Wild Winter Steelhead Research Articles

Historical Records Reveal Changes to the Migration Timing and Abundance of Winter Steelhead in Olympic Peninsula Rivers, Washington State, USA

AbstractWe analyzed multiple historical data sources (circa 1948–1960) to estimate migration timing and abundance of Olympic Peninsula winter steelhead Oncorhynchus mykiss in the Quillayute, Hoh, Queets, and Quinault rivers, Washington, to provide context for contemporary (circa 1980–2017) population trends. Contemporary wild winter steelhead migrations peak 1–2 months later than historical migrations, and migration timing breadth has contracted by up to 26 d (a 37% reduction of the interquartile range of the migration timing distribution). Migration timing changes coincide with an era of peak industrial forestry and introductions of early migrating hatchery winter steelhead stocks. We estimate that contemporary mean wild winter steelhead abundance has declined by 55% across populations compared to circa 1948–1960 historical means, with 1920s records suggesting declines of up to 77% in the Queets River. Migration timing shifts and the magnitude of population declines are not evident in modern fisheries monitoring records, which began around 1980. Our results demonstrate how modest extensions of the period of record (e.g., 30 years) increase the power to identify population changes that are not readily apparent from contemporary fisheries monitoring programs. Historical fisheries data can help managers to avoid the shifting baseline syndrome and provide important reference points for rebuilding population diversity and abundance.

Factors influencing density, distribution, and mesohabitat selection of juvenile wild salmonids and residual hatchery winter steelhead

To best manage Eagle Creek National Fish Hatchery, negative interactions between hatchery salmonids and Endangered Species Act listed wild salmonids in the Eagle Creek Basin need to be minimized. Our objectives were: 1) to compare summer rearing densities in two similar streams, where one stream received a release of hatchery salmonids and one stream did not receive a release of hatchery salmonids, 2) to determine if residual hatchery winter steelhead were present in the Eagle Creek Basin, and 3) if so, determine how their presence and density relates to mesohabitat selection and distribution of naturally produced salmonids. A comprehensive snorkel survey identified significantly higher densities of juvenile coho salmon rearing in North Fork Eagle Creek, compared to upper and lower Eagle Creek. We found age 0 winter steelhead in significantly higher densities in upper Eagle Creek as opposed to lower Eagle Creek and North Fork Eagle Creek. Residual hatchery steelhead were located only in Eagle Creek and were rearing in the same 15 mesohabitat units that contained the estimated majority of wild fish populations. In Eagle Creek, the probability of occurrence for all species, regardless of origin, was highest in the vicinity of the hatchery. Residual hatchery winter steelhead density indicated a negative relationship with age 0 winter steelhead density. Due to residual hatchery winter steelhead being present in only 15 sampled habitat units we recommend future sampling effort be focused in areas with known populations of residual hatchery winter steelhead to determine if a distinct relationship between these population densities exists. From these data it is unclear if residual hatchery steelhead are affecting densities, distributions, and mesohabitat selection of wild salmonids in the basin. However, while we were unable to detect any direct impacts of residual hatchery fish on the wild population, these results do suggest the potential exists for competitive ecological interactions between hatchery and wild populations.

The Effect of an Introduced Summer Steelhead Hatchery Stock on the Productivity of a Wild Winter Steelhead Population

AbstractWe investigated the effect of a hatchery program for summer steelhead Oncorhynchus mykiss on the productivity of a wild winter steelhead population in the Clackamas River, Oregon. We used a suite of Ricker and Beverton–Holt stock–recruitment models that incorporated species interaction variables to demonstrate that when high numbers of hatchery summer steelhead adults were present the production of wild winter steelhead smolts and adults was significantly decreased. We found that large releases of hatchery smolts also contributed to the decrease in wild adult productivity. Averaged over the results of our models, a 50% decline in the productivity parameter (the number of recruits per spawner at low densities) and a 22% decline in the maximum number of recruits produced in the basin were observed when high numbers of hatchery fish were present. We concluded that over the duration of the hatchery program, the number of hatchery steelhead in the upper Clackamas River basin regularly caused the total number of steelhead to exceed carrying capacity, triggering density‐dependent mechanisms that impacted the wild population. The number of smolts and adults in the wild winter steelhead population declined until critically low levels were reached in the 1990s. Hatchery fish were removed from the system in 2000, and early results indicate that the declining trends have reversed.

