Which animals are most affected by fishing?

MichaelStJules

Note: Following this project, I am still extremely uncertain as to whether fishing is good or bad for animals on net.

Abstract

Fishing has both direct and indirect effects on populations, e.g. through the effects of fishing predators on their prey and trophic cascades. Whether fishing is — on the margin or on average — good or bad for wild animal welfare overall in the near term depends on potential tradeoffs between different groups of animals. In this piece, I narrow down which groups of animals are most affected by fishing, directly or indirectly. I also assess how the populations of some of these groups have been affected by fishing so far and have trended over time. Unfortunately, I’m not able to answer whether fishing has been or is good or bad on net, but I outline next steps.

Key takeaways

It seems the aggregate moral weight of food webs and the morally-weighted population effects of fishing are dominated by copepods, macrozooplankton crustaceans (krill, and planktonic shrimp, planktonic mysids and amphipods), pelagic decapod shrimp and/or fish, especially forage fish, which are small pelagic fish that are prey to larger fish (more).
My best guess is that all fishing together has increased fish population numbers historically by disproportionately reducing the populations of predators of forage fish and so increasing forage fish populations more (more). Wholly eliminating fishing would therefore probably decrease fish populations overall compared to recent levels.
It’s very unclear what impact all fishing together has had on the populations of copepods, macrozooplankton crustaceans and pelagic decapod shrimp, because food webs are too complex and variable to combine indirect effects qualitatively, and I found no published direct analysis of the issue.
Taken together, I am clueless about the near-term welfare effects of (historical and marginal) fishing on wild marine animals. I recommend against work aimed at decreasing (or increasing) fishing effort or with relatively large effects on fishing effort, because I am deeply uncertain about whether such work is good or bad overall.
I expect the issues to explore that are most likely to dissolve cluelessness about whether fishing is good or bad overall in the near term are
1. the magnitudes and signs of population effects and trends,
2. average welfare across the dominant groups above, so that we can decide whether increasing (or decreasing) different groups’ population is good or bad,
3. the mental capacities of copepods, so that we can (try to) rule them out as dominant or confirm their domination,
4. one’s own views about moral weights across dominant groups, aggregation, risk and ambiguity.
What I might recommend most is getting access to and running existing simulation models (FishMIP, Blanchard et al., 2024, Coll et al., 2020, Lotze et al., 2019) on counterfactual changes to fishing activity we are attempting to effect and checking the effects across animal populations. Specifically, someone could ask for the absolute numbers used to calculate the % changes for supplementary tables 5, 6 and 7 from Coll et al. (2020), and whether they have these numbers for zooplankton or copepods in particular. Think tanks and academics would be best-placed to do this.

Acknowledgements

Thanks to Brian Tomasik, Vasco Grilo, Ren Ryba and Spencer Ericson for helpful feedback. Thanks especially to Spencer for editing help and the push to wrap up this project. All errors are my own.

Full document

I lay out my reasoning and calculations in a document. It's not polished, but I've decided to stop here to move onto other work.

You can view the doc here, and you can comment on the doc here.

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Nithin Ravi1d5

What are your takeaways for backfire effects from interventions to reduce aquaculture?

MichaelStJules1d5

I'm clueless about the sign of the effects on wild aquatic animal (based on this project), and the effects on wild aquatic animals could be more important than the effects on farmed aquatic animals.
Reductions in animal agriculture, including aquaculture, have a high risk of backfiring overall, in case they're bad for wild terrestrial arthropods. In particular, animal agriculture, including aquaculture, tends to decrease wild terrestrial arthropod populations through land use (for crops and/or pasture), and possibly substantially (Attwood et al., 2008, Tables 3 and 4), so reducing animal agriculture in general can increase wild terrestrial arthropod suffering by increasing their populations.
Aquaculture tends to have smaller effects on wild terrestrial arthropods than land vertebrate farming due to lower land use per kg of output/protein, and a targeted reduction of aquaculture — and not a broader reduction across animal agriculture in general — will, via substitution effects, shift some animal production towards land vertebrate farming and increase fishing pressure (and have highly uncertain net effects on wild aquatic animals, but actual wild capture production could go up or down overall [1][2]). This could reduce or even flip the wild terrestrial animal effects in 3.
Based on my own unpublished calculations, the targeted reduction of shrimp farming in particular seems good for farmed animals + wild terrestrial animals together (if you think wild arthropods have bad or ~neutral lives in expectation, and your moral weights for shrimp are high enough), although still highly uncertain for wild aquatic animals. However, my calculations need more review.
Not a backfire effect, but work to reduce aquaculture seems to reduce insect and brine shrimp farming in expectation, and this would, on my view, count in its favour. I don't know if these effects or the effects on wild animals would be more important, because I haven't really looked into it enough.