Steelhead Oncorhynchus Mykiss Research Articles

Empirical and model‐based evaluation of a step‐pool stream restoration project: Consequences for a highly valued fish population

AbstractObjectiveWe sought to measure a step‐pool restoration project's effects on a steelhead Oncorhynchus mykiss population and explore the capability of process‐based modeling to enhance understanding of the results.MethodsWe used before‐after–control‐impact monitoring in combination with a process‐based, individual‐based, spatially explicit fish population model to evaluate a stream restoration project that reconfigured the channel and primarily added step pools to a reach of a second‐order stream in northwestern California.ResultFive years of monitoring both before (2012–2016) and after (2018–2022) restoration indicated that restoration caused substantial increases in the abundance and biomass of steelhead. Individual growth rates and retention of fish in the study reach did not exhibit consistent patterns, even in the first 2 years after restoration, when fish abundance and biomass exhibited extreme increases of about fivefold. Model simulations predicted about a twofold increase in the abundance and biomass of steelhead in the restoration reach, which corresponded with the empirical results 4–5 years after restoration. The model also predicted a similar increase in the production of steelhead out‐migrants, a response we did not attempt to measure in the field.ConclusionStep‐pool restoration benefitted steelhead. The model's correspondence with empirical observations indicates its potential applicability to more complex resource management questions in the study area, such as how restoration will combine with changes in climate to affect the sustainability of salmonid populations.

Encounter rates and catch‐and‐release mortality of steelhead in the Snake River basin

AbstractObjectiveThe potential influence (i.e., impact rate) of catch‐and‐release fisheries on wild steelhead Oncorhynchus mykiss is poorly understood and is a function of the abundance of wild fish, how many fish are encountered by anglers (i.e., encounter rate), and the mortality of fish that are caught and released. In Idaho, estimates of wild steelhead encounter rates have been derived using the number of wild and hatchery steelhead passing Lower Granite Dam, the number of hatchery steelhead harvested, and the number of hatchery steelhead caught and released. The method includes assumptions that hatchery and wild steelhead have equal encounter rates and catch‐and‐release mortality is 5% for wild steelhead. Here, we investigated wild and hatchery steelhead encounter rates by anglers, estimated catch‐and‐release mortality, and concatenated both aspects to examine how existing recreational steelhead fisheries influence wild steelhead mortality.MethodsWe sampled, tagged, and released 1,251 spawn‐year 2020 (SY2020) and 1,956 spawn‐year 2021 (SY2021) adult steelhead at Lower Granite Dam with T‐bar anchor tags and passive integrated transponder (PIT) tags to estimate steelhead encounter rates and catch‐and‐release mortality. Differences in survival of caught steelhead and those not reported as caught were evaluated using detections at various locations (e.g., PIT arrays, weirs).ResultEstimated encounter rates were 43.7% (95% credible interval; 28.2%, 100.0%) for wild fish and 46.7% (29.6%, 100.0%) for adipose‐clipped fish in SY2020. In SY2021, encounter rates were 47.2% (32.4%, 100.0%) for wild fish and 52.3% (37.1%, 100.0%) for adipose‐clipped fish. Based on detections of caught fish and those not reported as caught, catch‐and‐release mortality of wild steelhead was estimated to be 1.6% (0.0%, 5.2%). Wild steelhead impact rates were 0.7% (0.0%, 2.7%) in SY2020 and 0.7% (0.0%, 2.8%) in SY2021.ConclusionEstimated rates of impact on wild steelhead were consistent and low across years despite major differences in the structure of the fisheries. Our results suggest assuming that encounter rates are equal between hatchery and wild steelhead, and that steelhead catch‐and‐release mortality is 5%, will likely lead to a conservative estimate of the wild steelhead impact occurring from catch‐and‐release fisheries.

Weirs: An effective tool to reduce hatchery–wild interactions on the spawning grounds?

