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Geographic variation in density, demography, and life history traits of a harvested, sex-changing, temperate reef fish

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Abstract:

Geographic variation in ecological and environmental factors may lead to intraspecific differences among populations. For the California sheephead (Semicossyphus pulcher), an important predator in kelp forests and a target of commercial and recreational fisheries, we evaluated the degree to which different populations exhibited variation in density, demography, and life history traits. We assessed biogeographic patterns of abundance through underwater visual census at 39 sites spanning a major portion of the species range (southern California, USA, to Baja California, Mexico) and made collections from seven focal sites to investigate geographic differences in demography and life histories. California sheephead densities were significantly greater in the southern part of their range and at offshore islands than along the mainland coast. At the focal sites, we found significant spatial variation in density, fecundity, size structure, growth rates, annual survivorship, and the timing of maturation and sex change. Density- and temperature-dependent effects helped to explain the intraspecific differences in these parameters. Studies such as this one will allow for demographic plasticity to be incorporated into future stock assessments. Management of temperate reef fishes may best be achieved on smaller spatial scales as we increase our understanding of geographic variation among populations.

La variation géographique des facteurs écologiques et environnementaux peut mener à des différences intraspécifiques entre les populations. Nous avons évalué le degré de variation dans la densité, la démographie et les traits du cycle biologique chez différentes populations du labre californien (Semicossyphus pulcher), un important prédateur dans les forêts de varech et la cible des pêches commerciales et sportives. Nous avons évalué les patrons biogéographiques d'abondance par des inventaires visuels sous-marins à 39 sites couvrant une partie importante de l'aire de répartition de l'espèce (sud de la Californie, É.-U., à la Basse-Californie, Mexique); nous avons aussi fait des prélèvements à sept sites choisis afin d'étudier les différences géographiques de démographie et de cycle biologique. Les densités de labres californiens sont significativement plus grandes dans la partie sud de l'aire de répartition et près des îles du large que le long de la côte du continent. Aux sites choisis, il existe une variation significative de la densité, de la fécondité, de la structure en taille, des taux de croissance, de la survie annuelle et du calendrier de la maturation et du changement de sexe. Des effets dépendants de la température et de la densité aident à expliquer les différences intraspécifiques de ces variables. Des études comme la nôtre permettront d'incorporer la plasticité démographique dans les évaluations futures des stocks. La gestion des poissons des récifs tempérés se fait de façon optimale à des échelles spatiales plus restreintes à mesure que s'accroît notre compréhension de la variation géographique entre les populations.

Document Type: Research Article

Publication date: February 1, 2011

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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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