What we know and don’t know about escaped farmed salmon

It can be hard to distinguish between myths and facts in the debate concerning escaped farmed salmon and their genetic influence on wild salmon. Not everyone knows that wild and farmed Atlantic salmon in Norway have exactly the same genes. Scientists from Nofima have performed a critical review of current knowledge.

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Portrettbilde av Celeste Jacq
Celeste Jacq

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What is farmed salmon?

  • From 1971 to 1974, wild salmon were collected from 40 Norwegian rivers, and these form the basis for much of today’s farmed salmon. Consequently, the farmed salmon contains no genes that the wild salmon does not have.
  • After 9-10 generations of artificial selection, gene variants exist that favour traits such as growth, later sexual maturity and specific disease resistance to a significantly higher degree in farmed salmon than wild salmon.
  • Farmed salmon and wild salmon are therefore different based on how well adapted they are to the environment in which they reside, but all the farmed salmon’s genes originate from the wild salmon.

We know that escaped farmed salmon can crossbreed with wild salmon. We also know that a smaller proportion of the offspring from escaped farmed salmon survive through a generation than the offspring from wild salmon. The closer related a salmon is to farmed salmon, the lower the probability it will survive in the wild.

“This is natural selection; the individuals which are least adapted die before they have reproduced and started a new generation,” says Celeste Jacq, the report’s corresponding author.

This is what we don’t know

It is natural that the genetic profiles of salmon populations change over time, and we know that this is the case. However, we do not know if this is the result of natural selection or influence from escaped farmed salmon, hydropower developments, acid rain or other factors. Small salmon populations will also be exposed to incidental genetic changes as a result of interbreeding.

Overall, we know little about the consequences over time of interbreeding between wild and farmed salmon populations.

  • What is the actual long-term genetic contribution from farmed salmon to wild salmon?
  • In studies where changes in genetic variation have been observed in wild populations over time, change has been found in some rivers, but far more rivers do not experience any change. What causes these differences?
  • We do not know if genetic change is the same as damage. Several have equated change in gene variation in wild salmon populations with damage, but there is no scientific evidence to claim that the wild salmon has a reduced ability to survive as a consequence of these changes.

Suspected offenders

Jacq is interested in management authorities taking into account the fact that escaped farmed salmon may be an important cause of genetic changes, and that this may have negative consequences. However, she is worried that myths will gain a foothold as truths.

“Field data collected in different studies has so far been good, but it has not always provided grounds for the conclusions that have been drawn,” says Jacq. “You can compare the farmed salmon with a person who is a suspect in a criminal case and has been prejudged because they were in the wrong place at the wrong time. The person may well be guilty, but it is also possible that the actual offender goes free. The role of research here is to obtain evidence and act in accordance with that.”

Jacq believes that with today’s technology we can find out a huge amount, and that research must go a step further so that we can have knowledge-based resource management of the wild salmon.

Nofima, in collaboration with other management institutes, is now applying for funding for a research project to quantify the genetic effects of escaped farmed salmon on wild salmon.

“We need to see the full picture, and a joint effort like this can help us to discuss this further on common grounds,” concludes Jacq.

Nofima was commissioned to write the report by the Fishery and Aquaculture Industry Research Fund (FHF). The Norwegian Institute of Nature Research (NINA) received the same commission.

Breeding and genetics  

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