Substrate composition and emergence success of fall chinook salmon in the Snake River
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The percentage of fine sediment particles in stream channel substrate is inversely related to emergence success of chinook salmon (Oncorhynchus tshawytscha) embryos. We used a previously published method to relate substrate composition at seven fall chinook salmon spawning sites in the Snake River implicitly to emergence success. We used dome suction to sample substrate at four spawning sites in the upper reach of Snake River and three in the lower reach. Mean percent fines <6.4 mm and <0.85 mm were less in upper reach samples than in lower reach samples. In laboratory tests, mean emergence success decreased from 47 to 10% as the mixtures of percent fines <6.4 mm and <0.85 mm increased in substrate mixtures. A regression equation developed from the laboratory data to predict mean emergence success from mean percent fines <6.4 mm and <0.85 mm had an r2 value of 0.94. Predicted emergence success based on substrate composition in the Snake River ranged from 46 to 48% for sites in the upper reach, and from 29 to 47% for sites in the lower reach. These predictions of emergence success are slightly higher than those reported in the literature for chinook salmon spawning habitat. Based on the combination of field and laboratory findings, we conclude that substrate composition at the seven spawning sites we studied in the Snake River should not limit fall chinook salmon production.