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Hierarchical analysis of relationships between brook trout (Salvelinus fontinalis) density and stream habitat features

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Abstract:

We used hierarchical linear regression to examine relationships between brook trout (Salvelinus fontinalis) density and habitat features nested at three levels: sections within reaches, reaches within streams, and streams within a basin. Brook trout density and environmental variables were quantified at 600 stream sections distributed among 120 reaches and 22 streams in the Cascapedia River basin, Quebec, Canada. Decomposition of variance showed that variation in density among streams was small relative to that among sections or reaches and not statistically significant. Density was influenced by habitat variables at both the section (current velocity, woody debris, cover) and reach (subbasin area, height increment at flood, valley width) levels. A cross-level interaction between current velocity and subbasin area pointed to a "contextual" effect: density showed stronger decline with current velocity in larger subbasins than in smaller subbasins. This result suggests that there was no single "best scale" for examining fish–environment relationships. Accounting for contextual effects by use of hierarchical models can enhance our understanding of how habitat features influence fish densities at multiple spatial scales.

La régression linéaire hiérarchique nous a permis d'examiner les relations entre la densité d'ombles de fontaine (Salvelinus fontinalis) et les caractéristiques environnementales emboîtées à trois niveaux hiérarchiques : les sections à l'intérieur des tronçons, les tronçons à l'intérieur des tributaires et les tributaires à l'intérieur d'un bassin. Nous avons échantillonné les poissons et les variables environnementales dans 600 sections réparties sur 120 tronçons et 22 tributaires de la rivière Cascapédia (Québec), Canada. La décomposition de la variance montrait que la variation de la densité entre tributaires n'était pas significative et était plus faible que celle entre sections ou entre tronçons. La densité était influencée par des caractéristiques environnementales aux niveaux des sections (vitesse du courant, débris ligneux, couvert) et des tronçons (superficie du sous-bassin, augmentation de la hauteur à la crue, largeur de la vallée). L'interaction entre la vitesse du courant et la superficie du sous-bassin suggérait l'existence d'un effet contextuel : l'influence négative de la vitesse du courant sur la densité était plus forte dans les grands sous-bassins que dans les petits sous-bassins. Les résultats indiquent qu'il n'y avait pas d'échelle « optimale » pour l'analyse des rélations poissons–environnement. L'examen des effets contextuels à l'aide des modèles hiérarchiques peut améliorer notre compréhension des relations poissons–environnement à plusieurs échelles spatiales.

Document Type: Research Article

Publication date: May 1, 2007

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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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