Joseph H. Anderson

Reproductive success of captively bred and naturally spawned Chinook salmon colonizing newly accessible habitat

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.

Selection on breeding date and body size in colonizing coho salmon, Oncorhynchus kisutch.

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.

The Influences of Body Size, Habitat Quality, and Competition on the Movement and Survival of Juvenile Coho Salmon during the Early Stages of Stream Recolonization

Abstract Understanding the factors influencing the success of juvenile Pacific salmon Oncorhynchus spp. in newly colonized habitats is essential to their recovery in large areas across the West Coast of the United States and Canada. We studied biotic and abiotic factors associated with survival during the early stages of colonization and population establishment of juvenile coho salmon O. kisutch in Rock Creek, a tributary of the upper Cedar River in the Lake Washington basin of Puget Sound, Washington. The stream was occupied by resident fishes (e.g., rainbow trout O. mykiss, cutthroat trout O. clarkii, speckled dace Rhinichthys osculus, and several sculpins Cottus spp.), but adult coho salmon and other anadromous fishes had been excluded by a dam from 1901 until fish ladder installation in 2003. We defined logistic regression models and used an information-theoretic approach to predict apparent survival with various combinations of individual fish condition, location competition, and local habitat quali...

Summer Distribution and Growth of Juvenile Coho Salmon during Colonization of Newly Accessible Habitat

Abstract Pacific salmon Oncorhynchus spp. are capable of exploiting vacant habitat, but most research has focused on straying and colonization by adults. However, dispersal of juveniles of stream-rearing species, such as coho salmon O. kisutch, may also be an important component of colonization. Installation of fish passage structures on the Cedar River, Washington, and subsequent adult migration into the newly accessible habitat provided a rare opportunity to investigate colonization as coho salmon regained access to 33 km of habitat from which they had been excluded for more than a century. In this study, we describe the spatial distribution and growth patterns of the first two generations of juvenile coho salmon produced in the new habitat. Snorkel surveys in the Cedar River revealed patchy distributions of juvenile coho salmon that largely matched the distribution of adults spawning the previous fall, and higher densities occurred in lower reaches (i.e., those not far upstream from the dam). However, ...

Monitoring Climate Impacts: Survival and Migration Timing of Summer Chum Salmon in Salmon Creek, Washington

AbstractIn rivers of the Pacific Northwest, climate change is predicted to increase flow variability and water temperature, which may ultimately affect salmonid survival and the seasonal timing of key life history transitions. Summer Chum Salmon Oncorhynchus keta, native to tributaries flowing into Hood Canal and Strait of Juan de Fuca in Washington State, are particularly vulnerable to flow and temperature changes given their early spawn timing, yet relatively little is known regarding their juvenile life history. We investigated how flow and incubation temperatures influenced juvenile survival and timing of Chum Salmon in Salmon Creek between 2008 and 2016. Egg-to-migrant survival ranged from 0.9% to 46.3%, and was negatively related to the peak flow experienced during egg incubation from November 1 to January 31. Warm temperatures advanced emergence timing, as the number of days between the median spawning date and the median juvenile migration date was negatively related to average stream temperature ...