Summary

Aquatic noise comes from ships, seismic surveys to find oil and gas, sonar, and other sources. It causes marine animals stress and masks their communications, among other effects on marine ecosystems.
Aquatic noise can be reduced by lobbying for international agreements to slow down ships, adopting various technologies, and protesting against seismic surveys.
Usually, aquatic noise is considered an environmental or conservationist issue, and these seem to be the dominant concerns of the few organizations working on reducing aquatic noise. In this text, I analyzed whether animal advocates should work on decreasing aquatic noise as it potentially stresses wild fish.
My tentative conclusion is that most likely, ocean noise interventions wouldn’t be cost-effective compared to current farmed animal interventions, although there is some small chance that it’s more cost-effective than them. I attempted to analyzed the cost-effectiveness of a campaign prevent seismic surveys to find oil and gas, but conclusions seem too uncertain to inform decisions.
Pursuing wild animal welfare (WAW) interventions that are also good for the environment and conserving species could help the WAW movement find allies in these important fields. Also, it might be good for the reputation of the WAW movement to have a concrete intervention that they could to point to.

Context and conclusions

I’ve spent some months trying to find a wild animal welfare (WAW) intervention that is:

Tractable (can in principle be funded >$100K/yr starting in 2023 even if we choose not to do so),
Non-controversial (>40% support and <30% oppose in a US poll), and
Directly cost-effective (10%+ as cost-effective in expectation as chicken welfare corporate campaigns).

The intervention that seemed most likely to satisfy these criteria was trying to reduce aquatic noise. I think that most likely, it is much less than 10% as cost-effective as chicken welfare reforms, but there is a small chance that some aquatic noise interventions could be even more cost-effective than corporate chicken welfare campaigns. Also, perhaps the cost-effectiveness bar is too high because the last funded animal welfare intervention by EA donors might not meet it.

Aquatic noise would be my personal choice if someone decided that we should fund some WAW intervention now to grow the movement. But overall, it’s unclear whether the effective animal advocacy movement should spend resources on solving this issue. Experiments investigating how noise impacts species with very many individuals (such as arctic krill and lanternfish) might inform this decision. But based on my conversations with aquatic noise experts, such experiments are likely to cost hundreds of thousands of dollars and might have inconclusive results.

I think that it could be worthwhile for one or two people who care about WAW to try to have an academic career in aquatic noise (if there are no such people already), or to do WAW outreach to academics already working in the area. This could help a lot to identify how promising this cause is from the WAW perspective and to identify the best opportunities to help animals.

What aquatic noise is, and why I thought reducing it could be a promising WAW intervention

The main sources of aquatic noise are:

Ships and boats
Seismic surveys (usually to find oil and gas)
Sonar
Pile driving and other offshore construction
Wind farms
Acoustic deterrent devices used by fish farms
Dynamite fishing

This list is in the order of importance that many articles seem to give to each source (e.g., Duarte et al. (2021), Širović et al. (2021), Hildebrand (2004), Williams et al. (2018)), often implicitly. I haven’t seen any analysis on the relative importance of these sources, perhaps because it depends on the situation so much.

The list doesn’t include deep-sea mining, but it may become an important noise source in the future. It also doesn’t include a possibility of an acoustic system that acts like an underwater GPS (Ghaffarivardavagh et al. (2020)), which could substantially contribute to aquatic noise. I don’t know how likely it is that such a system would be implemented.

Because of all this noise, the ocean is much louder than it used to be. For example, Hildebrand (2004) claims that “informed estimates suggest that noise levels are at least 10 times higher today than they were a few decades ago.” Note that this does not mean that animals perceive the noise as 10 times louder. Humans perceive a tenfold increase in sound pressure as only a doubling of sound loudness. It’s unclear how fishes perceive sound, especially because they perceive not only sound pressure but also the particle motion component of sound (Nedelec et al (2016)).

According to Bar-On et al. (2018, “Supplementary Material”), there are roughly 10¹⁵ wild fishes in the world. That’s about 5,000 times more than all vertebrates farmed for food, including farmed fish. And the number of marine invertebrates is many times higher than the number of fishes. Sound is very important to marine animals, partly because sound travels much farther than light underwater. It’s possible that a significant portion of marine animals (especially fish and mammals) could be at least somewhat disturbed by aquatic noise a lot of the time. I reasoned that anything that has such a huge potential for causing suffering should be closely examined.