AbstractObjectiveHatchery‐produced salmon and steelhead Oncorhynchus mykiss mitigate for habitat loss and support valuable commercial, recreational, and tribal fisheries. However, excessive interactions between hatchery and wild fish can also cause harm to wild populations. Weirs have been implemented as a management tool to remove returning hatchery‐origin Chinook Salmon O. tshawytcha adults to reduce the proportion of hatchery‐origin spawners (pHOS) in spawning areas used by their wild counterparts. Using a decade of data since new weirs were implemented, our objective was to evaluate the efficacy of this management approach.MethodsWeirs were installed in six tributaries of the lower Columbia River, Washington. Using data from both weir operations and spawning ground surveys, we quantified weir efficiency (the proportion of upstream migrants captured by the weir) and resultant pHOS in wild spawning areas and evaluated evidence for unintended effects of weirs on naturally spawning salmon in years with (2011–2017) and without weirs (2002–2010) in one population by evaluating weir effects on spawner apparent residence time, distribution, and recruitment to the juvenile stage.ResultWeir efficiencies were highly variable across years and locations (7.3–100.0%). Estimates of pHOS were variable among populations and years (interannual population mean range: 11.9% to 75.2%) but were higher in all but 2 of the 43 population‐year combinations than needed to maintain recovery‐plan‐targeted levels of population viability using quantitative genetic model‐based standards identified by the Hatchery Scientific Review Group. Several factors contributed to the proportion of hatchery spawners exceeding pHOS standards at the population level, including fish passing weirs during freshets, spawning below weir sites and in tributaries without weirs, and imperfect marking of hatchery‐released juveniles. In the sole watershed with sufficient pre‐weir data to evaluate before–after changes, we documented a downstream shift in the spatial distribution of redds, lower apparent residence time of spawners, and lower production of parr in years following weir installation.ConclusionOur results indicate that using weirs as a tool to reduce hatchery–wild interactions on the spawning grounds is challenging. Weir implementation reduced pHOS; however, in most cases, resulting pHOS was not low enough to facilitate fit and viable wild populations. Weirs also were associated with unintended negative impacts to the single population where we had adequate before and after weir implementation data to evaluate effects. These impacts may be harmful to recovery efforts and offset the intended benefits of weirs to wild populations. Our study highlights the need for adaptive management to realize the goals intended for weirs, underscores the need for experimental design approaches, and identifies opportunities for future work.

Spatial and temporal overlap between hatchery‐ and natural‐origin steelhead and Chinook Salmon during spawning in the Klickitat River, Washington, USA

AbstractObjectiveA goal of many segregated salmonid hatchery programs is to minimize potential interbreeding between hatchery‐ and natural‐origin fish. Our objective was to assess this on the Klickitat River, Washington, USA.MethodsWe used radiotelemetry to evaluate spatiotemporal spawning overlap between hatchery‐ and natural‐origin steelhead Oncorhynchus mykiss and spring Chinook Salmon O. tshawytscha. We estimated percentages of tagged fish that spawned naturally in the Klickitat River subbasin, emigrated from the Klickitat River, or died before spawning. A kernel density analysis was used to estimate probability of spatiotemporal overlap between hatchery‐ and natural‐origin spawners.ResultFor steelhead, 12% of hatchery‐origin and 50% of natural‐origin fish spawned naturally. For spring Chinook Salmon, 18% of hatchery‐origin and 44% of natural‐origin fish spawned naturally. Tag loss may result in underestimates in these percentages. Most hatchery‐origin steelhead (90%) spawned downstream of river kilometer (rkm) 32, and 75% spawned from November to mid‐March. The majority of natural‐origin steelhead (64%) spawned upstream of rkm 32, and 75% spawned from mid‐March to late May. Spawn timing of hatchery‐origin Chinook Salmon (early August to mid‐September) overlapped with that of natural‐origin Chinook Salmon (late July to late September), and fish of both origins spawned in the same 30‐km reach of the river. We estimated the percentage of hatchery‐origin spawners (pHOS) on the natural spawning grounds to be 12% for steelhead and 40% for spring Chinook Salmon across all study years. For steelhead, we estimated the overlap probability to be 25% (95% CI = 22.5–28%). For spring Chinook Salmon, tight spatial clustering of hatchery‐origin fish resulted in a lower overlap estimate of 21% (13–31%).ConclusionWe suggest adjusting pHOS estimates using these overlap estimates or similar spatiotemporal data on actual spawner proximity and possible interactions, and that these types of analyses be used in conjunction with gene flow analysis to accurately evaluate effects of individual hatchery programs.

