Spring Chinook Salmon Oncorhynchus Tshawytscha Research Articles

Comparing standard‐ and reduced‐size passive integrated transponder (PIT) tags for monitoring juvenile wild spring Chinook Salmon

AbstractObjectivesAnnual migration monitoring can help to discern patterns and environmental factors that impact growth, survival, and movement timing in small fish. Mark–recapture methods form the basis for such monitoring, and the standard 12‐mm passive integrated transponder (PIT) tag has emerged as an essential tool for studies of juvenile salmonids. A smaller, 9‐mm PIT tag now provides the potential to conduct mark–recapture studies on smaller fish. We evaluated relative performance of the 9‐mm tag, which is similar in design to its 12‐mm predecessor.MethodsFor this comparison, we tagged and released approximately 8400 wild spring Chinook Salmon Oncorhynchus tshawytscha parr in Valley Creek, Idaho, from 2011 to 2013. Tag‐size cohorts were of similar average body size and were tagged in equal numbers. We estimated survival and detection probability for each cohort over two river segments.ResultsIn both segments, survival varied among years, but we observed no significant differences between tag‐size groups. At Valley Creek, average detection rates of fish with 9‐mm tags were a little less than one‐half the rates of fish with 12‐mm tags and were significantly lower in all 3 years. At Lower Granite Dam, detection rates were again lower for 9‐mm tags, but the differences were much smaller (3%–12%) and were not statistically significant.ConclusionWe found that 9‐mm tags can be as effective as 12‐mm tags and may allow for better inference to smaller (<55‐mm) non‐tagged fish. However, the lower detection rates of the 9‐mm tags could lead to less precise estimates, and site‐specific detection rates should be considered for studies that rely on these tags.

Integrating spatial stream network models and environmentalDNAto estimate current and future distributions of nonnative Smallmouth Bass

AbstractObjectiveClimate change is fueling the rapid range expansion of invasive species in freshwater ecosystems. This has led to mounting calls from natural resource managers for more robust predictions of invasive species distributions to anticipate threats to species of concern and implement proactive conservation and restoration actions. Here, we applied recent advances in fish sampling and statistical modeling in river networks to estimate the current and future watershed‐scale spatial distribution of nonnative Smallmouth BassMicropterus dolomieu.MethodsWe integrated a spatial stream network (SSN) model of stream temperature, landscape environmental covariates, and Smallmouth Bass occurrence data based on environmental DNA (eDNA) detections to develop an SSN species distribution model (SDM) representing current Smallmouth Bass distributions in the Chehalis River, Washington State, a large coastal river basin of ongoing watershed‐scale restoration. The SDM was informed by spatially intensive eDNA sampling from 135 locations in the main stem and major tributaries. We then applied downscaled climate change projections to the SSN SDM to predict Smallmouth Bass range expansion in the basin by late century.ResultWe identified high levels of spatial autocorrelation at hydrological distances of ≤10 km in our eDNA data set, underscoring the importance of applying an SSN modeling framework. Stream temperature was identified as the most important environmental covariate explaining variability in Smallmouth Bass occurrence. Model predictions estimated that current suitable summer habitat for Smallmouth Bass habitat spans 681 km and is projected to nearly double by late century (1333 km) under a moderate climate change scenario. Current and future suitable habitat for Smallmouth Bass is prevalent in important tributaries for spring Chinook SalmonOncorhynchus tshawytscha, a species of major conservation concern in the Chehalis River and more broadly along the Pacific coast. In both the main stem and tributaries, the SSN SDM predictions of the upstream leading edges of Smallmouth Bass closely align with (within 4.8 km) edges identified by spatially intensive eDNA sampling.ConclusionOur study highlights the value of integrating SSN models with rapidly growing eDNA data sets for accurate and precise riverine fish distribution estimation. Our application provides crucial insights for anticipating the impacts of shifting invasive species on Pacific salmon Oncorhynchusspp. in a warming world.

