing does not occur in all locations where there is water, so our understanding is that this issue is not addressed as a default. Where nets and fishing is addressed, the common messaging is that anti-malaria nets 1. should be used in the home as crucial malaria protection and 2. when no longer able to be used to protect sleeping spaces, should not be used for fishing. Messaging can include how nets can be repurposed at their end of their useful life of covering sleeping spaces. It is commonly understood and a reality that non-viable nets can have a useful second life, for example to cover window openings, to cover small crop areas, as a barrier/fencing and in other ways." Rob Mather, Chief Executive Officer, Against Malaria Foundation, email to GiveWell, April 8, 2024 (unpublished).

• 15

  From notes on fishing with ITNs written by Against Malaria Foundation, provided to GiveWell, September 2024 (unpublished)

  • “For each province a series of communication activities are conducted, including tv/radio emissions, billboards/posters and village criers.
  • An important part of these activities is around raising awareness to the population on the correct use of nets.
  • Before creating the radio spots/key messages to be delivered, a "community diagnosis" is conducted for each health zone. This consists of consulting local leaders, village chiefs, and community health workers to understand the main causes of concern regarding net use. These are then addressed with tailor-made messaging.
  • In health zones that are fluvial or water-based, this messaging will include mention of not using nets for fishing in the affected communities i.e. not necessarily across the whole health zone. This is because health zones are large and affected communities usually represent a small percentage (~20%) of the total communities in a health zone.
  • By design, however, in health zones where this is not a problem, misuse of nets for fishing is not mentioned to avoid a situation where the communication gives the idea to householders in the first place.”

• 16

  Notes on fishing with ITNs written by Against Malaria Foundation, provided to GiveWell, September 2024 (unpublished) discussed fines being commonplace for the misuse of ITNs in countries including the DRC, Nigeria, and Uganda.

• 17

  We’d roughly guess that ITNs provide 0.2 to 1 years of effective coverage in hot spots (25th-75th percentiles; central estimate 0.55). That could reduce the hot spot harms to around a -30% adjustment or increase it to ~ -100%. See these cells in our rough back-of-the-envelope calculation.

• 18
  • “Small species and juvenile fish have the highest level of biological production (Morgan et al. 1980), the highest level of essential micronutrients since they are consumed whole, and they only need sun drying for preservation. Catching fish in proportion to their productivity, so-called balanced harvest (Garcia et al. 2012), which favours small fish, is also the most sustainable and least disturbing to ecosystem structure and resilience (Law et al 2012, 2013)." - Kolding, Zweitan, and Mosepele (2015)
  • “Thus, in a multi-species small-scale fishery, e.g. Mozambique, where food security is the prime concern, 5 kg of small fish are more valuable than 1 kg of large. Clearly, [mosquito net fishing] contribute[s] to food security, and a far more nuanced analysis is required to understand any system-level effects.” - Tilley et al (2020)

• 19
  • "Our results indicate a substantial removal of juveniles from coastal seagrass meadows, many of which are commercially important in the region or play important ecological roles. We conclude that the use of mosquito nets for fishing may contribute to food insecurity, greater poverty and the loss of ecosystem functioning." - Jones and Unsworth (2019)
  • "Although human toxicity to the pyrethroid insecticides that impregnate ITNs is traditionally thought to be low, recent scientific advances have shown that pyrethroid exposure is associated with a host of human health issues, including neurocognitive developmental disorders, diabetes, and cardiovascular disease." and “Small mesh sizes allow the capture of very small-bodied fish species and juveniles of larger-bodied fish species as has been documented in Mozambique (Jones and Unsworth 2020), which can limit the longer-term availability of fish and lead to fishery decline and collapse, depending on the local ecological conditions." - Larsen et al (2021)

• 20

  In this investigation and past investigations into this topic, we’ve spoken with partners at Against Malaria Foundation and Malaria Consortium, two academics with experience in fisheries research, and Aisling Leow and Tom Hird from Rethink Priorities. We’ve also had informal conversations with three other malaria experts, a forecasting expert, and a water engineer.

• 21

  From Impact of mosquito nets on fisheries, Rethink Priorities (2024):

  • “Samoilys et al. (2019) observed the use of different fishing gear in six rural villages dependent on small-scale fishing across 80 km of coastline in Mozambique. Based on interviews with 2,454 fishers, the study found that on average mosquito nets were used by 27% of fishers, but this varied from 10% to 42% across villages.
  • A report on destructive fishing activities in the South coast of Kenya finds that 3% of those surveyed use small size mesh nets, like mosquito nets (Munyi, 2024). However, the underlying data is from interviews conducted in 2007- 2008, and the data collection section does not indicate the sample size. We guess that around half of small-mesh nets are ITNs–this is highly uncertain but does not significantly impact our bottom line.
  • Hondo et al.(2023) included data from surveys with 280 individuals conducted in lake-side villages in Benin in 2020. The authors find that two thirds of those surveyed use mosquito nets for fishing.”

• 22
  • Mutuku et al 2013 assessed that 6 of 2,786 nets (0.2%) found in households surveyed in coastal Kwale County, Kenya, were used for fishing. While we aren’t sure how many households in this area are engaged in fishing total, but we take a guess of around 20% given its location and reports in one town within Vanga subdistrict (part of the surveyed area) that around 19% of the population engaged in fishing. Based on this, we’d estimate that around 1% of fishers are using mosquito nets (0.2% / 20% = 1%).
  • Millat-Martinez et al. 2021 finds 30% of nets were repurposed for fishing two years after a mass distribution campaign in the Lihir Islands in Papua New Guinea. “Repurposed nets were reported serving as fishing nets (30.4 %).” Again, we are unsure of the number of people engaged in fishing with these repurposed nets, and of the total population engaged in fishing. We roughly guess that the fraction of people using nets is equal to the fraction of nets used to fish (30%) and that about half of the population is engaged in fishing for subsistence or livelihood. This would suggest 60% of fishers are using mosquito nets.
  • McLean et al 2014 report that over 87% of households surveyed across 7 villages in Lagosa Ward, Tanzania, had used a mosquito net for fishing at some point. We are uncertain how often these fishers used ITNs to fish, and how many people are engaged in fishing total, but we’d guess that this estimate might suggest that close to 100% of people fishing have used mosquito nets at some point (e.g. if 87% of households fish and all those who fish use ITNs to do so).

• 23
  • Ranaivomanana et al 2023 surveyed boats fishing in the Bay of Toliara and estimated that ~30% used mosquito-net trawls or beach seines with mosquito-net codends: “ Five fishing gears are commonly used in the area, including 10-45 mm mesh-size gillnets, handlines, spear guns, mosquito-net trawls, and beach seines with mosquito-net codend (Table 1).
    • “ Table 1 states that 14.7% of boats used mosquito-net trawls and 14.4% used beach seines. 14.7+14.4% = 29%.
  • Against Malaria Foundation shared two small studies from the DRC showing nets accounted for ~15-30% of fishing gear, writing “Two studies focused on the fishing industry were published.
    • The first is from Pool Malébo which is the wide part of the Congo river between Kinshasa and Brazabville. It reports that ITNs make up 27% of the fishing accessory used by fishermen/women. The report is here, data is from 2019 and report published in 2022.
    • Another study published in 2023 shows the same indicator as 15% - 26% from site to site.” – Notes from AMF provided to GiveWell, September 2024
    • AMF also noted that “while these studies do show that nets are used in these areas with high fishing activity, the percentages give no indication as to the overall % of distributed nets that go to be used in fishing.”
  • Total estimate averaging the three studies above, using the midpoint of the range from the third: (29% + 27% + (15% + 26%)/2)/3 ~25%.

