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Presented at the NABS Annual meeting, Vancouver, British Columbia, 2004
in Fish Ecology 2
Impacts of non-native brook trout on endangered juvenile chinook salmon in Idaho streams
K.H. Macneale, B.L. Sanderson, and P.M. Kiffney. NOAA Fisheries, Northwest Fisheries Science Center, 2725 Montlake Blvd. East, Seattle, WA 98112 USA
In streams throughout the Salmon River basin in Idaho, the presence of non-native brook trout (Salvelinus fontinalis) is correlated with reduced survival of juvenile chinook salmon (Oncorhynchus tshawytscha). To identify potential mechanisms, we made in-stream observations of individual chinook and brook trout, quantifying their distribution, habitat use and overlap, and interactions with neighboring fish. In Summit Creek, where native trout are rare and the abundances of brook trout and chinook are approximately equal, we completed 278, 5-min observations while snorkeling and used multiple regression analyses to identify variables explaining encounter rates, outcomes of encounters, and feeding rates. Encounters among fish were frequent, with chinook displaced most often by larger brook trout. The size of neighboring fish was significant along with other environmental variables in explaining the rate and outcome of encounters. Brook trout were on average >1.5x larger than chinook in late summer, indicting their potential impact on chinook feeding behavior is large. Fish stomach contents were also examined to identify diet overlap and direct predation of brook trout on chinook. Efforts to recover threatened chinook will likely be most effective when impacts of non-native species are understood and considered.
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