Postrelease mortality of spring Chinook Salmon from a mark‐selective recreational fishery in the Yakima River, Washington

AbstractObjectiveFishery managers often implement mark‐selective fishing regulations that provide harvest opportunity on abundant hatchery salmon populations while requiring release of at‐risk natural‐origin populations. However, implementing these decisions requires fisheries managers to account for postrelease mortality of any natural‐origin fish caught and released by anglers, which can be variable and is unknown for spring Chinook Salmon Oncorhynchus tshawytscha recreational fisheries in eastern Washington. Therefore, the objective of this study was to estimate and examine the factors affecting, the postrelease mortality of spring Chinook Salmon caught and released from an inland recreational mark–selective fishery in the Yakima River, Washington.MethodsWe conducted a 2‐year paired control and treatment radio‐telemetry study using 171 treatment fish caught and released during a recreational fishery and 194 control fish captured in a nearby fishway. Subjects were subsequently tracked throughout the summer, and postrelease mortality was estimated on September 1. Stepwise logistic regression was used to analyze potential explanatory variables recorded at the time of capture.ResultThe estimated postrelease mortality of these fish was 12% (95% CI = 2–23%) just prior to the onset of spawning. We also inferred using logistic regression that anatomical hook location explained most of the variation in mortality rates of angled fish.ConclusionOur estimate of postrelease mortality is similar to estimates derived in other studies for recreational freshwater Chinook Salmon fisheries as well as the current 10% rate used to manage Columbia River spring Chinook Salmon recreational fisheries.

A correlation between seasonally changing photoperiod, whole body lipid, and condition factor in juvenile spring Chinook salmon (Oncorhynchus tshawytscha).

The regulation of lipid stores is a central process for the physiology and ecology of fishes. Seasonal variation in lipid stores has been directly linked to survival of fishes across periods of food deprivation. We assessed whether a seasonally changing photoperiod was correlated to seasonal changes in energetic status to help better understand these important processes. Groups of first feeding Chinook salmon fry were introduced to a seasonal photoperiod cycle, but the point of entrance into the seasonal cycle varied from near the winter solstice (December), to either side of the spring equinox (February & May). Temperature and feeding rate were similar for all treatments. Subsequently, condition factor and whole body lipid content were assessed through a seasonal progression. Throughout most of the experiment, length and weight did not differ between the different photoperiod treatments, however whole body lipid and Fulton's condition factor did. Furthermore, changes in both whole body lipid and Fulton's condition factor in all treatment groups followed a similar seasonal pattern that was inversely related to day length (highest K and lipid levels found during days with the least light). These results suggest that regardless of age or size, there is a correlation between seasonal changes in photoperiod and changes in body composition in juvenile Chinook salmonids.

Partial-year continuous light treatment reduces precocious maturation in age 1+ hatchery-reared male spring Chinook Salmon (Oncorhynchus tshawytscha).

Hatchery programs designed to conserve and increase the abundance of natural populations of spring Chinook Salmon Oncorhynchus tshawytscha have reported high proportions of males precociously maturing at age 2, called minijacks. High proportions of minijacks detract from hatchery supplementation, conservation and production goals. This study tested the effects of rearing juvenile Chinook Salmon under continuous light (LL) on minijack maturation in two trials. The controls were maintained on a simulated natural photoperiod for both trials. For trial 1, LL treatment began on the summer solstice 2019 or the autumn equinox 2019 and ended in late March 2020 (LL-Jun-Apr and LL-Sep-Apr, respectively). A significant reduction in the mean percent of minijacks (%MJ) was observed versus control (28.8%MJ) in both LL-Jun-Apr (5.4%MJ) and LL-Sep-Apr (9.3%MJ). Trial 2 was designed to evaluate whether stopping LL treatment sooner was still effective at reducing maturation proportions relative to controls. LL treatments began on the summer solstice 2020 and continued until the winter solstice (LL-Jun-Dec) or the final sampling in April 2021 (LL-June-Apr). LL-Jun-Dec tanks were returned to a simulated natural photoperiod after the winter solstice. Both photoperiod treatments showed a significant reduction in mean %MJ from the control (66%MJ): LL-Jun-Dec (11.6%MJ), LL-Jun-Apr (10.3%MJ). In both trials, minijacks had higher body weights, were longer and had increased condition factor when compared to females and immature males in all treatment groups at the final sampling. In both trials, there was little or no effect of LL treatment on fork length or body weight in immature males and females versus controls, but an increase in condition factor versus controls was observed. This study shows that continuous light treatment reduces minijack maturation in juvenile male spring Chinook Salmon and could provide an effective method for Spring Chinook Salmon hatcheries interested in reducing minijack production.