• 24From Hondo et al 2023, 89 of 180 (49%) surveyed professional fishermen reported using mosquito nets for fishing while 100 of 102 (98%) seasonal fishermen reported using mosquito nets for fishing. See table 4.

• 25

  “An online survey was conducted to collate information on the prevalence and characteristics of MNF as it was the fastest and most cost effective way to collate information from various locations in the world. Two separate surveys were used, one for individuals who had knowledge of small-scale artisanal fishing and another for individuals involved in malaria control efforts in fishing areas of developing countries. Fisheries scientists/officers, ecologists, conservation, development and health practitioners were targeted and contacted by email, social media and subscribed mailing lists.” - Gurung, 2015.

• 26

  “The majority of respondents (41/54) stated that MNs were used in addition to existing gears. Eight respondents stated that MNs were used instead of existing gears with a respondent in Tanzania suggesting that MNs are replacing other small mesh size nets” - Gurung, 2015

• 27

  “The jahoto net was introduced in 1989 (Langley 2006) is between 300-800 m in length and has a fall length of 12m made from thicker nylon than most other nets (force #3) and has a small mesh size around 1 finger/ 1 thumb width (Figure 18). It is designed for catching small shoaling fish close to the shore and for this reason it is often used with a mosquito net (makarakara) pocket in the centre to retain the smallest of the fish and often when seine netting. “Gough et al, 2009, see figure 18.

• 28

  “ A jahoto or feripe net will often have a mosquito net cod end at the back where the fish will collect as the net is pulled towards the shore. Ropes are attached to both ends of the net and the fishermen pull the net in towards the beach (Figure 24). The first pirogue collects up the net whilst the second collects the fish caught in the net. “ Gough et al, 2009

• 29Source: NOAA Teacher at Sea blog.
  
• 30If around 80% of ITN fishers use other gears, and half their catch is attributable to ITNs (a highly uncertain guess), then total share of ITN fishers’ catch attributable to ITNs is 80%*50% + 20%*100% = 60%.
• 31

  The difference between this adjustment and the portion of the previous adjustment attributable to other gears is that the previous adjustment accounts for the share of catch attributable to other gears being used in conjunction with ITNs, while this adjustment accounts for the possible behavioral response of fishers using alternative gear instead of ITNs (e.g. replacing ITNs with cloth).

• 32

  “The word Kutanda previously related to a traditional form of fishing mainly conducted by women using cloth, now used to describe the predominantly female form of MNF. More broadly throughout East Africa this practice may also be referred to as ‘Tandilo’ fishing (Bush et al., 2017)....‘There have always been Kutanda fishers, I can’t remember when, we have fished since childhood with Kapulana [cloth skirts]. Before these nets were free we could buy them from Tanzania.’ (Female respondent, FGD Lalane).‘ ” - Short et al, 2020

• 33

  ““All women basically use the small mesh nets now (MNs). Before they would use kangas (the cloth material they use as skirts/dresses - this was a traditional fishing method before) but since MNs are easier and fairly cheap in local stores the kangas have been replaced.” - Gurung, 2015

• 34

  “When asked what gears were used before mosquito nets were available, 11 of 24 of MNF households said they used larger nets not targeting small fish, four referred to tandilo fishing using cloths or sacks to catch small fish, while three said they did not fish at all before mosquito nets were available.” - Bush et al, 2017.

• 35

  Emphasis added: “The RAM Legacy database – first launched in 2009 – is led by a team at the University of Washington – and is the most widely used in research and is adopted by the UN Fisheries Division. Back in 2009, it covered 166 of the world’s fish stocks, which accounted for around 20% of global fish catch.10 Today, it covers over 1,200 fish stocks, which is more than 50% of the global catch.
  It covers many of the world’s key fishing regions: the United States, Canada, Norway, Iceland, Europe, Peru, Chile, Argentina, high-seas tuna fisheries, New Zealand, and Japan, plus most of the major fisheries of South Africa and Australia.
  Unfortunately, there are key regions where we have very little data. The database is missing data from most Asian, African, and Latin American fisheries. We see this in the map, which details the coverage of fish stocks in the RAM database. Most fisheries across Europe and the Americas have good coverage. Most fisheries across Asia do not.” - Hannah Ritchie and Max Roser (2021) - “Fish and Overfishing”

• 36

  “In 2019, among FAO’s 16 Major Fishing Areas, the Southeast Pacific (Area 87) had the highest percentage (66.7 percent) of stocks fished at unsustainable levels, followed by the Mediterranean and Black Sea (Area 37) 63.4 percent (Figure 24). In contrast, the Northeast Pacific (Area 67), Eastern Central Pacific (Area 77), Western Central Pacific (Area 71) and Southwest Pacific (Area 81) had the lowest proportion (13–23 percent) of stocks fished at biologically unsustainable levels. Other areas varied between 27 percent and 45 percent in 2019 (Figure 24). “ - "State of World Fisheries and Agriculture 2022 | FAO

• 37

  See Figure 26 of the FAO’s The state of world fisheries and aquaculture 2022 report here

• 38

  “Overall annual catch was 35% lower (-640 t*year-1) than the estimated catch in the Bay of Toliara in 1990 (Laroche & Ramananarivo 1995). This severe decline corresponded to a 58% decline in the spatial catch rate (12 t*km-2*year-1 to 5.0 t*km-2*year-1) as fishing grounds expanded from 153 km² to 273 km² over the ~30-year period.” - Ranaivomanana et al 2023

• 39

  “Our findings suggest that mosquito-net trawls exacerbated fishing pressure on coral reef fishes, which likely contributed to the dramatic decline in overall catch.” - Ranaivomanana et al 2023

• 40

  “The extremely low standing stock biomass estimated in this study is probably caused by long-term overexploitation of the near-shore fisheries for Kenya and Tanzania. The tralwabble areas of Kenya and Tanzania are heavily exploited by semi-commercial trawlers for penaeid shrimps with high fish bycatch levels (Bwathondi et al., 2002; Fulanda et al., 2011; Mungaet al., 2012). The over-exploitation by artisanal fishers, high fish bycatch levels in commercial trawlers, together with the larger spatial coverage in this study, often including areas of low productivity, likely explains the very low standing stock biomass estimated in this study. Furthermore, our study did not include schools of pelagic clupeidae(Sardinellaspp.)that were included in the historical estimates.” - Kaunda-Arara et al, 2016

• 41

  “The analysis shows that the current effort of 65,232 net-hauls has a yield of 6,000 tonnes, indicating that the Usipa fishery is currently overexploited over the optimum bio-economic level and even beyond the open access yield. We recommend reducing the fishing effort by 54% to realize the best economic benefits (Production at MEY) and end overfishing to protect the fishery from biological and economic collapses.” - Gumulira, Forrester & Lazar, (2019)

• 42

  “The long-term rising trend in inland fisheries production can partially be attributed to improved reporting and assessment at the country level. Nevertheless, many of the data collection systems for inland waters are still unreliable, or in some cases non-existent; furthermore, improvements in reporting may also mask trends in individual countries. Equally important, many countries do not report catches for inland fisheries, or they report only partial catches, while FAO estimates a proportionately higher amount of the total catches for inland waters compared with marine waters.” - "State of World Fisheries and Agriculture | FAO (2022) | FAO

• 43

  For example, a technical paper from the UN FAO states, “There is no clear consensus or precise estimates of suitable thresholds for de ning status of stocks.” - Review of the state of world marine fishery resources | FAO (2011)

• 44

  We think that the ITN distribution would lead to short-term increases in yield (due to increased efficiency), but eventual declines. We’re not sure the exact timeline on which this would occur, but our overall guess reflects that we think the declines outweigh short-term benefits in overfished fisheries.

