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Consumption of Migrating Juvenile Salmonids by Gulls Foraging below a Columbia River Dam
Author(s) -
Ruggerone Gregory T.
Publication year - 1986
Publication title -
transactions of the american fisheries society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.696
H-Index - 86
eISSN - 1548-8659
pISSN - 0002-8487
DOI - 10.1577/1548-8659(1986)115<736:comjsb>2.0.co;2
Subject(s) - foraging , fishery , salmo , juvenile , chinook wind , biology , oncorhynchus , fish <actinopterygii> , juvenile fish , ecology
Consumption of migrating juvenile Pacific salmon Oncorhynchus spp. and steelhead Salmo gairdneri by gulls was estimated below the turbine area of Wanapum Dam on the Columbia River in 1982. Foraging success of the gulls, chiefly ring‐billed gulls Larus delawarensis, averaged 65% during bright light conditions and 51% during the evening. The number of salmonids consumed by gulls ranged from 50 to 562 fish/h. Multiple‐regression analysis indicates that the number of salmonids consumed by gulls is significantly affected by the passage rate of fish through the turbines and spillgates, and by light intensity. The number of salmonids consumed by gulls foraging below the turbines during 25 d of peak salmonid migration was approximately 111,750 to 119,250 fish or 2% of the estimated spring migration. Although some salmonids consumed by gulls had been killed when passing through the turbines, the mortality of salmonids caused by gulls is potentially important. Inexpensive measures could be implemented to discourage foraging by gulls below the turbine area of Columbia River dams, thereby enhancing survival of emigrating salmonids.