Northwest Fisheries Science Center

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Document Type: Journal Article
Center: NWFSC
Document ID: 7521
Title: Indirect effects of impoundment on migrating fish: temperature gradients in fish ladders slow dam passage by adult Chinook salmon and steelhead
Author: Christopher C. Caudill, Matthew L. Keefer, T. S. Clabough, G. P. Naughton, Brian J. Burke, C. Peery
Publication Year: 2013
Journal: PLoS ONE
Volume: 8
Issue: 12
Pages: e85586

 Thermal layering in reservoirs upstream from hydroelectric dams can create temperature gradients in fishways used by upstream migrating adults. In the Snake River, Washington, federally-protected adult salmonids (Oncorhynchus spp.) often encounter relatively cool water in dam tailraces and lower ladder sections and warmer water in the upstream portions of ladders. Using radiotelemetry, we examined relationships between fish passage behavior and the temperature difference between the top and bottom of ladders (T) at four dams over four years. Some spring Chinook salmon (O. tshawytscha) experienced T ≥ 0.5 °C. Many summer and fall Chinook salmon and summer steelhead (O. mykiss) experienced T ≥ 1.0 °C, and some individuals encountered ΔT > 4.0°C. As ΔT increased, migrants were consistently more likely to move down fish ladders and exit into dam tailraces, resulting in upstream passage delays that ranged from hours to days. Fish body temperatures equilibrated to ladder temperatures and often exceeded 20°C, indicating potential negative physiological and fitness effects. Collectively, the results suggest that gradients in fishway water temperatures present a migration obstacle to many anadromous migrants. Unfavorable temperature gradients may be common at reservoir-fed fish passage facilities, especially those with seasonal thermal layering or stratification. Understanding and managing thermal heterogeneity at such sites may be important for ensuring efficient upstream passage and minimizing stress for migratory, temperature-sensitive species.

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