• 45Source: Fish and Overfishing, Our World in Data
  
• 46

  One contextual factor particularly relevant to ITNs is that they likely catch disproportionately small fish. This is discussed more more. We suspect there are many other such contextual factors that would impact our estimate of the depletion in fish stocks coming from an increase in fishing intensity due to ITNs, including the size of body of water being fished, the variety of species being fished, and alternative methods of fishing used.

• 47

  For example, Short et al (2020) note that kutanda fishing targets a particular species, g.oyena: “Our results suggest that rather than indiscriminate, MNF may actually be a highly selective method compared to legal gears. Certainly for Kutanda with the vast majority of its catch being comprised of just a single species; G. oyena.” - Short et al (2020).

• 48

  Using the first five rows of our back-of-the-envelope calculation above, we estimate a depletion of 1.35% (25% * 40% * (1-60%))/ (1 - 25% * 40% * (1-60%) * (1+65%) = 1.35% due to increased fishing intensity from ITNs. See this row of our BOTEC

• 49

  We've elected not to model the effects of the small mesh size of ITNs for fishing in hotspots explicitly due to our uncertainties around where hotspots are and how fishing in those areas may differ from typical areas. We instead rely on the percentage adjustment implied by our overall estimates.This is a source of uncertainty in our estimate of the harms due to ITN fishing in hot spots.

• 50

  On the removal of juvenile fish, we identified one study that looks at fish caught with mosquito nets at sites in northern Mozambique and another in Madagascar. Additionally, we identified a survey in which several dozen respondents verified juvenile capture. We remain unsure of both the overall scale of juvenile removal across sub-Saharan Africa, and how harmful juvenile removal is.

  • "In this study, we present the first detailed analysis of the sustainability of these fisheries by examining the diversity, age class, trophic structure and magnitude of biomass removal. Dragnet landings, one of two gear types in which mosquito nets can be utilised, were recorded across ten sites in northern Mozambique where the use of Mosquito nets for fishing is common. Our results indicate a substantial removal of juveniles from coastal seagrass meadows, many of which are commercially important in the region or play important ecological roles." Jones and Unsworth (2019).
  • “ From May 2018 to April 2019, size distribution and composition of coral reef fish catches were monitored through a participatory landing survey in southwestern Madagascar....Overall, 47% of individual fish were juveniles. Fish length differed significantly among gears (Figure 4). Mosquito net trawls (6.3 cm median length, P < 2.10-16, Appendix 3) and beach seines (7.3 cm, P = 0.023, Appendix 3) caught significantly smaller fish than gillnets (15.2 cm) and handlines (14.6 cm), while spearguns caught significantly larger fish that both latter gears (18.7 cm, P = 0.0007, Appendix 3). Small fish (≤9 cm, 72% of total catch) were mostly harvested by mosquito net trawls (80%) and beach seines (20%). Medium-sized fish (915 cm, 16% of total catch) and large fish (>15 cm, 6.5% of total catch) were mainly harvested by other gears. Juveniles were 54-96% of overall catch numbers of seven predominant, large-sized fish families (Scaridae, Lethrinidae, Siganidae, Acanthuridae, Synodontidae, Mullidae, and Labridae). Juvenile fish were a small proportion (from 0 % to 22.1 %) of the catch of smallsized fish families (Gobiidae, Syngnathidae, Pomacentridae, Apogonidae, Bleniidae, and Leiognathidae, Table 4) that were mainly harvested by mosquito net trawl and beach seine.” Ranaivomanana et al (2023)
  • “Fifty-nine respondents cited presence of juveniles in MN [mosquito-net] catch….Although it is impossible to verify the specific biological knowledge of every respondent, enough respondents were able to identify fish to family or species level, and verify juvenile capture at this scale to warrant investigation. Within the literature this is the biggest concern pertaining to MNF due to the undermining of size-selective management [5], and the potential for growth and/or recruitment overfishing of stocks that are relied upon by other user groups.” Short et al 2018

• 51

  “This increase in [mosquito net fishing] prevalence included a process of conversion to Kutanda from the use of traditional cloth fishing gear, and uptake of Chicocota methods by local men, as opposed to just encouragement of new entrants to the fishery. There have always been Kutanda fishers, I can’t remember when, we have fished since childhood with Kapulana [cloth skirts]. Before these nets were free we could buy them from Tanzania. (Female respondent, FGD Lalane) ” - Short et al, 2020

• 52

  Short et al (2018) state that juvenile capture “is the biggest concern pertaining to MNF due to the undermining of size-selective management, and the potential for growth and/or recruitment overfishing of stocks that are relied upon by other user groups,” but advocates of a balanced harvest approach argue that the capture of fish of all sizes may “reduce fishing impact on ecosystem structure and increase the aggregate yield”. Additionally, at least one author has argued that there is insufficient scale of juvenile catch to cause harms, even under the size-selective management paradigm.

• 53

  “Many economies and people are dependent on fisheries and aquaculture for food, livelihoods and revenue generation. Greenhouse gas accumulation, climate change and the associated impacts in terms of sea-level rise, ocean acidification and changes in salinity, precipitation, groundwater and river flows, water stresses and extreme weather events are changing the productivity of aquatic habitats, modifying the distribution and productivity of both marine and freshwater fish species. Such changes are affecting the seasonality of biological and biophysical processes as well as increasing direct risks to human well-being, infrastructure and processes throughout the fisheries and aquaculture production chain.” Assessing climate change vulnerability in fisheries and aquaculture - FAO - Assessing climate change vulnerability in fisheries and aquaculture

• 54

  See Figure 7 of Short et al 2020, which shows that virtually all g. Oyena caught in a survey in Mozambique were caught using “kutanda” or “chicocota” fishing, which both involve the use of mosquito nets.

• 55

  We've elected not to model the potential toxic effects of ITNs for fishing in hotspots explicitly due to our uncertainties around where hotspots are and how fishing in those areas may differ from typical areas. We instead rely on the percentage adjustment implied by our overall estimates.This is a source of uncertainty in our estimate of the harms due to ITN fishing in hot spots.

• 56

  See the results section of Love (2023) for the lethality of two pyrethroids, alpha-cypermethrin and deltamethrin, on D. magna (water fleas) and P. promelas (fathead minnows) pg 85-89

• 57

  “In order to equate the data from this chapter to a “real world” scenario, a pan lake equivalent to 1,000m3 was selected. Using this size pan lake, our experiments would be the equivalent of using 472 (average of 141,000cm2) nets together to reach the same proportion. When this calculation is used for the 1cm2 net size, this is the equivalent of fishing with 23 nets in a 1,000m3 pan lake.” Love 2023. We round 23 and 472 to “20 to 500” in the body of the text.

• 58

  As a rough comparison, to match that concentration in Lake Tanganyika (volume 18,500 km^3) would require around 370 billion nets (20*18,500*1000^3/1000). This comparison is intended as a crude sense check and has a number of limitations (e.g. concentration would likely be higher in heavily fished areas near the shore, particularly in stagnant areas with more suspended sediment, some mosquito nets used for fishing in a real lake may be older and already have lost much of their insecticide content).

