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The effect of cloud cover on the development of habitat quality indices for juvenile Atlantic salmon (Salmo salar)

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We tested the validity of the predictions made by a habitat probabilistic index (HPI) developed using a description of the physical conditions (depth, flow velocity, grain size) used and avoided by parrs during days of different cloudiness. Thirteen surveys were designed to estimate the number and the distribution of parrs actively foraging within a 300-m reach of a river. During these surveys, the number of parrs actively foraging ranged from 12 to 118, cloud cover ranged from 5% to 100%, and water temperature ranged from 16.5 °C to 21.7 °C. The number of parrs actively foraging was negatively related to cloud cover (r2 = 0.44 to 0.88) but was independent of water temperature. HPI models developed under low (<33%) and intermediate (34–67%) cloud cover explained 82% to 98% of the local variations of fish density. The HPI model developed under high cloud cover (67–100%) was unable to predict fish distribution observed during cloudy days. Our results suggest that HPI models developed when cloudiness is >67% may have a limited predictive power.

Nous avons testé la validité des prédictions faites par un indice probabiliste d'habitat (IPH) développé à l'aide d'une description des conditions physiques (profondeur, vélocité du courant, taille du substrat) utilisées et évitées par des tacons durant des jours de différents couverts nuageux. Nous avons effectué treize survols visant à estimer le nombre total, la distribution et les conditions utilisées et évitées par les tacons qui s'alimentent activement dans une section de 300 m de rivière. Durant ces survols, le nombre de tacons s'alimentant de façon active a varié entre 12 et 118, le couvert nuageux a varié entre 5 % et 100 % et la température de l'eau a varié entre 16,5 °C et 21,7 °C. Le nombre de tacons s'alimentant de façon active a été négativement relié au couvert nuageux (r2 = 0,44 à 0,88) mais a été indépendant de la température de l'eau. Les modèles IPH développés sous un couvert nuageux faible (<33 %) et intermédiaire (34–67 %) ont expliqué 82 % à 98 % des variations locales de la densité des tacons. Le modèle IPH développé sous un couvert nuageux important (67–100 %) a été incapable de prédire la distribution des poissons lors de jours nuageux. Nos résultats suggèrent que les modèles IPH développés lorsque le couvert nuageux >67 % peuvent avoir un pouvoir prédictif limité.

Document Type: Research Article

Publication date: November 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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