Aquatic noise disturbs marine animals and affects ecosystems at many levels:

Noise directly causes stress to mammals and some fishes. After reading more than 100 papers on the subject, it’s still very unclear to me just how much stress noise causes. Science simply doesn’t have the answers yet.
Noise causes stress and masks the communications of whales (Rolland et al. (2012)). This could reduce their populations. Whales are important for nutrient cycling in the ocean, which affects very many animals and enables more animals to exist.
Similarly, noise also makes fish communication more difficult, which may also make their mating more complex, possibly leading to declines in some populations (which probably leads to increases in other populations).
Noise causes physiological damage to animals that are close to the source of the sound. For example, it can compromise hearing ability.
Engås et al. (1996) observed that a five-day seismic survey caused a greater reduction in the number of large fishes than that of small fishes in the exposed area. Possible reasons for the difference include different swimming speeds, habituation rates, and hearing abilities. In any case, such changed distributions could significantly alter ecosystems.
There is also some evidence that noise increases fish mortality by predation (Simpson et al. (2016)).

Other than the first effect (direct stress), it’s unclear whether these effects are overall positive or negative for animal welfare. I have encountered this same problem when analyzing most WAW interventions. That is, I found that their most important effects are on the numbers of various wild animal species and it’s very difficult to determine whether these effects are good or bad for WAW. Reducing aquatic noise seems a bit more robustly good for WAW than many other WAW interventions, partly because it seems at least plausible that the stress it causes directly could outweigh these indirect effects on animal numbers.^[1] However, I am unsure if this is a valid argument for pursuing aquatic noise reduction over other WAW interventions because this seems like problem of cluelessness which applies to all interventions (WAW and otherwise).

How aquatic noise can be reduced

Most of the proposed solutions to aquatic noise involve lobbying governments and international organizations for stricter regulations. One brief list of possible ways to reduce aquatic noise is in section IV of the report Reduce the noise!, which was created for the EU by nonprofits working on aquatic noise. A longer discussion of possible actions is in Duarte et al.’s (2021) section “Pathways to healthy ocean soundscapes.” These sources highlighted two main solutions:

Slowing down ships (which also makes them more fuel-efficient).
Adopting various alternative technologies.
- For shipping and offshore construction, quieter technologies already exist (Duarte et al.’s (2021))
- For marine seismic surveys, an alternative and potentially less harmful technology called marine vibroseis is being developed but is not yet commercially available (Weilgart (2016), Duarte et al. (2021)). However, one expert told me that it’s unclear whether it would really reduce the harm that much.

Duarte et al. (2021) suggest that international cooperation is very important for the adoption of these mitigation measures, as both marine ecosystems and some sound sources cross national boundaries. Lewandowski and Staaterman (2020) reviewed ten international agreements and noted that nine of them “are voluntary in nature or offer both binding and non-binding options for member nations.” The one exception applies only to the EU. The paper also describes why international agreements on aquatic noise may be difficult to achieve.

There might also be some local solutions too. For example, the Port of Vancouver reduced docking fees for quieter ships. The Reduce the noise! report claims that this has substantially decreased measured noise levels.

Here are some other ideas for tackling the issue:

Perhaps some seismic surveys could be stopped or downscaled in the future via public campaigns. Later in this post, I analyze a large seismic survey plan along the US that was stopped or delayed, possibly because of a public campaign. There is an ongoing campaign against seismic surveys in South Africa. Also, OceanCare did similar campaigns in 2014-2015:
- A seemingly successful campaign in Austria and Croatia which (according to the website) prevented oil exploration
- A campaign in Spain that seemingly achieved protection of some areas important for mammals and possibly prevented some seismic exploration
- An unsuccessful campaign in Greece
- An unsuccessful campaign in the Maldives
There is also a proposal to implement an acoustic system that acts like an underwater GPS (Ghaffarivardavagh et al. (2020)), which could substantially contribute to aquatic noise. We could lobby against such initiatives if they are more seriously considered in the future. My impression was that such a campaign might be worth EA resources due to its scale: the proposed system would produce noise throughout the ocean all of the time.
Criteria have been developed for estimating the aquatic noise damage on marine mammals (e.g., Southall et al. (2019)), environmental assessments estimate how many marine mammals will be impacted (e.g., here), and seismic surveys are stopped if some marine mammals are observed in a sensitive range. WAW advocates could try to ensure that similar criteria are developed and used for species with more animals (various fish species). However, there are significant knowledge gaps that need to be addressed to develop such criteria, and I also feel that it would be unlikely to be used if it was developed.
Many people working on this issue seem to think that raising awareness about the issue is very important. My uninformed impression is that raising awareness amongst general population can only be effective if there is a concrete short-term goal in mind for people to work toward.
More research could make it easier to argue for measure to reduce noise.

