Pacific salmon Oncorhynchus spp. from the Snake River basin experience a wide range of environmental conditions during their freshwater, estuarine, and marine residence, which in turn influence their survival rates at each life stage. In addition, researchers have found that juvenile out-migration conditions can influence subsequent survival during estuarine and marine residence, a concept known as the hydrosystem-related, delayed-mortality hypothesis. In this analysis, we calculated seasonal, life-stage-specific survival rate estimates for Snake River spring-summer Chinook salmon Oncorhynchus tshawytscha and steelhead O. mykiss and conducted multiple-regression analyses to identify the freshwater and marine environmental factors associated with survival at each life stage. We also conducted correlation analyses to test the hydrosystem-related, delayed-mortality hypothesis. We found that the freshwater variables we examined (the percentage of river flow spilled over out-migration dams and water transit time) were important for characterizing the variation in survival rates not only during freshwater out-migration but also during estuarine and marine residence. Of the marine factors examined, we found that the Pacific Decadal Oscillation index was the most important variable for characterizing the variation in the marine and cumulative smolt-to-adult survival rates of both species. In support of the hydrosystem-related, delayed-mortality hypothesis, we found that freshwater and marine survival rates were correlated, indicating that a portion of the mortality expressed after leaving the hydrosystem is related to processes affected by downstream migration conditions. Our results indicate that improvements in lifestage-specific and smolt-to-adult survival may be achievable across a range of marine conditions through increasing spill percentages and reducing water transit times during juvenile salmon out-migration.The adult abundance of Pacific salmon Oncorhynchus spp. is determined by survival across multiple life stages and a high degree of variation exists at each life stage (Bradford 1995), across-years (Peterman 1987; Pearcy 1992) and withinyears (Scheuerell et al. 2009). Pacific salmon experience a wide range of environmental conditions during periods of freshwater, estuarine, and marine residence, which in turn influence survival rates at each life stage. However, quantifying the relative importance of freshwater and marine factors on survival is often complicated by the lack of life-stage-specific

During 1993–1994, 78 adult striped bass Morone saxatilis captured in the Albemarle Sound–Roanoke River (AR) system were tagged with ultrasonic transmitters to examine summer patterns of distribution, migration, and habitat selection. Additionally, 626 striped bass were collected by electrofishing during 1993 to assess summer condition. Water temperatures within Albemarle Sound rose well above suitable levels for striped bass, but dissolved oxygen remained within tolerance limits. No stratification of temperature or dissolved oxygen occurred and no substantial thermal refuges were located. Telemetered striped bass were found throughout the Albemarle Sound system, selecting for deep water or structure. No evidence of migration to the Atlantic Ocean was found. During summer AR striped bass 325 mm total length or longer were in relatively poor condition, as evidenced by the extensive occurrence of red dermal lesions and ectoparasites. Relative weight (condition based on a standard weight at length) of commercially caught AR striped bass varied seasonally, exhibiting low values during May–August but normal values for the remainder of the year.

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...

Faulkner et al. (2019) presented data and analyses to support a hypothesis that bypass encounters by juvenile Chinook Salmon Oncorhynchus tshawytscha and steelhead O. mykiss at hydropower dams are not harmful (e.g.,

Models for making preseason forecasts of adult abundance are an important component of the management of many stocks of Pacific salmon Oncorhynchus spp. Reliable forecasts could increase both the profits from fisheries and the probability of achieving conservation and other management targets. However, the predictive performance of salmon forecasting models is generally poor, in part because of the high variability in salmon survival rates. To improve the accuracy of forecasts, we retrospectively evaluated the performance of eight preseason forecasting models for 43 stocks of pink salmon O. gorbuscha over a total of 783 stock-years. The results indicate that no single forecasting model was consistently the most accurate. Nevertheless, across the 43 stocks we found that two naïve time series models (i.e., those without explicitly modeled mechanisms) most frequently performed best based on mean raw error, mean absolute error, mean percent error, and root mean square error for forecasts of total adult recruits. In many cases, though, the best-performing model depended on the stock and performance measure used for ranking. In 21% of the stocks, a new multistock, mixed-effects stock-recruitment model that included earlysummer sea surface temperature as an independent variable along with spawner abundance demonstrated the best performance based on root mean square error. The best-performing model for each pink salmon stock explained on average only 20% of the observed variation in recruitment. Owing to the uncertainty in forecasts, a strong precautionary approach should be taken to achieve conservation and management targets for pink salmon on the West Coast of North America.