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Objective: In a southcentral Alaska stream system, we conducted a study to evaluate the effect of trap type (galvanized and nylon coated), bait type (salmon roe cured with and without sodium sulfite), and soak times (1 h and 24 h) on captures of juvenile salmon using Gee‐style minnow traps. This was undertaken due to the limited research on this topic, aiming to determine how variations in methodology affected captures in juvenile salmon. Methods: We employed a three‐way fixed factorial design to sample 176 stream reaches (with a single trap in each each) from June 2021 to September 2021, capturing 296 Coho Salmon Oncorhynchus kisutch and 105 Chinook Salmon O. tshawytscha. Result: We found an estimated 78% decrease in captures of Coho Salmon when nylon‐coated traps were used instead of galvanized traps, and we found that trap type showed no effect on number of captures for Chinook Salmon. Additionally, we did not detect effects of bait type and soak time on the number of captures for either species. Not surprisingly, there was a positive relationship between Julian date and temperature with captures for both species. Additionally, for Coho Salmon, we found a quadratic relationship between water velocity and captures. Conclusion: Understanding and accounting for these factors will help researchers to maximize trapping efficiency, standardize protocols, and determine the extent to which results are comparable across studies employing different methods. Impact statementOur study examined how different trap materials, bait types, and soak times affect the capture of juvenile salmon. We found that using nylon‐coated traps decreased Coho Salmon by 78%, while trap type had no effect on Chinook Salmon. These findings help researchers optimize trapping methods, ensuring accurate and comparable results. [ABSTRACT FROM AUTHOR]

Objective: This study compares the probability of detecting juvenile Coho Salmon Oncorhynchus kisutch using both environmental DNA (eDNA) techniques and underwater visual count (UVC) surveys in northern California rivers. Here, UVC surveys commonly have detection probabilities (p) surpassing 0.90, providing an ideal setting to examine the performance of newer eDNA methods. We also evaluate the potential for using eDNA concentrations to predict the count of Coho Salmon within pool habitats. Methods: We conducted paired eDNA and UVC surveys in 96 pools across 25 stream reaches within the Smith River basin, California. Method-specific p and the effect of environmental covariates were estimated using multiscale occupancy modeling. We used generalized linear models to evaluate the relationship of fish counts to eDNA concentrations and habitat covariates. Result: The eDNA and UVC methods showed a high degree of agreement in detecting the presence of Coho Salmon within a pool (93% agreement) and survey reach (80% agreement). Detection probabilities for eDNA (peDNA) and for UVC (pUVC) were similar and high at median levels of pool residual depth and contributing basin area (peDNA = 91%, pUVC = 89%). Contributing basin area (a proxy for discharge) had a strong, negative effect that was more pronounced for peDNA than for pUVC (e.g., in the largest basins, peDNA = 34% whereas pUVC = 77%). We did not find eDNA concentrations to be a good predictor of Coho Salmon counts in small pools. Conclusion: This study demonstrates that eDNA methods yielded nearly identical results to UVC surveys in catchments <36 km2 and can provide a highly effective approach for determining the distribution of Coho Salmon. However, additional investigation is required before eDNA could be used to estimate relative abundance in small pools. [ABSTRACT FROM AUTHOR]

Objective: Hatcheries are used to help supplement populations of Pacific salmon Oncorhynchus spp. for conservation and fisheries purposes and to provide stewardship opportunities. In British Columbia, small community-run hatcheries typically focus on the latter and generally do not know the efficacy of their release approaches, unlike larger production hatcheries. Methods: We used acoustic telemetry to track the survival and behavior of 90 hatchery-reared Coho Salmon O. kisutch smolts, released from a community hatchery, through Burrard Inlet and into the Strait of Georgia. This is the first study to track Coho Salmon smolts released directly into a marine environment and one of very few studies to track them in an oceanic setting. Result: Smolt survival was lowest through the first 3 km of the migration at 37%, and the estimated cumulative survival to the final array (~20 km from release) was 10-23%. The presence of numerous predators in the region suggests that predation is a possible explanation for poor survival over the relatively short migration distance. Travel rates ranged from ~4 to 18 km/day, depending on the migration segment, which is slower than the marine migration of smolts from other species, likely increasing exposure to predators. However, we found potential evidence of "predator swamping," as survival estimates across migration segments were highest for the final of our three release groups and poorest for the first release group, with intergroup survival estimates increasing by 7-12% in the final three migration segments. Releasing smolts at high densities and at night, as our partner hatchery currently does, likely improves smolt survival. Conclusion: Our work demonstrates how acoustic telemetry can be used to examine hatchery practices and propose potential improvements. Saltwater readiness and the release location are factors that our results suggest may warrant future attention to potentially improve marine survival of Coho Salmon smolts. [ABSTRACT FROM AUTHOR]

Objective: In the western United States, juvenile salmon Oncorhynchus spp. and steelhead O. mykiss are especially vulnerable to streamflow depletion in the dry season. Releasing water from off‐channel storage into small streams is a novel restoration strategy to offset impacts from anthropogenic flow alteration on salmonid fishes. To date, no studies have evaluated the ecological effects of small‐scale flow augmentations. Here, we quantify the effects of one such augmentation project on habitat connectivity, water quality, invertebrate drift, and juvenile salmonid movement and survival. Methods: Our study took place in a northern California stream and included an unusually wet summer (2019) and a more typical dry summer (2020). We used categorical and time‐series analyses in a before–after, control–impact (BACI) design, along with capture–mark–recapture methods to evaluate the ecological impacts of a 13.9‐L/s flow augmentation. Result: We found that differences in ambient streamflows between the two years mediated the physical and ecological effects of the flow augmentation treatment. In the dry year, habitat connectivity and dissolved oxygen markedly increased at sites over 1.5 km downstream from the point of augmentation, whereas during the wet year, the effects on those variables were negligible. In both years, invertebrate drift marginally increased after augmentation. Interpool movement of wild juvenile steelhead and stocked Coho Salmon O. kisutch increased after augmentation during the dry summer but not during the wet summer. Flow augmentation increased the survival probability for salmonids, with a larger effect during the dry summer (24% higher survival for Coho Salmon and 20% higher survival for steelhead) than during the wet summer (no effect was observed for steelhead survival, and Coho Salmon survival increased by 11%). Conclusion: This study indicates that appropriately designed small‐scale flow augmentations can improve conditions for rearing salmonids in small streams, particularly during dry years. More broadly, it provides empirical evidence that efforts to restore summer streamflow in small, salmon‐bearing streams can yield significant ecological benefits. Impact statementThere is growing interest in using novel approaches to offset human‐caused impacts on freshwater ecosystems. One approach involves releasing water from off‐channel storage directly into small, flow‐impaired streams to benefit endangered fishes—especially during the driest times of the year. This study explores how one of these "flow augmentation" projects affects the habitat, prey, and survival of threatened salmon and steelhead in a small coastal California stream. [ABSTRACT FROM AUTHOR]