Caspian Tern Management to Increase Survival of Juvenile Salmonids in the Columbia River Basin: Progress and Adaptive Management Considerations

Predation by Caspian terns Hydroprogne caspia is a factor limiting the recovery of some Endangered Species Act‐listed populations of salmonids from the Columbia River basin, especially steelhead Oncorhynchus mykiss. This prompted the development and implementation of two separate management plans, one in the Columbia River estuary and the other in the Columbia Plateau region, to reduce the impact of Caspian tern predation on smolt survival. Caspian terns nesting at managed breeding colonies within the basin were relocated to alternative nesting islands created for terns outside the basin. Both plans were successful in significantly reducing smolt losses to Caspian terns nesting at managed sites; however, new developments have led to regression in smolt survival gains associated with tern management. Adaptive management to prevent terns at managed colonies from relocating to nest elsewhere in the basin and to improve nesting opportunities for Caspian terns outside the basin are needed to maximize the survival benefits to Endangered Species Act‐listed salmonids from management. Adaptive management is also necessary to ensure the long‐term viability of the Pacific Flyway population of Caspian terns, whose breeding population has declined by more than 50% since the two management plans were implemented.

Growth performance of Rainbow Trout in reservoir tributaries and implications for steelhead growth potential above Skagit River dams

AbstractObjectiveIn the Pacific Northwest (USA), Pacific salmon Oncorhynchus spp. populations have been declining significantly for decades, prompting stakeholders to respond with a variety of conservation and restoration measures. One such measure being considered in the Skagit River basin (Washington, USA) is the introduction of steelhead Oncorhynchus mykiss (anadromous Rainbow Trout) above the impassable Gorge, Diablo, and Ross dams to bolster their populations. Because freshwater growth is key to survival at subsequent life stages, we evaluated current trends in size and growth of Rainbow Trout among key tributaries to Gorge, Diablo, and Ross reservoirs using empirical data collection and bioenergetics modeling.MethodsFor nine candidate streams, a bioenergetics model was used to assess how temperature and prey consumption affected growth performance of Rainbow Trout between annuli 1 and 2, and 2 and 3. Thermal scenarios were created to evaluate how fish growth responded to temperature variability while total annual consumption was constrained within empirical growth estimates. We then compared these results to back‐calculated size thresholds established by size‐at‐age observed in wild steelhead adults that returned to the Skagit River below the dams.ResultOf the streams proposed for introductions, there was one instance (McMillan Creek) in the nominal simulations where growth met or exceeded the size at annulus 2 or 3 of a returning adult steelhead (24.9 g at annulus 2 and 50.3 g at annulus 3). Modeled growth under different thermal scenarios showed that colder temperatures (0.1–10.7°C, Canyon Creek) produced higher growth than under the nominal or warm scenarios (2.0–15.3°C, Canyon Creek), as well as one additional tributary where size at annulus 2 or 3 (±2 SE) was comparable to the threshold established by adult steelhead below the dams (Big Beaver Creek, annulus 3).ConclusionThese results suggest Rainbow Trout growth is most limited by prey availability in the examined upper Skagit tributaries.

