Predation on salmon smolts, Salmo salar L., in the estuary of the River Surna, Norway



The post-smolt stage of salmon, Salmo salar L., is subject to heavy mortality in Norway. Each year 35 000 hatchery-reared smolts are stocked in the River Surna. Smolt stocking at sea and in the fjord resulted in recovery rates of adult salmon which were up to three times better than those resulting from river stockings. This was supposed to be due to by-passing some predators. In 1984 and 1985 predators and their predation on smolts were studied in the R. Surna estuary. Cod, Gadus morhua, were found to prey heavily on smolts, and a total mortality up to 24.8% was found in a small restricted area. Cod are thought to assemble in the Surna estuary in the spring, foraging on the smolt run.