Run timing and spatial locations of spawning habitats are often used to identify stocks for conservation planning or management of salmonid fishes. Although complex stock structure is most common within large watersheds with diverse habitats, even small drainages can produce multiple co‐occurring spatially or temporally isolated populations or "stocks." This project sought to address the potential existence of stock structure of Coho Salmon Oncorhynchus kisutch in a small coastal watershed on Kodiak, Alaska that supports vital subsistence and recreational fisheries and is currently managed as a single stock. We radio‐tagged a total of 348 adult Coho Salmon upon freshwater entry into the Buskin River across three spawning seasons (2015–2017) and tracked in‐river movements to the final locations where mortality signals were recorded. We identified two primary spawning habitats within the system: main‐stem and lake tributaries, with 54% (range of 47% to 61%) of tagged fish with determined fates tracked to main‐stem river spawning areas and 46% (range 39% to 53%) presumably spawning in small tributaries of the 1‐km2 Buskin Lake at the headwater of the watershed. Despite distinct spatial differences in spawning locations, main‐stem and tributary spawners did not differ in migration timing into freshwater (difference in run timing of main‐stem versus tributary spawners = 1 d) nor body size (main‐stem mean body length, mideye to tail fork = 625 mm, tributary mean = 613 mm). Unexpectedly, we determined nearly 70% of all Coho Salmon spent at least some time in Buskin Lake, including 54% of main‐stem spawners, suggesting a potential role of Buskin Lake as an important staging habitat for premature migrating adult Coho Salmon who enter freshwater in advance of final maturation. We also identified areas consistently used for holding prior to spawning that could be used in spatial management planning and during times of necessary conservation to ensure integrity of the stock for the future. [ABSTRACT FROM AUTHOR]

Knowledge of population structure facilitates the effective management of species that are harvested in mixed‐stock fisheries. In this study, we analyzed genetic variation at 19 microsatellite loci for 14 populations of Coho Salmon Oncorhynchus kisutch in the Yukon River. We then used this data to estimate the stock composition of adults that were harvested in a lower river test fishery. The Coho Salmon populations in the Yukon River exhibited a high degree of geographically based genetic structure (GST = 0.078), with a strong genetic disjunction between the lower and upper river populations. Further substructure was observed among the upper river populations, which allowed for the estimation of stock composition to areas within this region. Analyses involving simulated and real mixtures indicated that this level of divergence can be used to apportion Coho Salmon to regions and areas accurately (95–100%). The stock composition estimates for the test fishery revealed that the spawning migration was evenly divided (50:50) between the lower and upper river populations. The upper river populations generally had earlier migration timing, comprising 66% of the mixture in the beginning and 33% at the end. The largest component of the upper river region was Tanana at 44%, followed by Nenana at 5%, and Porcupine at 1%. While escapement monitoring is essential for the management of Coho Salmon, it is limited by funding shortfalls. However, mixed‐stock analysis in conjunction with sonar enumeration can provide information on stock‐specific proportions, abundances, and migration timings that can increase our knowledge and ability to manage Coho Salmon populations in the Yukon River. [ABSTRACT FROM AUTHOR]

Projected intensification of drought as a result of climate change may reduce the capacity of streams to rear fish, exacerbating the challenge of recovering salmonid populations listed under the Endangered Species Act. Without management intervention, some stocks will likely go extinct as stream drying and fragmentation reduce juvenile survival to unsustainable levels. To offset drought‐related mortality, fish rescue programs have proliferated, whereby juvenile salmonids are captured and transferred to off‐site rearing facilities. However, the efficacy of this potential conservation tool remains poorly understood. We developed a life cycle model to examine the implications of fish rescue on the abundance of Coho Salmon Oncorhynchus kisutch across serial life stages. The simulation model examines scenarios with varying quantities of rescued fish, time in captivity, drought severity, and reduced smolt‐to‐adult return rates. Our results indicate that fish rescue can increase the abundance of adults and lower extinction risk, particularly for fish held in captivity for a full year. However, fish rescue can also decrease the abundance of adults and increase extinction risk if fish are held only for summer and there is limited winter habitat. We found that when fish rescue did increase returns, it functioned more like a stock enhancement program than a drought mitigation tool and it would likely lead to consecutive generations of captive rearing, which has been shown to have negative effects on fitness. We translated our model into an R Shiny application (https://shiny.wdfw‐fish.us/CohoPopulationDynamics/) that allows users to explore how fish rescue affects Coho Salmon population dynamics through customized parameterization of the model to represent different systems or different assumptions about the effects of fish rescue. [ABSTRACT FROM AUTHOR]

The utility of commercial salmonid Oncorhynchus spp. traps in the U.S. Pacific Northwest was recently revisited for the first time in decades to enable selective harvesting of hatchery‐origin salmonids while reducing mortality of Endangered Species Act (ESA)‐listed salmonids. Modifications to historical gear designs resulted in dramatic improvements in salmonid bycatch survival rates relative to conventional commercial gears in the lower Columbia River. Expanding upon this work, an experimental commercial fish trap was further modified to largely eliminate net contact, air exposure, handling, and crowding of fish. Studies were conducted from May to November 2019 in the lower Columbia River to estimate survival of bycatch and evaluate potential benefits from the modified passive capture design. Analyzed through two separate survival estimation techniques, the modified trap demonstrated no detectable effect on salmon release survival and a significant improvement over the previous prototype design. Estimated through a paired release–recapture methodology, the relative survival effect of catch and release compared to controls over a 400‐km migration was 1.017 (SE^ = 0.032) for adult Sockeye Salmon O. nerka. For adult Coho Salmon O. kisutch that were held captive for a 48‐h postrelease period, estimated survival (S) was 1.000 (lower 95% confidence limit: S ≥ 0.978). These results suggest that trap modifications can be made to significantly reduce bycatch mortality of ESA‐listed salmonids and provide increased opportunity for harvest of hatchery‐origin salmonids. [ABSTRACT FROM AUTHOR]

