Aquaculture: code of practice

Sets out standards expected from Aquaculture Production Businesses in Scotland (“APBs”) in order to provide for the containment of fish on fish farms and to prevent their escape in relation to marine mammal interactions.

Section 2: Containment measures

Section 2.1: Guidance on containment measures


21. Containment measure – for the purposes of this Code, a containment measure is any measure used to prevent or mitigate against interactions between farmed fish and marine mammals. Examples include anti-predator nets, and measures that actively deter seals such as ADDs. Section 2.1 provides information and guidance concerning the use of appropriate containment measures by APBs. All of these containment measures are non-lethal and include deterrent measures that are continually in place and do not seek to directly alter the behaviour of seals such as tensioned nets and deterrent measures that can be actively deployed in order to directly alter the behaviour of seals such as ADDs. Thereafter, the following Section 2.2 provides a list of mandatory standards concerning containment measures to which APBs must adhere under this Code.

The importance of containment measures at fish farms

22. Successful containment at fish farms is essential for minimising the risk of escape of farmed fish. Marine mammals (in particular, seals) may damage nets leading to the escape of farmed fish. In addition to the risk of escape, the failure of containment measures may lead to other detrimental consequences, including, but not limited to, physical damage to nets; entry of seals into fish pens;[5] seal depredation of farmed fish; and stress and welfare consequences for farmed fish.

23. Seals are opportunistic hunters and will exploit weaknesses in containment. The key to ensuring appropriate containment at fish farms for the purpose of addressing marine mammal interactions is maintaining proper net tensioning and repairing weak points as soon as they arise. As seals are capable of moving on land, care should be taken to ensure that walkways and pen sides do not provide a route for seals to enter nets.

24. It is important to minimise opportunities for seals to associate fish pens as a food source. Thompson et al (2021)[6] suggests that most seal attacks at fish farms occur at the base of nets, and evidence that most fish are bitten through the mesh of the net and that this occurs largely from underneath the net. They also note that dead fish lying at the bottom of the fish pen may attract seals that then learn to take fish through nets in this manner.

25. Seals may also gain access to pens by ripping holes in the net wall. New materials such as HDPE, particularly stainless-steel core HDPE type netting materials, may serve to mitigate against this, although long-term evidence regarding the efficacy of HDPE nets at reducing seal depredation is still to be obtained (Thompson et al, 2021).

Appropriate containment measures

26. Chapter 4 of the Code of Good Practice for Scottish Finfish Aquaculture[7] recommends adoption of the following containment measures:

  • The use of tensioned or false-bottomed nets;
  • The use of predator nets;
  • The use of seal blinds to cover the dead fish basket;
  • The daily removal of any dead fish (subject to weather and the ability of farmers to access their facilities).

27. As recommended in Marine Scotland’s Technical Standard for Scottish Finfish Aquaculture,[8] sufficient tensioning of nets may deter predators, as insufficient tension may lead to the distortion of nets, allowing seals to push further into a fish pen, and forming folds to trap fish.

28. The use of predator nets should be handled carefully to address certain risks. For example, the use of such nets has the potential to impede water flow to farmed fish, which may cause welfare issues. In addition, installation of predator nets should be done in a manner that ensures that they do not pose a risk of entanglement of marine mammals or birds.. For example, the risk of entanglement can be reduced by following the manufacturer’s guidelines (e.g., increasing the tension on the predator net, for example with an additional weighting system). Reducing the mesh size of the predator net may also decrease the entanglement risk, although this should be considered against the increased drag created and the reduced flow of water. Before installing predator nets, an important factor to consider is the vicinity of the fish farm to any protected areas (e.g., Special Areas of Conservation for marine mammals and Special Protection Areas for birds), including by consulting with NatureScot, if appropriate.

The use of acoustic deterrent devices (ADDs)

Acoustic deterrent device (ADD) – ADDs operate by introducing loud, low to mid frequency sound (usually 1 to 20 kHz) into the marine environment to deter seals from fish farms. The Code considers all types of device that emit sounds for the purpose of keeping an animal away from an area, including startle devices, to be a form of ADD.

29. As addressed in Section 1 of this Code, as they undertake their business, APBs must comply with the existing legal and regulatory framework applicable to them, including in relation to marine mammal protection. For example, any proposal to use predator control measures, including ADDs, must be compatible with the Habitats Regulations, which afford protection to cetaceans by prohibiting their deliberate or reckless capture, injury, disturbance and killing. Such proposals must also be consistent with the protections for seals within Part 6 of the Marine (Scotland) Act 2010 from intentional or reckless injury, taking and killing.

30. In order to be compliant with the species-based protection measures applicable to cetaceans under the Habitats Regulations, the use of any ADD must be in accordance with Marine Scotland’s Information Note and Frequently Asked Questions for the Operators of Finfish Farms on the use of Acoustic Deterrent Devices and the Requirement for a European Protected Species Licence.[9] It is important to note that even in scenarios where it is concluded that an EPS Licence would not be required for the use of an ADD (for example, in circumstances where there are no cetaceans present at the location) harm to all marine mammals, including seals, must be avoided. If you are planning to use an ADD at your fish farm, you must consult Marine Scotland using the following contact details Marine Scotland - Licensing Operations Team (“MS-LOT”), to ensure that such planned use will avoid harm to marine mammals.

The use of novel forms of containment measures

31. As the aquaculture industry continues to evolve, novel forms of non-lethal containment measures may emerge. Examples may include deterrent measure that affect other senses of seals rather than hearing, such as taste, touch or vision. Before any such novel measures are deployed, it will be necessary for APBs to consult with Marine Scotland to ensure the suitability of the intended measure. The mandatory standards contained within this Code apply to novel forms of containment measures, including novel methods that are being trialled .

32. As in relation to all of their conduct, APBs must continue to comply with the existing legal and regulatory framework, including in relation to marine mammal protection and farmed fish welfare, and this must be taken into account in considering the suitability of any novel containment measures.

Section 2.2: Mandatory standards for APBs in relation to containment measuresin relation to marine mammal interactions

1. If no containment measures in relation to marine mammal interactions are required in relation to marine mammal interactions this must be reported to Marine Scotland (see Section 3 for further details).

2. Where containment measures in relation to marine mammal interactions are necessary, you must deploy at least one of the following non-lethal measures to contain fish at your fish farm:

  • The use of tensioned or false-bottomed nets, or alternatively the use of predator nets;
  • The use of seal blinds to cover any dead fish baskets;
  • Daily removal of any dead fish (subject to weather and the ability of farmers to access their facilities).

3. When using your equipment, you must do so only in accordance with the manufacturer’s guidelines, where available, and any relevant consents.

4. When using your equipment, you must do so in such a manner as to reduce the likelihood of access to fish pens by marine mammals.

5. You must not take any deterrent action which is specifically targeted at a marine mammal calf or pup.

6. You must not feed or attempt to feed a marine mammal for any purpose, including for the purposes of deterrence (i.e., taste aversion).

7. You must not attempt to actively deter a marine mammal which is demonstrating signs of aggression (including charging, lunging, or vocalising), except when necessary to deter a marine mammal from endangering personal safety.

8. If you plan to deploy an ADD you must consult Marine Scotland and obtain any relevant consents or you must demonstrate to Marine Scotland that the planned use will not harm marine mammals.

9. Prior to using any novel measure of non-lethal deterrence, you must consult with Marine Scotland to ensure the measure will not harm marine mammals.



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