Determining Optimum Size at Release for Hatchery‐Origin Tucannon River Spring Chinook Salmon Using PIT Tags

AbstractThe Tucannon River spring Chinook Salmon Oncorhynchus tshawytscha hatchery program has consistently failed to reach the program target adult (age 4 and older) smolt‐to‐adult return (SAR) rate of 0.87%. This has resulted in the hatchery program falling short of meeting its hatchery adult return goal of 1,152 fish. To determine whether hatchery fish released at a larger size would increase the number of returning adults, we released 95,256 PIT‐tagged, hatchery‐origin spring Chinook Salmon with known FLs (range = 73–212 mm) categorized into five length‐classes (<120, 120–139, 140–159, 160–179, and ≥180 mm FL) over eight brood years (2006–2013) to examine how size at release affected the smolt‐to‐adult survival (SAS) rate to the Columbia–Snake River system and the SAR rate to the Tucannon River. We used this information to determine an optimum size range at release to maximize adult returns to the Tucannon River and determine whether the program target SAR of 0.87% was achieved by any of the length‐classes. Return of hatchery adults (age 4 and older) for both SAS and SAR peaked for the 140–159‐mm length‐class. Smaller size at release resulted in lower survival, whereas fish larger than this size range matured prematurely either as minijacks or jacks and the majority never made it back to the Tucannon River. Based on this study, to maximize adult returns, hatchery smolts from the Tucannon River spring Chinook Salmon hatchery program should be released in the 140–159‐mm range. None of the length‐classes came close to reaching the adult SAR target of 0.87% (SAR for fish that were 140–159 mm at release was 0.15%). The expectation that changes to smolt size will lead to reaching the 0.87% SAR target is unrealistic for this population under current hatchery rearing and environmental conditions.

Efficacy of a Short‐Term Captive Broodstock Program Compared with Hatchery‐Origin Spring Chinook Salmon Derived from the Same Population

AbstractWe examined the efficacy of a one‐generation (five brood years: 1997–2001) captive broodstock program for spring Chinook Salmon Oncorhynchus tshawytscha by comparing survival rates of captive broodstock progeny (CBP; F2) with that of hatchery‐origin fish (HOR) from a conservation hatchery supplementation program in which both groups were derived from the Tucannon River (Washington State) population for the 2000–2006 brood years. Survival rates compared were egg to fry, fry to smolt, egg to smolt, total (ages 3–5) and adult (ages 4+) smolt‐to‐adult‐return (SAR) survival, and total (ages 3–5) and adult (ages 4+) progeny‐to‐parent (P:P) ratio. Total escapement and adult P:P ratios were also examined to determine if observed demographic benefits to the population continued after the captive broodstock program ended. The CBP group had lower within‐hatchery survival than the HOR group, with significant differences in survival at the egg‐to‐fry and egg‐to‐smolt stages due to poor egg viability. Mean untransformed total and adult SARs for the CBP were half those of the HOR group; however, SARs did not differ significantly. The CBP also had significantly lower total and adult P:P ratios than the HOR group and were below replacement for six of the seven brood years. While the captive broodstock provided additional fish for release that would not have been available otherwise, overall the CBP performed poorly and below expectations compared with the HOR group, both within the hatchery and after release. The captive broodstock program provided a short‐term demographic boost, most notable in the 2008–2010 return years, but the benefit did not carry over after the program ended.