Accurate estimates of age composition are essential for fisheries management, but evaluation of protocols to estimate age data are rarely conducted. Herein, known‐age Pacific salmon Oncorhynchus spp. from six hatchery stocks were used to examine accuracy of multiple scale‐aging protocols and to assess how errors in age assignment may affect age composition estimated from scale data. Accuracy reached 1.0 for one stock of Coho Salmon Oncorhynchus kisutch, over 0.9 for three stocks of spring Chinook Salmon Oncorhynchus tshawytscha, and was no higher than 0.8 for two stocks of fall Chinook Salmon. For all hatchery stocks, accuracy increased and bias decreased when readers had auxiliary information about a fish's fork length and sex. Results suggest that a protocol that collects scales from above the lateral line, provides auxiliary information on fork length and sex, allows readers to exclude individuals for which age appears unclear, and uses an arbitrator to assign age when two initial readers disagree may produce the most accurate and unbiased age data from scales. This study highlights the importance of assessing patterns in age errors both qualitatively and quantitatively. A general pattern of overestimating age for younger age‐classes and underestimating age for older age‐classes was evident. This pattern in age errors could affect age composition estimates for adult Pacific salmon and other species with few (e.g., two to six) age‐classes. In addition, individual variation in demographic rates may affect individual patterns identified on scales; thus, for stocks with more extensive individual demographic variability, like fall Chinook Salmon stocks, accuracy may be lower and bias higher, resulting in less accurate estimates of age composition. [ABSTRACT FROM AUTHOR]

Hydraulic heterogeneity can strongly influence habitat selection by stream fishes. Velocity gradients created by channel roughness and flow obstructions may be particularly important for species that feed on drifting invertebrates, where maintaining focal points in low‐velocity microhabitats adjacent to faster water allows fish to scan a larger water volume for prey while minimizing swimming costs. However, these velocity gradients are rarely integrated into habitat suitability criteria used for defining instream flow requirements, which are generally based on mean column velocity measurements at the focal point location. It is also unclear how velocity gradient exploitation differs among sympatric drift‐feeding species. We measured the use of velocity gradients by two sympatric juvenile salmonids, Coho Salmon Oncorhynchus kisutch and steelhead O. mykiss, in a midorder cobble–boulder‐dominated river. We compared focal point velocities of fish to adjacent velocities within their foraging area and compared the magnitude of velocity and kinetic energy gradients between species. We then explored how lateral velocity gradients may bias instream flow assessments by deriving two sets of velocity habitat suitability curves (HSCs): conventional HSCs using average water column velocities measured at focal point locations and spatially averaged HSCs incorporating adjacent velocities (four body lengths from focal points). These contrasting HSCs were then used as input into the physical habitat simulation model to predict the influence of flow on habitat availability. Both species often used focal velocities that were lower than adjacent points, but the magnitude of these velocity gradients was higher for steelhead, consistent with known differences in foraging behavior, habitat selection, and physiology. Incorporating adjacent velocities into HSCs resulted in a ~40% (steelhead) and ~10% (Coho Salmon) increase in flows predicted to optimize habitat availability. Thus, small‐scale heterogeneity in velocity used by drift‐feeding fish can lead to large biases in flow assessments. [ABSTRACT FROM AUTHOR]

This study examined salmonid assemblages upstream of a culvert connecting the Mirror Lake Complex with the lower Columbia River before and after the culvert was modified to improve habitat connectivity and fish passage. Initially the culvert limited water flow between the Columbia River and the Mirror Lake Complex. The outlet and interior of the culvert were reconfigured to create a more "natural" and suitable passageway for salmonids through the removal of riprap and the strategic placement of boulders, cobbles, gravels, baffles, and weirs. Prior to the culvert modification, three sites were sampled monthly between April and August of 2008, 5.0 and 0.5 km upstream of the culvert and immediately downstream of the culvert. After the culvert modification, the same sites were sampled from 2009 to 2012, with two additional sites added in 2010. Sites near the culvert supported Chinook Salmon Oncorhynchus tshawytscha, Coho Salmon O. kisutch, and Chum Salmon O. keta, while sites further from the culvert supported unmarked Coho Salmon and Rainbow Trout O. mykiss, steelhead (anadromous Rainbow Trout), and Cutthroat Trout O. clarkii. Clear trends in salmonid occurrence were not observed, although densities of Chinook Salmon tended to be higher in years postmodification than before modification. Culvert modifications should focus on alleviating site‐specific fish passage conditions to result in substantial changes to habitat connectivity. [ABSTRACT FROM AUTHOR]

Abstract: Recent genetic studies, meta‐analyses, and retrospective analyses have documented reduced productivity of wild salmon and steelhead Oncorhynchus mykiss that interbreed with hatchery‐reared fish, raising concerns about the long‐term viability and recovery of at‐risk stocks. In 2007, the Oregon Department of Fish and Wildlife discontinued a Coho Salmon Oncorhynchus kisutch hatchery program at the Salmon River to support recovery of a wild Coho Salmon population in the Oregon Coast Evolutionarily Significant Unit. This decision constituted a unique management “experiment,” allowing for direct measurement of the wild population's response after the discontinuation of a decades‐old hatchery program. We used a before–after, control–impact design to examine whether selected viability metrics of the naturally produced population in the Salmon River changed after the hatchery program ended. We compared metrics for the 2006–2013 broods, representing periods after the hatchery program ended, to those for the 1995–2005 broods, when the hatchery program was still releasing 200,000 smolts annually. We also examined neighboring populations during similar time periods to account for changes or variation due to other factors. Although hatchery‐origin spawners previously had accounted for most of the adults returning to the Salmon River, the naturally produced population did not collapse, and two viability metrics improved significantly after the Coho Salmon hatchery program ended: (1) adult abundance increased and (2) spawn timing expanded and moved closer to the historical timing. Recruits‐to‐spawner ratios in the Salmon River, although initially low, are now approximately equal to those of neighboring populations. The results indicate that hatchery closure can be an effective strategy to promote wild population recovery. However, considerable variability in population trends and environmental conditions will require continued monitoring to verify the long‐term resilience and viability of the wild population. [ABSTRACT FROM AUTHOR]

