Consumption of migrating juvenile salmonids by gulls foraging below a Columbia River dam
juvenile, salmonids, Columbia River, salmon, steelhead, light conditions, turbines, light intensities, migration, mortality, dams, survival
Journal or Book Title
Transactions of the American Fisheries Society
Consumption of migrating juvenile Pacific salmon (Oncorhynchus spp.) and steelhead(Salmo gairdneri) by gulls was estimated below the turbine area of Wanapum Dam on theColumbia River in 1982. Foraging success of the gulls, chiefly ring-billed gulls (Larusdelawarensis), averaged 65% during bright light conditions and 51% during the evening. Thenumber of salmonids consumed by gulls ranged from 50 to 562 fish/h. Multiple-regressionanalysis indicates that the number of salmonids consumed by gulls is significantly affected by thepassage rate of fish through the turbines and spillgates, and by light intensity. The number ofsalmonids consumed by gulls foraging below the turbines during 25 d of peak salmonid migrationwas approximately 111,750 to 119,250 fish or 2% of the estimated spring migration. Althoughsome salmonids consumed by gulls had been killed when passing through the turbines, themortality of salmonids caused by gulls is potentially important. Inexpensive measures could beimplemented to discourage foraging by gulls below the turbine area of Columbia River dams,thereby enhancing survival of emigrating salmonids.