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Seasonal variations in stable isotope ratios of juvenile coho salmon (Oncorhynchus kisutch) from western Washington rivers

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Salmon carcasses provide a marine derived nutrient (MDN) subsidy to river systems, but the extent to which it affects juvenile salmon growth is unclear. To evaluate temporal and spatial nutrient contributions from watershed sources and MDNs using stable isotopes, Skagit River (Washington, USA) juvenile coho salmon (Oncorhynchus kisutch) were collected. Muscle samples were taken from fry through smolts to measure temporal changes in 15N and 13C. 15N and 13C levels declined from emergence until fall, when they approached values for resident cutthroat trout (Oncorhynchus clarkii) collected above anadromous barriers. Muscle 13C was highly variable and did not increase subsequently. However, coho salmon 15N increased during the winter. March coho salmon parr 15N levels suggested high variability in carcass availability for consumption. During the next spring, 15N levels again declined. In Griffin Creek, a Snoqualmie River tributary, a significant relationship between carcass density and 15N and 13C levels was found in March coho salmon parr. At high spawner densities, some parr 15N exceeded carcass values; however, parr 13C increased moderately. These findings show that stable isotope data provide insights on seasonal sources of nutrients. In addition, results indicate that March coho salmon parr 15N levels would be a useful index of carcass availability for overwintering juvenile consumption.

Les carcasses de saumons représentent une allocation de nutriments d’origine marine (MDN) aux systèmes fluviaux; il n’est cependant pas clair dans quelle mesure cet apport affecte la croissance des jeunes saumons. Nous avons prélevé de jeunes saumons coho (Oncorhynchus kisutch) dans la Skagit (Washington, É.-U.) afin d’évaluer à l’aide d’isotopes stables les contributions temporelles et spatiales provenant des sources du bassin versant et des MDN. Des analyses d’échantillons de muscle des divers stades, des alevins aux saumoneaux, ont permis de mesurer les changements temporels de 15N et de 13C. Les valeurs de 15N et de 13C diminuent de l’émergence jusqu’en automne au moment où elles s’approchent des valeurs observées chez les truites fardées (Oncorhynchus clarkii) récoltées en amont des barrières pour la migration anadrome. Les valeurs de 13C du muscle sont très variables et n’augmentent pas par la suite. En revanche, les valeurs de 15N du saumon coho croissent pendant l’hiver. Les valeurs de 15N des tacons en mars indiquent une grande variabilité dans la disponibilité des carcasses à consommer. Au printemps suivant, les valeurs de 15N déclinent à nouveau. Dans Griffin Creek, un tributaire de la Snoqualmie, il existe une relation significative entre la densité des carcasses et les valeurs de 15N et de 13C mesurées chez les tacons de saumons coho en mars. Aux fortes densités de reproducteurs, les valeurs de 15N de certains tacons surpassent celles des carcasses. Par ailleurs, les valeurs de 13C des tacons augmentent modérément. Ces observations montrent que les mesures des isotopes stables fournissent des informations sur les sources de nutriments au cours des saisons. De plus, nos résultats indiquent que les valeurs de 15N chez les tacons des saumons coho en mars pourraient servir d’indice commode de la disponibilité des carcasses à consommer par les jeunes au cours de l’hiver.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: 2008-04-01

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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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