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Effects of disturbance on contribution of energy sources to growth of juvenile chinook salmon (Oncorhynchus tshawytscha) in boreal streams

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Abstract:

We used stable isotopes of carbon in a growth-dependent tissue-turnover model to quantify the relative contribution of autochthonous and terrestrial energy sources to juvenile chinook salmon (Oncorhynchus tshawytscha) in five small boreal streams tributary to the upper Yukon River. We used a tissue-turnover model because fish did not grow enough to come into isotopic equilibrium with their diet. In two streams, autochthonous energy sources contributed 23 and 41% to the growth of juvenile salmon. In the other three, fish growth was largely due to terrestrial (i.e., allochthonous) energy sources. This low contribution of autochthonous energy appeared to be related to stream-specific disturbances: a recent forest fire impacted two of the streams and the third was affected by a large midsummer spate during the study. These disturbances reduced the relative abundance of herbivorous macroinvertebrates, the contribution of autochthonous material to other invertebrates, and ultimately, the energy flow between stream algae and fish. Our findings suggest that disturbances to streams can be an important mechanism affecting transfer of primary energy sources to higher trophic levels.

L'utilisation d'isotopes stables de carbone dans un modèle de remplacement de tissus relié à la croissance a permis de quantifier les contributions relatives des sources d'énergie autochtones et terrestres chez les jeunes saumons quinnat (Oncorhynchus tshawytscha) dans cinq petits ruisseaux de la région boréale, tributaires du cours supérieur du fleuve Yukon. Nous avons utilisé un modèle de remplacement de tissus, car les poissons ne croissent pas assez pour atteindre un équilibre isotopique avec leur régime alimentaire. Dans deux des ruisseaux, les sources d'énergie autochtones contribuent à 23 et 41 % de la croissance des jeunes poissons. Dans les trois autres, la croissance des poissons est due en grande partie aux sources terrestres (i.e., allochtones) d'énergie. Cette faible contribution de l'énergie autochtone semble reliée à des perturbations spécifiques au ruisseau : deux des ruisseaux ont été récemment affectés par un incendie de forêt et le troisième a été perturbé par une inondation de mi-été durant notre étude. Ces perturbations ont réduit l'abondance relative des macroinvertébrés herbivores, la contribution de la matière autochtone aux autres invertébrés et, en fin de compte, le flux d'énergie entre les algues et les poissons dans les cours d'eau. Nos résultats laissent croire que les perturbations des cours d'eau peuvent être des mécanismes importants qui affectent les transferts des sources primaires d'énergie aux échelons trophiques supérieurs.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: April 1, 2003

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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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