FEATURE Extirpación y reintroducción de salmón plateado por tribus autóctonas en la cuenca del Río Columbia RESuMEN: la captura de salmónidos anádromos en la cuenca del Río Columbia ha sido fundamental para la nutrición, economía, cultura y creencias religiosas de las tribus nativas de Norte América. El desarrollo de la agricultura, la construcción de presas, urbanización y sobre pesca que siguieron a la llegada de los colonizadores europeos, dieron como resultado reducciones dramáticas de las corridas de salmón y causaron un impacto negativo en el bienestar de la gente tribal. Las agencias pesqueras federales y estatales trataron de mitigar estas pérdidas y de reconstruir algunas poblaciones de salmónidos, sin embargo clasificaron al salmón plateado como de menor importancia para las pesquerías, permitiendo así que llegara a la extinción funcional. A mediados de la década de 1990, tanto las agencias pesqueras como las tribus oriundas del Río Columbia encabezaron esfuerzos para restablecer el extirpado salmón plateado, comenzando con los ríos Yakima, Wenatchee, Methow y Clearwater. Los programas se iniciaron utilizando individuos juveniles de los stocks cultivados en la parte baja del Río Columbia, mismos que se aclimataban o se liberaban directamente cerca de hábitats potenciales para el desove. Posteriormente, en una etapa transitoria, se produjeron juveniles a partir de reproductores recolectados en las cuencas. En la actualidad, cada vez más peces están regresando a estos ríos, una parte de los cuales es el producto de desoves naturales. Los resultados sugieren que el salmón plateado se está adaptando a sus nuevos ambientes y está creando poblaciones locales naturales. ABSTRACT: Harvest of anadromous salmonids in the Columbia River basin has been fundamental to the nutrition, economy, and cultural and religious beliefs of the regional Native American tribes. Agricultural development, dam construction, urbanization, and overharvest following colonization byEuropean-origin settlers, however, resulted in dramatic reductions in salmon runs and negative impacts to the well-being of tribal peoples. Federal and state fishery agencies attempted to mitigate for the loss and to rebuild some salmonid populations but deemed Coho Salmon of lesser importance for upriver fisheries and allowed them to go functionally extinct. In the mid1990s, fishery agencies of the Columbia River Treaty tribes spearheaded efforts to reestablish the extirpated Coho Salmon, beginning in the Yakima, Wenatchee, Methow, and Clearwater rivers. The programs were initiated with juveniles from composite lower Columbia River hatchery stocks, acclimated or direct released near potential spawning habitat, then were transitioned to producing juveniles with broodstock collected in-basin. Increasing numbers of fish are now returning to these rivers, a portion of which is the product of natural spawning. Results suggest that the Coho Salmon are adapting to their new environments and founding local naturalized populations.

Coho salmon were extirpated in the mid‐20th century from the interior reaches of the Columbia River but were reintroduced with relatively abundant source stocks from the lower Columbia River near the Pacific coast. Reintroduction of Coho salmon to the interior Columbia River (Wenatchee River) using lower river stocks placed selective pressures on the new colonizers due to substantial differences with their original habitat such as migration distance and navigation of six additional hydropower dams. We used restriction site‐associated DNA sequencing (RAD‐seq) to genotype 5,392 SNPs in reintroduced Coho salmon in the Wenatchee River over four generations to test for signals of temporal structure and adaptive variation. Temporal genetic structure among the three broodlines of reintroduced fish was evident among the initial return years (2000, 2001, and 2002) and their descendants, which indicated levels of reproductive isolation among broodlines. Signals of adaptive variation were detected from multiple outlier tests and identified candidate genes for further study. This study illustrated that genetic variation and structure of reintroduced populations are likely to reflect source stocks for multiple generations but may shift over time once established in nature.

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Individual variation in life‐history traits can have important implications for the ability of populations to respond to environmental variability and change. In migratory animals, flexibility in the timing of life‐history events, such as juvenile emigration from natal areas, can influence the effects of population density and environmental conditions on habitat use and population dynamics. We evaluated the functional relationships between population density and environmental covariates and the abundance of juveniles expressing different life‐history pathways in a migratory fish, Chinook salmon (Oncorhynchus tshawytscha), in the Wenatchee River basin in Washington State, USA. We found that the abundance of younger emigrants from natal streams was best described by an accelerating or near‐linear function of spawners, whereas the abundance of older emigrants was best described by a decelerating function of spawners. This supports the hypothesis that emigration timing varies in response to density in natal areas, with younger‐emigrating life‐history pathways comprising a larger proportion of emigrants when densities of conspecifics are high. We also observed positive relationships between winter stream discharge and abundance of younger emigrants, supporting the hypothesis that habitat conditions can also influence the prevalence of different life‐history pathways. Our results suggest that early emigration, and a resultant increase in the use of downstream rearing habitats, may increase at higher population densities and with greater winter precipitation. Winter precipitation is projected to increase in this system due to climate warming. Characterizing relationships between life‐history prevalence and environmental conditions may improve our understanding of species habitat requirements and is a first step in understanding the dynamics of species with diverse life‐history strategies. As environmental conditions change—due to climate change, management, or other factors—resultant life‐history changes are likely to have important demographic implications that will be challenging to predict when life‐history diversity is not accounted for in population models.

1) Individual variation in life-history traits can have important implications for the ability of populations to respond to environmental variability and change. 2) In migratory animals, flexibility in the timing of life-history events, such as juvenile emigration from natal areas, can influence the effects of population density and environmental conditions on habitat use and population dynamics. 3) We evaluated the functional relationships between population density and environmental covariates and the abundance of juveniles expressing different life-history pathways in a migratory fish, Chinook salmon (Oncorhynchus tshawytscha), in the Wenatchee River basin in Washington State, USA. 4) We found that the abundance of younger emigrants from natal streams was best described by an accelerating or near-linear function of spawners, whereas the abundance of older emigrants was best described by a decelerating function of spawners. This supports the hypothesis that emigration timing varies in response to density in natal areas, with younger-emigrating life-history pathways comprising a larger proportion of emigrants when densities of conspecifics are high. 5) We also observed positive relationships between winter stream discharge and abundance of younger emigrants, supporting the hypothesis that habitat conditions can also influence the prevalence of different life-history pathways. 6) Our results suggest that early emigration, and a resultant increase in the use of downstream rearing habitats, may increase at higher population densities and with greater winter precipitation. Winter precipitation is projected to increase in this system due to climate warming. 7) Characterizing relationships between life-history prevalence and environmental conditions may improve our understanding of species habitat requirements and is a necessary first step in understanding the dynamics of species with diverse life-history strategies. 8) As environmental conditions change – due to climate change, management, or other factors – resultant life-history changes are likely to have important demographic implications that will be challenging to predict if life-history diversity is not accounted for in population models.