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Hydropower has long been an effective form of renewable energy, but the development of the resource has negatively impacted fishes throughout the world. Formulating recovery plans to mitigate these effects requires a firm understanding of species‐specific provenance, life history and life stage habitat requirements. However, the importance of this information is often only recognised after a substantial population decline, when obtaining it becomes demographically challenging. We provide a case study for this scenario and present a post hoc approach to gain insight into these critical data gaps for Burbot Lota lota in the upper Kootenai River in Montana and British Columbia. The population once supported a robust tribal and recreational harvest but declined following impoundment and these fisheries have remained closed or curtailed for nearly 20 years. The reasons for the decline are unknown and actions to assist recovery have been constrained by limited information regarding natal origin, life history and habitat use. We addressed this issue using strontium isotope ratios (87Sr/86Sr) in otoliths collected over four decades in Lake Koocanusa, the reservoir on the Kootenai River above Libby Dam. Due to the geologic heterogeneity of the basin and resulting variation in water 87Sr/86Sr, the assignment probability for Burbot to their region of natal origin approached unity. Otolith 87Sr/86Sr also indicated the population was comprised of mainstem‐ and tributary‐origin forms and their relative abundance changed over time. Mainstem Burbot was most abundant during the 1970s and 2000s, whereas tributary forms dominated between these periods. We suggest ecosystem changes following impoundment contributed to this shift in life history forms and the overall decline of the population. Our findings underscore the need for additional investigations of these impacts to guide restoration efforts. [ABSTRACT FROM AUTHOR]

Altering the timing and magnitude of discharge fluctuations can minimize the adverse effects of operating hydroelectric dams on the productivity of downstream salmon populations. Hydroelectric operations at Priest Rapids Dam during the mid-1970s resulted in dewatering of fall Chinook salmon (Oncorhynchus tshawytscha) redds, causing mortality of intragravel life stages. Since then, a series of operational constraints have been implemented at Priest Rapids Dam to reduce the effects of discharge fluctuations on the population of fall Chinook salmon that spawns and rears downstream from the dam. Initial protections that focused on preventing redd dewatering were subsequently increased to include postemergence life stages. We used stock-recruit analyses to identify changes to the population's freshwater productivity that occurred over a 30-year period and coincided with changes to dam operations. We observed a 217% increase in productivity that corresponded with constraints enacted to prevent redd dewatering and an additional 130% increase that coincided with enactment of constraints to limit stranding and entrapment of juveniles. The information gained from this study may be used to guide efforts elsewhere to mitigate the effects of hydroelectric dam operations on downstream fish populations. La modification du moment et de la magnitude des fluctuations des debits peut minimiser les effets nefastes de l'exploitation de barrages hydroelectriques sur la productivite de populations de saumons en aval. Les activites hydroelectriques au barrage de Priest Rapids, au milieu des annees 1970, ont entrame l'assechement des nids de frai automnaux de saumon quinnat (Oncorhynchus tshawytscha), causant une mortalite parmi les stades de vie intragravier. Depuis, un ensemble de contraintes operationnelles a ete mis en ceuvre au barrage de Priest Rapids dans le but de reduire les effets de la fluctuation des debits sur la population automnale de saumons quinnat qui fraie et grandit en aval du barrage. Les premieres mesures de protection, axees sur la prevention de l'assechement des nids de frai, ont ete elargies pour inclure la protection des stades de vie post-emergence. Nous avons utilise des analyses stock-recrutement pour cerner les changements a la productivite en eau douce de la population qui ont eu lieu sur une periode de 30 ans et qui ont coincide avec les modifications des activites d'exploitation du barrage. Nous avons observe une augmentation de 217 % de la productivite correspondant aux contraintes mises en place pour prevenir l'assechement des nids et une augmentation supplementaire de 130 % coincidant avec la mise en cuvre des contraintes visant a limiter l'echouage et le piegeage des juveniles. L'information obtenue dans le cadre de l'etude pourrait servir a orienter les efforts visant a attenuer les effets de l'exploitation d'autres barrages hydroelectriques sur les populations de poissons en aval. [Traduit par la Redaction], Introduction Operation of hydroelectric dams changes the hydrologic characteristics of the river environment, which affects the availability and quality of fish habitat (Pringle et al. 2000; Bunn and Arthington 2002). [...]

A total of 1154 acoustic-tagged subyearling fall Chinook salmon (Oncorhynchus tshawytscha) were monitored during their movement through Lower Monumental Reservoir, Snake River, Washington, USA. A release--recapture design was developed to partition their fates into migration, delayed migration (i.e., holdover or temporary residualization), and mortality using a series of standard detection arrays augmented with individual intrareach autonomous receivers. The standard detection arrays were used in conjunction with traditional release--recapture models to estimate the joint probabilities of migrating and surviving through the reservoir. Closed population estimators were used to estimate the abundance of tagged fish still alive in the river reaches and to differentiate mortality from delayed migration. Over the course of the study from 15 August to 14 November 2007, delayed migration rates increased and mortality rates generally declined. A minimum of 10.6% of the fish were estimated to have delayed migration in the reservoir during the study period. Resume: Nous avons suivi un ensemble de 1 154 saumons chinook (Oncorhynchus tshawytscha) d'automne ages de moins d'un an et porteurs d'une etiquette acoustique au cours de leurs deplacements a travers le reservoir Lower Monumental, sur la riviere Snake, Washington, E.-U. Nous avons mis au point un plan de liberation--recapture afin de repartir leur sort en migration, migration retardee (c'est-a-dire arret ou residence temporaire) et mortalite a l'aide de reseaux standards de detection avec en plus des recepteurs autonomes individuels dans les differentes sections de riviere. Les reseaux standards de detection ont ete utilises conjointement avec des modeles traditionnels de liberation--recapture afin d'estimer les probabilites conjointes de migrer et de survivre a travers le reservoir. Des estimateurs de population fermee ont servi a determiner l'abondance des poissons marques encore vivants dans les sections de riviere et de distinguer la mortalite de la migration retardee. Au cours de l'etude, du 15 aout au 14 novembre 2007, les taux de migration retardee ont augmente et les taux de mortalite ont en general decline. Nous estimons qu'un minimum de 10,6% des poissons ont retarde leur migration dans le reservoir durant la periode d'etude. [Traduit par la Redaction], Introduction The coexistence of different life history strategies within a species or population complicates the nature of scientific inquiry and the specification of management plans to accommodate the alternative life [...]