Feeding behaviour and diet of goosanders (Mergus merganser) in relation to salmonid seaward migration (original) (raw)

1993, Aquatic Living Resources

ala as J. A., T. G. Heggberget, P. A. Bj$rn, O. Rcitan, Aquat. Living Resour., 1993, 6, 31-38. Foraging activities of goosanders (Anatidae, Mergus merganser) were studied in relation to seaward migration of smolt in the River Halselva in northern Norway, 1987Norway, -1989. Birds aggrcgatcd in the estuary in June, during mass migration of smolts. Whcn present in the estuary males and females spent 28.7 and 35.6% of their time feeding. Only 15% of dives resulted in birds' bringing prey to the surface and about 25% of prey found in goosander stomachs wcrc salmonids. For hatchery-reared smolts released in the estuary, average length taken did not differ from that available; for wild smolts of Arctic char, however, smaller fishes than those available were takcn. For 1989, we estimate that goosanders took 1 % of the hatchcry-reared smolts released in the estuary, and 2% of the wild smolts whcn smolts passed the estuary during seaward migration. As it is likely that less fit smolts (e. g. sick, injured, small) are most pronc to predation, we argue that such a level of predation on migrating smolts from goosanders has only a minor impact on salmonid production. Suggestions to reduce predation are discussed.