Yakima River Basin Research Articles

Host Fish Associations of the California Floater (Anodonta californiensis) in the Yakima River Basin, Washington

Abstract Freshwater mussels play an important role in stream ecosystems but are declining worldwide. The California floater (Anodonta californiensis, Lea 1852), formerly widespread throughout the Pacific Northwest, is listed as a federal species of concern and a candidate species for state listing in Washington (WA). Because freshwater mussels are obligate parasites on fish, conservation and restoration efforts require understanding specific host fish species. We found a previously undocumented population of A. californiensis in the upper Yakima River Basin in WA and determined its host fishes through a combination of laboratory and field studies. Two fish species, speckled dace (Rhinichthys osculus) and torrent sculpin (Cottus rhotheus), were confirmed as hosts for A. californiensis. Two fish species, three-spine stickleback (Gasterosteus aculeatus) and redside shiner (Richardsonius balteatus), were identified as hosts for A. californiensis in the laboratory portion of this study. Our results fill a sign...

Evaluating Steelhead Kelt Treatments to Increase Iteroparous Spawners in the Yakima River Basin

AbstractSteelhead Oncorhynchus mykiss are iteroparous, distinguishing them from Pacific salmon Oncorhynchus spp. that are semelparous. In this study we evaluated enhancement techniques that exploit this life history strategy to facilitate species restoration and recovery. In the Columbia River basin, where the natural ecosystem has been substantially altered over several decades due to human influence, all steelhead populations are listed as threatened or endangered under the U.S. Endangered Species Act. One factor believed to be limiting survival of Columbia River kelt (postspawned) steelhead is poor migration success to the ocean past several dams. We evaluated three treatments for kelts captured in the Yakima River basin from 2002 to 2011: (1) transport and release below Bonneville Dam (to provide unimpeded access to the ocean); (2) short‐term reconditioning (holding and feeding in an artificial environment to facilitate gonad maturation) with transport; and (3) long‐term reconditioning. These treatments were compared with an in‐river migration control group to identify differences in the rate at which kelts survived and returned to Prosser Dam for potential repeat spawning (hereafter repeat spawners). The long‐term reconditioning treatment exhibited the highest return rate of repeat spawners (range, 11.5–17.6%). The short‐term reconditioning treatment with transport downstream from Bonneville Dam had a 3.2% return rate. The transport only treatment exhibited the lowest return rate (0.9%); this was only one‐third of the control group's return rate (2.7%). Our results indicate that long‐term steelhead kelt reconditioning is more successful than either transportation or in‐river migration alternatives at increasing potential repeat spawner abundance and providing recovery benefits in river systems that have experienced substantial losses in natural productivity due to loss of habitat and habitat connectivity.Received June 23, 2015; accepted February 27, 2016 Published online July 15, 2016

Interannual variability in the effects of physical habitat and parentage on Chinook salmon egg-to-fry survival

Mortality during incubation is believed to be a major factor limiting the recovery of many salmon populations, though direct field measurements of egg-to-fry survival are rare or small in scale. To determine the effects of physical habitat (river reach, fine sediment intrusion, scour), parentage (mating, source of gametes) on Chinook salmon (Oncorhynchus tshawytscha) egg-to-fry survival and developmental stage at emergence across a basin, we constructed 324 artificial redds in nine reaches over 4 years in the Yakima River Basin, Washington, USA. Mean egg-to-fry survival ranged from 49% to 69% annually from 2009 to 2012 brood years. Survival was significantly different among reaches in 2010, but not in 2009, 2011, or 2012, while mating was a significant factor in all years but 2010. In contrast, developmental stage differed significantly among reaches and matings in all 4 years. Percentage of fines, days-in-gravel, and median particle size explained only small (<10%) additional amount of variation in survival or developmental stages. Our results suggest that parentage and reach within a basin are major factors influencing egg-to-fry survival, but their relative influence varies annually, presumably depending on the magnitude of high flows and scour during incubation.

