Hi Amanda, I have a few points of clarification regarding the evidence on shrimp stunning and Shrimp Welfare Project’s Humane Slaughter Initiative.

We acknowledge it is true that academic peer-reviewed evidence is limited (although we’re excited to report that the Stirling study is no longer a pre-print and has been published in Aquaculture). That being said, our intervention is informed by more evidence than just the peer-reviewed literature. We (and, sometimes, the industry) have access to more evidence than what’s published or able to be communicated publicly. 

It may be useful to clarify what we mean by “research” and “evidence-building” in this context. Beyond peer-reviewed studies, evidence-building for humane slaughter means reducing uncertainty across several linked questions, including: whether electrical stunning can quickly render shrimp insensible under controlled conditions; whether it works reliably during commercial harvests; what parameters, protocols, and equipment designs improve outcomes; whether producers are using stunners as intended; and how monitoring systems can make that implementation more verifiable over time.

In practice, that means the evidence base is built from multiple sources: lab studies, field observations, stunner data, producer feedback, behavioral indicators, equipment iteration, implementation protocols, and MEL systems. This is not a linear process where all the research happens first and implementation only begins later. Field implementation is part of the learning which often reveals the constraints, failure modes, and practical questions that the next round of research needs to answer.

Recently, The Center for Responsible Seafood (TCRS) published a summary of a study conducted by the University of Stirling^[1]. In a field visit in April 2026, researchers compared electrical stunning and ice slurry on an Indian farm. An excerpt reads:

“In summary, to meet ethical and welfare concerns, shrimp benefit from rapid stunning immediately after harvest. Electric stunning provides a rapid and effective stun as shown by the lack of response to subsequent cold exposure, but the process triggers a strong muscle contraction and elevated blood lactate. Cold shock does not deliver an immediate stun.

The report found that, with ice slurry alone (referred to as cold shock or CS), “shrimp are highly likely to maintain neural sensibility during the CS stunning process,” and those animals “did incur an initial ca. 30 sec tail flip response (since they are not insensible).” 

“Therefore,” the researchers wrote, “best practice would suggest that ES needs to be followed by CS (ES+CS protocol).”

For those unfamiliar with TCRS, it’s quite an industry-aligned organisation, so their study coming to this conclusion is noteworthy. 

Through our Humane Slaughter Initiative, Shrimp Welfare Project’s team members have seen dozens of harvests using stunners, and we have collected thousands of photos and videos that have informed our intervention (e.g., which parameters work best in certain contexts, how the use of a pump/harvester could minimize time shrimps spent out of water, etc.). We can’t share most of that content publicly because our industry partners (and therefore, we) operate in a competitive market environment where confidentiality, trade secrets, and proprietary information are very important. We understand that many folks in the EA community would appreciate greater transparency, and we’re always trying to facilitate a productive exchange of knowledge about our work – hopefully, this comment will accomplish some of that. 

To respond to some of your specific points:

In 2021, Tesco and Hilton Seafood published a report on their use of a modified Optimar stunner in Vietnam. … This gives some reassurance for this particular machine, although I know from talking to people in the field that this machine was a modified version of the commercially available one.

Shrimp Welfare Project has visited that farm and observed the stunner in operation, and it is an early (yet almost-standard) Optimar model. It's a fish stunner that had its electrified "fingers" (which, when they touch animals on an electrified conveyor, complete the electric current and produce the stunning shock) lowered to reach much smaller animals, rather than a completely bespoke modification that could have fundamentally changed the stunner's parameters or operation. 

We've worked with Optimar to implement improvements over the years (we’re currently on version ~6), so the shrimp-specific finger-lowering adjustment is no longer a post-manufacturing modification, but a feature of the commercially-available standard model. Perhaps this is the source of the confusion? 

Regardless, the important takeaway here is that the 2020 case study used a stunner that is representative of the kind of stunners we support via our HSI program at present, and it concluded that electrical stunning at the recommended parameters was able to “deliver >97% stunning efficacy,” and followed by “immediate immersion in ice slurry achieving 100%” efficacy. 

Going into your next point about sample sizes, I wanted to note that this case study used 50kg samples per voltage tested. Since shrimps were 25-30g each at harvest, that’s ~1,700-2,000 animals per 50kg sample, though the report doesn’t state this explicitly. There were also 100 shrimps checked for stunning effectiveness at start-up. 

[re: Weineck et al.] The study uses a very small sample size (N = 6 for each intervention) which makes me uncomfortable recommending any action based on it. … [re: Stirling study] This study is also small (N = 4-6 per intervention) which again leads me to have limited confidence in conclusions. 

