There's a common claim that the distribution of antimalarial mosquito nets is bad because they are used for fishing. I usually hear this followed by the quick rebuttal "...but I can't imagine who has a problem with enabling needy people to fish!"

There is of course more merit to the objection. A discussion from 2018 on Future Perfect, which in turn cites Givewell's 2015 evaluation of the topic considering overfishing, environmental harms, and inefficient net distribution, but ultimately finding the problems all insignificant. I want to add some discussion of harms not discussed there.

Last year I was in Kenya conducting an interview on commons management, and it came up that people using mosquito nets for fishing was considered bad behavior especially because mosquito nets are fine enough to trap fish fry and juvenile fish, ruining future harvests. This appears to be a widespread and longstanding concern not directly addressed in either evaluation, partly due to lacking academic research now available. The upshot seems to be that thanks to juvenile catch the impact on fisheries is higher than indicated by those reports.

Here is a journalistic report from 2019, which summarizes this 2019 paper attempting to make a direct link to fishery decline in Mozambique seagrass from juvenile catch via mosquito net fishing. They document high percentage of juvenile catch (56%), with caveats as to time of day and year. They didn't provide a baseline comparison against responsible fishing methods (only other comparably unsustainable ones). Nor is a model of how much juvenile catch is needed to noticeably impact recruitment provided. Here's a subsequent 2023 paper I cannot access claiming significant harm to fisheries from mosquito net juvenile catch in Madagascar's coastal coral reefs (the abstract is confusing, so I am suspicious of its quality).

Belief in observable harms from mosquito net fishing seem to be common in affected communities, as per my interviewee, as well as various comments and tidbits sprinkled throughout academic research and news reporting, and in particular this 2022 survey in Zimbabwe. Poverty is usually given as the reason for doing it anyways. This suggests to me the practice is widespread, substantial enough for many communities to reach the same conclusions about its effects, and likely endemic wherever mosquito nets are distributed and fish resources exist. 

It remains unclear to me from these studies or from any larger meta-studies what the numerical prevalence of mosquito net fishing actually is worldwide and how large and how causal an impact they have on global fisheries.  (The best global overview so far, from 2018, is neither quantitative nor exhaustive, and was cited in the Future Perfect article.) But overall it is likely that millions of people mosquito net fish, I infer they do so usually in ecologically fragile coastal and riparian settings similar to those in the above studies, and the practice causes probable impacts to future food security.

In summary there's more evidence that mosquito net fishing causes substantial harm than previously discussed in this community (a harm to commons that is balanced against the harm of immediate hunger, of course). I think this is a relatively small update, unlikely to change my mind about the overall positive benefit of free mosquito net distribution. Work to mitigate the harms caused by mosquito net fishing while maintaining widespread mosquito net access to will probably come from non-EA entities. May also be of interest to ecologically minded readers and fish welfarists.





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Thanks for this, I'm trying to at least get a couple of numbers to get in the right ballpark to help people calibrate. Epistemic status: uncertain, a couple of hours of research. Takeaway: Probably billions of fish killed.

To get a higher end of the estimate of total fish killed as a result of mosquito net fishing, the appendix of the paper you link to gives an example of a single large-scale fishery in Madagascar where 68.7 million fish were killed in 2018-2019 by 75 families. 

Unless I'm misreading, this looks like 80-90% of the total fish numbers were caught through mosquito net trawler (27.7% by weight, but much smaller fish on average, so a higher number).

This other paper in Mozambique provides another example - they two fishers catch around 35kg of (mostly tiny, < 20 mm, so 1-10g?) fish a day, so I guess around 10,000 fish a day? Over 2 million a year (so similar ballpark to Madagascar). 

These are the locations at which mosquito net fishing had been observed in this study (data mostly from 2015), with a rapidly rising trajectory.   

I can't seem to find any better data on the scale of fishing at all of these locations, so I have no idea whether it's closer to 50 or 10000 locations where mosquito nets are used for fishing to a similar extent to those in these articles, but 25 million fish * 50 locations would be 1.25 billion fish.  

I think it's safe to assume that at least 1 billion fish, possibly orders of magnitude higher, are killed yearly through mosquito net fishing, most of whom wouldn't be killed if it weren't for the distribution of mosquito nets (due to the small mesh sizes). 

Of course, to make a reasonable welfare calculation, you shouldn't just look at the number of animals killed and how painful their deaths must have been. You also have to consider how long these fish would have lived for counterfactually, the quality of their lives and suffering involved in their counterfactual deaths, as well as broader ecosystem effects etc. 

But @Dylan Matthews's claim that "There is little research on what fishing with these nets actually does to fish or people — but also little reason to think the magnitudes of these effects are remotely near the number of lives saved by nets" strikes me as indefensible.  

Causing billions of fish to experience a painful death is not just a rounding error, and it may well be worth reevaluating whether bednets have had a positive net impact or not. 

Late to the party, but isn't the relevant thing for AMF donors the counterfactual number of fish killed by mosquito nets distributed by AMF? It seems like AMF has higher rates of nets being used properly than other charities. 

I couldn't track down comparative data on whose bednets seem to be the most responsible - presumably it's more whoever distributes the most nets in areas close to major fisheries, rather than % of appropriate use.

I also don't know whether the marginal bednet will increase this kind of fishing much (there might already be a glut of bednets).

But these are all important questions that I don't think GiveWell or AMF have ever taken seriously.

Thanks so much for this! I’d only been thinking about the potential harms to people with fish welfare as a side note. You’re absolutely right that we can get a decent estimate on the added burden of fish suffering here, which will be relevant to the calculations of many EAs

Fish welfare would be a big factor in my model about the net utility of free malaria nets. However, it seems really hard to calculate because we don't know the average net qualia of fish in these regions. If it is negative, then overfishing may be a positive thing for their welfare. 