• 59
  • “P. promelas has a moderately forked caudal fin, 8 dorsal fin rays, 7 anal fin rays and 44-50 lateral line scales. The maximum length recorded for the fish is 10 cm but length can range from 2.5 cm to 7.5 cm long.” - Wakefield 2012
  • We believe that 2.5 to 7.5 centimeters is relatively small, though we haven’t investigated what percentage of biomass caught is accounted for by fish of this size.

• 60

  “For capture fisheries, FAO statistics [12] reported that, in 2017, Africa produced 7.0 million tonnes of marine capture fisheries and 3.0 million tonnes of inland fisheries. However, Kolding et al. [36] estimated substantially higher production (about 20 million tonnes) from inland fisheries based on the total freshwater resources available in Africa (e.g., lakes, rivers, reservoirs, flood plains, and swamps).” Chan et al (2021)

  • 7.0 million tons of marine fisheries and 3.0 million tons inland implies 3/10 = 30%. 7.0 million tons of marine fisheries and 20.0 million tons inland implies 20/27=75%.

• 61

  “Repurposed nets were reported serving as fishing nets (30.4 %), fruits and seedlings protection (26.6 %), covering up food (19.0 %) and bed linen (11.5 %).” - Millat-Martinez et al (2021)

• 62

  The authors of the study write, “Strategies to prevent malaria and alternative uses given to LLINs were asked with an open question, and household heads were prompt to list as many options as they considered relevant.” After a brief review of the questionnaire, it seems possible to that households would have listed fishing as a use if they ever used a net to fish or, potentially, even if they thought fishing was a possible alternative use of their nets, since the data collection tool simply reads “other uses of bed nets in this house”. - Millat-Martinez et al (2021)

• 63

  See the life spans for different net types in the Results and Discussion section Ali et al (2014)

• 64

  See the Net360 case study by Verifact. We are uncertain of the reliability of this finding as we are unfamiliar with the author (Verifact) and there is no discussion of methods or peer review.

• 65

  See Ritchie and Roser, (2021, updated 2024)

  • “What we see clearly is that the deeper the trawl digs into the sediment, the more biota we kill. Otter trawls have the lowest impact: they dig just 2.4 centimeters into the sediment, and around 6% of organisms are lost. Beam trawls lose 14%. Towed dredges dig twice as deep, and one-fifth of organisms are killed off. The most damaging method is hydraulic dredging: it digs deep into the sediment at 16 centimeters, and 41% of organisms are destroyed as a result.”
  • “For the ecosystem to get back to its pre-trawling state takes a few years if it’s left alone. In their analysis, Hiddink and colleagues found average recovery times (where ‘recovery’ means getting back to 95% of pre-trawling biomass levels) in the range of 1.9 to 6.4 years. The differences here were dependent on the method used – the shallower otter trawls caused less damage and recovered more quickly than the deep hydraulic trawling – and the environmental context, such as the type of seabed. This finding was consistent with previous studies, finding recovery to be in the range of years [this study, for example, reports a 4-5 year recovery time across multiple commercial trawling sites].”

• 66

  Since we’d intend to capture the effects of the 2024 campaign in the “baseline” fish stocks for the 2027 campaign, we’d model the total depletion in 2027-2028 as (100%-3%)*(100%-3%) - 1= -5.91%.

• 67

  Per capita sources of protein - Our World in Data

• 68

  (20%+16%+17%+16%+16%+16%+14%+17%) / 8 = 16.4%

• 69

  Child malnutrition remains a significant public health concern in the DRC, with acute malnutrition rates stuck at 6.5 % for over two decades. Insecurity exacerbates the malnutrition crisis in Eastern DRC | ReliefWeb (2023)

• 70

  (6.5+9+16)/3 ~= 10.

• 71

  From our page on CMAM: “Children with MAM and SAM are at greatly elevated risk of dying compared to non-malnourished children. In the locations we support, we estimate that children with untreated MAM are roughly 2.5 times more likely to die than children without malnutrition over a one-year period following measurement of their weight and height. We estimate that children with untreated SAM are roughly 7 times more likely to die than children without malnutrition. Our estimates are based on evidence from historical studies of mortality in children with untreated malnutrition.”

  • We take the midpoint of these two for this analysis, and assume children with acute malnutrition are 4.75x more likely to die on average. 1 / 4.75 ~= 21%.

• 72

  To identify channels of harm from ITN fishing, we conducted a broad literature review via Google Scholar search. The main non-fishery-depletion-related harm we encountered was increased consumption of toxic chemicals. For example, a review of the potential consequences of ITN fishing in low-income countries by Larsen et al (2021) concludes (emphasis added):

  • “Fishing communities in malaria-endemic regions are seemingly caught between competing sustainable development goals (Trisos et al. 2019). As we have summarized, ITNs reduce malaria transmission and save lives—millions since widescale distributions—but are also oftentimes used as fishing nets. Numerous questions remain as to the impacts of fishing with ITNs for the ecosystems affected and the humans who live in them. We consider the following questions to be of greatest importance:
    • How do the pyrethroid chemicals in an ITN act once the ITN is used as a fishing net? Do the nets provide a constant contamination source of pyrethroids, or do the pyrethroids leach out quickly into the environment?
    • What is the bioaccumulative nature of pyrethroids in aquatic environments?
    • Some argue that mosquito net fishing is beneficial to the world’s poor (Tilley et al. 2020). Small fish when eaten whole are more nutritious than meat from larger fish (Thilsted 2012), and taking young fish may be less detrimental to some fisheries than taking big old fat fecund females, referred to as BOFFFs (Hixon et al. 2014). But, will the harvest of immature individuals severely inhibit recruitment? In general, how is mosquito net fishing impacting fisheries and food security?
    • Pyrethroids have been implicated as a risk factor for a host of human diseases, including neurodevelopmental disorders (Viel et al. 2015; Xue et al. 2013), diabetes (Park et al. 2019), and cardiovascular disease (Bao et al. 2020). Are we seeing bioaccumulation in fish that then exposes humans to pyrethroids, and, if so, is this having a detrimental effect on human health?
    • Pyrethroids are highly toxic in aquatic environments, and related research suggests there are a host of deleterious effects of pyrethroid ingestion on human health. Given the cash value of fish, the ease of ITN fishing, and limited alternative income generating opportunities, distribution of ITNs into fishing communities without strong fisheries management may present a serious challenge to fishery health, aquatic biodiversity, and perhaps even human health.”

• 73
  • Amweg et al, 2009 found that sampling of urban creeks and wetlands after mosquito control spraying showed PBO levels well below the concentrations needed to enhance pyrethroid toxicity. The abstract states, "These results suggest that environmental PBO concentrations rarely, if ever, reach concentrations needed to increase pyrethroid toxicity to sensitive organisms."
    • We haven’t reviewed this work closely and aren’t sure how the amount of PBO sprayed compares to the amount of PBO in typical ITNs. If ITN fishing leads to a higher concentration of PBO in the water than spraying, it could increase toxicity more than spraying. We aren’t sure how likely this is.
  • One of the companies responsible for producing ITNs used in campaigns that GiveWell funds, BASF, has published toxicity analyses for several of the chemicals used in ITNs, including chlorfenapyr and alpha cypermethrin. Comparing these results to the toxicity analysis of PBO found in the EU regulatory assessment report, we see that the additional chemicals being used in newer ITNs, PBO and chlorfenapyr, have LC50s, a measure of the concentration at which a chemical is lethal to 50% of organisms of a certain species, indicative of much lower toxicity than a reference pyrethroid, alpha cypermethrin.
    • We have not analyzed these results from BASF in-depth and view a potential conflict of interest in these results coming from a chemical manufacturer. Therefore we continue to include an estimate of potential harms from non-fishery depletion causes, including ingestion of pesticides, in our model.

