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Late-season mortality during migration of radio-tagged adult sockeye salmon (Oncorhynchus nerka) in the Columbia River

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We radio-tagged 577 adult sockeye salmon (Oncorhynchus nerka) returning to the Columbia River in 1997 to determine how migration behaviors were related to migration success in an altered river system. The probability of successful migration declined dramatically for late-entry individuals, concomitant with declines in discharge and the onset of stressful temperatures. Long dam passage times were not related to unsuccessful migration at most dams. However, when migration histories were analyzed across multiple dams or reservoirs, relatively slow migration was significantly associated with unsuccessful migration, suggesting potential cumulative effects. Median passage times at dams were rapid (7.9–33.4 h), although 0.2%–8% of salmon took more than 5 days to pass. Reservoir passage was also rapid, averaging 36.8–61.3 km·day–1, and appeared to compensate for slowed migration at dams. Rates observed in the unimpounded Hanford Reach suggest that total predam migration rates may have been similar to current rates. Overall, our results suggest that cumulative effects may be more important than negative effects of passage at single dams and that hydrosystem alteration of temperature regimes in the migration corridor may have an important indirect negative impact on adults.

Nous avons muni d'émetteurs radio 577 saumons rouges (Oncorhynchus nerka) qui retournaient dans le Columbia, afin de déterminer de quelle manière les comportements migrateurs sont reliés au succès de la migration dans un système hydrographique modifié. La probabilité d'une migration réussie diminue de façon spectaculaire chez les individus qui arrivent tard, au moment où le débit diminue et où les températures accablantes s'installent. Dans la plupart des barrages, la durée prolongée de traversée n'est pas reliée à l'insuccès de la migration. Cependant, lorsque le parcours de la migration au travers plusieurs barrages et réservoirs est analysé, il y a une relation significative entre une migration relativement lente et l'insuccès de la migration, ce qui indique la possibilité d'effets cumulatifs. La durée médiane du passage des barrages est courte (7,9–33,4 h), bien que 0,2–8 % des poissons mettent plus de 5 jours à les traverser. La traversée des réservoirs est aussi rapide, à une vitesse moyenne de 36,8–61,3 km·jour–1, et semble compenser le ralentissement de la migration aux barrages. Les taux observés dans la section Hanford qui ne contient pas de réservoir indiquent que les taux de migration avant l'érection des barrages ont dû être semblables aux taux actuels. En gros, nos résultats indiquent que les effets cumulatifs peuvent être plus importants que les effets négatifs causés par le passage des barrages individuels et que la modification des régimes thermiques du système hydrographique dans le corridor de migration peut avoir un important impact négatif indirect sur les adultes.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: 2005-01-01

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  • Published continuously since 1901 (under various titles), this monthly journal is the primary publishing vehicle for the multidisciplinary field of aquatic sciences. It publishes perspectives (syntheses, critiques, and re-evaluations), discussions (comments and replies), articles, and rapid communications, relating to current research on cells, organisms, populations, ecosystems, or processes that affect aquatic systems. The journal seeks to amplify, modify, question, or redirect accumulated knowledge in the field of fisheries and aquatic science. Occasional supplements are dedicated to single topics or to proceedings of international symposia.
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