Many of the studies that involve animal testing like this use small sample sizes. In speaking with scientists who specialize in invertebrate biology, it’s understandable why these studies would be designed with small sample sizes. If the desired effect size is large for the variables tested (as is often the case here) and the standard deviation among individuals is only moderate (as is expected to be the case here), this is not necessarily a limitation. It’s statistically appropriate, and even often ethically mandated – by institutional standards and/or the Three R Principles of animal research. This is only to say: we should not have a knee-jerk response to sample size. 

That said, we recognize that the actual findings are not a clean on/off, but rather a subtle, dose-dependent difference between responders and non-responders. Our confidence would increase if there were more animals tested to generate more data to support precise parameters for effective stunning. At the same time, the direction of the findings is still informative, especially as they converge with other evidence, including the TCRS study and our own field data. 

Based on this data, it is unclear if electric shock followed by ice slurry provides any benefit over ice slurry alone, provided the animals are kept in ice slurry until they are fully dead. (It is unclear how long that would take, though.) …  A sufficiently strong electrical shock with proper ice slurry (which is hard to implement in practice) does not provide much improvement over proper ice slurry alone.

I don’t think the Stirling paper supports this.

At 2.5–5 °C (which would be a high-performing slurry temperature by current commercial standards) cold shock was slow and unreliable as a route to neurological insensibility. Using the paper’s threshold of Ptot <10% of baseline brain activity, only 4 out of 5 shrimp reached this threshold, and this occurred after 28 minutes. One animal did not appear to reach the Ptot <10% threshold within the 30-minute observation period.

At −2.5 °C, all shrimp reached Ptot <10% within 4 minutes. However, achieving and maintaining a −2.5 °C slurry consistently during commercial harvests, especially in tropical climates and under high biomass loading, is likely to be extremely difficult. We are exploring this avenue, including deepchill-type technology, but at present we are only moderately optimistic about its practical feasibility. At the moment, maintaining these kinds of temperatures is far from “proper ice slurry,” and more appropriately understood as a rare exception in real-world production settings. 

The best-supported approach in the paper is electrical stunning (ES) followed by cold shock (CS). In the effective ES + CS group, all animals that did not tail flip after cold exposure reached Ptot <10% after 3 minutes of cold shock. There’s limited research on the relationship between tail flipping and neural insensibility / loss of consciousness^[2], so our confidence in this correlation would increase with more data. But it’s important to reiterate that, based on the best available knowledge from the Stirling lab (which they clearly state in the paper), absence of tail flipping after cold exposure is aligned with neurological insensibility^[3].

Here is a video that shows shrimp in ice slurry – the first group has been electrically stunned, and the second group has not. The second clip shows a nearly ideal ice slurry in a production setting, with a temperature around 1 degree C. What you see in that video is consistent with what we’ve seen at shrimp farms around the world: that even when in a highly controlled ice slurry, shrimps flip their tails for multiple minutes. 

Insufficient electrical stunning with proper ice slurry may be worse than ice slurry alone.

This would be true for basically all stunning methods, across land and aquatic animals. If a percussive stunning bolt is insufficiently administered to a cow’s head, then the slaughter process would be more painful than if a stunning method hadn’t been poorly attempted. 

Electrical stunning without proper ice slurry slaughter poses real potential for causing harm.

A few things here:

• Our intervention is not electrical stunning on its own, without an adequate kill step (more on this below).
• We don’t just send stunners to producers – an important part of our intervention is that we train them on how to use the machines properly and help them implement higher-welfare ice slurry protocols. 

Additionally, this line of reasoning would seem to contradict your argument in your post, that:

“Many shrimp harvests do not use ice slurry, or do not use it properly (not cold enough, not long enough, etc.).” 

There’s a tension here worth flagging: on the one hand, your comparison of electrical stunning vs. ice slurry assumes an idealized version of “proper” ice slurry – cold enough, maintained long enough, carefully managed. But when it comes to what electrical stunning would look like in real-world harvest conditions, your concern raised is precisely that ice slurry is often not implemented properly. If poorly implemented ice slurry undermines the case for electrical stunning, then the same realism has to apply when ice slurry itself is proposed as the alternative. Either way, the fair comparison is between the two methods as they would actually be implemented – and in our view, that comparison favors electrical stunning followed by ice slurry as the kill method.