Organizations that work or have worked on the issue of aquatic noise include:

Some more organizations are listed here and here, but I got the impression that most of them don’t actively work on the issue that much and are just sympathetic to the cause. Also, some organizations in these lists are now defunct.

An expert within the field told me that about 300 people are working on the issue of aquatic noise, and almost all of them are academics. Most of the research and harm mitigation efforts target the protection of marine mammals and some fishes that are commercially important to fishers. The impact of noise on most fishes and invertebrates seems to be neglected.

Impact on WAW movement building

Since the WAW movement is in its infancy, some argue that the impact of the first few interventions on shaping the WAW movement and its image is more important than the direct impact on animals. Hence, in this section, I speculate how working on aquatic noise might impact the WAW movement.

It might be good for the WAW movement-building to have an intervention that could be highlighted as a tangible example of what the movement is already doing. And it’s important that this highlighted intervention is not controversial, as it might otherwise just turn people away. While I haven’t seen a public opinion poll about this, my intuition is that most people would support most aquatic noise mitigation interventions as they are also good for the environment.

People often assume that:

What is good for the environment and species conservation is also always good for wild animals.
The less human intervention there is, the better.

Some people have suggested that it’s important that early WAW interventions challenge these beliefs, because any analysis that ignores natural wild animal suffering is very incomplete. Tackling aquatic noise would not challenge these assumptions, while something like vaccinating wild animals for their own sake could challenge it (at least if it was done in a way where many people would hear about it). However, in Šimčikas (2021), I argue that perhaps challenging these assumptions is less important in the long term because most of the expected wild animal suffering in the far future might be caused by humans (by spreading wildlife beyond Earth).

Any analysis of WAW would also be very incomplete without considering the welfare of small animals. Public campaigns to reduce aquatic noise (e.g., campaigns against seismic surveys) could help normalize the care for small wild animals by discussing how noise might cause stress to them and how this is bad for its own sake (not just because it’s bad for the environment).^[2] Doing this in a context where most people already agree with our conclusions for environmental or conservationist reasons would make it more likely that people agree with those arguments, although they may not contemplate them deeply. But my guess is that the effects of such interventions on the attitudes of the public and academia would likely be very minor.

People who already support reducing aquatic noise might want to see who these new allies working on the issue are. This might lead to a few more people checking out the WAW ideas, and it would be valuable if their first impression of the movement was positive. More importantly, tackling the issue of aquatic noise would also give a good first impression of the WAW movement to conservationists and environmentalists in general — and we want people with expertise in these topics in the movement and as allies we can collaborate with.

In terms of shaping the WAW movement, I also think it is good that reducing aquatic noise focuses on the ocean because that is where the vast majority of animals live. Working on aquatic noise interventions could also help incentivize more research into invertebrate and fish stress, which might be important for the movement in the long term. For example, I have seen studies using various techniques to measure stress for these animals due to aquatic noise concerns. Perhaps these techniques could be reused in other contexts.

Seismic surveys

I asked someone from Ocean Conservation Research about the biggest victory of aquatic noise mitigation efforts so far. He said that it’s preventing (or at least delaying) seismic surveys along the East Coast of the US that were planned for 2012-2020. Hence, I investigated the effects of seismic surveys deeper. Note that I don’t know if it was really public campaigns that prevented those surveys and one reviewer thought that it seemed unlikely.

Seismic surveys use devices called airguns to produce extremely loud explosive impulses to map the seafloor over large areas of the ocean^[3] in order to find oil or gas. These explosions might happen every 10 seconds for weeks or months without stopping. See this short video for an explanation of how it works.

Marine animals are stressed by the noise for seismic surveys. I tried to get a sense of just how much they are stressed from existing studies. Overall, there are huge knowledge gaps in this area, but here is what existing studies suggest:

