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Habitat-, season-, and size-specific variation in diel activity patterns of juvenile chinook salmon (Oncorhynchus tshawytscha) and steelhead trout (Oncorhynchus mykiss)

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Juvenile salmonids that live in streams are sometimes nocturnal and may spend the day concealed in the stream substrate. We observed the diel activity patterns of juvenile chinook salmon (Oncorhynchus tshawytscha) and steelhead trout (Oncorhynchus mykiss) in two areas of the Bridge River, British Columbia, in all four seasons. In a reach with higher flows, most fish were nocturnal year-round, and they emerged from the substrate only at dusk to forage. In the reach with lower flows, some fish were active in the water column in the day in summer, but others remained concealed in the substrate until dusk. Parr and older fish were more nocturnal in summer than fry. All fish were nocturnal in winter. Because our study design controlled for temperature and photoperiod, we concluded that the differences in behaviour that we observed between reaches were due to habitat conditions that likely affected the trade-off between more risky daytime foraging and less efficient, but safer, nighttime foraging. Habitat-driven variation in activity patterns will likely affect the processes that regulate these populations and could make the prediction of the effects of ecosystem manipulations such as changes in flow very difficult.

Les saumons juvéniles qui vivent dans les cours d'eau sont quelquefois nocturnes et peuvent passer la journée cachés dans le substrat. Nous avons observé en toute saison les profils journaliers d'activité de juvéniles du Saumon quinnat (Oncorhynchus tshawytscha) et de la Truite arc-en-ciel anadrome (Oncorhynchus mykiss) dans deux sections de la rivière Bridge en Colombie-Britannique. Dans la section à débits plus élevés, la plupart des poissons sont nocturnes toute l'année et ils ne quittent le substrat qu'au crépuscule pour chercher leur nourriture. Dans la section à débits plus faibles, quelques poissons s'activent dans la colonne d'eau pendant la journée en été, mais d'autres restent cachés dans le substrat jusqu'au crépuscule. Les tacons et les poissons plus âgés sont plus nocturnes en été que ne le sont les alevins. Tous les poissons sont nocturnes en hiver. Parce que notre plan expérimental permet de tenir compte de la température et de la photopériode, nous concluons que les différences de comportement que nous avons observées dans les deux sections sont dues à des conditions d'habitat qui affectent le compromis entre la quête de nourriture de jour plus périlleuse et la quête de nuit plus sûre, mais moins efficace. Les variations dans les profils d'activité sous contrôle de l'habitat affectent vraisemblablement les processus qui assurent la régulation de ces populations; il peut alors devenir très difficile de prédire les effets de manipulations de l'écosystème, telles que des changements de débit.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: February 1, 2001

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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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