The science is clear that any stunning method can be reversible if it’s not followed by an adequate kill step. This is true for both electrical stunning as well as ice slurry that’s used for stunning. In the Humane Slaughter Initiative, our protocol calls for ice slurry as the kill step; importantly, we’re not using ice slurry as a stunning method, but rather a method to prevent the shrimps from recovering after the electric shock. We guide farm staff on how to do this ice slurry properly, including monitoring the temperature and replenishing the ice, etc. In our field experience, this process usually involves putting shrimps through the stunner, then directly into an ice bath for several minutes (as in this video and this video), and then into transport crates where they are packed with ice. In this slaughter method, the ice slurry prevents the shrimps from re-warming and recovering, rather than being the step that also stuns them. 

Doing a well-implemented ice slurry for stunning is much harder to do effectively in practice than an ice slurry for prevention of recovery/slaughter after electrical stunning. So, although these practices share the same name, their different purposes and application create a major distinction. We are more confident in ice slurry as a slaughter and recovery prevention method after electrical stunning, than ice slurry as a stunning method itself.

Overall, the evidence base for shrimp stunning is still developing and Shrimp Welfare Project acknowledges this and is actively working to develop it further, both through our own fieldwork and by coordinating with researchers, manufacturers, producers, and other industry actors. Given the scale of the problem, we do not think the right response is to wait for full certainty, as it would mean accepting a harmful status quo for billions of animals while the evidence accumulates. The direction of the evidence, our field experience, and the practical realities of commercial harvests so far all point the same way: electrical stunning is faster, more consistent, and more monitorable than industry-typical ice slurry stunning.

More importantly, it is somewhat illusory to think that all the necessary research and R&D can happen first, in isolation, and only then be translated into the field. In industry-facing work, implementation is often what makes the most useful research possible. Without producer buy-in, farm access, commissioning data, firsthand observations of real harvests, and tests in farm conditions, we would be left with a largely theoretical understanding of the problem. We would not know which constraints actually matter, which failure modes appear in practice, or what kinds of equipment, protocols, and monitoring systems can realistically work.

This is especially true in an industry that is often cautious about disclosure around its know-how. Building trust with producers and the wider industry is not incidental to the intervention; it is part of what makes practical progress possible. That is why we think collaborating with the industry is the most effective path: build trust, implement carefully, learn from the field, improve the technology, and strengthen the evidence base as we go. The field implementation work is what creates the conditions for practical, relevant R&D to happen.

Humane slaughter for shrimp is emerging as a higher-welfare standard, and the science on effective stunning is not fully settled. As I’ve outlined, there are things that would increase our confidence levels. But the available evidence indicates that well-implemented electrical stunning beats what is happening on most farms today. And it’s my view that responsible implementation now, alongside continued research, R&D, and monitoring, is one of the strongest bets we can make for reducing suffering at scale.

1. ^{^}

   This is an example of the fact that we have access to more data than that which is publicly available. In this case, the research summary is published online, but we also have access to the full scientific report (although we’re not at liberty to post or share it). There have been many instances like this over the years.

2. ^{^}

   Behavioral indicators are tricky because they’re not always a reliable indicator of unconsciousness. It’s like proving a negative: you can often infer consciousness from the presence of certain behaviors, but you cannot reliably infer unconsciousness from a lack of those behaviors alone. However, Stirling’s team measured behavioral indicators and investigated which of them correlated with EEG results, to determine which might be reliable. 

3. ^{^}

   Generally, when shrimps are electrically stunned, there’s one big tail flip when shrimps go through the stunner (likely a reflexive response), followed by immobility. The Stirling study found that this correlates with shrimps having one big EEG spike and then a drop, likely indicating a seizure analog followed by absence of brain activity (a loss of consciousness).

(I manage the FP Climate Fund, so my incentives run counter to my take). I hadn't had the time to examine this paper in detail, but I am quite skeptical of this Rethink Priorities paper. I think it is quite easy to string together assumptions that yield a high social cost of carbon, but I wouldn't treat this as an unbiased estimate.

For example, if I understand this correctly based on your description, they use the Rennert et al (2022) paper to derive the SCC from which they make adjustments.

https://www.nature.com/articles/s41586-022-05224-9/figures/1

The assumptions of that paper are clearly extremely pessimistic, probably by 2022 standards, but definitely by what would now be the consensus view.

For example, they assume close to 20/Gt annual emissions in 2100 as their median scenario and high emissions continue well into the 23rd century. In other words, we are more than a 100 years late in achieving net-zero in their median scenario despite all technological trendlines rendering this quite implausible.

Combining this with a low discount rate will give a high SCC, but I don't think this is close to a reasonable baseline for what a median expectation should be. (Obviously good to have a low discount rate from an EA perspective, but this requires that the modeling of the future is a bit more careful). Essentially, this means that most marginal carbon reduction modeled for the SCC will happen in worlds where this is implausibly valuable thereby inflating the SCC value.