Managing Expectations from Intensively Monitored Watershed Studies

AbstractIntensively monitored watershed (IMW) studies, the intent of which is to quantify habitat restoration effects on salmonid populations, have been underway in the Pacific Northwest, USA, for more than two decades. Lack of population‐level response to habitat improvements by target species in some IMWs may be related to incomplete knowledge of factors regulating fish abundance, excessively prolonged restoration application periods, underappreciation of natural environmental and population variability, failure to carry out restoration at a sufficiently large scale within a watershed, lack of sufficient time to document a posttreatment response, or an actual failure of the restoration activities in those locations to achieve population recovery objectives. However, knowledge gained from IMWs has yielded important insight into (1) the long‐term responses of salmon and steelhead Oncorhynchus mykiss to different types of restoration and (2) the importance of placing freshwater habitat improvements in the context of changes in anadromous salmonid survival and growth during other life history stages. Scientists, funding organizations, and policymakers should appreciate the potential value of IMWs as long‐term barometers of the status of salmon populations and their habitats in watersheds where restoration activities are occurring. This requires a commitment to prolonged monitoring and an acknowledgment that environmental recovery after habitat restoration may take decades.

Applications of Age–Length Keys for Assigning Ages to Juvenile Steelhead

AbstractMany population metrics for wild steelhead Oncorhynchus mykiss are unquantified due to complex early life history strategies and a lack of juvenile age data. Juvenile steelhead can rear in freshwater systems for up to 7 years, with overlapping size distributions among age‐classes. As logistics for sampling and aging fish can be challenging, there are benefits to utilizing age–length keys (ALKs). We examined the potential benefits of applying ALKs to unaged juvenile steelhead from a rotary screw trap and to determine whether stratifying trapping data by season could improve accuracy in assigning ages to unaged fish. Additionally, we examined the effects of reducing samples of aged fish using a uniform sampling design in which there was a fixed number of aged fish across all length intervals of the size distributions. Using a leave‐one‐out cross validation method with aged fish, we found that ALKs assigned unbiased ages to unaged fish. When including fish with assigned ages from ALKs, results of mean length‐at‐age and brood year abundance estimates between using proportional‐sampled aged fish and uniform‐sampled aged fish were comparable. Typically, absolute differences in estimated brood year abundances were improved if age‐assigned fish were included, and mean absolute error did not exceed 0.4 years for any of the methods examined. Although seasons had a significant effect on mean length at age, overall brood year estimates of juvenile abundance derived from stratifying data by season did not notably differ from pooling summer and fall seasons together, likely because there was a higher portion of juveniles emigrating in the fall compared to the summer. Age–length keys can benefit trapping operations and aid in filling data gaps in age‐based movement and survival for steelhead by being able to accurately assign ages to unaged fish and include more data for population analyses.

Flexible‐Pass‐Through Antennas for Half‐Duplex Passive Integrated Transponder Tags in Medium to Large Rivers Used to Study Size‐Selective Reservoir Passage

AbstractThe use of passive integrated transponder (PIT) tags for studying fish behavior and demography in medium‐large rivers is hindered by antenna designs that are susceptible to damage in those environments and low detection efficiencies. We designed a vertically oriented, flexible PIT tag antenna for half‐duplex tags that is simple to construct and deploy, resilient to the dynamic river environment, retains the higher detection efficiency of pass‐through antennas, and is suitable for rivers up to 30 m wide and 1.5 m deep. These “flexible‐pass‐through antennas” are economical to build and cost ~US$435 to $680 for a one‐ or two‐winding antenna, respectively. We used two flexible‐pass‐through antennas to test for size‐selective reservoir passage in juvenile steelhead Oncorhynchus mykiss (anadromous Rainbow Trout) and Rainbow Trout. We found that flexible‐pass‐through antennas withstood high flows and debris during a spring out‐migration season and provided data to reject the hypothesis of size‐selective fish passage at the Los Padres Dam and Reservoir on the Carmel River (California, USA).