Freshwater growth can provide a survival advantage to Interior Columbia River spring Chinook salmon after ocean entry

ABSTRACT: A prerequisite to effectively managing fish populations is to understand what factors and processes, including predation and changing environments, affect the survival of individuals. In anadromous fishes, the transition from freshwater to marine habitats is considered a critical period regulating population abundance due to high and variable mortality rates. During this period, conditions experienced in freshwater may influence size- and growth-selective mortality in the ocean. To determine if size- or growth-selective mortality occurred in juvenile Interior Columbia River spring Chinook salmon Oncorhynchus tshawytscha as they migrated through the Lower Columbia River and Estuary (LCRE) and during early marine residence, we examined 2 cohorts in years with differing survival (2016 and 2017). We reconstructed the size and growth of individual Chinook salmon from otoliths and compared these attributes in fish caught at 4 sites in the LCRE to those caught in the ocean off Oregon and Washington. We observed evidence of growth-selective mortality in 2017 but not 2016. Specifically, in 2017, when overall survival was lower, individuals caught in the ocean grew significantly faster in freshwater than individuals caught in the estuary. Given that the fish had resided in the ocean for an average of 30 d, these results indicate growth-selective mortality in 2017 occurred soon after ocean entry. The finding that growth in freshwater may impact marine survival adds to the growing body of evidence that processes occurring both prior to and after ocean entry impact the marine survival of this species.

Precocious Maturation of Hatchery‐Raised Spring Chinook Salmon as Age‐2 Minijacks Is Not Detectably Affected by Sire Age

AbstractJuvenile males produced in spring Chinook Salmon Oncorhynchus tshawytscha hatchery programs can exhibit high rates of maturation in freshwater as 2‐year‐old “minijacks.” This phenomenon is associated with high feeding rates and increased size and/or growth that juveniles experience in the hatchery environment, though studies also support a genetic component affecting age of maturation among salmonids, including precocious maturation in freshwater. This prompted a study to test whether the age of natural‐origin spring Chinook Salmon broodstock affects the rate at which their hatchery‐raised male progeny mature as age‐2 minijacks. In three consecutive brood years, we factorially mated age‐4 adult females with age‐3, age‐4, and age‐5 adult (jacks) male broodstock. In the latter two brood years, we also incorporated age‐1 precocious parr (microjacks) as sires. After communal rearing to the smolt stage (age 1), male juveniles were characterized as immature or as maturing minijacks based on plasma 11‐ketotestosterone concentration, and each was identified to its respective full‐sib progeny group via genetic parentage analysis. A generalized linear mixed model, performed for each brood year separately, was used to characterize expected precocious maturation rates by sire age, while controlling for potential effects of smolt body weight and individual parent identities. Multiple comparisons across sire ages within brood years were used to evaluate relative rates of precocious maturation. Estimates of the probability of minijack maturation among families within sire ages and brood years varied from as much as 0% to 100%, and no consistent effect of sire age on precocious maturation rate was observed. Exploratory analyses investigating additional effects of egg size, dam length, and spawn date also failed to identify consistent predictors of precocious maturation. Instead, variability was largely attributed to both dam‐ and sire‐specific effects, indicating a heritable component to precocious maturation, though not detectably associated with other measured attributes.

Assessing Accuracy and Bias of Protocols to Estimate Age of Pacific Salmon Using Scales

AbstractAccurate 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.

