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The wave-drag hypothesis: an explanation for size-based lateral segregation during the upstream migration of salmonids

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Abstract:

During their spawning migration, large salmon, e.g., chinook (Oncorhynchus tshawytscha), swim upstream further from the bank than smaller ones, e.g., sockeye (Oncorhynchus nerka). This pattern is counterintuitive because natural selection should favor behavior that minimizes migration costs, yet by traveling further from the bank, large fish will have to swim against faster currents. Existing theory predicts that they will expend more energy than necessary as a result. One explanation for this apparently paradoxical behavior is that large fish swim further from the bank to avoid wave drag, the resistance associated with the generation of surface waves when swimming close to the surface. Wave drag was incorporated into existing theory, and the resulting model was tested to determine whether it explained size-based lateral segregation of chinook and sockeye salmon in the Nushagak River, Alaska. The wave-drag model accurately predicted the migration corridor for both species. Existing theory worked well for sockeye but not for chinook. The key to these predictions is that wave drag scales according the ratio of maximum body diameter to submergence depth, so bigger fish need to swim deeper to escape its effects.

Durant leur migration de fraye, les grands saumons, tels que le saumon quinnat (Oncorhynchus tshawy tscha), nagent vers l'amont plus loin des berges que les petits saumons, comme le saumon rouge (Oncorhynchus nerka). Ce phénomène semble être contre-intuitif car la sélection naturelle devrait favoriser les comportements qui minimisent les coûts de la migration, alors que les gros poissons doivent faire face à des courants plus rapides en nageant plus loin des berges. Les théories actuelles prédisent qu'en fin de compte, ils dépenseront plus d'énergie que nécessaire. Une explication pour ce comportement apparemment paradoxal est que les gros poissons nagent plus loin de la berge pour éviter la traînée due aux vagues, soit la résistance associée à la formation de vagues de surface lorsque les poissons se déplacent près de la surface. L'incorporation de la traînée due aux vagues à la théorie actuelle a permis de vérifier si le modèle qui en résulte peut expliquer la ségrégation latérale en fonction de la taille des saumons quinnat et des saumons rouges dans la rivière Nushagak en Alaska. Le modèle de traînée due à la vague prédit de façon précise la position du corridor de migration des deux espèces. La théorie actuelle est adéquate pour le saumon rouge, mais non pour le saumon quinnat. Le point important de ces prédictions est que la traînée due à la vague croît en fonction du rapport du diamètre maximal du corps sur la profondeur de submersion. Ainsi, les poissons plus grands doivent nager en eau plus profonde pour échapper à ces effets.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: 2004-01-01

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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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