A Synthesis of Findings from an Integrated Hatchery Program after Three Generations of Spawning in the Natural Environment

AbstractThe Cle Elum Supplementation and Research Facility in the Yakima River basin, Washington, is an integrated spring Chinook Salmon Oncorhynchus tshawytscha hatchery program designed to test whether artificial propagation can increase natural production and harvest opportunities while keeping ecological and genetic impacts within acceptable limits. Only natural‐origin (naturally spawned) fish are used for hatchery broodstock. Spawning, incubation, and early rearing occur at a central facility; presmolts are transferred for final rearing, acclimation, and volitional release at sites adjacent to natural spawning areas, where returning adults can spawn with natural‐origin fish. The first wild broodstock were collected in 1997, and age‐4 adults have returned to the Yakima River since 2001. An unsupplemented population in the adjacent Naches River watershed provides a reference for evaluating environmental influences. The program has been comprehensively monitored from its inception. A synthesis of findings, many already published, is as follows: supplementation increased the harvest, redd counts, and spatial distribution of spawners; natural‐origin returns were maintained; straying to nontarget systems was negligible; natural‐origin females had slightly higher breeding success (production of surviving fry) in an artificial spawning channel, while the behavior and breeding success of natural‐ and hatchery‐origin males were similar; hatchery‐origin fish showed differences in morphometric and life history traits; high rates of hatchery age‐2 (minijack) production were reported, but the observed proportions of out‐migrating juvenile and adult (ages 4 and 5) returning males were comparable for hatchery‐ and natural‐origin fish; hatchery smolts did not affect the levels of pathogens in natural smolts; and the ecological interactions attributed to the program were within adopted guidelines. Continued study is required to assess the long‐term impacts on natural production and productivity.

Assessing climate-change risks to cultural and natural resources in the Yakima River Basin, Washington, USA

We provide an overview of an interdisciplinary special issue that examines the influence of climate change on people and fish in the Yakima River Basin, USA. Jenni et al. (2013) addresses stakeholder-relevant climate change issues, such as water availability and uncertainty, with decision analysis tools. Montag et al. (2014) explores Yakama Tribal cultural values and well-being and their incorporation into the decision-making process. Graves and Maule (2012) simulates effects of climate change on stream temperatures under baseline conditions (1981–2005) and two future climate scenarios (increased air temperature of 1 °C and 2 °C). Hardiman and Mesa (2013) looks at the effects of increased stream temperatures on juvenile steelhead growth with a bioenergetics model. Finally, Hatten et al. (2013) examines how changes in stream flow will affect salmonids with a rule-based fish habitat model. Our simulations indicate that future summer will be a very challenging season for salmonids when low flows and high water temperatures can restrict movement, inhibit or alter growth, and decrease habitat. While some of our simulations indicate salmonids may benefit from warmer water temperatures and increased winter flows, the majority of simulations produced less habitat. The floodplain and tributary habitats we sampled are representative of the larger landscape, so it is likely that climate change will reduce salmonid habitat potential throughout particular areas of the basin. Management strategies are needed to minimize potential salmonid habitat bottlenecks that may result from climate change, such as keeping streams cool through riparian protection, stream restoration, and the reduction of water diversions. An investment in decision analysis and support technologies can help managers understand tradeoffs under different climate scenarios and possibly improve water and fish conservation over the next century.

A geochemical study of the impact of irrigation and aquifer lithology on groundwater in the Upper Yakima River Basin, Washington, USA

The Yakima River, a major tributary of the Columbia River, is currently overallocated in its surface water usage in part because of large agricultural water use. As a result, groundwater availability and surface water/groundwater interactions have become an important issue in this area. In several sub-basins, the Yakima River water is diverted and applied liberally to fields in the summer creating artificial recharge of shallow groundwater. Major ion, trace element, and stable isotope geochemistry of samples from 26 groundwater wells from a transect across the Yakima River and 24 surface waters in the Kittitas sub-basin were used to delineate waters with similar geochemical signatures and to identify surface water influence on groundwater. Major ion chemistry and stable isotope signatures combined with principal component analysis revealed four major hydrochemical groups. One of these groups, collected from shallow wells within the sedimentary basin fill, displays temporal variations in NO3 and SO4 along with high δ18O and δD values, indicating significant contribution from Yakima River and/or irrigation water. Two other major hydrochemical groups reflect interaction with the main aquifer lithologies in the basin: the Columbia River basalts (high-Na groundwaters), and the volcaniclastic rocks of the Ellensburg Formation (Ca–Mg–HCO3 type waters). The fourth major group has interacted with the volcaniclastic rocks and is influenced to a lesser degree by surface waters. The geochemical groupings constrain a conceptual model for groundwater flow that includes movement of water between underlying Columbia River basalt and deeper sedimentary basin fill and seasonal input of irrigation water.

