Abundance estimates of wild and hatchery Pacific salmon Oncorhynchus spp. are important for evaluation of stock status and density‐dependent interactions at sea. We assembled available salmon catch and spawning abundance data for both Asia and North America and reconstructed total abundances of pink salmon O. gorbuscha, chum salmon O. keta, and sockeye salmon O. nerka during 1952–2005. Abundance trends were evaluated with respect to species, regional stock groups, and climatic regimes. Wild adult pink salmon were the most numerous salmon species (average = 268 × 106 fish/year, or 70% of the total abundance of the three species), followed by sockeye salmon (63 × 106 fish/year, or 17%) and chum salmon (48 × 106 fish/year, or 13%). After the 1976–1977 ocean regime shift, abundances of wild pink salmon and sockeye salmon increased by more than 65% on average, whereas abundance of wild chum salmon was lower in recent decades. Although wild salmon abundances in most regions of North America increased in the late 1970s, abundances in Asia typically did not increase until the 1990s. Annual releases of juvenile salmon from hatcheries increased rapidly during the 1970s and 1980s and reached approximately 4.5 × 109 juveniles/year during the 1990s and early 2000s. During 1990–2005, annual production of hatchery‐origin adult salmon averaged 78 × 106 chum salmon, 54 × 106 pink salmon, and 3.2 × 106 sockeye salmon, or approximately 62, 13, and 4%, respectively, of the combined total wild and hatchery salmon abundance. The combined abundance of adult wild and hatchery salmon during 1990–2005 averaged 634 × 106 salmon/year (498 × 106 wild salmon/year), or approximately twice as many as during 1952–1975. The large and increasing abundances of hatchery salmon have important management implications in terms of density‐dependent processes and conservation of wild salmon populations; management agencies should improve estimates of hatchery salmon abundance in harvests and on the spawning grounds.

Horizontal ocean transport can influence the dynamics of higher‐trophic‐level species in coastal ecosystems by altering either physical oceanographic conditions or the advection of food resources into coastal areas. In this study, we investigated whether variability in two North Pacific Current (NPC) indices was associated with changes in productivity of North American Pacific salmon stocks. Specifically, we used Bayesian hierarchical models to estimate the effects of the north‐south location of the NPC bifurcation (BI) and the NPC strength, indexed by the North Pacific Gyre Oscillation (NPGO), on the productivity of 163 pink, chum, and sockeye salmon stocks. We found that for salmon stocks located in Washington (WA) and British Columbia (BC), both the BI and NPGO had significant positive effects on productivity, indicating that a northward‐shifted bifurcation and a stronger NPC are associated with increased salmon productivity. For the WA and BC regions, the estimated NPGO effect was over two times larger than the BI effect for pink and chum salmon, whereas for sockeye salmon the BI effect was 2.4 times higher than the NPGO. In contrast to WA and BC stocks, we found weak effects of both horizontal ocean transport processes on the productivity of salmon stocks in Alaska. Our results indicated that horizontal transport pathways might strongly influence population dynamics of Pacific salmon in the southern part of their North American ranges, but not the northern part, suggesting that different environmental pathways may underlie changes in salmon productivity in northern and southern areas for the species under consideration.

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...

We expand on previous analyses of environmental factors related to productivity of Chinook salmon (Oncorhynchus tshawytscha) populations by analysing data on adult recruits per spawner from 24 wild (not hatchery) Chinook salmon stocks from Oregon through western Alaska. To determine the degree to which changes in productivity are shared and to help identify environmental variables that might be related to those changes, we estimated the magnitude and spatial characteristics of positive correlations in productivity trends among stocks separated by various distances. We used dynamic factor analysis to characterize shared time trends in productivity and found that these trends were most closely associated with the North Pacific Gyre Oscillation and, to a lesser extent, with the location of the bifurcation in the North Pacific Current as it reaches North America’s west coast. Chinook productivity patterns of separate populations have also become more synchronous in recent years, similar to results reported for other species of Pacific salmon. Such recent changes may reduce the resilience of the species to effects of climate change and habitat modification.

An important management challenge is to maintain productive populations of Pacific salmon ( Oncorhynchus spp.), despite highly variable environments and our weak understanding of future climatic conditions and mechanisms that link them to salmon. This understanding could be improved by including environmental covariates in salmon population models and applying advanced “meta-analyses” to large data sets to better estimate underlying functional relationships. However, the performance of such models needs to be determined in the context of an overall system. We therefore simulated a 15-population salmon fishery system and compared the performance (in terms of catch and an index of conservation concern) of 10 forecasting and stock assessment models, ranging from simple to complex, by stochastically simulating components of a salmon fishery using a “closed-loop simulation” (or “management strategy evaluation”) under a variety of plausible future climatic scenarios. We found that complex models perform better in some situations. However, their incremental benefits are small and are swamped by the large variability in outcomes of management actions caused by “outcome uncertainty”, which reflects noncompliance of fishing vessels with regulations as well as variation in catchability. Reduction of this outcome uncertainty should therefore be a top priority, as should evaluations of more complex stock assessment models before adopting them.