Norwegian salmon on the run threaten Swedish wild salmon

In Norway, the problem of escaped farmed salmon migrating up into salmon rivers and mixing with wild salmon has been noticed for more than 30 years. In recent times, there have also been suspicions that farmed salmon migrate up into western Swedish watercourses – but only now has this been confirmed. – We know that escaped farmed salmon can often swim far. Therefore, it is not surprising that Swedish salmon rivers are also affected, says Sten Karlsson, senior researcher at NINA. – Despite this, our results are important as we show for the first time that the problem is cross-border. A larger survey would now be needed that covers the entire distribution area of ​​salmon in Europe, Sten Karlsson continues. Norwegians accustomed to tracking escaped salmon

The work is based on analyzes with special DNA markers and statistical methods developed at NINA to identify farmed salmon and its offspring. In Norway, these methods are used every year to identify escaped farmed salmon and monitor how their genes are spread in a large number of Norwegian wild salmon stocks.

Sweden does not have its own sea-based cultivation of salmon for food production. Along the Swedish west coast there are just over 20 watercourses with wild salmon. Many of the west coast toes are small, which makes them particularly sensitive to the influence of farmed salmon as each farmed salmon that reproduces there constitutes a larger proportion of the spawning stock than in a larger population. Genes from cultivated Norwegian salmon in Swedish wild salmon The study includes samples from adult and young salmon from five watercourses: Örekilsälven, Göta älv, Ätran, Lagan and Rönne å. The adult salmon from Lagan and Göta älv were selected for that many of these fish in previous studies have been shown to be genetically different. In these specially selected samples, the proportion of genes from farmed salmon (escapes and hybrids between farmed and wild) was estimated at as much as 59 per cent (Lagan, 2008) and 75 per cent (Göta älvs hovedfåra, 2010). De analyzed the samples from other watercourses along the west coast and tributaries to the Göta River were randomly selected and without special suspicions about the presence of farmed salmon. Even in these cases, genes from farmed salmon of varying extent (2-14 percent) were detected. Calls for a Swedish monitoring program

– Our results are based on a relative limited material collected about 10 years ago. From studies in Norway, we know that the prevalence of farmed salmon often varies significantly between watercourses and years. Therefore, a more permanent monitoring program, like the Norwegian one, would also be needed in Sweden, says Stefan Palm. Salmon of genetic origin from Norway is also farmed in Scotland, where it also contains salmon. Therefore, it is not possible to determine with certainty where the farmed salmon along the Swedish west coast has escaped. But since Norway is closest geographically and the Norwegian production of farmed salmon is world-leading, a majority of the fish probably comes from Norwegian facilities.
Different types of salmon farming

Growing of Atlantic salmon (Salmo salar) for the food market takes place mainly in Norway, but also in Scotland, Chile and Canada with several countries. A majority of this farmed salmon (“farmed” in English) has its genetic origin from Norway, where, based on an original mix of several wild populations, extensive and successful breeding work has been carried out for a long time to change the characteristics of the fish. (adsbygoogle=window.adsbygoogle || ).push();