Climate change and Yakama Nation tribal well-being

The Yakima River Basin (Basin) in south-central Washington is a prime example of a place where competing water uses, coupled with over-allocation of water resources, have presented water managers with the challenge of meeting current demand, anticipating future demand, and preparing for potential impacts of climate change. We took a decision analysis approach that gathered diverse stakeholders to discuss their concerns pertaining to climate change effects on the Basin and future goals that were collectively important. One main focus was centered on how climate change may influence future salmon populations. Salmon have played a prominent role in the cultures of Basin communities, especially for tribal communities that have social, cultural, spiritual, subsistence, and economic ties to them. Stakeholders identified the need for a better understanding on how the cultural, spiritual, subsistence, and economic aspects of the Confederated Tribes and Bands of the Yakama Nation could be affected by changes in salmon populations. In an attempt to understand the complexities of these potential effects, this paper proposes a conceptual model which 1) identifies cultural values and components and the interactions between those components that could influence tribal well-being, and 2) shows how federal natural resource managers could incorporate intangible tribal cultural components into decision-making processes by understanding important components of tribal well-being. Future work includes defining the parameterization of the cultural components in order for the conceptual model to be incorporated with biophysical resource models for scenario simulations.

Identifying stakeholder-relevant climate change impacts: A case study in the Yakima River Basin, Washington, USA

Designing climate-related research so that study results will be useful to natural resource managers is a unique challenge. While decision makers increasingly recognize the need to consider climate change in their resource management plans, and climate scientists recognize the importance of providing locally-relevant climate data and projections, there often remains a gap between management needs and the information that is available or is being collected. We used decision analysis concepts to bring decision-maker and stakeholder perspectives into the applied research planning process. In 2009 we initiated a series of studies on the impacts of climate change in the Yakima River Basin (YRB) with a four-day stakeholder workshop, bringing together managers, stakeholders, and scientists to develop an integrated conceptual model of climate change and climate change impacts in the YRB. The conceptual model development highlighted areas of uncertainty that limit the understanding of the potential impacts of climate change and decision alternatives by those who will be most directly affected by those changes, and pointed to areas where additional study and engagement of stakeholders would be beneficial. The workshop and resulting conceptual model highlighted the importance of numerous different outcomes to stakeholders in the basin, including social and economic outcomes that go beyond the physical and biological outcomes typically reported in climate impacts studies. Subsequent studies addressed several of those areas of uncertainty, including changes in water temperatures, habitat quality, and bioenergetics of salmonid populations.

The effects of increased stream temperatures on juvenile steelhead growth in the Yakima River Basin based on projected climate change scenarios

Stakeholders within the Yakima River Basin expressed concern over impacts of climate change on mid-Columbia River steelhead (Oncorhynchus mykiss), listed under the Endangered Species Act. We used a bioenergetics model to assess the impacts of changing stream temperatures—resulting from different climate change scenarios—on growth of juvenile steelhead in the Yakima River Basin. We used diet and fish size data from fieldwork in a bioenergetics model and integrated baseline and projected stream temperatures from down-scaled air temperature climate modeling into our analysis. The stream temperature models predicted that daily mean temperatures of salmonid-rearing streams in the basin could increase by 1–2 °C and our bioenergetics simulations indicated that such increases could enhance the growth of steelhead in the spring, but reduce it during the summer. However, differences in growth rates of fish living under different climate change scenarios were minor, ranging from about 1–5 %. Because our analysis focused mostly on the growth responses of steelhead to changes in stream temperatures, further work is needed to fully understand the potential impacts of climate change. Studies should include evaluating changing stream flows on fish activity and energy budgets, responses of aquatic insects to climate change, and integration of bioenergetics, population dynamics, and habitat responses to climate change.

