Predicted extirpation of the dominant demersal fish in a large marine ecosystem: Atlantic cod (Gadus morhua) in the southern Gulf of St. Lawrence

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Abstract:

Atlantic cod (Gadus morhua) was the dominant demersal fish and most important predator in the southern Gulf of St. Lawrence ecosystem as recently as the 1980s. However, productivity of southern Gulf cod has declined, and the population is no longer viable even in the absence of fishing. We conducted population projections taking into account uncertainty in current abundance-at-age and uncertainty or variability in each of the components of population productivity (i.e., rates of recruitment, individual growth, and adult natural mortality). We defined extirpation as a spawning stock biomass less than 1000 t (<0.3% of historical levels). Based on these projections, at its current level of productivity, this population is certain to be extirpated within 40years in the absence of fishing and in 20years with fishery removals at the level of the total allowable catch in 2007 and 2008 (2000 t). Elevated natural mortality of adult cod (M) is the main factor contributing to the low productivity of this stock. Because M appears to be increasing, our projections are likely overly optimistic.

Aussi récemment que durant les années 1980, la morue franche (Gadus morhua) était le poisson benthique dominant et le plus important prédateur dans l’écosystème du sud du Golfe Saint-Laurent. Cependant, la productivité des morues du sud du golfe a diminué et la population n’est plus viable, même en l’absence de pêche. Nous avons fait des projections démographiques qui tiennent compte de l’incertitude au sujet des abondances actuelles en fonction de l’âge, ainsi que de l’incertitude ou de la variabilité associées à chacune des composantes de la productivité de la population (c’est-à-dire les taux de recrutement, de croissance individuelle et de mortalité naturelle des adultes). Nous avons défini l’extirpation comme correspondant à une biomasse du stock reproducteur inférieure à 1000 t (<0,3 % des valeurs du passé). D’après ces projections, au niveau actuel de productivité, cette population sera certainement extirpée en moins de 40 ans en l’absence de pêche et en 20 ans au rythme actuel des retraits dus à la pêche correspondant à la capture totale permise en 2007 et 2008 (2000 t). La mortalité naturelle accrue des morues adultes (M) est le facteur principal qui explique la faible productivité de ce stock. Comme M semble augmenter, nos projections sont vraisemblablement trop optimistes.

Document Type: Research Article

Publication date: November 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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