Diel shifts in habitat selection of newly emerged steelheadOncorhynchus mykissand Coho SalmonO. kisutchfry were investigated in three northern California coastal watersheds. Steelhead and Coho Salmon fry occupied shallow water near stream margins during both day and night; however, the proportion of fry within 0.5 m of the stream margin increased from 6% during the day to 44% at night. Similarly, the proportion of fry in 10 cm of water or less increased from 26% during the day to 76% at night. Reductions in depth and distance to stream margins were significant at all sites, suggesting that these behaviors are common attributes for steelhead and Coho Salmon fry in this region. These results also suggest that newly emerged fry are potentially vulnerable to becoming stranded due to reductions in stream stage and water surface area, particularly at night. Although our observations were undertaken to better understand the risks to salmonids from vineyard water use for frost protection, the results have implications for any anthropogenic streamflow changes during the spring season. Received September 6, 2016; accepted June 3, 2017Published online August 9, 2017 [ABSTRACT FROM AUTHOR]

The influences of large wood on Pacific salmon are well-studied, but such studies on nonsalmonid species such as lampreys are uncommon. To address this need, we evaluated the potential effects of large wood on larval lampreys (Pacific LampreyEntosphenus tridentatusand potentially Western Brook LampreyLampetra richardsoni) as well as on juvenile Coho SalmonOncorhynchus kisutchin a small, coastal, Oregon stream. Our objectives were to (1) identify instream habitat characteristics associated with the presence of larval lampreys and abundance of juvenile Coho Salmon and (2) evaluate how these characteristics were associated with instream wood. To address habitat use, we quantified presence of larval lampreys in 92 pools and abundance of juvenile Coho Salmon in 44 pools during summer low flows. We focused on a study reach where large wood was introduced into the stream between 2008 and 2009. Results indicated that presence of larval lampreys was significantly associated with the availability of fine sediment and deeper substrate. The abundance of juvenile Coho Salmon (fish per pool) was strongly associated with pool surface area and to a weaker extent with the proportion of cobble and boulder substrates in pools. Pools with wood, regardless of whether they were formed by wood, had significantly greater coverage of fine sediment, deeper substrate, and greater pool surface area. Taken together, these results suggest that instream wood can provide habitat associated with the presence of larval lampreys and greater abundance of juvenile Coho Salmon. Received September 11, 2016; accepted March 25, 2017 Published online May 31, 2017 [ABSTRACT FROM PUBLISHER]

Instream flow models link a physical habitat model that predicts flow-related changes in hydraulics to a biological model that predicts the response of fish to altered velocity and depth. Habitat suitability curves (HSCs) based on frequency of habitat use (fish occurrence relative to available habitat) remain the most widely used biological models in habitat simulations. However, in some contexts fish density may be a poor indicator of habitat quality, leading to biased predictions of optimal flow. We explore the use of bioenergetics to derive mechanistic HSCs based on the fundamental energetics of habitat use. Using flow-related changes in production of Coho SalmonOncorhynchus kisutchsmolt as reference data to evaluate model predictions, we found that bioenergetic-based HSCs matched the validation data better than frequency-based HSCs, which systematically underestimated optimal flows. However, biases remained using bioenergetic HSCs, suggesting that habitat suitability may not be independent of discharge as is often assumed. Declining invertebrate drift concentration, increasing temperature, and density dependence of growth at low flows are potential mechanisms of flow-related declines in habitat suitability; measuring these effects and incorporating them into flow models is an important step in further improving model predictions, particularly at low flows. Received December 3, 2015; accepted May 11, 2016 [ABSTRACT FROM AUTHOR]

The immobilization of fish during handling is crucial in avoiding injury to fish and is thought to reduce handling stress. Chemical sedatives have been a primary choice for fish immobilization. However, most chemical sedatives accumulate in tissues, and often food fishes must be held until accumulations degrade to levels safe for human consumption. Historically, there have been few options for nonchemical sedation. Carbon dioxide (CO2) has been widely used for decades as a sedative, and while it does not require a degradation period, it does have drawbacks. The use of electronarcosis is another nonchemical option that does not require degradation time. However, little is known about the latent and delayed effects on migration rates of adult salmonids that have been immobilized with electricity. We compared the travel times of adult Chinook SalmonOncorhynchus tshawytschaand Coho SalmonO. kisutchthrough a fishway at river kilometer (rkm) 4, and to rkm 16 and rkm 32 after being immobilized with either CO2or electronarcosis. Travel times of fish treated with either CO2or electronarcosis were similar within species. Because of the nearly instantaneous induction of and recovery from electronarcosis, we recommend it as an alternative to CO2for handling large adult salmonids. Received February 17, 2015; accepted June 27, 2015 [ABSTRACT FROM AUTHOR]

Like many rivers and streams in forests of the Pacific Northwest, California north coast rivers and streams have been depleted of downed wood through timber harvest and direct wood removal. Due to the important role of wood in creating and maintaining salmonid habitat, wood augmentation has become a common element of stream restoration. Restoration efforts in North America often focus on building anchored, engineered wood structures at the site scale; however, these projects can fail to meet restoration goals at the watershed scale, do not closely mimic natural wood loading processes or dynamics, and can be expensive to implement. For critically imperiled populations of Coho SalmonOncorhynchus kisutchin California, there is a strong impetus to achieve as much habitat restoration as possible in priority watersheds in the shortest time and with limited resources, so cost-efficient techniques are necessary. In this multi-site project, we investigated unanchored techniques for wood loading to evaluate cost and contribution to salmonid habitat in Mendocino County, California. Over a period of 6 years, 72.4 km of stream were treated with 1,973 pieces of strategically placed wood. We found that unanchored wood loading techniques were much less costly than commonly used anchored techniques, reliably improved habitat, and retained wood at high rates (mean = 92%) in small- to moderate-sized streams, at least over the short term (<6 years). The average cost of design and construction for the unanchored projects was US$259 per log, equivalent to 22% of the cost associated with the anchored wood augmentation methods examined here. Our results suggest that this unanchored wood loading approach has the potential to increase the pace and scale at which wood augmentation projects are implemented in the Pacific Northwest and beyond. Received January 22, 2014; accepted June 25, 2014 [ABSTRACT FROM AUTHOR]