Evidence of a ‘dinner bell’ effect from acoustic transmitters in adult Chinook salmon

The ‘dinner bell’ hypothesis posits that marine mammals hear or otherwise sense soundwaves produced by acoustic transmitters and use the signal to selectively prey on fish carrying them. A dual tagging study conducted during 2010 and 2011 supports this hypothesis. Results from this study revealed a significant difference in the survival of fish marked with passive integrated transponder (PIT) tags and those marked with active acoustic transmitters. Our objective had been to use both types of tags to study behavior and survival of migrating adult spring Chinook salmon Oncorhynchus tshawytscha at 2 different spatial scales. We tagged fish as they entered the Columbia River, USA, and monitored their survival and progress over a 193 km reach to Bonneville Dam (river km 234), its lowest impoundment. In 2010, estimated survival was 0.74 (95% CI, 0.62-0.86) for PIT-tagged fish but only 0.30 (0.15-0.45) for acoustic-tagged fish. Therefore, in 2011, we included archival tags and a sham acoustic transmitter group to help identify causes of the survival discrepancy. Survival was 0.75 (0.54-0.97) for sham transmitter fish and 0.73 (0.60-0.86) for PIT fish, but only 0.10 (0.00-0.24) for active acoustic transmitter fish. Our study area was replete with harbor seals Phoca vitulina, California sea lions Zalophus californianus, and Steller sea lions Eumetopias jubatus during both years. We suspect the most likely cause of survival differences between tag treatment groups was pinniped predation. Using temperature data from archival tags, we found evidence of such predation and support for a ‘dinner bell’ effect from acoustic transmitter tags.

Threats to Rearing Juvenile Chinook Salmon from Nonnative Smallmouth Bass Inferred from Stable Isotope and Fatty Acid Biomarkers

AbstractNonnative Smallmouth BassMicropterus dolomieuare increasingly sympatric with juvenile spring Chinook SalmonOncorhynchus tshawytschain the rivers of western North America. Understanding the potential effects of introduced Smallmouth Bass is essential to efficiently direct salmon management efforts, especially given the potential for upstream range expansion of Smallmouth Bass in response to the climate‐induced warming that many rivers may experience. However, the predatory and competitive threats of Smallmouth Bass to juvenile salmonids remain largely unexamined, particularly in salmon rearing areas. To address this knowledge gap, we collected stable isotope (δ13C and δ15N) and fatty acid data to assess the trophic role of Smallmouth Bass in the upstream reaches of the North Fork John Day River, a tributary of the Columbia River where the upstream invasion extent of Smallmouth Bass co‐occurs with the native predator Northern Pikeminnow and river‐rearing juvenile Chinook Salmon. We found that Smallmouth Bass and Northern Pikeminnow occupy divergent dietary niches, and there was little evidence of a strong predation or competition threat to juvenile Chinook Salmon from either predator. In addition, we found a disproportionate reliance on autochthonous resources across the entire community and low isotopic uniqueness, suggesting potential competition among the broader fish community given the scarcity of resources. Importantly, this study focused on the overlap between the upstream‐most habitats of encroaching Smallmouth Bass and downstream‐most habitats of juvenile Chinook Salmon. Therefore, the relative scarcity of rearing salmon in comparison with other available prey in this zone may limit current predation threats. The results from this study help guide resource‐limited managers that are tasked with conserving and restoring native salmonid populations.

Plasma 11‐Ketotestosterone in Individual Age‐1 Spring Chinook Salmon Males Accurately Predicts Age‐2 Maturation Status

AbstractHigh rates of precocious male maturation of spring Chinook Salmon Oncorhynchus tshawytscha as 2‐year‐old minijacks have been observed in Columbia River basin hatchery programs. Previously, minijack rates have been assessed by lethal sampling during the spring prior to release of the age‐1 smolts and measurement of plasma levels of 11‐ketotestosterone (11‐KT), the major androgen in salmonids. Analysis of plasma 11‐KT levels has been used for separation of male fish into two distinct groups: low levels for immature males and high levels for precociously maturing minijacks. However, no published studies have confirmed how accurately plasma 11‐KT levels measured in the spring prior to smolt release correspond to the maturation status of individual males the following fall spawning season. We utilized both lethal and nonlethal sampling to determine when to sample hatchery‐reared juveniles to obtain clear separation between immature and precociously maturing males and PIT‐tagged fish to determine whether plasma 11‐KT levels in the spring accurately predicted an individual's maturation status in the fall. The distribution of plasma 11‐KT values from fish sampled in February was not significantly bimodal, whereas that from fish sampled in April was strongly bimodal. Plasma 11‐KT levels measured nonlethally in April accurately predicted the maturation status of 99% of male fish, confirmed via the gonadosomatic index obtained the following September. Plasma 11‐KT levels increased from April to September in both immature and maturing males, although the percent increase in maturing males was 10 times greater than that experienced by the non‐maturing smolts. Our findings support the use of spring plasma 11‐KT level as an indicator of maturation status in Chinook Salmon juveniles, provided that an appropriate sampling time is selected.