• 74

  Tang et al 2018 reviewed studies of pyrethroid residues and identified 17 measurements of pyrethroid content in fish (see Fig 1, which is Table 6 from the paper), as well as an unpublished dissertation chapter (Love 2023)

• 75
  • (Emphasis added) Love 2023: “Bioaccumulation in juvenile FHM results can be seen in Figure 4-2, Figure 4-3, and Figure 4-4. Results from Low Sediment Fish can be seen in Figure 4-2. The

  average accumulation for week 1 was 0.69 ± 0.26 mg/kg. The average concentration for

  • week 4 was 1.10 ± 0.31 mg/kg.”
    The measurements in Tang et al (2018) were mostly less than 1 mg/kg = 1000 ng / g, but with one outlier measurement of 9.9 mg/kg in aquatic products in Zhejang, China. We collected the results from this paper in this spreadsheet; we found that the low end of the estimates averaged around 0.1 mg/kg, and the high end of the estimates averaged around 1.2 mg/kg.

• 76

  See p 120- 121. Love 2023

• 77

  “Out of nine investigated pesticides, only three pesticides (deltamethrin [a pyrethroid], carbofuran and cypermethrin [another pyrethroid]) were detected in fish and sediment samples. Deltamethrin in Cyprinus carpio ranged from 0.490 to 0.839 μg/g, mostly exceeding 0.5 μg/g as the maximum residual limit suggested by FAO-WHO, whereas it ranged from 0.214 to 0.318 μg/g in the sampled sediments.” - Jabeen et al 2015

• 78

  See Tang et al (2018)

• 79

  In Table 2 of Tang et al 2018 (image included in text below), we counted approximately 10 locations with measurements of over 5000ng/L (=5ug/L = .005mg/L = .005 mg/kg) of pyrethroids, out of 50 measurements. We “eyeballed” this, and could have miscounted.

• 80

  Tang et al 2018: “concentration (13000.00 ug L1) was trans-permethrin in the coastal watersheds of southern California. This was also the highest concentration of this residue reported at the global scale (not including China). The unusually high concentration was primarily due to an accident, but may have also been enhanced by spray drift during application, cleaning of spray equipment, or improper disposal of spraywaste (Delgado-Moreno et al., 2011).”

• 81

  The WHO’s acceptable daily intake (ADI) for pyrethroids depends on the particular compound involved. We checked two and saw that permethrin’s ADI is .05 mg/kg/day; while deltamethrin ADI is .01 mg/kg/day: .0024/.05 ~= 5%; .0024/.01 ~= 25%.

• 82

  See for example Bao et al, (2019) and Park, Park, and Choi (2019). In addition to the internal validity concerns described above, we also have external validity concerns about this evidence, since both of these studies involved samples of adults in the United States, who would have different channels of pyrethroid exposure than people living in other countries.

• 83

  See Table 4-1 of Love 2023.

• 84

  We estimate that around 0.1-0.5% of people use nets to fish (more). If households that do fish with nets eventually use most of the nets distributed to them to fish (more), then the fraction of nets used to fish would be similar.

• 85

  From Madumla et al (2022):

  • We saw one published focus-group discussion of households in Tanzania where just over half of respondents suggested burning as a way to discard nets. “More than half of all of respondent 55% suggested burning of LLINs as a means of disposal” -
  • The study also indicated that some nets are burned in the open air, which releases harmful chemicals. “However, these recommendations are not followed by the communities, which may result into careless handling and discarding of insecticidal nets in the environment including burning LLINs in an open air. This may lead to the release of dioxins, which is harmful to human health. “

• 86

  This calculation assumes a surface area of roughly 15 square meters per net (one net, a PermaNet 2.0, has dimensions 1.5m high x 1.9m wide x 1.8m long; if this were a rectangular net, we’d calculate a rough surface area of 14.5 m^2 = 1.5*1.9*2 + 1.5*1.8*2 + 1.9*1.8).

  • 282 million ITNs were distributed in 2022 (World Malaria Report, 2023 | WHO). We roughly estimate 1% were used for fishing at some point; that’s 2.82 million.
  • If all ITNs used for fishing were lost (likely a strong overestimate) 15 m^2 * 2.82 million ~ = 42 million m^2 = 42 km^2 of ITNs in the ocean.
  • A study from Richardson et al (2022) estimated: “2963 km2 of gillnets, 75,049 km2 of purse seine nets, 218 km2 of trawl nets, 739,583 km of longline mainlines, and more than 25 million pots and traps are lost to the ocean annually.” We haven’t reviewed this study closely, but it appears to be based off of surveys of fishers.
  • Accounting for purse seine nets alone, 42 km^2 / 75,049 km^2 ~= .05%.

• 87

  See this row of our simple cost-effectiveness analysis.

• 88

  See this row of our ITN cost-effectiveness analysis, the average across the countries is 1.7.

• 89

  This is discussed in detail in our intervention report.

• 90

  This is based on the guidance provided by the WHO in 2017 on the number of nets to procure per person: “However, for procurement purposes, since many households have an odd number of members, the calculation of LLINs required needs to be adjusted when quantifying at the population level. Therefore, in general, an overall ratio of 1 LLIN for every 1.8 persons in the target population should be used. This ratio can be adjusted as needed if there are data that support such adjustment.” Calc: 1/1.8 = 55%

• 91

  "AMF’s partners (either national health agencies or in-country non-profit organizations) gather data at the distribution stage of each campaign on the number of nets distributed to households.65 AMF has shared this data with GiveWell for previous campaigns, and we use this data as one input into our estimates of AMF’s cost per net (discussed above). Specifically, we use data on the proportion of nets that were purchased but not distributed in previous campaigns (e.g., because they are lost, stolen, damaged, or otherwise not accounted for) to estimate the proportion of nets that will be purchased but not distributed in the future. As of December 2023, we estimate that this proportion is 5% overall (varying somewhat by country, from 2% in Uganda to 10% in Guinea).66" (more)

• 92

  See this row of our ITN cost-effectiveness analysis, the average across the countries is 1.7.

• 93

  “All households reported owning a bed net at some point in time, with the median ownership duration of six to 12 months (minimum less than six months, maximum over five years). “ McLean et al, (2014).

• 94

  “We estimate that one AMF-purchased net confers 1.2 to 2 years of effective protection over the course of each three-year distribution cycle.” - GiveWell’s intervention report of ITN-distribution campaigns

• 95

  Some uncertainties about this estimate:

  • We aren’t sure how McLean et al measured duration of net retention, for example, if households were considered to still “own” nets once they used them for fishing (if so our estimate of effective coverage could be too high), or if “median ownership duration” included newly received nets that were still in use (if so, our estimate of effective coverage could be too low.)
  • The number reported by McLean et al isn’t adjusted for physical or chemical decay relative to trial settings. We’d guess this would be small in the first 6-12 months, but it could make our estimated coverage too high.

• 96

  “Ninety-two percent of MNF homesteads fished with old nets no longer deemed fit for beds.” Bush et al, (2016)

• 97

  (10% + 50%)/2 = 30%.

• 98

  See the average value across this row of our cost-effectiveness analysis which yields 52% of benefits from reduced under-5 mortality, implying that ~50% of benefits are from other factors.

• 99

  Both of our partners that implement ITN distributions expressed skepticism about our estimate of the prevalence of ITN fishing in a previous draft of this page (more). Against Malaria Foundation stated that based on their experience, including post distribution monitoring of AMF funded net campaigns, the number of nets used for fishing from AMF distributions is many orders of magnitude less than the general estimates we have proposed. Their estimate is less than 0.01%.