The Genetic Composition of Wild Steelhead Based on Spatial Proximity to a Hatchery

AbstractManagement of hatchery and wild stocks of steelhead Oncorhynchus mykiss within the same watershed requires careful consideration when management objectives include the use of the hatchery stock to meet fishery objectives while maintaining the genetic integrity of coexisting wild stocks. This scenario can be further complicated when management objectives for the hatchery stock include supplementation of natural production. The lower Clearwater River in Idaho provided an ideal location to evaluate hatchery steelhead genetic influence within a drainage with separate wild steelhead and supplementation management emphasis areas. We collected 813 genetic samples from wild juvenile steelhead from two sample years in 10 tributaries to the lower Clearwater River to explore genetic structure and assess hatchery influence. Overall, levels of genetic diversity of wild groups were comparable with those observed elsewhere in the Snake River basin. Estimates of effective population size of sample tributaries ranged from 22 to 198 spawners, with a median of 84. All but two tributaries had >50 spawners, and evidence of natural gene flow from other stocks was observed. Results of the study display three zones of hatchery influence in the lower Clearwater River: (1) no influence in lower tributaries with wild steelhead emphasis, (2) moderate influence in wild steelhead tributaries in close proximity to the hatchery facility, and (3) significant influence in hatchery‐supplementation tributaries. Interestingly, a number of wild steelhead reporting groups from elsewhere in the Snake River basin were observed in the assignments of study fish, suggesting movement of wild steelhead among larger drainage areas. Techniques outlined in this study can be used to monitor future hatchery influence in the Clearwater River drainage, track historic versus contemporary genetic influence in the drainage, and apply to other watersheds with hatchery and wild steelhead management objectives.

Higher Early Marine Mortality of Steelhead Associated with Releases of Hatchery Coho Salmon but Not Chinook Salmon

AbstractUnderstanding the drivers of mortality during critical life history periods is an important part of increasing our capacity to rebuild depressed salmonid populations. For threatened steelhead Oncorhynchus mykiss in Puget Sound, Washington, early marine predation has been implicated as a key source of mortality. Yet, the agents that mediate predation pressure are poorly understood. In this study, we characterize abundances of juvenile Coho Salmon O. kisutch and Chinook Salmon O. tshawytscha in Puget Sound and relate these abundance patterns to weekly steelhead survival to better understand whether pulses of hatchery‐released salmonids mediate steelhead survival. We found that weekly abundances of hatchery Coho Salmon and Chinook Salmon smolts vary by several orders of magnitude across weeks, indicating that large resource pulses are available to salmonid predators. We further found that weekly steelhead survival was significantly negatively related to abundances of hatchery‐released Coho Salmon but not Chinook Salmon, which had considerably smaller body sizes than both Coho Salmon and steelhead smolts. Together, our results suggest that releases of Coho Salmon into Puget Sound mediate mortality of steelhead smolts, possibly via increased predation pressure by shared predators.

Pedigree Analysis of an Integrated Hatchery Steelhead Program from the Mad River, California, Provides Insight into Life History Patterns and Informs Management

AbstractThe Mad River Hatchery supports one of the most important fisheries for steelhead Oncorhynchus mykiss in California. Although the Mad River Hatchery has stated goals of operating an integrated hatchery program that addresses demographic and genetic risks, very little monitoring of these goals has taken place. We applied parentage‐based tagging methods to assess the origin (wild versus hatchery), age structure, and spawn‐date heritability of steelhead returning to the Mad River Hatchery. We generated single nucleotide polymorphism genotypes at 96 loci for all adult steelhead broodstock spawned at Mad River Hatchery over a 9‐year period (2009–2017; N = 1,572) and identified 965 trios (mother, father, and offspring) using parentage analysis. Although the hatchery attempts to release 100% adipose‐fin‐clipped hatchery steelhead, our analysis uncovered a large difference in the proportion of hatchery‐origin broodstock individuals as estimated by pedigrees (0.87) and traditional adipose fin clipping (0.58). This difference presumably resulted from failure to clip or identify a clip in 100% of hatchery‐produced fish. Our analysis revealed the complete age structure of six cohorts of hatchery broodstock and showed substantial differences in different years for Mad River Hatchery steelhead. Pedigree‐based estimates of narrow‐sense heritability for spawn date were 0.242 to 0.470, indicating moderate to high heritability, and highlighting the opportunity for a strong response to selection on this trait imposed by hatchery spawning. The application of parentage‐based tagging provided critical information for understanding life history variation and the efficacy of management actions for Mad River Hatchery steelhead and provides a framework for minimizing domestication selection and associated reductions in fitness for naturally spawning fish in this integrated population.