Fish Occurrence in a Seasonally Inundated Floodplain of the Willamette River, Oregon

The dynamic nature of large rivers is often diminished by anthropogenic alterations resulting in simplified stream networks with decreased floodplain connectivity and ecological function which adversely impact native organisms. However, little is known about the importance of large river floodplains to fish communities in the Pacific Northwest, especially during winter high flows. Our objectives were to document seasonal use of a Willamette River floodplain for native and non-native fish by measuring: 1) fish community characteristics (species richness, native versus non-native status, relative abundance), 2) spawning and rearing, 3) timing of use and movement, and 4) use by federally protected juvenile spring Chinook salmon (Oncorhynchus tshawytscha). During fall 2011 through spring 2012, a floodplain was sampled with a backpack electrofisher and out-migrant trap. A total of 12 native and 11 non-native species were detected. During nine electrofishing samples, 691 fish were collected, of which 95% were native. An estimated 42,297 fish were captured by the out-migrant trap; 98% of which were native and most were age-0 threespine stickleback (Gasterosteus aculeatus). Native species were detected on the floodplain prior to non-native species and tended to emigrate from the floodplain before non-native species, leading to a higher potential of stranding for non-native species as waters recedes. This study documents use of floodplain habitat by native and non-native fish species for seasonal flood refuge, rearing and spawning. Our results demonstrate native fish communities could potentially benefit from conservation of existing floodplains and restoration of floodplains changed by land use practices and altered flow regimes.

Fall and Winter Microhabitat Use and Suitability for Spring Chinook Salmon Parr in a U.S. Pacific Northwest River

AbstractHabitat degradation has been implicated as a primary threat to Pacific salmon Oncorhynchus spp. Habitat restoration and conservation are key toward stemming population declines; however, winter microhabitat use and suitability knowledge are lacking for small juvenile salmonids. Our objective was to characterize microhabitat use and suitability for spring Chinook Salmon Oncorhynchus tshawytscha parr during fall and winter. Using radiotelemetry techniques during October–February (2009–2011), we identified fall and winter microhabitat use by spring Chinook Salmon parr in Catherine Creek, northeastern Oregon. Tagged fish occupied two distinct gradient reaches (moderate and low). Using a mixed‐effects logistic regression resource selection function (RSF) model, we found evidence that microhabitat use was similar between free‐flowing and surface ice conditions. However, habitat use shifted between seasons; most notably, there was greater use of silt substrate and areas farther from the bank during winter. Between gradients, microhabitat use differed with greater use of large wood (LW) and submerged aquatic vegetation in the low‐gradient reach. Using a Bayesian RSF approach, we developed gradient‐specific habitat suitability criteria. Throughout the study area, deep depths and slow currents were most suitable, with the exception of the low‐gradient reach where moderate depths were optimal. Near‐cover coarse and fine substrates were most suitable in the moderate‐ and low‐gradient reaches, respectively. Near‐bank LW was most suitable throughout the study area. Multivariate principal component analyses (PCA) indicated co‐occurring deep depths supporting slow currents near cover were intensively occupied in the moderate‐gradient reach. In the low‐gradient reach, PCA indicated co‐occurring moderate depths, slow currents, and near‐bank cover were most frequently occupied. Our study identified suitable and interrelated microhabitat combinations that can guide habitat restoration for fall migrant and overwintering Chinook Salmon parr in Catherine Creek and potentially the Pacific Northwest.