• 100

  Impact of mosquito nets on fisheries - Leow and Hird (2024)

• 101

  This is reverse engineered from an assumption of ~2 fishers per household and 5.3 people per household The 100% number is intended to be illustrative, based on household surveys from particular areas where almost all households use ITNs to fish, as well as anecdotal conversations that ITN fishing is highly common in some areas.

• 102

  See table 1, page 876 of Virdin et al (2023): calculation: 4.66 + 2.65 + 1.36 are involved in subsistence fishing or fish harvesting. (I don’t include pre or post-harvest activities).

• 103

  The Population Reference Bureau estimates a total population in Africa in 2016 of 1.2 billion, Population Reference Bureau, 2016 World Population Data Sheet, p. 10. 8.7 million / 1.2 billion = ~.7%

• 104

  See Table 12 of the FAO’s The state of world fisheries and aquaculture 2022 report here.

• 105

  Calculation: 5.5 million / 1.2 billion = 0.45%.

• 106

  “To evaluate the strategies engaged by individuals and households to reduce food and nutrition insecurity and alleviate poverty through small-scale fishery livelihoods—a term used here to refer to the capabilities, assets and activities required for a means of living or adequate stocks and flows of food and cash to meet basic needs23,24—two separate measures based on labour statistics were assessed: (1) employment, defined as all persons of working age who, during a short reference period (typically the week before the interview), were engaged in any activity to produce goods or services provided for pay or profit, including both part- and full-time employment to capture seasonal variation (with interviews conducted continuously throughout the year in almost all surveys, including both employed persons ‘at work’, that is, who worked in a job for at least one hour during the reference period, and employed persons ‘not at work’ due to temporary absence from a job or to working-time arrangements, such as shifts in work, flexitime and compensatory leave for overtime); and (2) subsistence, defined as working for one’s own consumption: workers who produce goods or services that are predominantly consumed by their own household, with no transaction occurring in the marketplace25, potentially including pre- and post-harvest activity in fisheries (and so referred to here as ‘subsistence fishing activity’, inclusive of any pre- and post-harvest activity).” - Virdin et al (2023)

• 107

  “The results from the 78 national datasets were extrapolated to the regional level using the geographic archetypes from ILO and subsequently to the global level. To correct for non-response bias in countries not included in the national datasets (which were selected based on the availability of information and not randomly), a weighted regression analysis based on independent variables considered as predictors was used, following recommendations by the ILO34. Weights of the different predictor variables were calculated as the inverse probability of selection (or inverse propensity score) to account for differences between the 78 countries for which data were collected and the world’s remaining countries to which the results were extrapolated (Supplementary Table 8). Using these weights to correct for non-response bias, the weighted regression analysis was conducted, essentially generating estimates based on assumed relationships between employment, subsistence and livelihood dependency variables and a set of predictor variables. The predictor variables used were chosen based on (1) strong correlation with the outcome variables (measured by the R squared) (Supplementary Table 9) and (2) availability worldwide. These included (1); Employment in agriculture, forestry and fishery; (2) Employment in industry and employment in services; (3) Total population; (4) gross domestic product (GDP) per capita (purchasing power parity); (5) GDP growth; (6) Value added in agriculture, forestry and fisheries. For marine small-scale fisheries, the additional predictor ‘Length of coastline (km)’ was included, whereas for inland small-scale fisheries, it was ‘Area of inland water bodies’ (Supplementary Table 9 provides predictor variables used).
  As a cross check, the resulting estimates were compared to: (1) data compiled on small- and large-scale fisheries employment in 58 national-level case studies and (2) government responses to a survey conducted by the United Nations Food and Agriculture Organization (FAO) with all member states during 2018 and 2019, conducted as part of the Illuminating Hidden Harvests global assessment of small-scale fisheries (Supplementary Fig. 7). Additionally, results were compared to publicly available datasets on aggregated employment in fisheries: (1) the International Labour Organization labor statistics database (ILOSTAT) data on employment in either fishing or aquaculture (aggregated) and (2) FAO data on employment in fisheries (aggregated between small and large-scale fisheries) (Supplementary Fig. 8). For countries where significant differences emerged, experts were consulted to help provide further explanations and eventually adjust estimates from the weighted regression analysis. A final check was comparison to a dataset of the global marine fishing effort, disaggregated between small and large-scale fishing, to identify any countries where zero small- or large-scale fishing effort occurred, but the estimates from surveys suggested a non-zero employment in fish harvesting35. Finally, the results are comparable to previous studies, such as World Bank12 (Supplementary Information provides more detail on the process of cross checks).“ - Virdin et al (2023)

• 108
  • For the underreporting from illegal or stigmatized fishers: As a rough triangulation, we guess that around 25% of people engaged in fishing might use ITNs in areas near distributions (more), including those who use them in conjunction with other gears (more). If none of those people reported fishing at all, then it would suggest 33% underreporting (25% / (100%-25%) = 33%)
    • We think some ITN fishers probably do report that they fish (since they aren’t specifically being asked about gear, may not live in places where ITN fishing is illegal or stigmatized, or also fish with other gears). This would suggest 33% is too large of an adjustment.
    • On the other hand, there is other illegal fishing that goes on and may not be reported. We tentatively guess these adjustments balance out.
  • For the difficulty of surveying people: We think particularly poor or hard-to-reach communities might be somewhat more likely to engage in subsistence fishing or agriculture, and this could lead to underestimation. We make an additional 17% adjustment because of this concern; we aren’t sure how to estimate it, but we tentatively guess it is about half as large as the problem of explicit misreporting, since we understand that Virdin et al attempt to account for non-response/missing data (though we are uncertain about the methodology used).

• 109

  (150% true population - 100% reported population = 50% missing population; 50%/150% = ⅓)

• 110

  The FAO estimates show a doubling in the total number of people employed in fishing from 1995 (3.1M) to the 2010s(5.7M), but little change from 2015 to 2020 (6.0M) (See Table 10 here). We haven’t attempted to divide these numbers by population to estimate any trends in the fraction of people engaged in fishing.

• 111

  From Impact of mosquito nets on fisheries, Rethink Priorities (2024):

  • “Samoilys et al. (2019) observed the use of different fishing gear in six rural villages dependent on small-scale fishing across 80 km of coastline in Mozambique. Based on interviews with 2,454 fishers, the study found that on average mosquito nets were used by 27% of fishers, but this varied from 10% to 42% across villages.
  • A report on destructive fishing activities in the South coast of Kenya finds that 3% of those surveyed use small size mesh nets, like mosquito nets (Munyi, 2024). However, the underlying data is from interviews conducted in 2007- 2008, and the data collection section does not indicate the sample size. We guess that around half of small-mesh nets are ITNs–this is highly uncertain but does not significantly impact our bottom line.
  • Hondo et al.(2023) included data from surveys with 280 individuals conducted in lake-side villages in Benin in 2020. The authors find that two thirds of those surveyed use mosquito nets for fishing.”

