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The effects of abiotic factors and intraspecific versus interspecific competition on the diel activity patterns of Atlantic salmon (Salmo salar) fry

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We conducted semi-natural experiments to measure the relative contribution of various environmental factors and intraspecific and interspecific competition with an exotic invader on the daytime and crepuscular activity levels of Atlantic salmon (Salmo salar) fry. We demonstrated that interspecific competition with the exotic rainbow trout (Oncorhynchus mykiss) significantly increases the daytime activity of Atlantic salmon. The effect of intraspecific competition on the daytime activity of salmon was half that of interspecific competition. This indicates that the effect of rainbow trout was a combination of increasing density and the identity of the competitor. We also demonstrated that the effect of rainbow trout was probably the result of territorial interference between species. Moreover, we showed that water temperature simultaneously played an important role in explaining daytime activity of Atlantic salmon. During twilight, we observed no effect of competition on salmon activity, but environmental cues other than temperature (e.g., invertebrate drift, cloud cover) became significant predictors of activity. Feeding and growth rates of Atlantic salmon were not affected by the different levels of competition. Nevertheless, the exotic species may have a major impact by exposing the native species to increased risks of daytime predation.

Nous avons mené des expériences en milieu semi-naturel pour mesurer les contributions relatives de divers facteurs du milieu, de la compétition intraspécifique et de la compétition interspécifique avec un envahisseur exotique sur les niveaux d'activité durant le jour et le demi-jour chez des alevins de saumons atlantiques (Salmo salar). Nous démontrons que la compétition interspécifique avec la truite arc-en-ciel (Oncorhynchus mykiss) exotique augmente significativement l'activité diurne de saumon atlantique. L'effet de la compétition intraspécifique sur l'activité diurne du saumon est la moitié de celui de la compétition interspécifique. Cela indique que l'effet de la truite arc-en-ciel est dû à une combinaison d'une densité accrue et de l'identité du compétiteur. Nous démontrons aussi que l'effet de la truite arc-en-ciel est probablement le résultat d'une interférence territoriale entre les espèces. De plus, nous montrons qu'au même moment la température de l'eau permet d'expliquer une partie importante de l'activité diurne chez le saumon atlantique. Au demi-jour, nous n'observons aucun effet de la compétition sur l'activité des saumons, mais des signaux du milieu autres que la température (par ex., la dérive des invertébrés, la couverture de nuages) deviennent des variables prédictives significatives de l'activité. Les taux d'alimentation et de croissance du saumon atlantique ne sont pas affectés par les différents niveaux de compétition. Les espèces exotiques peuvent néanmoins avoir un impact important en exposant les espèces indigènes à des risques accrus de prédation durant la journée.

Document Type: Research Article

Publication date: August 1, 2008

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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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