Marine mammals seem to be significantly stressed by ship noise (e.g., see Rolland et al. (2012)) and seem to be affected by seismic surveys tens of kilometers away (Kavanagh (2019), Weilgart (2007)). However, I did not focus on mammals as their numbers are low compared to invertebrates and fishes.
Studies on fishes are very conflicting:
- Some studies show that some fishes can be alarmed or startled when they are 2-10 kilometers away from the seismic surveys (Pearson et al. (1992), Carroll et al. (2017), Santulli et al. (1999), Hovem et al. (2012), McCauley et al. (2000)). I’m not sure how much can be inferred from these short alarm or startle responses, but they likely indicate at least short-term stress. Also, some studies show reduced catch rates or abundance of some fish species up to 30 kilometers away (Engås et al. (1996), Slotte et al. (2004)). If fishes reduce their feeding or choose to not enter or travel away from a noisy area, it shows that the noise probably causes them discomfort. If fishes are really affected at such a high radius for weeks or months at a time, then seismic surveys are probably causing at least a little bit of suffering to an enormous number of fishes.
- On the other hand, studies like Meekan et al. (2021), Popper et al. (2016), and Wardle et al. (2001) show that fishes may not significantly respond to seismic survey explosions that are meters away. The difference might be due to different fish species and different conditions. Also, these studies seem to be more often funded by the oil and gas industry. I’m not sure if that biases researchers in some way.
- Most studies examine short-term exposure to loud sounds, probably because they are easier to study. But according to one expert, a persistent exposure to less loud noises might also be causing stress to fishes, and this could be happening throughout the survey period.
- Overall, Popper and Hawkins (2019) claim that, “currently there are so many fundamental knowledge gaps on the potential effects of anthropogenic sound on fishes that it is almost impossible to reach clear conclusions on the nature and levels of sound that have potential to cause changes in behaviour or even physical harm.”
Generally, studies on invertebrates seem to suggest that most invertebrate species (with some exceptions, like cephalopods) are not affected unless they are very close to the source of the sound. On the other hand, McCauley et al. (2017) present evidence that airguns can kill zooplankton more than a kilometer away from the source. It’s unclear to me if surveys also cause suffering to zooplankton that are further away.

See the appendix for a more detailed analysis of how seismic surveys affect fishes and invertebrates.

Seismic surveys are more often done around coastal areas where fish density is probably higher. Since there are so many fishes, if a significant percentage of them are negatively affected by seismic surveys, that could be a big animal welfare concern. The number of small marine invertebrates is many times higher than the number of fishes. If at least some marine invertebrates are capable of suffering, and suffer as a result of these surveys, then this could be a very important animal welfare concern. Note that the same can be said about other sources of noise like shipping.

I don’t know how easy it is to do something about all this potential suffering. Since most of the talk about aquatic noise is how they affect big mammals, most of the harm mitigation efforts are targeted at them too. For example, if a whale or a dolphin is spotted in a sensitive range, a seismic survey is temporarily stopped. However, such pauses prolong the amount of time sound is in the ocean, which may increase harm to other animals. Perhaps animal advocates could advocate for harm mitigation measures that help all animals more.

It might also be possible to reduce the amount of seismic surveying. As mentioned above, I chose to focus on seismic surveys because of a claim that a large-scale seismic surveying plan was stopped by activists and scientists. The person I spoke to about it also claimed that the campaign he was a part of only spent about $250,000 on the effort. However, he also mentioned that he was raising awareness about this for many years prior and that there were other efforts to amplify the message. Even so, overall costs are probably still in the range of one or few million dollars to stop months or years of seismic surveying.

I haven’t been able to verify that the efforts of this campaign were really instrumental in stopping the surveys. It might also be that the surveys will still be done in the future and the campaign simply delayed them. Or it could be that surveys were stopped or delayed for unrelated reasons. Nevertheless, I tried to estimate the cost-effectiveness of this campaign, assuming that it really did stop seismic surveys. My reasoning was that if that effort was cost-effective from an animal welfare perspective, then it’s reasonable to expect that we could discover other cost-effective things to do in the space of aquatic noise.

The estimate turned out to be very speculative and quite complex. If anyone is interested, you can see the estimate here and described in text here. According to the estimate, the campaign potentially directly prevented one year of fish suffering per dollar spent. For comparison, I estimated that corporate campaigns to improve conditions for farmed chickens affect 9 to 120 years of chicken life per dollar spent. However, I think that these chicken campaigns are an outlier and that we should set the bar for worthwhile animal welfare interventions much lower.

There are many reasons why my cost-effectiveness estimate might be incorrect:

The estimate only considered the direct short-term stress caused by aquatic noise from seismic blasting. I assumed that fishes are only stressed for 20 minutes when they hear loud sounds from surveys. But they may also experience lower-level stress from persistent noise that lasts for weeks or months. Also, aquatic noise impacts WAW in many other ways which I discussed in the “What is aquatic noise” section but didn’t account for in the estimate.
As mentioned previously, the estimate assumes that campaigns really did stop the seismic surveys, but it’s unclear if that’s the case.
The estimate doesn’t take into account invertebrates and mammals.
The estimate is based on claims from the US Bureau of Open Energy Management, but it’s possible that they are biased or corrupt.