• 112
  • Mutuku et al 2013 assessed that 6 of 2,786 nets (0.2%) found in households surveyed in coastal Kwale County, Kenya, were used for fishing. While we aren’t sure how many households in this area are engaged in fishing total, but we take a guess of around 20% given its location and reports in one town within Vanga subdistrict (part of the surveyed area) that around 19% of the population engaged in fishing. Based on this, we’d estimate that around 1% of fishers are using mosquito nets (0.2% / 20% = 1%).
  • Millat-Martinez et al. 2021 finds 30% of nets were repurposed for fishing two years after a mass distribution campaign in the Lihir Islands in Papua New Guinea. “Repurposed nets were reported serving as fishing nets (30.4 %).” Again, we are unsure of the number of people engaged in fishing with these repurposed nets, and of the total population engaged in fishing. We roughly guess that the fraction of people using nets is equal to the fraction of nets used to fish (30%) and that about half of the population is engaged in fishing for subsistence or livelihood. This would suggest 60% of fishers are using mosquito nets.
  • McLean et al 2014 report that over 87% of households surveyed across 7 villages in Lagosa Ward, Tanzania, had used a mosquito net for fishing at some point. We are uncertain how often these fishers used ITNs to fish, and how many people are engaged in fishing total, but we’d guess that this estimate might suggest that close to 100% of people fishing have used mosquito nets at some point (e.g. if 87% of households fish and all those who fish use ITNs to do so).

• 113
  • Ranaivomanana et al 2023 surveyed boats fishing in the Bay of Toliara and estimated that ~30% used mosquito-net trawls or beach seines with mosquito-net codends: “ Five fishing gears are commonly used in the area, including 10-45 mm mesh-size gillnets, handlines, spear guns, mosquito-net trawls, and beach seines with mosquito-net codend (Table 1).
    • “ Table 1 states that 14.7% of boats used mosquito-net trawls and 14.4% used beach seines. 14.7+14.4% = 29%.
  • Against Malaria Foundation shared two small studies from the DRC showing nets accounted for ~15-30% of fishing gear, writing “Two studies focused on the fishing industry were published.
    • The first is from Pool Malébo which is the wide part of the Congo river between Kinshasa and Brazabville. It reports that ITNs make up 27% of the fishing accessory used by fishermen/women. The report is here, data is from 2019 and report published in 2022.
    • Another study published in 2023 shows the same indicator as 15% - 26% from site to site.” – Notes from AMF provided to GiveWell, September 2024
    • AMF also noted that “while these studies do show that nets are used in these areas with high fishing activity, the percentages give no indication as to the overall % of distributed nets that go to be used in fishing.”
  • Total estimate averaging the three studies above, using the midpoint of the range from the third: (29% + 27% + (15% + 26%)/2)/3 ~25%.

• 114

  Of ~18,500 nets used for fishing, we think 10,000 would be repurposed by households, and 8,200 would be used for fishing after being lost, stolen, or sold.

• 115

  We estimate 5% of nets procured do not reach households (AMF Charity Page)

• 116

  70% is a rough average across countries in an updated analysis of ITN-distribution campaigns in different countries, rounded for imprecision

• 117

  This is based on the guidance provided by the WHO in 2017 on the number of nets to procure per person: “However, for procurement purposes, since many households have an odd number of members, the calculation of LLINs required needs to be adjusted when quantifying at the population level. Therefore, in general, an overall ratio of 1 LLIN for every 1.8 persons in the target population should be used. This ratio can be adjusted as needed if there are data that support such adjustment.” Calc: 1/1.8 = 55%

• 118

  While our 25th-75th percentiles are not significantly different for this estimate relative to our other estimate, we think this estimate has fatter tails–if we used this method alone, we’d have trouble ruling out a 95th percentile outcome of 10% of households using nets.

• 119
  • From the Household Survey Indicators for Malaria Control: “The numerator for this indicator is obtained from asking the household respondent if there is any mosquito net in the house that can be used while sleeping and from determining whether each net found in a household is a factory-treated net that does not require any treatment (an LLIN) or a net that has been soaked with insecticide within the past 12 months. The denominator is the total number of surveyed households.” -p18Per the Household Survey Indicators for Malaria Control (June 2013), presence of such nets is typically verified at the time of interviews.

• 120

  “No, we haven’t seen nets in households that are used both for sleeping and for fishing. Nets that are extra are typically newer and being saved for later, once existing nets wear out, or for guests/in-laws etc. Mosquito nets that are used for fishing are going to be stored with other fishing gear, typically in the boats or in a shelter/storage area near the beach/river, because they’re wet and heavy and stinky. They are also frequently (depending on the type of fishing) sewn together into larger nets, or attached to fish traps made of reed/cane, making them unsuitable to keep at home.” - Hannah Koenker, Project Director at PATH, to GIveWell via email

• 121

  This is especially true since Against Malaria Foundation’s post-distribution monitoring suggests very high rates of nets found hanging in households during the day (around 40-86% of distributed nets are hanging 6-30 months after a campaign.) While we have uncertainties about the reliability of this data (see our charity report), any net hung in the household during the day is certainly not being used for fishing at that time.

• 122

  Koenker et al (2014), see Table 2.

• 123

  Santos et al 2020 find no self-reports of fishing with mosquito nets in two areas of Kenya. Mutuku et al 2013 assessed that 6 of 2,786 nets (0.2%) found in households surveyed in coastal Kwale County, Kenya, were used for fishing. “The survey included interviews with household heads and inspection of bed nets in 1176 households with 5526 individuals and 2,786 nets.” Table 7 reports that 6 nets were found to be used for fishing, accounting for only 2% of misused nets.

• 124
  • Millat-Martinez et al. 2021 finds 30% of all nets distributed were repurposed for fishing two years after a mass distribution campaign in the Lihir Islands in Papua New Guinea, while 43.4% were used only for sleeping under. We think this implies around half of repurposed nets were used for fishing (30.4/(100-43.4) ~= 50%). When asked about use of LLINs, a total of 1170 (43.4 %) household heads reported to have used LLINs only for the purpose of sleeping under…The most common alternative use for LLINs was fishing (818; 30.4 %).”
  • McLean et al 2014 report that over 87% of households surveyed across 7 villages in Lagosa Ward, Tanzania, had used a mosquito net for fishing at some point. “A total of 196 surveys were administered over a four-week period with a 100% response rate. Over 87% of households surveyed have used a mosquito bed net for fishing at some point.”

• 125

  “Respondents stated that no one would purchase a heavily worn ITN with many holes, but noted that fishermen recovered such nets once they were discarded and used them to patch other fishing nets.” - Berthe et al, 2019

• 126

  Our analysis of net durability (unpublished) suggests most nets (56%) are discarded after more than 2 years of use, and at the two-year mark, only half of nets are in good condition, implying most have some number of holes or tears.

• 127

  That’s because we think about 10% are repurposed and 10% of repurposed nets are used for fishing. 10%*10% = 1%. See above.

