Large effective population size and temporal genetic stability in Atlantic cod (Gadus morhua) in the southern Gulf of St. Lawrence

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Worldwide, many commercial fish stocks have experienced dramatic declines due to overfishing. Such fisheries-induced population reductions could potentially erode the genetic diversity of marine fish populations. Based on analyses of DNA extracted from archived and contemporary samples, this paper compares the genetic variability at nine microsatellite loci in a Canadian population of Atlantic cod (Gadus morhua) over 80years, spanning from before the fishery intensified to now when the population is at historically low abundance. Extensively validated genetic data from the temporally spaced samples were used to estimate the effective population size. Over the period, we observed no loss of either heterozygosity or allelic diversity. Several of the estimation methods applied could not distinguish the effective population size from infinity, and the lower 95% confidence limit on estimates was generally >500, suggesting that the effective population size is probably considerably larger than this. Hence, it appears that the southern Gulf of St. Lawrence cod stock has maintained genetic variability to sustain future evolution despite a dramatic population decline.

À l’échelle globale, plusieurs stocks commerciaux de poissons ont connu des déclins spectaculaires à cause de la surpêche. De telles réductions démographiques dues à la pêche pourraient potentiellement diminuer la diversité génétique des populations de poissons marins. S’appuyant sur des analyses d’ADN faites sur des échantillons archivés et contemporains, notre étude compare la variabilité génétique à neuf locus microsatellites dans une population canadienne de morues franches (Gadus morhua) sur une période de 80 ans couvrant le temps d’avant l’intensification de la pêche jusqu’à maintenant alors que la population connaît une abondance historiquement basse. Des données génétiques solidement validées provenant d’échantillons étalés dans le temps ont servi à estimer la taille effective de la population. Durant cette période, nous n’observons de perte ni d’hétérozygotie, ni de diversité allélique. Plusieurs des méthodes d’estimation utilisées ne peuvent pas distinguer la taille effective de la population de l’infini et la limite inférieure de l’intervalle de confiance de 95% des estimations est généralement>500, ce qui laisse croire que la taille effective est probablement beaucoup plus élevée que ce nombre. Il apparaît donc que le stock de morues du sud du golfe du Saint-Laurent a conservé la variabilité génétique nécessaire pour assurer son évolution future, malgré son déclin démographique spectaculaire.

Document Type: Research Article

Publication date: October 1, 2010

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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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