New research from the Marine Directorate of the Scottish Government has found farmed salmon DNA across roughly one fifth of Scotland’s salmon river network, adding to concerns about the long-term impacts escaped farmed salmon can have on wild populations.

The study, Scotland’s most comprehensive assessment of wild salmon genetics to date, tested 6,639 juvenile wild salmon across 834 river sites. In regions with marine salmon farms, 3.14% of the wild salmon genome was found to be derived from farmed fish, compared with 0.55% in areas without farms — nearly six times as much.

Farmed DNA was detected across 39% of the surveyed river network in salmon farming areas, compared with 15% in regions without farms. In Lochaber, at the centre of Scotland’s salmon farming activity, farmed DNA was found across 72% of the river network.

Researchers say the findings may underestimate the true extent of the issue because Scotland has no pre-aquaculture genetic baseline and the genetic test cannot detect escaped farmed salmon of Scottish genetic origin. The study also notes that when escaped farmed Atlantic salmon breed with wild Atlantic salmon, that genetic material is passed into the wild population and cannot be removed.

The situation in British Columbia is slightly different: farmed Atlantic salmon cannot interbreed with wild Pacific salmon. However, concerns around escaped farmed salmon remain, including their potential to act as vectors for disease and compete with native salmon for habitat and food.

As Canada moves toward its commitment to ban open-net pen salmon aquaculture in B.C. coastal waters by June 30, 2029, the Scottish findings offer another example of the consequences that can follow when farmed salmon escape into surrounding ecosystems, and reinforce the importance of keeping farmed salmon separated from wild populations.

Read more online at:
https://oceanographicmagazine.com/news/farmed-salmon-dna-is-now-present-in-a-fifth-of-scotland-s-rivers/