A stakeholder project to model water temperature under future climate scenarios in the Satus and Toppenish watersheds of the Yakima River Basin in Washington, USA

The goal of this study was to support an assessment of the potential effects of climate change on select natural, social, and economic resources in the Yakima River Basin. A workshop with local stakeholders highlighted the usefulness of projecting climate change impacts on anadromous steelhead (Oncorhynchus mykiss), a fish species of importance to local tribes, fisherman, and conservationists. Stream temperature is an important environmental variable for the freshwater stages of steelhead. For this study, we developed water temperature models for the Satus and Toppenish watersheds, two of the key stronghold areas for steelhead in the Yakima River Basin. We constructed the models with the Stream Network Temperature Model (SNTEMP), a mechanistic approach to simulate water temperature in a stream network. The models were calibrated over the April 15, 2008 to September 30, 2008 period and validated over the April 15, 2009 to September 30, 2009 period using historic measurements of stream temperature and discharge provided by the Yakama Nation Fisheries Resource Management Program. Once validated, the models were run to simulate conditions during the spring and summer seasons over a baseline period (1981–2005) and two future climate scenarios with increased air temperature of 1 °C and 2 °C. The models simulated daily mean and maximum water temperatures at sites throughout the two watersheds under the baseline and future climate scenarios.

Parental Effect as a Primary Factor Limiting Egg‐to‐Fry Survival of Spring Chinook Salmon in the Upper Yakima River Basin

AbstractFew field estimates of egg‐to‐fry survival of Chinook salmon Oncorhynchus tshawytscha exist, although it is one of the major factors thought to limit freshwater production and recovery of Chinook salmon populations. This is likely due to the challenges of estimating survival at this life stage, which is further complicated by the variety of methods that have been employed. Our study objectives were to (1) develop a method by which spring Chinook salmon egg‐to‐fry survival could be estimated at a large spatial scale, and (2) investigate the primary factors affecting survival in the natural environment. We conducted a field experiment using 81 artificial redds to test our proposed method for evaluating egg‐to‐fry survival at a basin scale and to evaluate the effects of parentage (adult mating), river reach, and fine sediment infiltration on survival in the upper Yakima River basin, Washington. Egg‐to‐fry survival and preemergent Chinook salmon fry developmental stage were significantly different among matings, but were not detectably different among reaches. Fine sediment accumulation in egg boxes from artificial redds was largely below published threshold levels, explained less than 6% of the variation in survival, and was not correlated with developmental stage. In contrast, survival of individual matings in the natural environment and those same matings incubated under controlled hatchery conditions were highly correlated. Our study suggests that in years of low scour and potentially ideal incubation conditions, parental effects play an important role in determining in situ egg‐to‐fry survival, and that extensive replication and tracking of gamete viability is needed to separate parental effects from environmental factors affecting survival. We provide standardized methods for collecting egg‐to‐fry survival data and outline a number of potential biases that should be addressed in future research.

Tradeoffs between homing and habitat quality for spawning site selection by hatchery-origin Chinook salmon

Spawning site selection by female salmon is based on complex and poorly understood tradeoffs between the homing instinct and the availability of appropriate habitat for successful reproduction. Previous studies have shown that hatchery-origin Chinook salmon (Oncorhynchus tshawytscha) released from different acclimation sites return with varying degrees of fidelity to these areas. To investigate the possibility that homing fidelity is associated with aquatic habitat conditions, we quantified physical habitat throughout 165 km in the upper Yakima River basin (Washington, USA) and mapped redd and carcass locations from 2004 to 2008. Principal components analysis identified differences in substrate, cover, stream width, and gradient among reaches surrounding acclimation sites, and canonical correspondence analysis revealed that these differences in habitat characteristics were associated with spatial patterns of spawning (p < 0.01). These analyses indicated that female salmon may forego spawning near their acclimation area if the surrounding habitat is unsuitable. Evaluating the spatial context of acclimation areas in relation to surrounding habitat may provide essential information for effectively managing supplementation programs and prioritizing restoration actions.

