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Foraging, growth, and loss rate of young-of-the-year Atlantic salmon (Salmo salar) in relation to habitat use in Catamaran Brook, New Brunswick

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The ideal despotic distribution predicts that individuals occupying preferred habitats will have higher fitness than those in less preferred habitats, whereas the ideal free distribution predicts that average fitness will be equal in all habitats. To test between these two alternatives, we studied habitat use in relation to foraging, growth, and loss rates of 216 individually tagged young-of-the-year Atlantic salmon (Salmo salar). Fish were observed by snorkelling between 2 July and 4 September 1999 in Catamaran Brook, New Brunswick. In a multiple logistic regression, the variables that best discriminated between the habitats used and not used by fish were mean flow velocity and water depth; the fish preferred habitats of intermediate flow velocity (6–48 cm·s–1) and depth (20–39 cm). Fish in preferred habitats experienced higher levels of food abundance and had higher foraging rates but did not differ in body size or growth rate compared with those in less preferred habitats, perhaps because of higher energetic costs. In addition, loss rate did not differ significantly between preferred and less preferred habitats. Our data suggest that salmonid populations at low density may be better described by an ideal free distribution rather than by an ideal despotic one.

La distribution idéale despotique prédit que les individus qui occupent les habitats convoités ont une meilleure fitness que ceux qui habitent les habitats moins recherchés, alors que la distribution idéale libre prédit que la fitness moyenne sera la même dans tous les habitats. Afin de choisir entre de ces deux hypothèses, nous avons étudié l'utilisation de l'habitat en fonction de la recherche de la nourriture, de la croissance et des taux de perte chez 216 jeunes saumons atlantiques (Salmo salar) de l'année marqués individuellement. La plongée en apnée nous a permis d'observer les poissons entre le 2 juillet et le 4 septembre 1999 à Catamaran Brook, Nouveau-Brunswick. Dans une régression logistique multiple, les variables qui permettent le mieux de discriminer les habitats utilisés et non utilisés par les poissons sont la vitesse moyenne du courant et la profondeur de l'eau; les poissons préfèrent des eaux de courant (6–48 cm·s–1) et de profondeur (20–39 cm) moyens. Par comparaison aux poissons dans les habitats moins recherchés, les poissons dans les habitats préférés ont des densités de nourriture et des taux d'alimentation plus grands, mais ils ne diffèrent pas en taille ou en taux de croissance, probablement à cause de coûts énergétiques plus élevés. De plus, les taux de perte ne varient pas entre les habitats préférés et ceux qui le sont moins. Nos données indiquent que les populations de salmonidés de faible densité peuvent être décrites plus précisément par la distribution idéale libre que la distribution idéale despotique.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: 2004-12-01

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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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