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Response by trout populations in alpine lakes to an experimental halt to stocking

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Abstract:

Trout are often stocked into alpine lakes based on the generally untested assumption that resident populations would go extinct without stocking. The objectives of our study were to estimate the proportion of currently or formerly stocked alpine lakes in the Sierra Nevada, California, containing naturally reproducing trout populations (Oncorhynchus mykiss, Oncorhynchus mykiss aguabonita, Oncorhynchus clarki henshawi), identify characteristics of lakes associated with successful reproduction, and quantify the effects of stocking termination on trout density and individual growth rates in reproducing populations. We surveyed trout populations in 95 lakes in the John Muir Wilderness before and after a 4- to 8-year stocking halt and in 84 lakes in Sequoia–Kings Canyon National Park after a ≥20-year stocking hiatus. Based on recruitment during the no-stocking period, 70% and 68% of study lakes in the John Muir Wilderness and Sequoia-Kings Canyon National Park, respectively, contained reproducing populations. Results indicated that lakes with >2.1 m2 of spawning habitat and at elevations <3520 m nearly always showed evidence of reproduction. For reproducing populations, stocking termination did not result in significant changes in population density, but may have increased individual growth rates. We conclude that most trout stocking in Sierra Nevada alpine lakes could be permanently halted with only minimal impact on the recreational fishery.

Il arrive souvent que l'on ensemence des truites dans les lacs alpins, parce que l'on croit, généralement sans preuves, que les populations résidantes pourraient disparaître sans ces ensemencements. Les objectifs de notre étude sont d'estimer la proportion de lacs alpins dans la Sierra Nevada, Californie, contenant des populations de truites à reproduction naturelle (Oncorhynchus mykiss, O. m. aguabonita, O. clarki henshawi) qui sont actuellement ensemencés ou qui l'ont été dans le passé; nous voulons aussi identifier les caractéristiques des lacs dans lesquels la reproduction est réussie et étudier quantitativement les effets de l'arrêt des ensemencements sur la densité des truites et les taux individuels de croissance dans les populations qui se reproduisent. Nous avons fait l'inventaire de 95 lacs dans la région sauvage John Muir (JMW) avant et après un arrêt de 4–8 ans des l'ensemencements et de 84 lacs du parc national de Sequoia–Kings Canyon (SEKI) après un arrêt de ≥20 ans. D'après le recrutement observé durant l'arrêt des ensemencements, 70 % des lacs étudiés à JMW et 68 % de ceux de SEKI maintiennent des populations qui se reproduisent. Les lacs qui possèdent >2,1 m2 d'habitat de fraye et qui sont situés à <3520 m d'altitude montrent presque toujours des indices de reproduction. Chez les populations qui se reproduisent, l'arrêt des ensemencements ne cause pas de changement significatif de la densité de population et peut augmenter les taux individuels de croissance. En conclusion, la plupart des ensemencements de poissons dans les lacs alpins de la Sierra Nevada peuvent être abandonnés de façon permanente et l'impact sur la pêche sportive sera minime.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: November 1, 2004

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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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