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Historical trends in productivity of 120 Pacific pink, chum, and sockeye salmon stocks reconstructed by using a Kalman filter

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Abstract:

Temporal trends in productivity of Pacific salmon (Oncorhynchus spp.) stocks are important to detect in a timely and reliable manner to permit appropriate management responses. However, detecting such trends is difficult because observation error and natural variability in survival rates tend to obscure underlying trends. A Kalman filter estimation procedure has previously been shown to be effective in such situations. We used it on a Ricker spawner–recruit model to reconstruct indices of annual productivity (recruits per spawner (R/S) at low spawner abundance) based on historical data for 120 stocks of pink (Oncorhynchus gorbuscha), chum (Oncorhynchus keta), and sockeye (Oncorhynchus nerka) salmon. These stocks were from Washington, British Columbia, and Alaska. The resulting estimated temporal trends in productivity show large changes (on average 60%–70% differences in R/S and average ratios of highest to lowest R/S between 5.4 and 7.9 for the three species). Such changes suggest that salmon stock assessment methods should take into account possible nonstationarity. This step will help provide scientific advice to help managers to meet conservation and management objectives. The Kalman filter results also identified some stocks that did not share temporal trends with other stocks; these exceptions may require special monitoring and management efforts.

Il est important de détecter les tendances temporelles de la productivité des stocks de saumons du Pacifique (Oncorhynchus spp.) au moment opportun et de façon fiable pour permettre des actions de gestion appropriées. Il est cependant difficile de détecter ces tendances, car les erreurs d’observation et la variation naturelle tendent à masquer les tendances sous-jacentes. On a montré antérieurement qu’une méthode d’estimation à filtre de Kalman peut être efficace dans de tels cas. Nous l’utilisons donc dans un modèle de reproducteurs–recrues de Ricker afin de reconstituer les indices de productivité annuelle (recrues par reproducteur (R/S) dans des conditions de faible abondance des recrues) d’après des données du passé sur 120 stocks de saumons roses (Oncorhynchus gorbuscha), kéta (Oncorhynchus keta) et rouges (Oncorhynchus nerka). Ces stocks proviennent de l’état de Washington, de la Colombie-Britannique et de l’Alaska. Les tendances temporelles estimées de la productivité que nous obtenons montrent d’importants changements (en moyenne, des différences de 60%–70% dans le nombre de R/S et des rapports moyens entre les R/S les plus élevés et les plus bas de 5,4 à 7,9 chez les trois espèces). De tels changements indiquent que les méthodes d’évaluation des stocks de saumons devraient tenir compte de ce que les population peuvent ne pas être stationnaires. Cette procédure servira à fournir des avis scientifiques aux gestionnaires afin de leur permettre de rencontrer leurs objectifs de conservation et de gestion. Les résultats au filtre de Kalman ont aussi identifié certains stocks qui ne partagent pas les mêmes tendances temporelles que les autres stocks; ces exceptions peuvent requérir des efforts particuliers de surveillance et de gestion.

Document Type: Research Article

Publication date: September 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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