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Dempster T, Uglem I, Sanchez-Jerez P, Fernandez-Jover D, Bayle-Sempere J, Nilsen R, Bjørn PA
Coastal salmon farms attract large and persistent aggregations of wild fish: an ecosystem effect
Fish farming is an expanding enterprise worldwide with farms now common artificial structures in many coastal environments. Using an underwater video technique, Dempster and colleagues estimated wild fish aggregations at 9 salmon farms spread throughout coastal Norway (59°N to 70°N) and compared these to natural control locations. Wild fish were heavily aggregated at farms, with an average of over 10 t of fish, predominantly saithe Pollachius virens and Atlantic cod Gadus morhua, per farm. Their estimates imply that Norway’s 1200 salmon farms aggregate over 12000 t of wild fish on any day in summer, which represents an ecosystem scale redistribution of wild fish in coastal waters. Wild fish aggregations at fish farms are important in the context of disease transfer to and from farms and the vulnerability of wild fish to capture.
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