Also, even if my cost-effectiveness estimate was correct, it would be quite unclear what that means. I got the impression from Ocean Conservation Research that another win of this magnitude in the immediate future is unlikely as there are currently no other plans in the U.S. to produce this much aquatic noise that could plausibly be stopped. That said, as mentioned above, there have been some other seemingly successful campaigns to stop seismic surveys in Croatia and Spain, as well as an ongoing campaign in South Africa. Hence, similar efforts in the future might be possible.

Furthermore, if the campaign analyzed above really prevented these large-scale seismic surveys, by far the biggest effect might be reducing greenhouse gas emissions. Seismic surveys are the first step to find oil and gas. If it’s found, then offshore drilling likely follows. And I imagine that the more oil is available, the more oil is burned. This would have many effects on everything, including WAW. Offshore drilling might also cause oil spills which also have far-reaching consequences. This is not my area of expertise at all and I did not look into it, but it seems to me that preventing that much emissions for less than $1 million would be a very cost-effective climate change intervention. There is a slogan for this general approach to fight climate change: #KeepItInTheGround.

Perhaps there might be fewer seismic surveys in the future even without us doing anything as the world is trying to move on from using oil. Seismic surveys might also be used for deep-sea mining of some materials (Martin et al. (2021)) but I’m not sure what the scale of such surveys could be.

Questions for further research

If someone were to look into aquatic noise more, it might be better to look into shipping noise. Duarte et al. (2021) claims, “it may be easier to instigate noise reduction of activities that produce sound as a byproduct (e.g., shipping, construction), rather than intentionally (e.g., seismic surveys, military activities), through technological and/or regulatory measures, as demonstrated by recent progress in the shipping industry.” Also, ships seem to be the most important source of noise and it is predicted to continue growing (Kaplan & Solomon (2016)). When analyzing seismic surveys, I focused more on short-term stress caused by noise, but it’s possible that chronic stress is more important.

I considered suggesting funding studies to figure out whether efforts to reduce noise should be supported by animal welfare funders. For example, funding experiments in which fishes (or invertebrates) are put in a tank in the ocean, and their stress level is monitored as noise from ships varies. For fishes, stress could be measured by measuring cardiac output or cortisol levels. Similar experiments have been done (e.g., Jain-Schlaepfer et al. (2018)). The experiments I’ve found didn’t use the most populous species of aquatic animals and the most important sources of noise. Also, sound sources were often very close to fishes, but I think that for WAW it would be more important to know how noises that are further away affect fishes. I asked some researchers how much an experiment of this kind with fishes would cost, and they answered that it would be under $1 million USD, implying that it would cost hundreds of thousands USD. The estimate assumed that non-harmful methods would need to be employed, which increased the estimated cost significantly. Either way, I tentatively think that the price might be too high for the information value such experiments would provide. This is partly because results might be inconclusive and might not generalize to other species and environments.^[4]

Appendix: How seismic surveys affect animals

In the main article, I briefly described the effects seismic surveys have on fishes. In this appendix, I go into more depth on this topic.

Fish

In general, the effects of seismic surveys on fishes are mostly unknown (Popper & Hawkins (2019)). Nevertheless, available studies do give us some information about how much fish may be affected, and I analyze that information below.

In this section, I mention distances at which fish may be impacted by seismic noise. Note that the distance that sounds travel underwater can vary a lot depending on factors like depth, ocean floor type, temperature, etc. Hence, the distance at which airguns will affect fishes is not at all consistent even if the same types of airguns are used and the same species is observed. Nevertheless, I think these distances are indicative of what the radius of the sound might be. I pay special attention to the distance of impact because as the distance increases, the affected area (and hence the affected number of fish) increases exponentially since sound travels to all directions.

Studies that show minor or no impact

Meekan et al. (2021) claims that “the scientific evidence that catch rates are impacted by seismic surveys is often contradictory, with experimental studies providing contrasting results.” I very much agree with this assessment. These contrasting results are best illustrated by the table S1 from the Supporting Infromation Appendix of Meekan et al. (2021). The table doesn’t include studies that examine startle or alarm responses, nor lab studies that examine stress hormones. Startle and alarm responses show us when fishes can detect noise, but it’s unclear whether they indicate that fishes experience anything but a transient suffering from the responses. Multiple lab studies that examine stress hormones show that fishes can be stressed by recordings of ship or seismic survey noise.^[5] However, according to an aquatic noise expert I spoke to, lab conditions are too different from the conditions in the ocean to draw almost any conclusions about how fish are affected in the ocean.

