Wild Chinook Research Articles

Estimating the effects of smolt size and migration timing on salmon marine survival using a multivariate mixed‐effect model

Abstract When the conditions encountered by a migratory species are highly variable, the timing of migration and migrant condition are critical to survival. Spring/summer‐run Chinook salmon in the Snake River of the Northwestern United States are listed as threatened under the US Endangered Species Act because of decades of poor adult returns; juvenile smolt‐to‐adult survival is often 0.5% or less. Juveniles pass through eight dams en route to the ocean, and despite changes to the hydropower system, there has been little recent improvement in survival. We analysed the effect of migration date, fish length and their interaction on the survival to adulthood of 409,747 wild juvenile Chinook salmon as they migrated through a large, dynamic riverine ecosystem and through the ocean, measured over 20 years. Parametric 2D smoothers are often used to quantify unexplained heterogeneity across space; however, these same statistical models can be applied to 2D datasets to uncover patterns of covariance of two biological processes important to management actions. We employ Gaussian Markov random fields (GMRF) and a 2D smoother to estimates of fish survival to identify the nature of variation in survival with respect to length and date. We found significant effects of fish length, migration date and the date‐by‐length interaction on resulting riverine and marine survival. Unlike the gradual shifts in survival in relation to length and timing that marginal estimates demonstrate, we show that within year, changes in survival with length and timing are often more abrupt than previously thought. Synthesis and applications: Inter‐annually, we identified distinct combinations of fish length and migration timing leading to elevated smolt‐to‐adult survival. Often these ‘hotspots’ are compressed into fish sizes greater than 100 mm and passage timings of only a week or two, demonstrating that even modest shifts in body size and migration timing can have a significant effect on survival. Further research can concentrate on these distinct annual periods to identify sources of mortality that have previously been elusive.

How do Management Goals for Wild Chinook Salmon Align with Feasibility?

Evaluation of goals is crucial for effective management to conserve viable and diverse fish populations and to support harvest. Management of wild Chinook Salmon Oncorhynchus tshawytscha in the Snake River basin exemplifies the struggle to meet fisheries goals. Considering contemporary production of juvenile emigrants, it is imperative to determine the survival from emigration to adult (Se‐a) required to meet abundance goals. Increased anthropogenic impact on spawning and rearing habitats leads to higher Se‐a required to attain goals. Wilderness populations exhibit viability and could sustain fisheries with Se‐a lower than required elsewhere. Conversely, populations targeted for habitat restoration demand higher Se‐a to fulfill goals, indicating a need to enhance egg‐to‐smolt survival. However, Se‐a has fallen below the threshold needed for replacement in all populations, even at current low abundances. Despite these challenges, most populations still possess the potential to achieve abundance goals, emphasizing the importance of strategic interventions to bolster their resilience.

Predicting juvenile-to-adult survival in Chinook salmon using non-lethal scale-derived growth and regeneration indices

ABSTRACT Survival is often associated with body size, growth rate, and stress, but the latter two are more difficult to observe non-lethally. Non-lethal methods can be particularly important for endangered and culturally valuable species. With fish scales, growth and stress indices could be inferred without needing to sacrifice fish. We examined scales from ~350 wild Chinook salmon (Oncorhynchus tshawytscha) in Valley Creek and at Lower Granite Dam (Pacific Northwest, USA) in 2007–2019. From a von Bertalanffy model and scale circulus spacings, we estimated a brood-year-specific growth coefficient K (hereafter K ˆ ). Using the scale-derived K ˆ and other biological and environmental covariates, we examined how these potential predictors associated with juvenile-to-adult survival of >136,000 passive-integrated-transponder-tagged Chinook salmon from the Snake River Basin (Pacific Northwest, USA). We found that the effects on survival from brood-year-specific K ˆ , fork length of the tagged individuals, and interaction between K ˆ and fork length were positive. We also determined that the proportion of fish samples with regenerated scales (an indicator of stress) had a negative effect on survival. For further refinement of non-lethal, scale-derived indices on survival, we encourage examination of indices across populations, juvenile habitats, and juvenile life stages, and not simply a regional, brood-year-specific growth index.

Comparing Fishery Impacts and Maturation Schedules of Hatchery-Origin vs. Natural-Origin Fish from a Threatened Chinook Salmon Stock

Central Valley Spring-run Chinook (CVSC) are listed as threatened under the California and federal Endangered Species Acts, but how ocean fisheries affect CVSC is not routinely monitored or managed, largely because of data limitations. Most tag data for CVSC are from a hatchery program that may not sufficiently represent natural-origin fish in ocean and inland fishery recovery data. However, a discontinued tagging program for Butte Creek Wild Spring-run Chinook (BCWSC) provides for estimation of fishery impacts and maturation schedules for a limited set of years, which we compared with estimates for hatchery-origin fish for common years, while extending the hatchery-origin estimates over a wider time-frame. Additional scale-age data from BCWSC allow inferences about more recent maturation rates, conditional on harvest-rate estimates borrowed from other stocks. Overall, CVSC appear to experience low age-3 ocean fishery impact rates, but age-4 impact rates can be comparable to ocean harvest rates estimated for Sacramento River Fall Chinook. Tagging data from the years available indicate that ocean fisheries may reduce spawning run sizes (all ages combined) by 40% to 60% during periods of high fishing effort. Effects of ocean fishing on spawner abundance are weaker in years of reduced fishing or for cohorts displaying earlier maturation. It appears that maturation rates of hatchery-origin CVSC may have increased (i.e., earlier maturation) over the full time-period examined, and there may be indications of increasing maturation rates for BCWSC as well.

