Salmon farming - use of acoustic deterrent devices: report

4. SAWC evidence gathering and analysis

As outlined above, the situation is complex. There are three groups of animals involved: seals, cetaceans and fish. The welfare of the seals and cetaceans could potentially be adversely affected by ADD use, while the welfare of the fish may be adversely affected if ADDs cannot be deployed. In addition, since there is a conflicting legislative background, SAWC considers it timely to investigate the welfare implications of the use of ADDs for seals and cetaceans, and conversely the implications for the welfare of salmon and other farmed fish in the absence of ADD use. However, to justify the use of ADDs, there must be evidence that seals present a threat to the welfare issue of the salmon, both in terms of predation (causing mortality and injury), or in terms of stress causing an increase in disease and reduction in growth rates. There must also be evidence that ADDs are effective at protecting farmed fish from seals, to justify their use by the sector

Therefore the key questions are:

What are the welfare impacts of seals on farmed fish?

What are the welfare impacts of ADDs on cetaceans?

What are the welfare impacts of ADDs on seals?

Is the use of ADDs effective in deterring seals?

Are there effective and viable alternatives to ADDs?

Does the balance of harms and benefits support the use of ADDs in Scottish aquaculture?

To address these issues, a review of the published literature was carried out, which included scientific papers and governmental reports. This review showed that there were some studies available on the hearing ranges of seals and cetaceans and on their response to ADD-like sound transmission. However, only a small number of these studies are set in the Scottish context and in aquaculture^3,4,15. There are studies that simulate the transmission of sound in marine environments and use the resulting maps to predict possible effects on cetacean ranging behaviour¹⁶.

However, ADD use and design is continually changing, which may mean that the older literature does not represent the current situation. In particular, there is very little published research on whether the fish may suffer from stress due to the close proximity of seals to sea pens (by passing or 'patrolling' seals), which could lead to negative effects on fish welfare, leading to increased susceptibility to disease or impaired growth and development, and ultimately to economic losses.

SAWC used a number of approaches to update and augment this information. A survey of Scottish finfish industry groups and relevant NGOs was carried out in September/October 2021 to attempt to gather this information directly. The survey asked for evidence or informed opinion on the effects of direct seal attacks on sea pens, the effects of seal presence on fish behaviour and feeding, disease rates and the perceived efficacy of ADDs or alternatives in deterring seals. Three producer organisations, three NGOs, the APHA and a researcher responded to the survey and provided informative responses (see Appendix III for a list of respondents).

However, there were still unanswered questions about current ADD design and efficacy, and potential effects on wildlife, so a series of interviews with experts was held to address these topics and a visit was made to a salmon farm.

Scientific and other quantitative evidence can be used to establish where welfare impacts or 'harms' exist, and also the severity of these harms and the number of animals affected. However, this type of analysis cannot easily be used to compare the relative impact of the different harms on the different species involved in this issue or weigh up the more intangible impacts on an animal's freedom to perform natural behaviours. To do this, three types of ethical analysis were used.

Firstly, an ethical matrix comprising four principles (welfare, flourishing, freedom and fairness), was used to assess the impacts on the different species and a qualitative approach was taken to reconcile the relative welfare impacts on the species involved. Ethical matrices are increasingly used to deal with complex and sometimes conflicting situations in food production¹⁷, conservation and animal welfare¹⁸. They can be beneficial in facilitating decision-making, where there are different value dimensions and competing interests for different stakeholders (in this case the different animal populations involved). In the present situation the matrix acted as a means to identify the main benefits and harms for each of the species involved, and the possible trade-offs between the welfare of different species.

Whilst the ethical matrix is designed to identify potential harms and benefits, it does not consider the severity, duration or frequency of these harms, nor does it consider the number of individual animals affected. The European Food Safety Authority (EFSA) uses these principles to determine the magnitude of impacts on animal welfare across a range of situations¹⁹. This approach was also applied to the current issue on ADD use.

Finally, the seven principles for ethical wildlife management²⁰ were also considered. These principles were developed by an international team as a means of applying ethical and evidence-based approaches to human-wildlife conflicts. Consideration of the principles facilitates an assessment of all human interactions and interests in the issue. Ultimately, because humans have placed the fish farms into the environment of the seals and cetaceans, it is important to consider what implications this may have, and what remedial actions might be taken by farmers and society.