The aforementioned table also doesn’t include Meekan et al. (2021) itself, which in my opinion provides the strongest evidence against seismic surveys affecting most fishes in a major way. It observed many species of fish during an actual seismic survey and found little to no effects on the abundance, composition, size structure, movement, or behavior of demersal fish (most of the aquatic noise studies seem to be on demersal fish; I’m not fully sure why, but perhaps it’s because they are commercially important and fishers noticed decreased catches during and after seismic surveys). Meekan et al. (2021) also suggested that, “given similar physical environments (notably water depths) and life history stages, it is likely that our results are applicable to other locations and species of the same families of fishes.” However, note that Meekan et al. (2021) was funded by the oil industry.

Other studies that made me think that most likely seismic surveys don’t majorly impact most fishes include:

Popper et al. (2016): Hatchery-raised pallid sturgeon and paddlefish were “were held in cages as close as 1 to 3 m from the [air] guns.” Fishes were then returned to a hatchery where they were “monitored every 12 h for 7 days post-exposure.” Fishes did not show any kind of distress and all animals survived this period. Necropsy results indicated that experimental and control groups had the same rate of injuries.
Wardle et al. (2001): Fish behavior was observed on a reef as an airgun was fired. The investigators found that several species of fishes showed almost no response and did not change their patterns of movement.
- McCauley et al. (2003) pointed out that in Wardle et al. (2001), “the fastest repetition rate used was around once per minute which is much less than a conventional seismic survey of a shot every 5-15 s. The air-gun was also fixed in position, unlike the typical rapidly increasing signal expected from an approaching air-gun source. Thus the fact that Wardle et al did not see the ‘alarm’ response [...] or the increase in startle/alarm responses and ‘huddling’ behaviour seen with increasing air-gun level described in our trials, may have been an artefact of the exposure regime. The shot spacing may have been long enough for the fish to fully recover from the alarm response which initiated the C-turn, and the fact that the source was stationary meant it would not have constituted an approaching threat.”
Peña et al. (2013): “The real-time behaviour of herring schools exposed to a full-scale 3D seismic survey off Vesterålen, northern Norway, was observed using an omnidirectional fisheries sonar. [...] No changes were observed in swimming speed, swimming direction, or school size that could be attributed to the transmitting seismic vessel as it approached from a distance of 27 to 2 km, over a 6 h period. The unexpected lack of a response to the seismic survey was interpreted as a combination of a strong motivation for feeding, a lack of suddenness of the air gun stimulus, and an increased level of tolerance to the seismic shooting.”

Note that Popper et al. (2016) and Wardle et al. (2001) are also at least partially funded by the oil industry. Given large economic incentives of oil companies for there to be studies showing that seismic surveys have little effect on wildlife, I am somewhat concerned about the reliability of these studies that find no effect.

Studies that show a major impact

The studies below indicate that seismic surveys can affect some fish at large distances. If the radius at which seismic surveys cause stress can be as large as the studies below suggest, the number of animals affected could be huge. Compared to studies that show minor impact above, fewer of the studies below seem to have been funded by the oil and gas industry.

Studies that examine fish abundance or catch

I think that studies that examine fish abundance or catch are informative because if fishes reduce their feeding or choose to not enter or travel away from a noisy area, it shows that the noise probably causes them significant discomfort. Here is an overview of such studies:

Engås et al. (1996) showed that seismic surveys could reduce cod and haddock catch rates and abundance over 30 km away from the source.
- The results of this study have been disputed by a report for Norwegian Oil Industry Association (Gausland (2003)) which suggested that outside of the immediate survey area, decreased catch rates could have been caused by other factors.
Slotte et al. (2004) reported that during a seismic survey, the abundance of herring, blue whiting, and mesopelagic was much lower in the survey area, and higher 30 to 50 km away from the survey.
Paxton et al. (2017) found, “Videos recorded fish abundance and behavior on a nearby third reef 7.9 km from the seismic track. During seismic surveying, reef-fish abundance declined by 78% during evening hours when fish habitat use was highest on the previous three days without seismic noise.”

Studies that examine startle and alarm responses

Some studies examine whether fish exhibit startle and alarm responses when exposed to sound. Here is how Pearson et al. (1992) describes them:

“Startle responses were either flexions of the body followed by rapid swimming (olive rockfish) or a series of shudders and tremors with each airgun discharge ”

“We also observed a combination of general increases in activity and changes in schooling and water position, all of which we have categorized as “alarm” on the basis of analogy with the descriptions in Blaxter et al. (1981).”