Spawning Habitat of Hatchery Spring Chinook Salmon and Possible Mechanisms Contributing to Lower Reproductive Success

AbstractSpawning is a critical stage in the life history of salmonids. Spawning location has been reported to be a significant factor in the fitness differences between natural‐ and hatchery‐origin (natural and hatchery, respectively) female spring Chinook Salmon Oncorhynchus tshawytscha, although the mechanisms responsible remain uncertain. The objectives of this study were to compare the spawning distributions of hatchery and natural female spring Chinook salmon within the Chiwawa River, Washington, and determine whether spawning characteristics differ between hatchery and natural female Chinook Salmon or between channel types within the Chiwawa River. Over a 10‐year period, locations of female carcasses were examined to assess differences in the spawning distribution of hatchery and natural females. Additionally, a suite of metrics was measured from redds of known origin females to characterize the spawning location and redd characteristics. A greater proportion of hatchery females spawned in the lower watershed within plane‐bed channels than spawned upstream. Conversely, the majority of natural females spawned farther upstream in pool‐riffle channels. The distribution of hatchery fish was presumably strongly influenced by the hatchery acclimation–release location in the lower river. Given the geomorphic characteristics of plane‐bed channels, salmon were unable to build redds there similar to those in more typical pool‐riffle channels. Redds constructed in plane‐bed channels were smaller, shallower, and closer to stream banks than redds in pool‐riffle channels. Limited differences were detected in redd characteristics between natural and hatchery females in pool‐riffle channels. Smaller hatchery females constructed smaller redds with lower tailspill relief than did larger natural fish. As the results of differences in spawning distribution and fish size, redds constructed by hatchery females were more susceptible to environmental sources of mortality than were redds constructed by natural females. This study provides insight into the possible mechanisms responsible for the reported lower reproductive success among hatchery females spawning in the natural environment.Received December 14, 2016; accepted May 24, 2017 Published online July 31, 2017

Interactions of baseflow habitat constraints: Macroinvertebrate drift, stream temperature, and physical habitat for anadromous salmon in the Calapooia River, Oregon

Abstract The Calapooia River in western Oregon supports a small winter steelhead trout (Oncorhynchus mykiss) population and historically supported spring Chinook salmon (Oncorhynchus tshawytscha). Early timber harvesting removed the riparian forest, and log transportation practices simplified the channel. Those disturbance legacies continue to affect fish habitat by limiting shade and channel complexity, complicating conservation efforts. To evaluate juvenile salmonid rearing potential, macroinvertebrate drift, thermal regime and physical habitat were measured at eight sites in 24 km of the upper river during late summer baseflow. Overall physical habitat was simple, with few functioning instream structures or pools. During the 22‐day drift study, flows declined and maximum site stream temperatures ranged from 23.1°C at the lower end to 16.4°C 24 km upstream. Macroinvertebrate drift concentrations ranged from 0.7–13.7 ind. m−3 with biomasses from 0.02–1.23 mg m−3. Drift concentration biomass was higher upstream (P = 0.006) than downstream and declined overall (P < 0.001) during the study. Drift biomass was dominated by five taxon groups – Baetis tricaudatus, Calineuria californica, Hesperoperla pacifica, Simulium spp., and Chironomidae, which were 65% of total biomass. During twilight, total biomass and biomass of B. tricaudatus, Simulium spp., and Chironomidae (both larvae and adults) were higher. Total drift declined dramatically over the study period owing to decreases in drift concentration and a 58% decline in discharge, greatly reducing overall drift and available food resources for juvenile‐rearing salmonids. The upper catchment, both with cooler temperatures and higher food availability, provided the best conditions for juvenile anadromous salmonids to survive late summer conditions. Conservation consequences of climate change‐induced alterations in flow and temperature may further affect habitat quality for juvenile salmonids in this catchment in the coming decades.