Abundance and Migration Success of Overshoot Steelhead in the Upper Columbia River

AbstractSummer steelhead Oncorhynchus mykiss may enter freshwater almost a year before spawning and potentially make long migrations (>1,000 km) to interior headwater habitats. However, in response to suboptimal freshwater habitat conditions (e.g., warmer water temperatures), adult summer steelhead may exhibit complex behaviors during upstream migration in the Columbia River basin. Steelhead may migrate upstream of their natal tributary (hereafter, referred to as “overshoot”) and spend days to several months before subsequently migrating downstream (hereafter, referred to as “fallback”) to their natal tributary to spawn. An expansion of an existing Bayesian patch occupancy model, derived from observations of adult steelhead that were PIT‐tagged to estimate population‐specific abundance upstream of the tagging location, incorporated downstream detection locations to estimate the abundance of overshoot fallbacks. Overshoot steelhead abundance at the tagging location was estimated based on the relationship between the number of known overshoot fallbacks (i.e., the number of steelhead that overshot and successfully migrated downstream to their natal tributary) and their model‐estimated abundance. During the study period (2010–2017), the annual mean proportion of overshoot steelhead that successfully migrated downstream of the tagging location (Priest Rapids Dam) was 0.59 (SD = 0.14). The number of dams encountered by overshoot steelhead during their downstream migration was negatively correlated with their downstream migration success probability. Improved downstream passage survival for adult steelhead will increase the abundance of affected populations while reducing potential genetic introgression of upstream populations (i.e., strays). This is the first study to estimate the abundance of overshoot and fallback steelhead, providing the data necessary for scientists to estimate potential conservation benefits of improved downstream survival. For example, surface flow passage routes (e.g., sluiceways and temporary spillway weirs) are very effective in guiding and passing adult steelhead downstream of Columbia River hydroelectric projects and data from this assessment show that changes in dam operations throughout the downstream migration period may maximize conservation benefits.

Size and Distribution of Parr Produced from Natural‐ and Hatchery‐Origin Steelhead Spawning Naturally in a Small Pacific Northwest Coastal Stream

AbstractRecent studies suggest that steelhead Oncorhynchus mykiss produced from local hatchery‐origin (HOR) adults have lower lifetime fitness than their natural‐origin (NOR) counterparts. To increase our understanding of this pattern, we compared age‐1 parr size and distribution produced by a local integrated population of HOR and NOR adults spawning naturally across a range of environmental conditions. Across 8 years, we used genetic parentage assignments and field measurements of parr in conjunction with creek temperature and flow data to find small, nonbiologically significant differences in size between parr of different parent origins. This suggests that parr produced by HOR adults are acquiring enough resources to grow at a rate similar to that of parr produced by NOR adults. In contrast to origin, we found strong positive associations between mean size of parr and annual mean water temperature and summer flow. Additionally, the distribution of parr was similar and HOR‐produced parr were not skewed relative to the location of the hatchery. Parr occupying the full extent of accessible and suitable habitat might be a positive outcome for hatchery programs seeking to supplement an existing population or replace an extirpated population. However, these results also imply that HOR fish could be competing with NOR fish for food and space, which might be less desirable if the goal of the hatchery program is harvest and not supplementation. Our results highlight the importance of clearly articulated goals for the hatchery program, as the observed pattern could be deemed a benefit or a risk depending on the hatchery's purpose. Lastly, projections for higher water temperatures and reduced summer flows, when considered in the context of the correlations we observed for size of parr, imply that coastal steelhead populations could start experiencing negative climate impacts with respect to steelhead parr growth metrics during the summer in the next few decades.

