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Predation by northern squawfish on live and dead juvenile Chinook salmon

January 1, 1992

Northern squafish Ptychocheilus oregonensis is a major predator of juvenile salmonids Oncorhynchus spp. migrating downstream through the Columbia River. High predation rates occur just below dams. If northern squafish selectively consume salmonids killed or injured during dam passage, previous estimates of predation mortality may be too high. We conducted laboratory experiments that indicate northern squafish prefer dead juvenile chinook salmon O. tshawytscha over live individuals. When equal numbers of dead and live chinook salmon were offered to northern squafish maintained on a natural photoperiod (15 h light: 9 h darkness), significantly more (P < 0.05) dead than live fish were consumed, both in 1,400-L circular tanks and in an 11,300-L raceway (62% and 79% of prey consumed were dead, respectively). When dead and live juvenile chinook salmon were provided in proportions more similar to those below dams (20% dead, 80% live), northern squafish still selected for dead prey (36% of fish consumed were dead). In additional experiments, northern squafish were offered a proportion of 20% dead juvenile chinook salmon during 4-h periods of either light or darkness. The predators were much more selective for dead chinook salmon during bright light (88% of fish consumed were dead) than during darkness (31% were dead).

Publication Year 1992
Title Predation by northern squawfish on live and dead juvenile Chinook salmon
DOI 10.1577/1548-8659(1992)121<0680:PBNSOL>2.3.CO;2
Authors Dena M. Gadomski, Judy A. Hall-Griswold
Publication Type Article
Publication Subtype Journal Article
Series Title Transactions of the American Fisheries Society
Index ID 70180663
Record Source USGS Publications Warehouse
USGS Organization Western Fisheries Research Center