The process of salmon colonization in the upper Cedar River and Rock Creek, Washington, following the installation of a fish ladder at Landsburg Diversion Dam in 2003, offered an opportunity to measure the effects of interspecific interactions on the dynamics of resident fish populations. Rapid recolonization by Coho SalmonOncorhynchus kisutchprovided a natural experiment to determine the influence of Coho Salmon densities on the growth, movement, and survival of resident Coastal Cutthroat TroutO. clarkii clarkiirelative to other abiotic and biotic factors such as habitat quality, environmental conditions, and conspecific density. During 14 seasonal sampling events from 2005 to 2009, we PIT-tagged 1,851 and recaptured 394 Cutthroat Trout in Rock Creek, collected habitat data, enumerated fish populations, and monitored fish movements with PIT tag antenna arrays. Trout growth varied significantly among seasons and was greatest during spring and early summer. Mean juvenile Coho Salmon density in summer and fall increased eightfold from 0.04 to 0.32 and from 0.08 to 0.68 fish/m2, respectively, approaching levels seen in established populations, but did not explain variation in trout growth, movement, or survival. Summer growth of trout parr and fry were both negatively correlated with the density of conspecifics but were positively correlated with total salmonid density. Additionally, trout parr growth was positively correlated with stream discharge, whereas trout fry growth was negatively correlated with initial size and declined during the course of the study. However, abiotic and biotic explanatory variables accounted for little of the variation in trout growth, movement, and survival, suggesting that a great deal of individual variation exists. Overall, trout were largely unaffected by Coho Salmon colonists despite large increases in juvenile Coho Salmon density, though this may change if salmon populations continue to grow. Received October 18, 2013; accepted May 5, 2014 [ABSTRACT FROM AUTHOR]

Partial migration, the behavior pattern in which a portion of a population migrates while others do not, is a widespread phenomenon with ecological and evolutionary consequences. Most Coho SalmonOncorhynchus kisutchfrom Puget Sound, Washington, migrate to feed over the continental shelf or offshore in the North Pacific Ocean, but some remain in the semiestuarine waters of Puget Sound and are termed residents. The objective of this study was to determine which of several factors influenced residency in Puget Sound Coho Salmon. Coded wire tag recovery data showed that resident Coho Salmon were smaller than their migratory counterparts, and we used this size difference and the relative catch patterns along the coast and in Puget Sound to classify Coho Salmon caught in Puget Sound between November and August as residents. We then analyzed the effects of location of origin, day of release, weight at release, hatchery or wild rearing, and year on the proportion of fish caught as residents. Based on 268 release groups between 1975 and 1992, we classified 3.4% of fish recovered as residents, 61.3% as migrants, and 35.3% as ambiguous because they were recovered in Puget Sound in September and October, when residents and migrants were mixed. The proportion of residents varied as a function of year, basin, and day of the year. Releases into south Puget Sound produced the highest proportion of residents, and resident fish tended to be recovered in the basin where they entered Puget Sound. While other factors may influence residency in Coho Salmon, the effects of day of release and location of origin may be useful for management of these populations, as the tendency to remain in Puget Sound or migrate to the coast affects the fisheries in which the fish are taken and their growth rate, their uptake of contaminants, and their role in food webs. Received August 15, 2013; accepted February 3, 2014 [ABSTRACT FROM AUTHOR]

Coho salmon Oncorhynchus kisutch are a threatened species in California. In the Shasta River, they may be caught in an ecological trap that is exacerbating their decline. Adults appear to have equal preferences for spawning habitat that reduces the survival of their young and that of apparently similar quality where survival would be more likely. The primary cause of juvenile mortality is water withdrawals, which degrade summer water quality and create barriers to movement to habitats with more suitable rearing conditions. The situation has been exacerbated by the addition of gravel to support spawning fall-run Chinook salmon O. tshawytscha, creating habitat that is also attractive to spawning coho salmon in locations where juvenile coho salmon survival will be extremely low. The Shasta River acts as a conceptual model of how habitat degradation and ecologically naive restoration actions may combine to create severe ecological traps for nontarget species. Received March 10, 2011; accepted October 11, 2011 [ABSTRACT FROM AUTHOR]

A simultaneous-equation equilibrium model of international salmonid markets is used to examine the combined effect of variability in the landings of Alaska's sockeye salmon Oncorhynchus nerka and increases in the production of Chile's Atlantic salmon Salmo salar, coho salmon O. kisutch, and rainbow trout O. mykiss on Alaska's sockeye salmon exvessel prices and revenues. While Atlantic salmon, coho salmon, and rainbow trout from Chile and sockeye salmon from Alaska are not identical commodities, they compete in many of the same domestic and international markets, and Alaska's earnings in those markets have declined as Chile's production has increased. Although Alaska's average annual harvests have remained nearly constant, Alaska's production is now a small percentage of the total salmonid production in a world that eats significantly more salmonids than it did 25 years ago. Nevertheless, our model indicates that sockeye salmon prices continue to be sensitive to interannual variations in the quantity of sockeye salmon harvested in Alaska and to changes in the quantity of Atlantic salmon, coho salmon, and rainbow trout produced in Chile. However, the model indicates that exvessel revenues are less sensitive than exvessel prices and that Alaska's recent levels of sockeye salmon landings have been near the maximum of the total exvessel revenue curve. In addition, the model suggests that because Alaska's share of the production of high-value salmon (Chinook, coho, and sockeye salmon) has declined, exvessel prices for sockeye salmon are now less sensitive to changes in Chilean production of Atlantic salmon, coho salmon, and marine-reared rainbow trout. The implication of these findings is that, under current market conditions, exvessel revenues from Alaska's sockeye salmon fisheries can be maximized by maintaining catches at or near historic levels and that exvessel prices are unlikely to continue to decline as rapidly as they did in the 1990s. [ABSTRACT FROM AUTHOR]