Counting the Parts to Understand the Whole: Rethinking Monitoring of Steelhead in California’s Central Valley

Steelhead (Oncorhynchus mykiss expressing an anadromous life history) in the Sacramento and San Joaquin rivers and their tributaries in California’s Central Valley (CCV) belong to a Distinct Population Segment (DPS) that is listed as threatened under the US Endangered Species Act. Although contemporary management and recovery plans include numerous planned and ongoing efforts seeking to aid in DPS recovery—such as gravel augmentation, manipulation of spring flows, and restoration of rearing and spawning habitat—a paucity of data precludes the possibility of evaluating the effect of these actions on populations of Steelhead in CCV streams. Knowledge gaps relating to historic and current abundance, population-specific ratios of resident and anadromous life-history expression, and the influence of hatchery-reared fish remain largely unaddressed. This is partly a result of aspects of Steelhead biology that make them difficult to monitor, including the multitude of factors that contribute to the expression of anadromy, polymorphic populations, and migration periods that coincide with challenging field conditions. However, these gaps in understanding are also partly the result of an institutional focus on Chinook Salmon (Oncorhynchus tshawytscha) and a pervasive notion that actions benefiting Chinook populations will also benefit Steelhead populations. To evaluate these gaps and to suggest approaches for assessing DPS recovery actions, we review available data and existing monitoring efforts, and consider the actions necessary to inform the development of targeted O. mykiss monitoring programs. Current management and recovery goals focus on abundance estimates of Steelhead only, yet current monitoring is insufficient for reliable estimates. We argue that a reallocation of monitoring resources to better understand the interaction between resident O. mykiss and Steelhead would provide better data to estimate the vital rates needed to evaluate the effects of recovery actions.

Integrating Ecosystem Models with Long‐Term Monitoring to Support Salmon Recovery

AbstractOkanogan summer‐run Chinook Salmon Oncorhynchus tshawytscha holding in the Similkameen River near Oroville, Washington. Photo credit: Brian Miller, Confederated Tribes of the Colville Reservation.The Ecosystem Diagnosis and Treatment model (EDT) is a deterministic, life cycle‐based habitat model developed to support the conservation and recovery of declining Pacific salmon Oncorhynchus spp. and steelhead Oncorhynchus mykiss in the Pacific Northwest. Originally conceived in the 1990s, the current generation of EDT is proving its value as a data synthesis and analysis platform, capable of transforming complex environmental data into useful quantitative metrics to guide decision making. Here we describe the integration of EDT with long‐term research, monitoring, and evaluation in the Okanogan River in the state of Washington to support the ongoing conservation and recovery of steelhead listed under the Endangered Species Act. The lessons learned in this important Columbia River subbasin demonstrate the value of EDT as an adaptive management tool that is both effective and transferable. Modeling tools like EDT are one of many technological advances that will help resource managers identify priority habitats for conservation and restoration.