Thanks for the post Rachel! I admire you looking into the topic. 

However, one to add is that AMF monitors net usage uniquely stringently and this likely leads to far fewer people using the nets for fishing.  (or at least they did until 2015)

From a 2015 article:
However, AMF takes a number of steps to stop misuse. We believe that each of them has contributed to the success of our distributions.

  1. Malaria education is key. We work closely with local health officials, the front line health teams and the village and community leaders, to ensure the community is fully aware of the connection between sleeping under intact nets and preventing malaria.

  2. AMF uses extremely rigorous pre-distribution surveys to determine precise net needs, followed by independent checks when the nets are given out to ensure no nets are diverted away from households that need them.

  3. AMF conducts post-distribution check-ups to ensure nets are being used as intended every 6-months during the 3 years following a distribution. People are informed that these checks will be made by random selection, and via unnannounced visits. This gives us a data-driven view of where the nets are and whether they are being used properly. We publish all the data we collect: example here. This type of follow up work is currently unique to AMF, although we hope the practice will become more widespread where it is feasible.

At AMF, the extensive data we have collected verifies that the number of nets we have distributed that are used for fishing is immaterial.

Given that AMF is the main bednet distributor that EAs give to (Malaria Consortium distributes medicine), I think the negative impact of EA-influenced bednet distribution is lower than one might assume from your post!

Thank you for adding this clarification! It's good to determine whether EA-driven funds are unlikely to be substantially exacerbating the issue. Other bednet distributors besides AMF may have worse outcome tracking methods but that is outside of the EA community scope to discipline.

One minor caveat to your clarification is that many of the nets are reused for fishing only after they are considered too worn out for bednet use, at which point even distributors using AMF's methodology may no longer be tracking their utilization.

Noting that even with AMF's tracking methodology I'm not seeing strong evidence that nets distributed are not being diverted even within AMF's tracking period:

For example, this survey shows about 36% utilization as intended at the 18 month mark. Since they don't need to be brand new to be used as fishing nets, some portion of the other 64% might be serving an economically productive second life. (The link to underlying data sadly appears to be broken at the moment, and no detailed report is provided, only the overview.)

Also, AMF has documented far fewer surveys than 'monitor every distribution effort every six months for three years' as implied by the 2015 article Marzhin cites - actually doing so may be cost prohibited. Furthermore no surveys have been published since 2019, I'm assuming COVID was a major contributor there. All the tracking here:

'I think this is a relatively small update, unlikely to change my mind about the overall positive benefit of free mosquito net distribution'

Have you actually run a back of the envelope calculation on this? I'm kind of worried we are all massively biased on this topic because it would be so embarrassing for EA if mosquito net distribution turned out to be net negative. 

I haven't - even after this much research I don't feel epistemically confident enough to do so. I welcome anyone else to do it!

Some useful tips/data points for people to narrow down uncertainty:

    • "The study's authors estimate that the three interventions averted 663 million cases of malaria in the 15 year period. Insecticide-treated bed nets were by far the most important intervention of the three, preventing 68% of the averted cases."
  • World Bank on African fisheries
    • "Fisheries contribute to Africa’s economy. Currently, fisheries and aquaculture directly contribute $24 billion to the African economy, representing 1.3% of the total African GDP in 2011. The sector provides employment to over 12 million people (58% in the fishing and 42% in the processing sector). While fishing jobs are almost entirely taken by men, 59% of the processing work is done by women. Employment multiplier effects are remarkable: for example, for every fisherman job, 1.04 additional onshore-job is created in Mauritania, while this ratio reaches 3.15 in Guinea, illustrating the potential for further job creation through value chain development."
    • To narrow down the uncertainty further, you probably want to 
      • look at what percentage of fisheries specifically are in places that are likely to have MNF
      • remove "aquaculture" (fish farms) from the relevant stats.
  • I haven't thought much about what the marginal effects of nets on marginal fisheries is; I think someone who explores this for an hour or so can draw some reasonable-looking curves.

(I originally thought fisheries will be a small enough fraction of the African economy that the upper bound of assuming 100% of bednets are used for MNF still isn't enough to be net negative; I no longer think that is certain).

Definitely outside of my capabilities, but somebody should! 

Some extra context on scope:

  • UNICEF directs about 30 million nets per year over the last few years. Not sure if counts partners and whether AMF counts as a partner.
  • By compare AMF has donated 250 million nets over the last 18 years, averaging 14 million per year.
  • Global net production is about 480 million per year, unsure what percent are charitably distributed vs purchased.
  • Presumably use of purchased nets is scarcely tracked at all.
  • Price per net is about $2 to distributors. Unsure what they are on the market, guessing around $3.

Executive summary: There is some evidence that using mosquito nets for fishing harms fish populations more than previously thought, but likely not enough to outweigh the benefits of distributing free mosquito nets. 

Key points:

  1. Mosquito nets can catch juvenile fish, harming future fish populations.
  2. Some surveys and studies link mosquito net fishing to fisheries decline, but the full global impact is unclear.
  3. Mosquito net fishing seems widespread where nets are distributed and fishing resources exist.
  4. The overall benefits of mosquito net distribution probably still outweigh the fishing harms.
  5. Further mitigation work could come from outside EA, while preserving net access.



This comment was auto-generated by the EA Forum Team. Feel free to point out issues with this summary by replying to the comment, and contact us if you have feedback.

I think this summary captured the article's main points quite well. Good bot!

Could nets be made such that their mesh size increases when they get soaking wet?

PS: Are the insecticides also a problem? Are there biodegradable insecticides?

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