This alone probably leads to an overestimate of the SCC of a factor of 5x or more and this came up from looking at the paper for 5min.

Okay cool, that’s helpful. It seems like the root disagreement is not whether research is ever worth funding, but how clear the research —> impact path should be, and perhaps how short.

My guess from this/reading your other comments is that ~ 2 major things underpin a difference between you and I in terms of excitement about WAW/WAI. Both connect to the fact that cost-effectiveness is always a comparative claim. So on the one hand, I probably rate WAWS as more cost-effective to promote than you do, but importantly, I also rate other things as less cost-effective than you do (making the bar easier to clear).

Towards the latter point: I care a lot about indirect and unintended effects of interventions on all sentient beings. This means that, without a good understanding of ecology and WAW, the cost-effectiveness of the vast majority of potential animal welfare interventions is basically not knowable. For a variety of reasons connected to (what I view as) the failure of the taste/price/convenience model, I don’t have that much confidence that merely inventing cultivated meat will be enough to change diets. But even if it was, I don’t have any idea exactly how those diets will change (small animal replacement problems), or how the resulting land use changes will affect wild animal welfare. I’m pretty consequentialist in my ethics, so I’m not comfortable helping some farmed animals at the expense of billions to quadrillions of wild animals. As someone who hates factory farming this is a hard place for me to sit, and I’m probably not ethically pure on it — I still am vegan and support farmed animal advocacy financially. But in response to the uncertainty about how shrimp stunning, cultivated meat, vegan advocacy, etc. affects wild animals, the only thing I can see to do is research it, and my calculations of cost effectiveness of those other activities is correspondingly really really wide, making research a cost-effectiveness-competitive thing to do.

My guess is that you don’t share this view at all and may even think it’s sort of dumb! That’s fine, but arguing about whether WAI in particular is cost-effective won’t help us make progress on this disagreement (which I think is also the source of disagreement between you and the vast majority of other people who are excited about WAWS). Instead, if you wanted to change my mind that WAI was a good giving opportunity, you’d need to show me that I should not care about the effects of land use change resulting from factory farming elimination or cultivated meat production on wild animal welfare (among a variety of other things).

The second source of disagreement is how much the sort of field-building work WAI does leads into interventions, and how soon. Using cultivated meat as a benchmark: yes, we already have cultivated meat, but we have no way to produce it cost effectively at scale. I’m not a cultivated meat expert, but barring some kind of revolutionary development I would assume that we’re more than 5 years away from scaled cultivated meat deployment? If that’s right, there are definitely interventions in WAW that could realistically be available on that timeline. We already have a variety of contraceptive products that work in the lab for rodents. I’m in the middle of designing a targeted research program that (I hope) will get us to the point of a cost-effective, scalable deployment within 5-8 years. Similarly, I’ve designed a research agenda that I believe, within ~ 3-5 years of research, maybe less, could answer to a degree of confidence I’d be willing to act on whether bird-window collision prevention is net positive to promote. Another angle I’m pursuing is wildlife vaccination — it might not pan out, but if it does, I would expect to be ready to recommend an intervention within no more than 10 years. Whether that’s good enough probably depends on how quickly you think other interventions will start benefiting animals; you might think cultivated meat replacement will be here in much less time than I do.

Connecting this back to WAI: although I’m not doing this work at WAI, none of it would be possible without WAI. My work there and the field-building work they’ve done give me the tools I need to do this more intervention-focused research, and the research WAI does/supports is the substrate by which these ideas have been generated. If the work I’m doing now continues to make progress, I’ll need scientists who get the basic ideas to carry it out. And once I rule in/rule out the ideas I already have, I’ll need there to have been more research in the meantime to support more ideas and ways to help animals.

None of this is that dissimilar to what GFI does for cultivated meat. If I understand correctly, the product didn’t really exist before EAs got into it, and a huge amount of EA and animal advocacy money went towards not just object level research but building university groups so there would be a talent pipeline, lobbying to make more money available, etc. And WAI is working on a harder problem at an earlier stage, so things are a little slower/less tractable, but the scale is commensurately higher.

I don’t really expect you or others with values focused on shorter timelines/direct effects only to be convinced — I think it’s fine for EAs to differ on what they mean by “cost-effective.” Some people want “strong evidence for immediate-ish impact” and others want to take a bunch of high risk, high reward bets and expect that at least a couple pan out. Both are legitimate investment strategies, and WAI is likely to be most appealing to people who (1) are very worried about indirect effects or (2) prefer the latter cost-effectiveness definition.