Captively reared animals can provide an immediate demographic boost in reintroduction programs, but may also reduce the fitness of colonizing populations. Construction of a fish passage facility at Landsburg Diversion Dam on the Cedar River, WA, USA, provided a unique opportunity to explore this trade-off. We thoroughly sampled adult Chinook salmon (Oncorhynchus tshawytscha) at the onset of colonization (2003–2009), constructed a pedigree from genotypes at 10 microsatellite loci, and calculated reproductive success (RS) as the total number of returning adult offspring. Hatchery males were consistently but not significantly less productive than naturally spawned males (range in relative RS: 0.70–0.90), but the pattern for females varied between years. The sex ratio was heavily biased toward males; therefore, inclusion of the hatchery males increased the risk of a genetic fitness cost with little demographic benefit. Measurements of natural selection indicated that larger salmon had higher RS than smaller fish. Fish that arrived early to the spawning grounds tended to be more productive than later fish, although in some years, RS was maximized at intermediate dates. Our results underscore the importance of natural and sexual selection in promoting adaptation during reintroductions.

Pacific salmon (Oncorhynchus spp.) are at the center of social–ecological systems that have supported Indigenous peoples around the North Pacific Rim since time immemorial. Through generations of interdependence with salmon, Indigenous Peoples developed sophisticated systems of management involving cultural and spiritual beliefs, and stewardship practices. Colonization radically altered these social–ecological systems, disrupting Indigenous management, consolidating authority within colonial governments, and moving most harvest into mixed-stock fisheries. We review Indigenous management of salmon, including selective fishing technologies, harvest practices, and governance grounded in multigenerational place-based knowledge. These systems and practices showcase pathways for sustained productivity and resilience in contemporary salmon fisheries. Contrasting Indigenous systems with contemporary management, we document vulnerabilities of colonial governance and harvest management that have contributed to declining salmon fisheries in many locations. We suggest that revitalizing traditional systems of salmon management can improve prospects for sustainable fisheries and healthy fishing communities and identify opportunities for their resurgence.

While it is widely recognized that financial stock portfolios can be stabilized through diverse investments, it is also possible that certain habitats can function as natural portfolios that stabilize ecosystem processes. Here we propose and examine the hypothesis that free-flowing river networks act as such portfolios and confer stability through their integration of upstream geological, hydrological, and biological diversity. We compiled a spatially (142 sites) and temporally (1980-present) extensive data set on fisheries, water flows, and temperatures, from sites within one of the largest watersheds in the world that remains without dams on its mainstem, the Fraser River, British Columbia, Canada. We found that larger catchments had more stable fisheries catches, water flows, and water temperatures than smaller catchments. These data provide evidence that free-flowing river networks function as hierarchically nested portfolios with stability as an emergent property. Thus, free-flowing river networks can represent a natural system for buffering variation and extreme events.

Selection during the colonization of new habitat is critical to the process of local adaptation, but has rarely been studied. We measured the form, direction, and strength of selection on body size and date of arrival to the breeding grounds over the first three cohorts (2003-2005) of a coho salmon (Oncorhynchus kisutch) population colonizing 33 km of habitat made accessible by modification of Landsburg Diversion Dam, on the Cedar River, Washington, USA. Salmon were sampled as they bypassed the dam, parentage was assigned based on genotypes from 10 microsatellite loci, and standardized selection gradients were calculated using the number of returning adult offspring as the fitness metric. Larger fish in both sexes produced more adult offspring, and the magnitude of the effect increased in subsequent years for males, suggesting that low densities attenuated traditional size-biased intrasexual competition. For both sexes, directional selection favoured early breeders in 2003, but stabilizing selection on breeding date was observed in 2004 and 2005. Adults that arrived, and presumably bred, early produced stream-rearing juvenile offspring that were larger at a common date than offspring from later parents, providing a possible mechanism linking breeding date to offspring viability. Comparison to studies employing similar methodology indicated selection during colonization was strong, particularly with respect to reproductive timing. Finally, female mean reproductive success exceeded that needed for replacement in all years so the population expanded in the first generation, demonstrating that salmon can proficiently exploit vacant habitat.