Chinook salmon emergence phenotypes: Describing the relationships between temperature, emergence timing and condition factor in a reaction norm framework

AbstractWater temperature can have a profound influence on development and distribution of aquatic species. Salmon are particularly vulnerable to temperature changes because their reproductive and early development life phases are spent in freshwater river systems where temperature fluctuates widely both daily and seasonally. Flow regulation downstream of dams can also cause temperature regime changes, which in turn may spur local adaptation of early life‐history traits. In a common garden laboratory incubation experiment, we exposed spring Chinook salmon (Oncorhynchus tshawytscha) embryos to four temperature regimes: warm stable, cold stable, daily variation and below dam. We found that fry from warmer thermal regimes emerged earlier than those from colder regimes both in terms of calendar date and temperature units and that warmer temperatures caused fry to emerge less developed. There was also a significant effect of family on both emergence timing and development level at emergence. By combining measurements of physiological and behavioural traits at emergence and interpreting them within a reaction norm framework, we can better understand which populations might be more vulnerable to altered thermal regimes.

Juvenile life-history diversity and population stability of spring Chinook salmon in the Willamette River basin, Oregon

Migratory and rearing pathways of juvenile spring Chinook salmon (Oncorhynchus tshawytscha) were documented in the Willamette River basin to identify life histories and estimate their contribution to smolt production and population stability. We identified six primary life histories that included two phenotypes for early migratory tactics: fry that migrated up to 140–200 km shortly after emergence (movers) and fish that reared for 8–16 months in natal areas (stayers). Peak emigration of juvenile salmon from the Willamette River was in June–July (subyearling smolts), March–May (yearling smolts), and November–December (considered as “autumn smolts”). Alternative migratory behaviors of juvenile salmon were associated with extensive use of diverse habitats that eventually encompassed up to 400 rkm of the basin, including tributaries in natal areas and large rivers. Juvenile salmon that reared in natal reaches and migrated as yearlings were the most prevalent life history and had the lowest temporal variability. However, the total productivity of the basin was increased by the contribution of fish with dispersive life histories, which represented over 50% of the total smolt production. Life-history diversity reduced the variability in the total smolt population by 35% over the weighted mean of individual life histories, providing evidence of a considerable portfolio effect through the asynchronous contributions of life histories. Protecting and restoring a diverse suite of connected habitats in the Willamette River basin will promote the development and expression of juvenile life histories, thereby providing stability and resilience to native salmon populations.

Genetic monitoring guides adaptive management of a migratory fish reintroduction program

AbstractDams contribute to declines in fish abundance, in part, by blocking access to historical habitat. When fish ladders are infeasible, fish can be trapped below a dam and transported above to provide access to habitat. However, this conservation strategy has received little attention in the literature, and many questions regarding efficacy remain unanswered. Here, we used a genetic parentage approach to evaluate cohort replacement rate (CRR), defined as the number of future spawners produced by a spawner, for a spring Chinook salmon Oncorhynchus tshawytscha trap and transport reintroduction program. We used CRRs to determine if the population can sustain itself in the absence of immigration, which is important when assessing demographic viability. We also evaluated the effects of release locations and dates on the fitness of reintroduced fish. Counts of adult offspring per spawner were used to estimate fitness of salmon reintroduced in 2007 and 2008. We found that fitness decreased slightly as adults were released later in the spawning season in 2007, but not in 2008. Release location did not affect fitness in either year. We also found a seasonal decline in the likelihood that a Chinook salmon collected at the trap and transport facility was produced above the dam. Finally, 2007 and 2008 CRRs were both well below one, indicating that improvements are needed to achieve demographic stability. We demonstrate that genetic monitoring of a reintroduction program helped to inform demographic viability assessments, and suggest that our approach may be broadly applicable to other philopatric species.