Unlocking water markets: an experimental approach

Despite decades of advocacy by water resource economists, water markets (leases and sales of water rights between willing buyers and sellers) have largely failed to develop in the western US. Although there are a number of explanations for this failure, we explore one potential reason that has received less attention in the economics and policy literature: farmers as sellers may have preferences for different elements of a water market transaction that are not captured in the relative comparison of their profits from farming and their profits from agreeing to a deal. We recruited irrigators with senior water rights in the upper Yakima River Basin in Washington state to participate in a series of experimental auctions. These auctions asked participants to imagine that they owned and operated a 100-acre timothy hay farm with a given level of net revenue (i.e. an induced value). Participants then reacted to series of offers for 1-year leases from hypothetical buyers where several attributes of the lease varied across tasks. These attributes were the type of buyer (the state Department of Ecology, an irrigation district, or a developer), the management of the water bank (run by the state or by a new nonprofit), the lease type (split-season and full-season), and the offer price. Participants were paid in relation to their hypothetical farms‟ earnings. This paper presents results from 7 sessions with irrigators (n=49) and a comparison group of undergraduates (n=38). Our results show that irrigators are more likely to accept split-season than fullseason leases (controlling for differences in farm profits). Compared to the Dept of Ecology, they are more likely to accept a lease from an irrigation district and less likely to accept an offer from a Developer. They do not, however, have strong preferences over the management of the water bank. Although offer price was statistically significant in both groups, we find students were more influenced by offer price. Students had no detectable preferences over lease type, although some preferred a state-run water bank when leasing to a developer. Most notably, we find farmers were far more likely than students to reject offers from buyers even though it would increase their winnings from the experiment. Our results could be used in ongoing water supply policy debates in the Basin to simulate the amount of water that could be freed by water markets.

Homing and Spawning Site Selection by Supplemented Hatchery‐ and Natural‐Origin Yakima River Spring Chinook Salmon

AbstractIt is well known that salmon home to their natal rivers for spawning, but the spatial scale of homing within a river basin is poorly understood and the interaction between natal site fidelity and habitat‐based spawning site selection has not been elucidated. Understanding the complex trade‐offs among homing to the natal site, spawning site selection, competition for sites, and mate choice is especially important in the context of hatchery supplementation efforts to reestablish self‐sustaining natural spawning populations. To address these questions, we examined the homing patterns of supplemented Yakima River spring Chinook salmon Oncorhynchus tshawytscha released from satellite acclimation facilities after common initial rearing at a central facility. Final spawning location depended strongly on where fish were released as smolts within the upper Yakima River basin, but many fish also spawned in the vicinity of the central rearing hatchery, suggesting that some fish imprinted to this site. While homing was clearly evident, the majority (55.1%) of the hatchery fish were recovered more than 25 km from their release sites, often in spawning areas used by wild conspecifics. Hatchery and wild fish displayed remarkably similar spawning distributions despite very different imprinting histories, and the highest spawning densities of both hatchery and wild fish occurred in the same river sections. These results suggest that genetics, environmental and social factors, or requirements for specific spawning habitat may ultimately override the instinct to home to the site of rearing or release.

Climate change impacts on water management and irrigated agriculture in the Yakima River Basin, Washington, USA

The Yakima River Reservoir system supplies water to ~180,000 irrigated hectares through the operation of five reservoirs with cumulative storage of ~30% mean annual river flow. Runoff is derived mostly from winter precipitation in the Cascade Mountains, much of which is stored as snowpack. Climate change is expected to result in earlier snowmelt runoff and reduced summer flows. Effects of these changes on irrigated agriculture were simulated using a reservoir system model coupled to a hydrological model driven by downscaled scenarios from 20 climate models archived by the 2007 Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report. We find earlier snowmelt results in increased water delivery curtailments. Historically, the basin experienced substantial water shortages in 14% of years. Without adaptations, for IPCC A1B global emission scenarios, water shortages increase to 27% (13% to 49% range) in the 2020s, to 33% in the 2040s, and 68% in the 2080s. For IPCC B1 emissions scenarios, shortages occur in 24% (7% to 54%) of years in the 2020s, 31% in the 2040s and 43% in the 2080s. Historically unprecedented conditions where senior water rights holders suffer shortfalls occur with increasing frequency in both A1B and B1 scenarios. Economic losses include expected annual production declines of 5%–16%, with greater probabilities of operating losses for junior water rights holders.

