Atlantic Salmon

Salmo salar

Escapes and Introductions

Escapees from aquaculture facilities can potentially impact on habitats and species in the receiving water bodies. Problems could occur due to competition, potential disease transfer, establishment of non-native species, interbreeding with wild populations, and impacts on sensitive habitats.

The contribution of non-native species to the growth of the global aquaculture industry and the economic benefits that it has brought to many countries cannot be underestimated. However, minimising the escapes of non-native aquaculture species must be a high priority for resource managers, conservationists and the aquaculture industry1. Atlantic salmon is farmed on large-scales as a non–native species (in Chile, west coast North America, Tasmania ,but the species has been shown to be a poor colonizer2, 3, and research to date has not shown farming salmon has led to the establishment of viable populations in the wild of non-native species4.

There are also concerns that farmed salmon, which come from selected breeding programmes, will interbreed with wild salmon populations if they escape; damaging the native population genetic integrity and weakening wild stocks (genetic introgression). However, this requires that farmed salmon escapees survive until maturation, successfully reproduce and produce viable offspring, and these traits are often compromised in domesticated animals reared in captivity1,2. Genetic introgression has been demonstrated in wild salmon2,5 but proven deleterious effects have yet to be detected and there is little scientific evidence to support claims that salmon farming has caused the widespread declines in wild salmon fisheries6.

With any open water containment system there is the potential for stock to escape and prevention is the key to mitigating Atlantic salmon escapes. Escapes from farms can occur both through repeated low-number incidents and through large-scale events. Technical and operational failures can lead to escapes: cages can be breached in storms; holes can appear through wear and tear; predator interaction and operational accidents can occur, and so on. Improvements to salmon net-pen design/standards and farm management have led to reductions in escapes7, 8, 9.

Losses due to escapes represent a considerable financial loss to a farm, so it is in its interest to prevent them. Mitigation should ideally include the following five elements10:

  • Mandatory reporting of all escape incidents
  • Establishment of mechanisms to analyse and learn from escape reporting
  • Conduct mandatory, rapid, technical assessments to determine the causes of escape incidents involving large numbers of fish
  • Introduction of technical standards for sea-cage aquaculture equipment coupled with an independent mechanism to enforce the standard
  • Mandatory training of fish farm staff in escape-critical operations and techniques

Recapturing fish after escape (at or close to the point of escape) is a logical management option, however evidence suggests that fish tend to disperse rapidly from the point of release and recapture efforts are often delayed after large-scale escape events, which typically occur during storms. These two factors mean that few attempts to recapture salmon after large-scale escape incidents have been successful11. Improved netting materials, enhanced engineering standards and equipment build quality, better staff training around vessel handling and use, and efforts to deter predators, have done much to reduce escape incidents from net-pens12,13, whilst the biosecurity of land-based RAS facilities means that escape risks are minimal within these systems.

References

  1. Cook, E.J et al, 2007. Non-Native Aquaculture Species Releases: Implications for Aquatic. (Chapter 5 in Aquaculture in the Ecosystem, p155-184)
  2. Heino, M. et al, 2015. Genetic introgression of farmed salmon in native populations: quantifying the relative influence of population size and frequency of escapees. Aquaculture Environment Interactions, Vol 6, 2015 p185–190
  3. Seafood Watch
  4. ASC Salmon Standard
  5. Karlsson, S. et al, 2016. Widespread genetic introgression of escaped farmed Atlantic salmon in wild salmon populations. ICES Journal of Marine Science 73(10), 2016
  6. Little, D. and Shepherd, C.J., 2014. Aquaculture: are the criticisms justified? II - Aquaculture’s environmental impact and use of resources, with special reference to farming Atlantic salmon
  7. Seafood Watch
  8. Seafood Watch
  9. Seafood Watch
  10. Jensen, O et al, 2010. Escapes of fishes from Norwegian sea-cage aquaculture: causes, consequences and prevention. Aquaculture Environment Interactions, Vol 1, 2010 p71–83
  11. Dempster, T. et al, 2016. Recapturing escaped fish from marine aquaculture is largely unsuccessful: Alternatives to reduce the number of escapees in the wild. Reviews in Aquaculture, April 2016
  12. Marine Scotland
  13. Bridger, C.J.et al, 2015. Physical containment approaches to mitigate potential escape of European-origin Atlantic salmon in south coast Newfoundland aquaculture operations. DFO Canadian Science Advisory Secretariat Research Document, 2015