Calculation of in-season marine survival rate forecasts for coho salmon Oncorhynchus kisutch can provide valuable support for in-season harvest management decisions because annual variability in marine survival accounts for a large proportion of total recruitment variability. We present a new forecasting model that utilizes coded wire tag (CWT) recovery information from early occurring fisheries to provide in-season marine survival forecasts that are timely enough to inform harvest management decisions for subsequent fisheries. We evaluate performance of the CWT model by using retrospective analyses on four coho salmon indicator stocks from northern British Columbia, Canada. For each stock, model selection analysis was used to identify which of three time-varying fishery catchability models used within the CWT model maximized forecasting performance. A Bayesian approach to parameter estimation was then applied to the best CWT model to generate probabilistic forecasts of marine survival rate for six consecutive weeks of in-season forecasting in each year. Although forecasted posterior distributions were wide in some cases, the posterior mode tracked marine survival relatively well in comparison with postseason marine survival estimates based on recoveries from all fisheries and the spawning grounds. Average percent forecast biases based on posterior modes were -1, -4, 19, and 57% for the four indicator stocks in the final week of forecasting. The lower tails of the posterior distributions were well defined, which is most relevant to identifying years of conservation concern due to extremely low marine survival. We conclude that timely in-season recovery and analysis of CWT information could improve the level of information available to inform in-season harvest management decisions. [ABSTRACT FROM AUTHOR]

Protocols to assess stream channel response to disturbances often focus on physical aspects of the stream at the reach scale without measurements of fish populations. In this study, estimates of juvenile salmon abundance in 511 habitat units within 25 reaches of 12 streams were made over 4 years and juxtaposed with measurements of physical habitat at the habitat unit, reach, and watershed scales. Fish ranged in size from about 50 to 160 mm fork length. The amount of variation among densities differed by species and geographic scale. For most species, the habitat unit scale accounted for the most variation. Relationships between salmon density and measurements at the habitat unit scale varied. At the reach scale, we observed a negative relationship between abundance of coho salmon Oncorhynchus kisutch parr and number of pools. A positive relationship appeared between coho salmon parr and large wood. At the watershed scale, a positive relationship was observed between coho salmon parr and valley morphology. Valley morphology also entered the model for cutthroat trout O. clarkii. Differences in salmonid densities observed between northern and southern watersheds were attributed to differences in landforms, geology, and soils among islands in southeast Alaska. Simple habitat measures, such as pool counts, were not good predictors of fish abundance. However, geomorphic measures from multiple scales that are accompanied by estimates of fish abundance can provide managers with an integrated picture of watershed productivity and a better means to evaluate features that influence productivity. [ABSTRACT FROM AUTHOR]

We examined three types of models for preseason forecasting of the abundance of Queets River coho salmon Oncorhynchus kisutch: (1) a simple model in which estimates of smolt production are multiplied by projected marine survival rates, (2) a Ricker spawner-recruitment model, and (3) a regression model relating log-transformed adult recruitment to smolt production. Each type of model was formulated with and without environmental variables that influence production and survival. We attempted to use a nonparametric generalized additive model (GAM) to guide the selection of the environmental variables and the form of the regression model. The GAM model was derived through a stepwise selection strategy based on the Akaike information criterion. Parametric approximate models were developed for each selected GAM model, and their performance was compared with postseason estimates of abundance using three criteria: the mean absolute percentage error, the largest absolute percentage error, and the probability of being included in the 90% prediction interval. This paper shows that the GAM approach is useful in constructing forecasting models by identifying promising relationships with predictor variables and improving abundance forecasts through the incorporation of environmental variables. [ABSTRACT FROM AUTHOR]

Numerous artificial side channels have been constructed in British Columbia and the Pacific Northwest to compensate for habitat loss from floodplain development. We reviewed data from published studies on natural and restored side channel habitats to determine how design features influence productive capacity for juvenile coho salmon Oncorhynchus kisutch. Average density and biomass of coho salmon parr were significantly higher in stream-type side channels (3.4 parr/m² and 8.01 g/m², respectively) than in pond-type side channels (0.8 parr/m² and 2.37 g/m²). Although total parr biomass was three times higher in stream-type side channels, average parr weight was 47% lower, suggesting greater density-dependent limitation of growth from higher recruitment of juveniles to stream-type habitats. Parr abundance declined from late summer to early spring in both side channel types but appeared to decrease more quickly in stream-type side channels, suggesting greater self-thinning in stream-type habitat from mortality or immigration to slower pond or main-stem habitat as fish sought lower velocities for overwintering. Fish density in a single off-channel complex that contained both stream and pond habitats (fish were able to move between habitats) was also higher in stream habitats, although fish were significantly larger in pond habitats than in stream habitats. Parr density in stream-type side channels was constant with increasing channel size, whereas density in pond-type side channels was a decreasing function of side channel area. Smolt production data were more limited and variable, and production was not significantly different between stream- and pond-type side channels. Smolt density (smolts produced/m² of channel habitat) was also a decreasing function of total side channel area, indicating that the optimal side channel habitat size (or pond size within a side channel complex) was below 5,000-10,000 m². Side channels that incorporate a diversity of flowing- and standing-water areas are most likely to provide the variety of habitats (i.e., spawning, summer rearing, and overwintering) required by salmonids to complete their life cycle. [ABSTRACT FROM AUTHOR]

