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The relation between age-0 rainbow trout (Oncorhynchus mykiss) abundance and winter discharge in a regulated river

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We identified and experimentally tested a discharge–abundance relation that predicted, based on the mean river discharge in the second half of winter (15 January – 31 March), the spring abundance of age-0 rainbow trout (Oncorhynchus mykiss) in a section of the Henrys Fork of the Snake River, Idaho, with complex bank habitat. We also considered a competing hypothesis in which autumn abundance determined spring abundance. We established that large abundances of age-0 trout were present in autumn (34 000 – 81 000) and lower abundances remained in spring (8000 – 15 000). Winter loss of age-0 trout was initiated in January. Spring abundance in 1996–1998 was related to autumn abundance (r2 > 0.99) and mean discharge in the second half of winter (17.1–22.8 m3·s–1; r2 > 0.99) but not mean discharge in the first half of winter (15.1–21.1 m3·s–1; r2 = 0.11). We experimentally maintained a high discharge (20–21 m3·s–1) in the second half of winter in 1999 to test model predictions. Autumn abundance failed to predict spring abundance (observed = 11 109; predicted = 6822; 95% prediction interval = 4669–8975). However, the discharge–abundance model accurately predicted spring abundance (predicted = 11 980; 95% prediction interval = 10 728 – 13 231). Higher discharge in the second half of winter may have provided more bank habitat at a critical time for survival.

Nous avons découvert et vérifié expérimentalement une relation entre le débit et l'abondance qui prédit, d'après le débit moyen de la rivière durant la seconde moitié de l'hiver (15 janvier – 31 mars), l'abondance des truites arc-en-ciel (Oncorhynchus mykiss) d'âge 0 au printemps dans un secteur à habitats de berge complexes dans le tributaire the Henrys Fork de la rivière Snake en Idaho. Nous avons aussi examiné une hypothèse de rechange qui relie l'abondance au printemps à l'abondance à l'automne. Les abondances de truites d'âge 0 sont fortes à l'automne (34 000 – 81 000) et plus faibles au printemps (8000 – 15 000). La perte de truites d'âge 0 commence en janvier. L'abondance au printemps en 1996–1998 était fonction de l'abondance à l'automne (r2 > 0,99) et du débit moyen dans la seconde moitié (17,1–22,8 m3·s–1; r2 > 0,99), mais pas dans la première moitié (15,1–21,1 m3·s–1; r2 = 0,11) de l'hiver. Nous avons maintenu expérimentalement un débit élevé (20–21 m3·s–1) pendant la seconde moitié de l'hiver en 1999 pour vérifier les prédictions du modèle. L'abondance en automne n'a pas permis de prédire l'abondance au printemps (observée = 11 109; prédite = 6822; intervalle de prédiction 95 % = 4669–8975). En revanche, le modèle basé sur le débit et l'abondance a prédit de façon précise l'abondance au printemps (prédite = 11 980; intervalle de prédiction 95 % = 10 728 – 13 231). Le fort débit durant la seconde moitié de l'hiver accroît probablement les habitats de berge à un moment critique pour la survie.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: February 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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