• 128

  “FGD participants confirmed what had been anecdotally reported before the study: that many ITN recipients sell their nets to fishermen. Across all study sites, participants reported that one could sell a new ITN for 300–1000 Malawian kwacha (MK) (US$0.40–1.40) at the prevailing exchange rate during the study, depending on the location and the condition of the net. ITNs fetched less in sparsely populated northern lakeside communities and more in the more densely populated south. A lightly used ITN might yield MK 200–800 (US$0.30–1.10). Respondents stated that no one would purchase a heavily worn ITN with many holes, but noted that fishermen recovered such nets once they were discarded and used them to patch other fishing nets. Although none of the respondents reported selling their own ITN, many stated that selling ITNs was easy and could name places where buying and selling of nets took place. In a few other cases where participants knew of an ITN being sold, they stated that it was often children and adolescents who stole the ITN and sold it without their parents’ knowledge to have some money. In a few of these instances, participants mentioned that youth and men would sell the ITNs for money for beer.“ - Berthe et al 2019

• 129

  “Ten FGDs were conducted with 55 individuals. Although malaria was widely recognized as a significant threat and bed nets were freely distributed in the camp, many households did not own or use them. IDPs converged on the following reasons for low bed net ownership and use: inconvenience of net installation and sale of nets to meet immediate needs such as food. One hundred households, comprised of 411 individuals, were surveyed in Birambizo. The burden of malaria was high (45/78 (58%) of children <5 were positive for malaria by RDT) and bed net utilization was low (29/100 (29%) households owned a bed net, and 85/411 (20%) individuals slept under a bed net the previous night). Children <5 were more likely to use a bed net than older children or adults (OR 3.4 (95%CI 2.0–5.8), p<0.0001). Compared to 29 bed nets currently in use by study participants, 146 bed nets had been sold (82%) or exchanged (18%) either in the camp (27%) or in the neighbouring village market (73%).” - Brooks et al 2017

• 130

  We guess this number because we assume fishers live in households with 4-6 people, which is around the average we see in areas we have supported campaigns in the past (more). Households receive 1 net for every 2 people, so a household with 4 people would receive 2 nets and a household with 6 people would receive 3 nets.

• 131

  “Four predominant MNF methods were identified from the literature, and clarified further by our survey: Single-net use, with nets largely unaltered and operated by individuals or pairs, dominated across all regions (53%, n = 105), followed by multiple nets sewn together for use by small groups of fishers (34%), then use as a cod end of larger seine nets (10%) and finally just three reports of insecticide fishing, the details of which remain unconfirmed but where in one case additional DDT is thrown in to the water along with the MNs. Numerous other methods were described by survey respondents, including a number of trap designs, ‘scoop’ or ‘dip’ nets, and the use of static ‘set’ nets used to funnel fish, sometimes with photographic evidence” - Short et al 2018.

• 132

  Larsen et al (2018). See Fig 7(B)

• 133

  Short et al (2020). See Fig 2, top and bottom left panel

• 134

  We explain how we arrived at this figure here.

• 135

  From Hondo et al 2023, 89 of 180 (49%) surveyed professional fishermen reported using mosquito nets for fishing while 100 of 102 (98%) seasonal fishermen reported using mosquito nets for fishing. See table 4.

• 136

  See this cell of our analysis of DHS/MIS surveys.

• 137

  An average across this row of our cost-effectiveness analysis for ITNs suggests 55% of the population is over age 14.

• 138

  Use of mosquito nets for fishing is illegal in many countries including, e.g., Malawi: “On the other hand, use of mosquito nets for fishing is illegal in many countries including Malawi because the small mesh size traps juvenile fish and can cause devastating declines in fish population.“ Identifying and Mitigating
  Misuse of Insecticide-Treated Nets for Fishing Toolkit | U.S. President’s Malaria Initiative (2018)

• 139

  We previously framed the prevalence of ITN fishing in terms of the fraction of households using ITNs for fishing rather than the fraction of people doing so, but we chose to frame our final estimate in terms of people using ITNs to fish. That’s because we believe the malaria protection benefits of nets scale with the number of people protected, so we wanted to express the scale of potential misuse in terms of people as well. Additionally, estimating the fraction of people engaged in the practice requires fewer assumptions about household sizes and how common it is for multiple people to fish with ITNs in a single household.
  The quantitative estimate at that time we shared this page with our partners was that there are 1-2% of households where at least one member uses an ITN to fish at some point after distribution. Intuitively, this is larger than the fraction of people who use nets to fish because we guess most household members don’t fish. In hot spots we estimate 2 people per household might fish, but we’d guess the overall number is lower once we take non-hot-spot fishers into account. As a rough comparison, if we assume 1.3 ITN fishers per household with one ITN fisher and 5.2 people per household, then our estimate of 0.1% to 0.5% of people scales up to around 0.4% to 2% of households (0.1% * 5.2 / 1.3 = 0.4%, 0.5% * 5.2 / 1.3 = 2%).

• 140

  “For the two Nigerian states (Ondo and Anambra), this conclusion is unlikely to be true. Our field staff stated that the fishing communities use proper fishing nets and they have not seen evidence of ITNs being used for fishing there.” - Malaria Consortium, feedback on a section of a draft version of this page describing our previous estimate that 1-2% of households use ITNs to fish (unpublished).

• 141

  See our conversation notes here.

• 142

  As examples:

  • “Congo River mosquito net fishing” led us to this article on ITN fishing in Kisangani, DRC: DRC fishing community turns to tourism as stocks dwindle | Ndebo (2022)
  • “Lake Kivu mosquito net fishing” led us to this article on mosquito net fishing in Rwanda - Rwanda: Over 30,000 Illegal Fishing Nets Confiscated - Rep

• 143

  “Core interventions for malaria vector control are applicable for all populations at risk of malaria in most epidemiological and ecological settings, namely: i) deployment of insecticide-treated nets (ITNs) that are prequalified by WHO, which in many settings are long-lasting insecticidal nets (LLINs); and ii) indoor residual spraying (IRS) with a product prequalified by WHO. Once high coverage with one core intervention has been achieved, supplementary interventions – namely the deployment of chemical or biological larvicides – can be used in addition to the core interventions in specific settings and circumstances.” WHO, Guidelines for Malaria Vector Control, 2019, p. xiv.

• 144

  WHO, World malaria report 2022, p. xxv, "Distribution and coverage of malaria prevention" section.

• 145

  We’re not sure why this is. Anecdotally, two factors we’ve heard that may be driving this are:

  • Nets are widely seen as an effective malaria prevention tool. There was a significant global advocacy effort to encourage high coverage of nets, and national malaria programs and malaria stakeholders are broadly agreed on their importance for malaria control.
  • There is strong community demand for nets, since they are visible compared to other malaria control tools. Communities have also been receiving them for a long time, and developed an expectation of continued supply.

• 146

  We estimate that 63% of nets distributed in GiveWell-funded campaigns are used. (more)

• 147

  “Stopping the free distribution of ITNs may slightly improve the fisheries situation, though such drastic measures must be balanced against the community-level benefit of ITN coverage [7,8].” - Larsen et al 2018

• 148

  “Therefore, a better understanding of how MNF fits into overall livelihood strategies is needed, rather than simply implementing bans and excluding fishers from management. As the first study of the prevalence and context of MNF in a coastal area, this study begins to inform the debate on its social and ecological impacts. We hope that it will promote stakeholder collaboration and further investigations into the role of MNF within fisheries management, rural livelihoods, and coastal ecosystems.” - Bush et al 2017

• 149

  Conversation with researcher Neil Lobo, University of Notre Dame (unpublished)

• 150
  • Source: The average value for ‘# of nets present in serviceable condition’ in all rows for month 18 in the DRC was 52%. AMF communicated to us that an additional 19% of nets were present but torn for a total of 71% of nets present. (unpublished conversation)
  • The ~90% estimate is consistent with our survey-based estimate above which found that among nets discarded by households (i.e. no longer available in the household for sleeping under and not given away) within 2-16 months of a distribution, about 10% were repurposed or misused in some way, around 50% thrown away, and around 40% were destroyed.
  • AMF also conducted a review of 5 distributions (unpublished) where they observed either a higher frequency of nets being used for other purposes or where circumstances suggested a higher risk of ITN fishing. Among around 1600 comments regarding alternative uses of nets, 9 (0.5%) mentioned fishing in some way.

• 151

  See for example, Ritchie and Roser 2021/2024: “We don't have good stock assessments across Asia, Africa (except South Africa), and much of Latin America.”