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

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.Résumé : 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 différen-ces 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; ce...

Magnitude and Trends in Abundance of Hatchery and Wild Pink Salmon, Chum Salmon, and Sockeye Salmon in the North Pacific Ocean

“…The reason for the increase in abundance of wild pink salmon and sockeye salmon populations is not completely clear, but evidence leans toward increased survival rates (at least for some populations in northern areas; i.e., Alaska and Russia), increased spawning populations (Dorner et al 2008), or both. For instance, sockeye salmon from Bristol Bay showed substantial increases in survival rate (measured as recruits per spawner) since the early to mid-1970s, even after correcting for within-stock density-dependent effects related to spawner abundance (Peterman et al 1998(Peterman et al , 2003.…”

“…The largest portion of salmon population data on the West Coast of North America came from 120 populations of pink salmon, chum salmon, and sockeye salmon that were previously described by Peterman et al (1998), Pyper et al (2001Pyper et al ( , 2002, Mueter et al (2002b), and Dorner et al (2008), the latter of which includes the original data set through the early 2000s. The database was updated with catch and spawning abundance values from recent regional reports, run reconstructions (Starr and Hilborn 1988;English et al 2006), and data that were not included in those specific populations.…”

“…Some of these data have been used in a variety of earlier investigations (e.g., Pyper et al 2001Pyper et al , 2002Mueter et al 2002b;Dorner et al 2008), including a North Pacific-wide simulation study demonstrating that density dependence in the ocean was an important factor contributing to the observed trends in hatchery and wild salmon abundance (Mantua et al 2009). …”

On signals of phase transitions in salmon population dynamics

“…This was done using the tabulated results of Kalman-filtered estimates of within-timeseries variation in r published by Dorner et al [38] from which we calculated and compared the average standard deviation in r within timeseries to the standard deviation of average r among populations.…”

Aquaculture-induced changes to dynamics of a migratory host and specialist parasite: a case study of pink salmon and sea lice

“…Accordingly, we focus on behaviour for r < 2 because above 2, increases in r will drive a period-doubling cascade. When numerical analysis required fixing a value for r, we use the empirical estimate, which is consistent with the range of pink salmon population growth rates estimated for numerous stocks from Washington through Alaska (Dorner et al 2008).…”