Effect of predation on the low-density dynamics of vendace: significance of the functional response

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Abstract:

During the past 20 years, there have been prolonged vendace (Coregonus albula) recessions in several Finnish lakes. Hypotheses have been proposed that predation by brown trout (Salmo trutta m. lacustris) or perch (Perca fluviatilis) on young-of-the-year vendace could prevent the recovery of the vendace stocks from a low-density state. In this study, dynamic modelling was applied to examine the effect of predation, assuming a dome-shaped spawning stock–recruitment relationship for vendace, type II or III functional responses to predation by brown trout and perch, and a constant rate of fishing. The results showed that the form of the functional response is crucial in determining the significance of the predation on vendace stocks that have a steep dome-shaped stock–recruitment relationship. In all cases, however, predation by perch had more effect than that by brown trout, probably due to perch occupying the pelagic zone when the vendace stock is sparse. This may make the mortality of vendace increase with decreasing population density (depensatory mortality) at certain density levels.

Au cours des 20 dernières années, il y a eu des reculs continus dans les populations de la Petite marène (Coregonus albula) dans plusieurs lacs de Finlande. On a posé en hypothèse que la prédation des Truites brunes (Salmo trutta m. lacustris) ou de la Perchaude (Perca fluviatilis) sur les jeunes marènes de l'année empêche vraisemblablement le rétablissement des stocks de marènes qui sont à densité faible. Notre étude utilise pour examiner les effets de la prédation une modélisation dynamique qui présume que la relation entre le stock des reproducteurs et le recrutement suit une courbe en dôme, que la prédation des Truites brunes et des Perchaudes correspond à une réponse fonctionnelle de type II ou III et que le taux de pêche est constant. Les résultats montrent que la forme de la courbe de réponse fonctionnelle est un élément essentiel pour déterminer l'impact de la prédation sur des stocks de marènes, lorsque la relation du stock des reproducteurs et du recrutement suit une courbe en dôme accentuée. Dans tous les cas, cependant, la prédation par la perchaude a plus d'effets que celle exercée par la truite, probablement parce que la perchaude occupe la zone pélagique lorsque les densités de marènes sont basses. Ceci peut avoir comme effet d'accroître la mortalité de la marène lorsque la densité de la population diminue (mortalité par effet Allee) à certains niveaux de densité.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: October 1, 2001

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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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