The placement of log and boulder structures in streams is a common and often effective technique for improving juvenile salmonid rearing habitat and increasing fish densities. Less frequently examined has been the use of these structures by adult salmonids. In 2004, spawner densities and redd counts of coho salmon Oncorhynchus kisutch in seven Oregon streams were compared between 10 reach pairs: reaches with artificially placed boulder weir structures (treatment) and reaches without weirs (control). In addition, based on annual spawner survey data collected from 2001 to 2005, redd density of steelhead O. mykiss and spawner and redd densities of coho salmon were examined to assess differences among main-stem reaches with boulder weirs, main-stem reaches without weirs, and tributary reaches without weirs throughout one basin (West Fork of the Smith River [WFS]). Numbers of coho salmon spawners and peak redd counts were significantly higher (P ≤ 0.05) in treatment reaches than in control reaches in the first study. In contrast, no differences existed in coho salmon spawner counts or steelhead redd counts among reaches within WFS. Coho salmon redd densities differed significantly among the three reach types in WFS; redd densities in tributary reaches were higher than those in main-stem reaches either with or without boulder weirs. Both spawner density and redd density were positively correlated with percent gravel. Results from these two related studies suggest that the placement of boulder weirs in bedrock channels leads to localized increases in spawner abundance, although other factors (e.g., amount of spawning area or gravel) appear to influence coho salmon and steelhead spawner abundance. and redd construction at a watershed scale. This also suggests that gravel sources are an important factor to consider when placing boulder weirs or other instream structures designed to improve spawning habitat. [ABSTRACT FROM AUTHOR]

We assessed the relative importance of various factors contributing to spawning site use by a population of threatened coho salmon Oncorhynchus kisutch in Freshwater Creek, California, and created a predictive model of spawning habitat selection based on logistic regression analysis. We excluded sampling sites that previous studies had established as unsuitable on the basis of depth and substrate criteria and asked why fish chose particular locations and not others in seemingly suitable habitat. We evaluated surface water velocity, depth, substrate size composition, gravel inflow rates, vertical hydraulic gradient, geomorphic channel units, hyporheic water physicochemistry, cover, and proximity to other redds not in sampling sites during the 2004-2005 spawning season. In univariate comparisons with unused sites, coho salmon selected sites with a smaller median particle diameter, a larger percentage of gravel-pebble substrate, and higher gravel inflow rates. Based on multivariate logistic regression, the probability of a site's being used for spawning was best modeled as a positive function of the gravel-pebble fraction of the substrate, location at a pool or run tail, and the presence of existing redds in close proximity to the site. This model explained 38% of the variation in the data and was a better predictor of spawning habitat use than a more traditional model based on depth, velocity, and substrate. Our results highlight the potential importance of social behavior in contributing to habitat selection by spawning salmonids. [ABSTRACT FROM AUTHOR]

Estimating the stock proportions of mixed-stock fishery samples by means of genetic stock identification has played an important role in the management of salmon fisheries. In addition, stock identification of individual fish has applications for population studies, forensic cases, and management issues. We examined 11 microsatellite DNA loci in 84 populations of coho salmon Oncorhynchus kisutch sampled at 78 locations from southern British Columbia to northern California to construct a database of microsatellite allele frequencies. We then evaluated the applicability of the database for estimating stock proportions in a mixed fishery and assigning individuals to their regions of origin. The loci were highly polymorphic: observed heterozygosity ranged from 0.754 to 0.943. Using genetic distance calculations, we identified six major geographic regions and 15 smaller subregions into which the populations grouped. Computer simulations and a sample of 143 coho salmon with known origins showed that the database was sufficient to make accurate stock proportion estimates to the 15 subregions. For the sample of fish with known origins, individual assignments to region of origin were 82.5% accurate for all samples and 97.8% accurate for those where P was greater than 0.95. We used the database to estimate stock proportions and densities of 2,344 coho salmon sampled over eight summers in a juvenile marine ecology study conducted off the coasts of Washington and Oregon. Columbia River juveniles were caught at higher densities than coastal fish throughout the summer. Fish from Columbia River and coastal sources were captured both north and south of their points of sea entry in early summer and at higher densities than in late summer. September catch of Columbia River juveniles was correlated with adult abundance in the following year, indicating that year-class strength for this stock is largely set during the first summer in the ocean. [ABSTRACT FROM AUTHOR]

Historical 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-smoh 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. [ABSTRACT FROM AUTHOR]

Salmon 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 > 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. [ABSTRACT FROM AUTHOR]

Brook trout Salvelinus fontinalis, Atlantic salmon Salmo salar, coho salmon Oncorhynchus kisutch, and yellow perch Perca flavescens fed calcein for 5 d showed characteristic calcein scale marks 7-10 d postmarking. In fish fed 0.75 or 1.25 g of calcein per kilogram of feed, the percentage of fish that exhibited a calcein mark was 100% in brook trout, 93-98% in Atlantic salmon, 60% in yellow perch, and 0% in coho salmon. However, when coho salmon were fed 5.25 g calcein/kg feed, 100% marking was observed 7-10 d postmarking. Brook trout were successfully marked twice with distinct bands when fed calcein 5 months apart. Brook trout scale pixel luminosity increased as dietary calcein increased in experiment 2. For the second calcein mark, scale pixel luminosity from brook trout fed 1.25 g calcein/kg feed was numerically higher (P < 0.08) than scales from fish fed 0.75 g calcein/kg feed. Mean pixel luminosity of calcein-marked Atlantic salmon scales was 57.7 for fish fed 0.75 g calcein/kg feed and 55.2 for fish fed 1.25 g calcein/kg feed. Although feed acceptance presented a problem in yellow perch, these experiments provide evidence that dietary calcein is a viable tool for marking fish for stock identification. [ABSTRACT FROM AUTHOR]

Strobe lights effectively reduced fish entrainment into the large locks at the Hiram M. Chittenden Locks Project in Seattle, Washington. The anadromous salmonids of the Lake Washington system, Chinook salmon Oncorhynchus tshawytscha, coho salmon O. kisutch, sockeye salmon O. nerka, and steelhead O. mykiss, must pass through these locks en route to the Pacific Ocean. Of the available downstream passage routes, use of the large lock-filling culverts is considered the most harmful to fish because of potential entrainment contact with the barnacle-lined culvert walls. We evaluated the effectiveness of strobe lights for displacing fish from in front of the culverts and for reducing entrainment during large lock fills. From 3 May to 14 June 2002, we used split-beam hydroacoustics to estimate the number of fish entrained during paired light-on-light-off treatments. Results indicated that strobe lights significantly reduced (75%) entrainment, an estimated 1,427 fish being entrained during lights-off treatments versus 350 during lights-on. Effectiveness was also supported by t-tests on individual range strata in front of the culvert entrances: 1-m strata from the floor to 4 m above the floor indicated significant reduction in number of entrained fish during the lights-on treatments. Using strobe lights for reducing culvert entrainment probably increases juvenile salmonid survival through the locks. [ABSTRACT FROM AUTHOR]