“The alarm responses observed here appear to be extensions of behaviours typically seen or expected in escape from predators. Tight mills and “flash expansions” or loss of polarization have been observed in schools under attack by predators.”

I am not sure how much can be inferred from short startle or alarm responses, but they likely indicate at least short-term stress. Here are studies that found fishes exhibiting these responses far away from seismic airguns:

Pearson et al. (1992) claims that for captive rockfish, thresholds for startle and alarm responses would be 316 meters and 5.6 kilometers respectively, unless in shallow waters, where they would be 1 meter and 139 meters respectively.^[6]
Carroll et al. (2017): “Startle and alarm responses have been observed in captive fish several kilometres from the sound source, with European sea bass and the lesser sandeel responding at distances up to 2.5 and 5 km from a seismic source, respectively (Santulli et al., 1999, Hassel et al., 2004).” Santulli et al. (1999) is described below. I failed to understand the setup at Hassel et al. (2004) so I’ll just trust that Carroll et al. (2017) interpreted its results correctly.
- Santulli et al. (1999): “TV camera monitoring of fish indicated that, when the R/V was 2500 m away from the cage, most fish swam slowly against the stream flow. Few individuals had a rapid startle response, visible as a sudden change in swim speed and a sharp bend to one side synchronous to the air gun emission. When the vessel arrived at about 800 m from the cage, startle response to air gun pulses was displayed simultaneously by a larger proportion of fish. With vessel at the minimum distance of 180 m, the fish bunched in the central part of the cage, with random orientation.” “Behaviour observation indicates, furthermore, that sea bass recover normal status, i.e. they reoriented against stream flow, when the vessel is one mile away from the cage. The behavioural reaction observed in our experiment is in agreement with published findings relating to captive rockfish (Pearson et al., 1992) and to herring shoals (Blaxter et al., 1981)”
  - The study also showed that the fishes had increased cortisol levels due to the shooting, indicating stress.
Hovem et al. (2012): “Calculated sound exposure levels are compared with startle response levels for cod. Preliminary conclusions indicate a required distance in the range of 5-10 km, but dependent on the depth and the season. [...] At a distance of about 5 km, the sound level was determined to be equivalent to the threshold value for startle response in cod. Acoustic startle responses are strong with rapid escape reactions directed away from the sound source but the fish are likely to show other types of behavioral changes at lower sound levels than those causing startle responses.” It seems that the study took response thresholds form Karlsen and Eckroth (2011), but I wasn’t able to find this paper.
McCauley et al. (2000): “trials with captive fishes showed a generic fish ‘alarm’ response of swimming faster, swimming to the bottom, tightening school structure, or all three, at an estimated 2–5 km from a seismic source. Modelling the fish ear predicted that at ranges < 2 km from a seismic source the ear would begin a rapid increase in displacement parameters. Captive fish exposed to short range airgun signals were seen to have some damaged hearing structures, but showed no evidence of increased stress.”

Invertebrates

The current evidence seem to suggest that aquatic noise does not have a lot of impact on most invertebrates (with some exceptions like cuttlefish). See excerpts from overviews below.

Hawkins et al. (2012):

“One question that is very hard to deal with is the potential effect of man-made sounds on invertebrates. There are almost no data on hearing by invertebrates, and the few suggestions of hearing indicates that it is for low frequencies and only to the particle motion component of the sound field (e.g., Mooney et al. 2010, 2012). There are no data that indicate whether masking occurs in invertebrates or to suggest whether man-made sounds would have any impact on invertebrate behavior. The one available study, on effects of seismic exploration on shrimp, suggests no behavioral effects from sounds with a source level of about 196 dB re 1 µPa rms at 1 m (Andriguetto-Filho et al. 2005).”

“There are very few studies of the effects of seismic sounds on catches of invertebrates. Christian et al. (2003) examined changes in CPUE for snow crab caught in traps and before, during, and after exposure to an array of airguns. It was concluded that there was no detectable response in terms of the trap CPUE.”

Carroll et al. (2017):

“Previous field-based studies on adult populations revealed no evidence of increased mortality due to airgun exposure in scallops up to ten months after exposure (Parry et al., 2002, Harrington et al., 2010, Przeslawski et al., 2016), clams two days after exposure (La Bella et al., 1996), or lobsters up to eight months after exposure (Payne et al., 2007, Day et al., 2016a). Similarly, there was no evidence of mortality-associated population effects such as reduced abundance or catch rates in plankton a few hours after exposure (Parry et al., 2002), reef-associated invertebrates four days after exposure (Wardle et al., 2001), snow crabs up to 12 days after exposure (Christian et al., 2003), shrimp two days after exposure (Andriguetto-Filho et al., 2005), or lobsters weeks or years after exposure (Parry and Gason, 2006).”

