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Associations among Fish Length, Dam Passage History, and Survival to Adulthood in Two At‐Risk Species of Pacific Salmon: Response to Comment
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2021
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Source: Transactions of the American Fisheries Society, 150(2), 196-206
[PDF-365.80 KB]
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Journal Title:Transactions of the American Fisheries Society
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Description:The management of Snake River spring/summer Chinook Salmon Oncorhynchus tshawytscha and Snake River steelhead O. mykiss is a major concern for several federal, state, and tribal agencies. A primary issue is the effect of the Federal Columbia River Power System (FCRPS), composed of eight dams and reservoirs in the Snake and Columbia rivers, on adult return rate. Management decisions have been influenced by the hypothesis that the passage route that juveniles take through dams (i.e., through spillways, turbines, or juvenile bypass systems) strongly influences the adult return rate. The main hypothesized mechanism for differential survival rates is differences in latent mortality: that is, mortality suffered due to passage through the FCRPS that is expressed outside of the FCRPS. Because this latent mortality is not directly measurable, it must be indirectly inferred. Two patterns have been observed in or inferred from data analyses in the past and have become generally accepted during decades of debate: (1) smaller fish are more likely than larger fish to pass dams on the Snake and Columbia rivers via the juvenile bypass system passage route; and (2) among fish that complete migration through the entire hydropower system, those that passed more dams via juvenile bypass systems return as adults at lower rates. This has led to increased spill to prevent juveniles from passing through bypass systems and turbines, with a hypothesized decrease in latent mortality. The most important question to address is whether lower survival is caused by increased numbers of bypass system encounters or whether that pattern results because both increased encounters and decreased survival might be explained by another causative factor.
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Source:Transactions of the American Fisheries Society, 150(2), 196-206
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ISSN:0002-8487;1548-8659;
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Rights Information:CC0 Public Domain
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Rights Statement:This article is a U.S. Government work and is in the public domain in the USA
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