Bioenergetic models frequently rely on published values or models for estimating the energy density of fish, principally because of the cost and effort of obtaining direct measurements. In this study, we developed empirical models of energy density for free-ranging juvenile coho salmon Oncorhynchus kisutch and Chinook salmon O. tshawytscha sampled at sea from the west coast of Oregon to Kodiak Island, Alaska, and we evaluated the accuracy of published energy density models commonly used for these species. Our analyses showed that the energy density of juvenile coho and Chinook salmon was strongly correlated to percent dry weight and proximate constituents (especially lipid and, to a lesser extent, protein concentrations) but poorly correlated to body size and condition factor. Percent dry weight of whole fish was the single best predictor of energy density for both species, accounting for more than 90% of the variance in energy density. We also found that percent dry weight in the muscle tissue accounted for 65% of the variance in energy density. Changes in energy density mainly reflected changes in lipid composition. These results indicate that accurate estimates of energy density could be obtained at low effort and cost for juvenile coho and Chinook salmon simply by determining the water contents in whole-fish or muscle samples. Published models overestimate the energy density of juvenile coho and Chinook salmon collected from the Pacific Ocean. This may result from the extrapolation of the models to different size-classes, life stages, or habitats. More caution is needed when models are extrapolated to conditions beyond those that were used for their development. [ABSTRACT FROM AUTHOR]

We investigated whether sand seals form in the upper egg pocket of salmonid redds and improve egg survival in a sediment-impacted coastal stream in northern California. Sand seals can potentially reduce infiltration of detrimental finer sand and silt into the lower egg pocket. We predicted sand seals would form when the redds were exposed to streamflows high enough to entrain coarse sand and form seals. Using artificial redds of coho salmon Oncorhynchus kisutch, we conducted sediment analyses of the upper and lower egg pockets and found that protective sand seals formed in redds when discharge was two or more times the flow that entrains the median particle size of the streambed. When the coarse sand in the upper egg pocket was incorporated into a two-stage model that predicted survival to hatching and emergence, it greatly improved predictions in years with higher flows in both natural and artificial redds. However, the sand seals provided little protection when suspended sediment flux was high from logging or road construction. We built the model used for these predictions with data from artificial redds and applied it to natural redds during 6 years of different flow regimes. Predictor variables included cumulative flow above the entrainment flow, peak discharge, coarse sand in the upper egg pocket, fine sediment in riffle gravel, coarse sand in the upper and entire egg pocket, suspended sediment flux, and presence of predaceous worms. The model explained 67% of the variance in egg survival to emergence in coho salmon natural redds. We suggest that managers consider the complex interactions of streamflow, sediment transport, formation of sand seals, and fine-sediment infiltration when estimating salmonid reproductive success in sediment-impacted streams. [ABSTRACT FROM AUTHOR]

The use of beaver Castor canadensis ponds by juvenile coho salmon Oncorhynchus kisutch and other fishes has been well established. However, the population- level effects on coho salmon resulting from the widespread removal of millions of beaver and their dams from Pacific Coast watersheds have not been examined. We assessed the current and historic distributions of beaver ponds and other coho salmon rearing habitat in the Stillaguamish River, a 1,771-km² drainage basin in Washington and found that the greatest reduction in coho salmon smolt production capacity originated from the extensive loss of beaver ponds. We estimated the current summer smolt production potential (SPP) to be 965,000 smolts, compared with a historic summer SPP of 2.5 million smolts. Overall, current summer habitat capacity was reduced by 61% compared with historic levels, most of the reduction resulting from the loss of beaver ponds. Current summer SPP from beaver ponds and sloughs was reduced by 89% and 68%, respectively, compared with historic SPP. A more dramatic reduction in winter habitat capacity was found; the current winter SPP was estimated at 971,000 smolts, compared with a historic winter SPP of 7.1 million smolts. In terms of winter habitat capacity, we estimated a 94% reduction in beaver pond SPP, a 68% loss in SPP of sloughs, a 9% loss in SPP of tributary habitat, and an overall SPP reduction of 86%. Most of the overall reduction resulted from the loss of beaver ponds. Our analysis suggests that summer habitat historically limited smolt production capacity, whereas both summer and winter habitats currently exert equal limits on production. Watershed-scale restoration activities designed to increase coho salmon production should emphasize the creation of ponds and other slow-water environments; increasing beaver populations may be a simple and effective means of creating slow-water habitat. [ABSTRACT FROM AUTHOR]

We observed wild salmonid fry at sites downstream (treatment) and upstream (control) from experimental releases of hatchery-reared Chinook salmon Oncorhynchus tshawytscha smolts and coho salmon O. kisutch fry in two streams to estimate the effects of hatchery releases on the density, group size, microhabitat use, and size of wild fish. Most hatchery-reared Chinook salmon smolts that were released left treatment sites within a few days; hatchery-reared coho salmon fry remained at treatment sites for at least several weeks. We found limited evidence to suggest that the release of hatchery-reared Chinook salmon smolts or coho salmon fry caused consistent, significant effects on the density, group size, microhabitat use, or size of wild coho salmon fry in the two streams. We observed significant decreases in the densities of wild coho salmon and trout fry (steelhead [anadromous rainbow trout] O. mykiss and cutthroat trout O. clarki combined) after hatchery-reared Chinook salmon were released, but they did not occur when large numbers of hatchery fish were present at treatment sites. We observed an increase in the group size of wild coho salmon in one stream when Chinook salmon were released, but not in the other stream. We observed few changes in microhabitat use by wild coho salmon fry associated with the release of hatchery-reared fish; most changes were observed in only a single stream or occurred after only some of the releases. The lengths and weights of wild coho salmon fry over the sampling season were not significantly different between treatment and control sites in one study stream. These results suggest that small-scale releases of hatchery-reared Chinook or coho salmon have few significant ecological effects on wild salmonid fry in small, coastal Washington streams, particularly when wild fry occur at low densities. [ABSTRACT FROM AUTHOR]