“Behavioural studies on the response of marine invertebrates to seismic sound are also dominated by those using startle responses. Jetting and inking in squid have been observed during airgun operations, with startle responses occurring more frequently as sound levels increase (Fewtrell and McCauley, 2012), and scallops have shown a distinctive flinching response although no energetically costly responses such as swimming (Day et al., 2016a). Laboratory studies have also found inking and jetting of cuttlefish at frequencies of 80–300 Hz, sound levels above 140 dB re 1 μPa rms and 0.01 m·s‐ 2; although these responses disappeared at higher frequencies and lower sound levels (Samson et al., 2014). Unlike cephalopods, decapods only exhibited alarm behaviour when they were < 10 cm away from the sound source (Goodall et al., 1990) and showed no such behaviour in response to seismic sound at distances of 1 m or more (Goodall et al., 1990, Christian et al., 2003). Sound avoidance behaviours have a more lasting impact on populations than startle responses, particularly if animals migrate out of an area in which seismic surveys are conducted. Previous studies have found that neither squid (McCauley et al., 2000), snow crabs (Christian et al., 2003), nor shrimp (Celi et al., 2013) move to avoid low-frequency sounds, although the latter study was conducted in a tank in which shrimp may have been unable to detect the direction of the sound.”

Credits

This research is a project of Rethink Priorities. It was written by Saulius Šimčikas. Thanks to Michael Stocker for extensive consultations. Thanks to Jason Schukraft, Kim Cuddington, Marcus A. Davis, Michael Stocker, and William McAuliffe for helpful feedback on drafts of this article. Thanks to Katy Moore for copy-editing. All mistakes are my own. Also thanks to Ozy Brennan who wrote an article about aquatic noise that brought my attention to the issue. If you like our work, please consider subscribing to our newsletter. You can see more of our work here.

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Footnotes

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For example, Duarte et al. (2021) claims that, “Although there is clear evidence that noise compromises hearing ability and induces physiological and behavioral changes in marine animals, there is lower confidence that anthropogenic noise increases the mortality of marine animals and the settlement of their larvae.” In general, it seems possible that aquatic noise causes suffering and changes the species composition, but doesn’t change fish and invertebrate biomass much as it’s not the limiting factor for populations. This would make the effects of aquatic noise robustly negative for animal welfare.
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Note that we currently don’t have enough scientific evidence to support the claims about harm to invertebrates and most species of fishes. We can just speculate based on evidence about a few examined species that noise may harm some of these animals. But despite that, I’ve seen multiple organizations that claimed that noise affects all marine animals.
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In the case of surveys that were planned along the East Coast of the US, the planned seismic survey area was 854,779 km^2.
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Hawkins et al. (2012) claims that “It is not likely that a single threshold for onset of a behavioral response will be found because behavior is so varied between and within species, including between fishes of different ages and sizes, and the motivation of the fishes exposed to man-made sound sources will also vary. [...] Behavioral effects will be specific to the species and the habitat, and even time of year.” The same may also apply to stress response.
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An overview of lab studies that measure stress hormones such as cortisol: some studies showed that if you put various fishes in a bucket or an aquarium and play sounds to them, their cortisol levels increase. Nichols et al. (2015) found that “the cortisol concentration of giant kelpfish was elevated only in response to playback of noise recorded at the smallest distances from the boat engine (4 and 6 m), which produced the highest sound pressure inside aquaria (141.9 and 136.9 dB rms re 1 μPa, respectively).” Wysocki et al. (2006) showed that the three tested fish species had elevated cortisol levels if exposed to a ship noise (153 dB re 1 μPa) for 30 minutes. However, such experiments cannot be used to directly determine how a fish would respond to aquatic noise in the wild for a variety of reasons (Popper et al. (2019), Nichols et al. (2015)). The most important reason seems to be that all fishes are likely to perceive the particle motion component of sound (in addition to sound pressure) (Nedelec et. al. (2016)). Particle motion is expected to occur at higher levels in an acoustic environment created by playback of sounds into an aquarium compared to open water. It seems that this may only cause more stress to fishes compared to the conditions in the wild, so perhaps the results of these studies could be used to determine the upper bound of how much fishes may be stressed by various sound pressure levels.
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The sound propagation model used in this study seems different from other sources, and I’m not sure why. However, this is not my area of expertise so I don’t know what to make of it.

Reducing aquatic noise as a wild animal welfare intervention