Salmon Farms Could Help Recover Wild Fish Stocks

A research paper published this week in the Public Library of Science journal PLoS ONE by SINTEF Fisheries and Aquaculture, NINA and the Institute of Marine Research advances our understanding of how coastal salmon farms interact with wild saithe and cod populations.

Salmon farms are widespread artificial structures in Norway’s coastal ecosystems and they are well known to be highly attractive to wild fish. To investigate how wild cod and saithe were affected by salmon farms, Tim Dempster from SINTEF Fisheries and Aquaculture and co-authors compared diets, condition and parasite loads simultaneously between wild fish caught close to nine different salmon farms and control fish caught away from farms in nine locations throughout coastal Norway.

Salmon farms had a clear effect on the quality and quantity of wild fish diets, with fish that resided around farms typically having twice as much food in their stomachs. This greater access to food translated to greater body condition and liver size than control fish caught distant from farms.

Parasite loads of farm-associated wild fish were different from control fish, with increased external parasites such as mobile and attached sea lice, but decreased internal parasites, such as kveis. However, these modified parasite loads had little effect upon the condition of wild fish around farms as the greater access to food meant any effect was overridden by the greater access to food around farms.

Taken together, the traditional measures of fish condition the authors measured provided no evidence that salmon farms are poor habitats for wild cod and saithe in the short-term. The diet and condition data indicate that wild saithe and cod benefited from their associations with salmon farms through access to greater amounts of food. The better condition of these fish could mean that spawning is improved.

The authors conclude that as saithe and cod condition is enhanced by farms, an opportunity exists to protect wild fish around salmon farms where they are aggregated and vulnerable to fishing.

In this way salmon farms could assist in the recovery of cod stocks in southern Norwegian waters. Spatial protection from fishing would allow an opportunity for the enhanced condition that cod generate due to their association with salmon farms to increase their spawning success. However, the authors caution that other negative effects are possible and should be investigated further.

‘We need to go deeper into the interactions of wild fish with salmon farms to test for effects that may only be detectable with longer term studies’ said researcher, Tim Dempster. While wild fish around salmon farms appear to be in good condition, their body chemistry is modified due to feeding on waste feed pellets under farms. What long-term effects this may have on physiological processes, egg production or egg and larval quality of wild cod and saithe remains unknown. Similarly, whether salmon farms disrupt natural spawning migrations or behaviour can only be addressed with longer-term research.

The full scientific article ‘Proxy Measures of Fitness Suggest Coastal Fish Farms Can Act as Population Sources and Not Ecological Traps for Wild Gadoid Fish’ can be downloaded free at the following web address: http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0015646.