Validation of Scale‐Derived Ages in Wild Juvenile and Adult Steelhead Using Parental‐Based Tagging

AbstractAccurate age information is a critical component in fisheries monitoring, management, and research. The ability to assign accurate ages to fish by using nonlethal structures is vital in calculating cohort productivity for fish species with low abundances and variable life histories. A common nonlethal method to assign ages is by interpretation of patterns in scales. Validation of ages is not easily obtained for free‐ranging fishes; however, the development of genetic “tags” has expanded age validation opportunities. In this study, we used parental‐based genetic tagging to validate ages determined from scales collected from juvenile and adult steelhead Oncorhynchus mykiss in two streams within the Snake River basin. Juvenile scale ages were in agreement with 93% of the known ages. Adult scale ages were in agreement with 89% of the known ages. Although overall bias in juvenile ages was very low, we saw a slight positive bias in younger fish (young of the year and age 1) and a small negative bias in older juveniles (ages 2–4). A small negative bias in ages of adults was a consequence of errors in freshwater age. The errors observed did not significantly bias age compositions because the 90% confidence intervals about the age proportions based on scales contained the known proportions; therefore, scale analysis is an acceptable method for assigning ages to Snake River steelhead. We discuss the value of validated known‐age scales as a reference collection, and as an illustrative use, we constructed a circulus count guide to aid technicians in identifying missing annuli and distinguishing true from false annuli. To demonstrate the use of the circulus guidelines, we reanalyzed samples with age discrepancies, applying the circulus count data and the known age to identify mistakes.

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.

Capacity of Two Sierra Nevada Rivers for Reintroduction of Anadromous Salmonids: Insights from a High‐Resolution View

AbstractHistorically, anadromous steelhead Oncorhynchus mykiss and spring‐run Chinook Salmon O. tshawytscha used high‐elevation rivers in the Sierra Nevada of California but were extirpated in the 20th century by construction of impassable dams. Plans to reintroduce the fish by opening migratory passage across the dams and reservoirs can only succeed if upstream habitats have the capacity to support viable populations of each species. To estimate capacity in the Tuolumne and Merced rivers of the central Sierra Nevada, we used a high‐resolution approach based on remote sensing and dynamic habitat modeling. Our results suggested that for both species in both systems, sediment grain sizes would support widespread spawning and the water temperatures, depths, and velocities would generate ample capacity for fry and juveniles. However, the unregulated Merced River was consistently too warm for adult Chinook Salmon to hold in the dry season prior to spawning, while the regulated Tuolumne River maintained a cooler, more stable thermal regime with a capacity for thousands of holding adults. In our high‐resolution approach, we also discovered several specific physical controls on life history expression, including thermal constraints on the timing of spawning, hydraulic prompts for downstream migration of fry, divergence of the hydraulic niches of steelhead and Chinook Salmon, and a key but uncertain role for thermal tolerance in adult Chinook Salmon. Our results suggested that steelhead reintroduction could succeed in either system and Chinook Salmon could succeed in the Tuolumne River if passage strategies account for large numbers of migrant fry and juveniles driven downstream by winter storms and snowmelt. The Merced River appeared too warm for adult Chinook Salmon, which raises questions about the current limited understanding of thermal tolerance in holding adults. Our study shows how a high‐resolution approach can provide valuable insights on specific limiting factors that must be addressed for reintroduction to succeed.

The influences of pre- and post-smolt captive rearing environments on growth, maturation, body size, and reproductive success of steelhead (Oncorhynchus mykiss) released as adults

Conservation hatcheries designed to aid in recovery of imperiled fish population often implement atypical rearing and release strategies. We evaluated a conservation hatchery program for steelhead (Oncorhynchus mykiss) that hydraulically removed naturally spawned eggs and captively reared them in different freshwater hatcheries to the smolt stage and reared smolts in both fresh water and seawater to sexual maturity, before releasing the sexually maturing adults onto the spawning grounds. The adult steelhead added to the spawning population, accounting for most of the adults observed during snorkel observations. They produced 32% of the juvenile offspring sampled, and females were 2.9 times more successful than males. Reproductive success was positively correlated with female body size, which was influenced by pre-smolt and post-smolt rearing conditions and their effects on growth rate and age-at-maturity. Juvenile offspring of the released adults showed size and age differences from offspring of naturally returning steelhead, but exhibited very similar early marine survival rates.