Naturally Spawning Hatchery Steelhead Contribute to Smolt Production but Experience Low Reproductive Success

We used genetic mixture analyses to show that hatchery summer-run steelhead Oncorhynchus mykiss, an introduced life history in the Clackamas basin of Oregon, where only winter-run steelhead are native, contributed to the naturally produced smolts out-migrating from the basin. Hatchery-produced summer steelhead smolts were released starting in 1971, and returning adults were passed above a dam into the upper Clackamas River until 1999. In the 2 years of our study, summer steelhead adults, mostly hatchery fish, made up 60% to 82% of the natural spawners in the river. Genetic results provided evidence that interbreeding between hatchery summer and wild winter steelhead was likely minor. Hatchery summer steelhead reproductive success was relatively poor. We estimated that they produced only about one-third the number of smolts per parent that wild winter steelhead produced. However, the proportions of summer natural smolts were large (36–53% of the total naturally produced smolts in the basin) because hatchery adults predominated on the spawning grounds during our study. Very few natural-origin summer adults were observed, suggesting high mortality of the naturally produced smolts following emigration. Counts at the dam demonstrated that hatchery summer steelhead predominated on natural spawning grounds throughout the 24-year hatchery program. Our data support a conclusion that hatchery summer steelhead adults and their offspring contribute to wild winter steelhead population declines through competition for spawning and rearing habitats.

Comparative Life History Characteristics of Hatchery and Wild Steelhead Trout (Salmo gairdneri) of Summer and Winter Races in the Kalama River, Washington

Life history information was collected from adult upstream migrant hatchery and wild steelhead trout (Salmo gairdneri) of summer-run and winter-run racial origin in the Kalama River, Washington, from 1976 to 1984. We found inter- and intraracial distinctions among many of the characteristics examined. In contrast with winter steelhead, summer steelhead generally had a temporally protracted time of return, fewer total age categories, fewer repeat spawners, and greater size at a given marine age. Compared with wild steelhead, hatchery steelhead generally had fewer saltwater age categories and a lower incidence of respawners. Based on differences in return timing, age composition, and size at maturity, we suggest that greater similarities currently exist between Kalama River hatchery and wild summer steelhead than between hatchery and wild winter steelhead.

Spawning Characteristics of Sympatric Populations of Steelhead Trout (Salmo gairdneri): Evidence for Partial Reproductive Isolation

We differentially tagged upstream migrant adult summer and winter steelhead trout (Salmo gairdneri) of hatchery and wild origin in the Kalama River, Washington, and subsequently observed them spawning under natural conditions in a tributary. We found that summer steelhead spawned within the study stream on a spatially random basis. The steelhead spawning interval was 6 mo long, during which hatchery summer steelhead spawned first, followed by wild summer, hatchery winter, and wild winter steelhead. Significant temporal spawning differences were found between hatchery summer and wild winter fish, and between wild summer and wild winter steelhead. We developed estimates of potential reproductive overlap between spawner groups that indicated that most reproductive activity involved members of the same spawner group. Estimated genetic exchange among groups was primarily between hatchery and wild fish within races. Of all possible spawner group comparisons, the smallest potential reproductive overlap estimated was between wild summer and wild winter steelhead. We concluded that, although wild summer and wild winter steelhead were not completely reproductively isolated, a substantial degree of successful gene flow restriction occurred, thereby providing a mechanism for the maintenance of racial identity. Additionally, spatial and temporal spawner segregation was of insufficient magnitude to prevent the potential infusion of hatchery steelhead genes into the wild summer steelhead population.