Abundance and Distribution of Precociously Mature Male Spring Chinook Salmon of Hatchery and Natural Origin in the Yakima River

AbstractPrecocious maturation of artificially propagated male Chinook salmon Oncorhynchus tshawytscha has the potential to alter abundance and distribution of males in freshwater and thereby influence ecological and genetic interactions with other fish in the natural environment. Between 1999 and 2007, the Cle Elum Supplementation and Research Facility has produced and released into the upper Yakima River basin of Washington an annual average of 124,573 males that mature precociously. We investigated the abundance and distribution of precociously mature male spring Chinook salmon of hatchery and natural (wild) origin during the spawning season (4–7 months after hatchery release) in the Yakima River. We counted the number of precocious males on the spawning grounds while snorkeling during the peak of spawning and electrofished to determine abundance and distribution of precocious males away from redds. We also collected Chinook salmon to determine percent precocity and size and age distributions. The number of precocious hatchery males on redds was less than 0.05% of the total number of fish released, and they were significantly less abundant on redds than precocious wild males. Between 1999 and 2007, the mean annual abundance of precocious age‐1 hatchery males observed on the spawning grounds was 22 fish (range, 0–78). Precocious hatchery and wild males were both found throughout the spawning range during the spawning season, but significant differences in distribution between origins were detected. Precocious hatchery males were proportionately more abundant in the most downstream sampling reach and less abundant in a tributary with no hatchery facilities. In addition, most precocious hatchery males were found downstream of spawning areas during the spawning season. It appears that many precocious hatchery males migrate downstream from release and fail to migrate back to the spawning grounds, or they die within the Yakima River before spawning. Thus, precocious male Chinook salmon resulting from hatchery production in the Yakima River do not contribute favorably to harvest and may pose ecological risks to other taxa, but most of these fish have a low probability of contributing genes to future generations.

Erosion control practices integrated with polyacrylamide for nutrient reduction in rill irrigation runoff

The objective of this research was to assess soil conservation practices for improving water quality of return flows from rill irrigation in the Yakima River Basin, Washington, by combining patch application of polyacrylamide (PAM) with an additional erosion control practice. A 2-year field study was conducted that combined PAM with (1) check dams, (2) surge irrigation, (3) surface drains, and (4) grass filter strips. The study was conducted at three sites: two vineyards (A and B) with silt loam soils at 1.2% slope and a cornfield with sandy loam soils at 0.2% slope. During irrigation events, water samples and flow records were taken at periodic intervals from each treatment to determine nutrient concentrations and loads (total nitrogen (TN), total Kjeldahl N (TKN), nitrate–N (NO 3–N), total phosphorus (TP), particulate P (PP), soluble phosphorus (SP), and sediment load (SL)). For all treatments and sites, TN and TP concentrations were compared to USEPA value concentrations in streams of the Xeric West for full support of aquatic life and drinking water standards. Results showed that TN exceeded the USEPA-reference condition of 0.36 mg TN/L in all samples, while 96% of the samples exceeded the USEPA-recommended TP concentration value of 0.1 mg/L. All samples showed NO 3–N concentrations below the USEPA drinking-water standard of 10 mg/L. The only nutrient component in irrigation runoff that was strongly related to SL was PP concentration ( r = 0.87). For TKN, significant concentration and load reduction between control and the other four erosion control practices ( P < 0.05) occurred only in vineyard A. As for PP, the four PAM integrated control practices showed statistically significant effects with respect to the PAM control in vineyard B only. Although PAM is an excellent practice to control soil erosion with widespread adoption, additional off-site treatment may be needed for nutrient concentrations in irrigation return flows to meet reference conditions that would fully support aquatic life.

Generating streamflow forecasts for the Yakima River Basin using large-scale climate predictors

Multifaceted demands on western water supply, such as irrigation and mandated biological flows, coupled with climate variability are increasing the importance of supply forecasting to water managers. In this study, we develop and examine the accuracy of a seasonal ensemble streamflow forecasting model for the Yakima River Basin. The model incorporates large-scale climate information, related to the Pacific North American (PNA) pattern, with the objective of increasing the skill of the forecasts for water managers and stakeholders in the basin. Our study has found that spring runoff in the Yakima Basin is strongly correlated (correlation significant at the 5% significance level) with two of the large-scale circulation patterns associated with the PNA pattern from the preceding fall and winter seasons. Incorporating such climate information into our forecasts allowed a longer lead-time (a season in advance) planning period for water managers and stakeholders from the current practice of an April 1st forecast. The ensemble nature of our streamflow forecasts provides continuous probability distributions that will help the decision maker to objectively quantify the associated risk with selected streamflow values.

