Dynamic geography of small pelagic fish populations in the California Current System on the regime time scale (1931–1997)

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Abstract:



Climate regime shifts in the Northeast Pacific appear to have forced population size changes associated with major geographical variations in the position of the center of distribution and bulk of biomass of Pacific sardine (Sardinops caeruleus). These findings help explain the disappearance of sardines around 60 years ago at the northern part of the California Current System and their return following the 1980s. The spatial processes described here differ from those suggesting that environmental regime shifts lead to progressive increase–decrease of stock abundance associated with homogeneous expansion–contraction of its distribution range around a fixed geographical center. Sardine population changes are seemingly related to environmental variability, whereas the spatial pattern of abundance for the northern anchovy (Engraulis mordax) appears to be inversely related to sardine population abundance. Anchovies increased where and when sardines were either absent or at a low population level. Thus, from the long-term and large-scale perspective, neither sardine nor anchovy populations conform to the simple homogeneous geographical range changes usually assumed. The sardine population changes its location within the ocean habitat in an evolving progression over a multidecadal time scale.

Les changements dans le régime climatique du nord-est du Pacifique semblent avoir causé des modifications de la taille des populations, ainsi que des variations géographiques importantes de la position du centre de répartition et de la position de l'essentiel de la biomasse chez la sardine du Pacifique (Sardinops caeruleus). Ces résultats expliquent la disparition, il y a une soixantaine d'années, des sardines de la partie nord du système du courant de Californie et leur réapparition après les années 1980. Les processus spatiaux que nous décrivons ici diffèrent de ceux qui laissent croire que des changements dans le régime environnemental mènent à des augmentations–déclins d'abondance de stock associés à une expansion–contraction de la répartition géographique autour d'un centre géographique fixe. Les changements dans les populations de sardines sont, semble-t-il, reliés à la variabilité de l'environnement, alors que le pattern spatial d'abondance de l'anchois du Pacifique (Engraulis mordax) paraît être en relation inverse avec la densité de population des sardines. Les populations d'anchois croissent où et lorsque les sardines sont ou bien absentes, ou présentes en petit nombre. Ainsi, vues à long terme et à grande échelle, ni les populations de sardines, ni celles d'anchois ne se conforment aux simples changements homogènes de répartition géographique que l'on suppose ordinairement. La population de sardines change sa position dans l'habitat océanique selon une progression évolutive à une échelle temporelle de plusieurs décennies.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: December 1, 2002

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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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