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Impacts of environmental change and direct and indirect harvesting effects on the dynamics of a marine fish community

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Abstract:

We describe dramatic shifts in the species composition of the marine fish community of the southern Gulf of St. Lawrence using a 35-year time series of catch rates in an annual bottom-trawl survey. We attempt to understand the causes of these changes using a traits-based approach that relates the similarity among species in their abundance trends to similarities in their ecological traits. We selected traits based on a priori beliefs of how each should reflect susceptibility to changes in a different external factor potentially affecting the community. We found evidence for an effect of ocean climate and top-down effects of fishing and seal predation, but not for bottom-up effects of prey availability on adult fishes. Mean body length in the community decreased dramatically in the 1990s. This reflected the removal of large-bodied fishes by fishing and sharp increases in the abundance of small fishes. The biomass of small fish was inversely correlated with an index of predation on those fish by larger fish, suggesting strong predator control of the abundance of small-bodied fishes. Our results suggest that changes in ocean climate combined with direct and indirect effects of harvesting can dramatically and rapidly alter the composition of marine fish communities.

Nous décrivons des changements importants de composition spécifique dans les communautés de poissons marins du sud du golfe du Saint-Laurent à partir d’une série chronologique de 35 années de taux de captures dans des inventaires annuels au chalut de fond. Nous tentons de comprendre les causes de ces changements à l’aide d’une méthodologie basée sur les traits qui met en rapport les similarités des tendances d’abondance chez les espèces et les similarités de leurs traits écologiques. Nous avons choisi les traits d’après notre perception a priori de comment chaque trait devrait refléter la susceptibilité aux changements d’un facteur externe particulier qui affecte potentiellement la communauté. Nous trouvons des indications de l’existence d’un effet du climat océanique et d’effets descendants de la pêche et de la prédation par les phoques, mais non d’effets ascendants de la disponibilité des proies sur les poissons adultes. La longueur corporelle moyenne dans la communauté a diminué de façon importante durant les années 1990. Cela reflète le retrait des poissons de grande taille par la pêche et un accroissement marqué des petits poissons. Il existe une corrélation inverse entre la biomasse des petits poissons et un indice de prédation des gros poissons sur les petits, ce qui laisse croire à un important contrôle de l’abondance des poissons de petite taille par les prédateurs. Nos résultats indiquent que les changements dans le climat océanique combinés aux effets directs et indirects de la récolte peuvent modifier de façons importante et rapide la composition des communautés de poissons marins.

Document Type: Research Article

Publication date: October 1, 2008

More about this publication?
  • 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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