Evaluating the Feasibility of Reestablishing a Coho Salmon Population in the Yakima River, Washington

AbstractHistorical returns of coho salmon Oncorhynchus kisutch to the Yakima River basin were estimated to range from 45,000 to 100,000 fish annually but declined to zero by the 1980s after decades of overexploitation of fishery, water, and habitat resources. In 1996, the Yakama Nation and cooperators initiated a project to determine the feasibility of reestablishing a naturally spawning coho salmon population in the Yakima River. The project explored the feasibility of successful coho salmon recolonization in the Yakima River by introducing stocks that had been reared in hatcheries for multiple generations. After 10–20 years of outplanting, we compared data for adult returns of known natural origin (i.e., returns from parents that spawned in the wild) and returns from hatchery releases. We found that fish of natural origin returned at a significantly larger size than those of hatchery origin. The mean egg mass and mean egg size of natural‐origin females were greater than those of hatchery‐origin females, but the differences were statistically significant for only one of three sample years. Natural‐origin adults returned 2–9 d later and spawned 5 d later than their hatchery‐origin counterparts. Preliminary indices of smolt‐to‐adult survival for natural‐origin fish were 3.5–17.0 times the survival indices of hatchery‐origin fish. The number of returns to the historical spawning habitats in upriver areas generally increased. Spawning surveys demonstrated the existence of robust and sustainable spawning aggregates in various locations in the basin. Hatchery releases from the local brood source (Yakima River returns) had significantly higher smolt‐to‐smolt survival than releases from out‐of‐basin (non‐Yakima River) hatchery broodstock, but some of these observed differences in survival may be partially attributable to differences in smolt size. We concluded that hatchery‐origin coho salmon with a legacy of as many as 10–30 generations of hatchery influence demonstrated an ability to reestablish themselves in the Yakima River (i.e, as a naturalized, nonnative population) after as few as 3–5 generations of outplanting in the wild.

Impacts of Early Stages of Salmon Supplementation and Reintroduction Programs on Three Trout Species

AbstractSalmon supplementation and reintroduction programs have the potential to negatively impact other valued fish taxa that are not the targets of enhancement (nontarget taxa (NTT)). Impacts of the supplementation of spring Chinook salmon Oncorhynchus tshawytscha and the reintroduction of coho salmon O. kisutch (hereafter supplementation) on populations of rainbow trout O. mykiss, steelhead (anadromous rainbow trout), cutthroat trout O. clarkii, and bull trout Salvelinus confluentus were evaluated after 5 years of stocking approximately 1 million yearling smolts in the upper Yakima River basin between 1999 and 2003. Field methods included backpack electrofishing and snorkeling in tributaries and drift‐boat electrofishing in the main stem. We used three sequential steps in our evaluation: (1) we determined whether spatial overlap occurred between supplemented fish and NTT; (2) if overlap occurred, we determined whether a change in abundance, size, or biomass occurred during supplementation; and (3) if a change occurred, we determined whether the change could be reasonably attributed to supplementation. Salmon rarely overlapped cutthroat trout or bull trout in tributaries, but some overlap with cutthroat trout occurred in relatively high elevations of the main stem and considerable overlap with rainbow trout occurred in tributaries and the main stem. Except in steelhead, the lower 90% confidence limit (CL) of abundance, size, and biomass was above the containment objective for NTT that overlapped significantly with salmon. We used rainbow trout as an analog for steelhead. The lower 90% CL of rainbow trout abundance and size in tributaries and the main stem and biomass in the main stem was below the containment objective for steelhead. However, comparisons of rainbow trout abundance, size, and biomass between tributaries and main‐stem sections with relatively high and low salmon abundances revealed that the change was probably not the result of supplementation (before–after control–impact paired site analysis: P &gt; 0.05). Our data indicate that early stages of salmon supplementation have not impacted trout species in the upper Yakima River basin beyond predetermined containment objectives.