Offshore spawning and year-class strength of northern cod (2J3KL) during the fishing moratorium, 1994-1996

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Abstract:

Two new surveys have been conducted in recent years to assess the status of the northern cod (Gadus morhua) stock (2J3KL). An offshore acoustic survey in spring sampled concentrations of spawning adults and estimated potential fecundity. A pelagic juvenile fish survey carried out in late summer measured cod year-class strength prior to settlement. Spawning biomass of offshore cod decreased from 11 700 t in 1994 to 2000 t in 1995 to 900 t in 1996 with a corresponding decrease in eggs spawned. This decline was mirrored in the distribution and abundance of pelagic juvenile cod. Natural mortality estimated between the egg and pelagic juvenile stages increased from –0.068·day–1 in 1994 to –0.084·day–1 in 1995 to –0.112·day–1 in 1996. The decline in year-class strength of cod appeared to result primarily from a reduction in the number of offshore spawners compounded by an increase in natural mortality during the egg and larval stages. The decline in spawners occurred 2 years after the implementation of a fishing moratorium and cannot be linked to fishing. The rapid decline in abundance of adult fish combined with increased natural mortality during the egg and larval drift is consistent with depensation.

Deux nouveaux inventaires ont été menés ces dernières années pour évaluer l'état du stock nordique (2J3KL) de la morue franche (Gadus morhua). Un inventaire acoustique au large au printemps a permis d'échantillonner les concentrations des adultes en fraye et d'estimer la fécondité potentielle. Un inventaire des jeunes poissons pélagiques en fin d'été a mesuré la force de la classe d'âge avant l'établissement au fond. La biomasse des géniteurs au large a décru de 11 700 t en 1994 à 2 000 t en 1995 et à 900 t en 1996 et le nombre d'oeufs pondus a baissé en conséquence. Ce déclin s'est reflété dans la répartition et l'abondance des jeunes morues pélagiques. La mortalité naturelle estimée entre le stade oeuf et le stade jeune poisson pélagique a augmenté de –0,068·jour–1 en 1994 à –0,084·jour–1 en 1995 et à –0,112·jour–1 en 1996. La réduction de l'importance des classes d'âges de morue semble être due principalement à une diminution du nombre de géniteurs au large, à laquelle s'ajoute une mortalité naturelle accrue durant les stades embryonnaire et larvaire. Le déclin des géniteurs s'est produit 2 ans après la mise en place d'un moratoire sur la pêche et ne peut donc être relié à la pêche. La diminution rapide de l'abondance des poissons adultes ainsi qu'une mortalité naturelle accrue durant la dérive des oeufs et des larves laissent croire à l'existence d'un effet Allee («depensation»).[Traduit par la Rédaction]

Document Type: Research Article

Publication date: July 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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