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NASCO Commissioned Review Examines Aquaculture Impacts on Wild Atlantic Salmon

Two NASCO-Commissioned papers on the effect of salmon aquaculture on wild Atlantic salmon populations have been produced by independent expert groups. The key points from each of these papers is summarised in the boxes below.

Does exposure to sea lice from aquaculture have a population- reducing effect on wild Atlantic salmon? A systematic review

Larsen, M.L, Rytwinski, T., Lennox, R.J., Gargan, P., Cooke, S.J., Harper, M., Dalvin, S., Shepard, S., Nilsen, F., Brady, D.C. and Vollset, K.W

Key Findings

  • evidence indicates that salmon lice from aquaculture negatively affects wild Atlantic salmon populations. Systematic review data show a reduction in survival and adult returns in salmon exposed to salmon lice;
  • increased mortality linked to salmon lice infestations is documented in countries with significant salmon aquaculture, including Norway, Ireland, and Scotland, suggesting a widespread impact across the North Atlantic; and
  • studies show a degree of bias due to limitations in study design, including inadequate documentation of salmon lice levels during out migration and the effectiveness of anti parasitic treatments. These biases suggest that the true impact of salmon lice on wild salmon populations may be greater than current estimates.

Recommendations

  1. Implement the NASCO ‘Guidance on Best Management Practices to address impacts of sea lice and escaped farmed salmon on wild salmon stocks’, across their entire North Atlantic range; specifically that ‘100% of farms to have effective sea lice management such that there is no increase in sea lice loads or lice-induced mortality of wild salmonids attributable to the farms’
  2. Expand monitoring of salmon lice to monitor and report sea lice levels in aquaculture areas regularly to ensure they remain within sustainable limits, particularly during key migration periods for wild salmon. And
  3. Increase transparency and data sharing by Governments and aquaculture operations to support transparent reporting and data sharing on lice levels and aquaculture practices, facilitating more effective research and conservation strategies.

Conclusion

Taken together, implementation of these recommendations, based on the findings of the current study, offers the opportunity to increase safeguards in protecting wild Atlantic salmon from the negative impacts of sea lice from marine salmon farms. Implementation of the NASCO Guidelines and commitment to rigorous monitoring and research will support the resilience of wild salmon populations and contribute to the sustainable management of salmonid aquaculture.

Genetic introgression of farmed Atlantic salmon in wild salmon populations throughout its native range

Bolstad, G., Bradbury, I., Gilbey, J., Gudmundsson, L. A., Karlsson, S., Kess, T., McGinnity, P., Thorstad, E. and Wringe, B.

Key Findings

  • comparison of existing data on the genetic integrity of wild Atlantic salmon to data on farmed salmon production shows the major producers of farmed salmon (Norway, Scotland, Canada, Iceland) in the North Atlantic have all undergone farmed-to-wild gene flow; and
  • using molecular genetic markers to investigate genetic introgression of escaped farmed salmon in 481 salmon rivers, genetic introgression was detected in 57 % (275) of the investigated rivers, throughout the North Atlantic.

Recommendations

  1. Implement the NASCO ‘Guidance on Best Management Practices to address impacts of sea lice and escaped farmed salmon on wild salmon stocks’, specifically that the International Goal of ‘100% farmed fish to be retained in all production facilities’ is achieved.
  2. Encourage and facilitate further monitoring of, and research on, genetic introgression.
  3. Follow up investigations to monitor future trends.
  4. Expand investigations to include more salmon populations in regions poorly covered so far.
  5. Encourage and facilitate further monitoring and research of genetic introgression on the resilience of wild salmon and its ability to cope with other anthropogenic stressors, and in particular climate change. And
  6. Encourage and facilitate collaboration between researchers and stakeholders throughout the North Atlantic.

Conclusion

Introgression of wild Atlantic salmon is widespread across the North Atlantic and is the most serious threat for the viability and ability to adapt to current and future environmental changes. The species-level alteration of wild Atlantic salmon and loss of intra-specific diversity from salmon aquaculture shown in the current study threatens the resilience of wild Atlantic salmon, a species that has declined to less than one third of its original abundance over the last 50 years.

While these papers have not yet been published, a ‘Policy Brief on the Effect of Salmon Aquaculture on Wild Atlantic Salmon Populations’ on the management implications of the key findings is available.