A Comparative Analysis of the Nutritional Quality of Salmon Species in Canada among Different Production Methods and Regions

Nutritional information of fresh seafood, including salmon, is not commonly available to the public, which can lead to misconceptions. The aim of this study was to determine the nutritional content of salmon fillets, comparing: (1) Canadian salmon, both wild (pink, chinook, and sockeye) and farmed (Atlantic salmon); (2) Canadian farmed Atlantic salmon grown in ocean net pens or land-based recirculating aquaculture systems (RAS); and (3) farmed Atlantic salmon raised in Canada compared with Scotland, Chile, and Ireland. Samples were purchased from retail stores in Canada and analyzed for moisture, crude protein, total lipid, fatty acids, amino acids, cholesterol, mercury, and color. The greatest differences in nutritional content were between species, rather than if it was wild or farmed. Compared to salmon raised in net pens, salmon raised in RAS had three times more eicosapentaenoic acid (EPA) + docosahexaenoic acid (DHA) per serving (0.7/100 g vs. 2.3/100 g, respectively), twice as much omega-3s (14% vs. 30%) and redder in color (24.7 vs. 30.1) but higher in saturated fats (18% vs. 24%). Scottish salmon had over double the amount of EPA + DHA per 100 g (1.6 g) than salmon from Canada (0.70 g), Chile (0.66 g), and Ireland (0.61 g). While nutritional content differed among salmon types, each type can provide dietary essential nutrients that can benefit consumers.

Life-cycle modeling reveals high recovery potential of at-risk wild Chinook salmon via improved migrant survival

Chinook salmon ( Oncorhynchus tshawytscha) in the Columbia River basin are threatened by anthropogenic changes to migratory corridors, estuaries, and natal habitats. Streams provide spatially heterogeneous natal habitats essential for salmon spawning and rearing life stages. We fit a statistical state-space model to salmon populations in Idaho's Middle Fork Salmon River (MFSR) to assess spatial variation in natal productivity and population growth. Our model integrated multiple long-term data sets to estimate variation in per-capita smolt production and smolt-to-adult (SAR) survival. Smolt production varied across stream segments, averaging 104.48 female smolts per spawning female, while SARs averaged 0.74%. Chinook salmon population growth rates exceeded replacement in 17% of segments (4 of 23). By increasing SARs to 1.8% (near the lower bound of Columbia River basin recovery targets), we predict that all 23 MFSR segments will yield positive population growth rates at contemporary (very low) spawner densities. Our analysis suggests that for Snake River basin populations within high-quality natal habitats, SAR improvements will elevate salmon population growth rates and enhance restoration of at-risk wild Chinook salmon.

Preliminary examination of sounds produced by Pacific salmon (Oncorhynchus spp.) during their fall spawning migrationa).

A preliminary description of sounds produced by three species of Pacific salmon was conducted to address the lack of quantified call characteristics in previous studies. Wild Chinook salmon (Oncorhynchus tshawytscha), pink salmon (O. gorbuscha), and coho salmon (O. kisutch) were diverted from a natural spawning migration in the Big Qualicum River located on Vancouver Island, British Columbia, Canada and held in the adjacent hatchery during the 2017 fall migration. Underwater sounds were opportunistically recorded continuously over four week in holding raceways containing Chinook only, coho only, or mixed pink and Chinook salmon, and examined for sounds. All groups produced sounds in three categories based on mechanism: hydrodynamic (surface splash), air movement (miscellaneous and 7 named types), and unknown mechanism (pulse). Pulse, gill-bubble fast repetitive tick air movement sounds, and miscellaneous air movement sounds occurred in all groups and differences in some characteristics of sounds were found between the species groups. Additionally, even though pink salmon were not recorded separately, data suggest they produce a very fast repetitive tick air movement sound more often compared to Chinook salmon. Our results represent the first detailed description of the types and characteristics of sounds produced by wild Pacific salmon.

Rapid Assessment of Fish Freshness for Multiple Supply-Chain Nodes Using Multi-Mode Spectroscopy and Fusion-Based Artificial Intelligence.

This study is directed towards developing a fast, non-destructive, and easy-to-use handheld multimode spectroscopic system for fish quality assessment. We apply data fusion of visible near infra-red (VIS-NIR) and short wave infra-red (SWIR) reflectance and fluorescence (FL) spectroscopy data features to classify fish from fresh to spoiled condition. Farmed Atlantic and wild coho and chinook salmon and sablefish fillets were measured. Three hundred measurement points on each of four fillets were taken every two days over 14 days for a total of 8400 measurements for each spectral mode. Multiple machine learning techniques including principal component analysis, self-organized maps, linear and quadratic discriminant analyses, k-nearest neighbors, random forest, support vector machine, and linear regression, as well as ensemble and majority voting methods, were used to explore spectroscopy data measured on fillets and to train classification models to predict freshness. Our results show that multi-mode spectroscopy achieves 95% accuracy, improving the accuracies of the FL, VIS-NIR and SWIR single-mode spectroscopies by 26, 10 and 9%, respectively. We conclude that multi-mode spectroscopy and data fusion analysis has the potential to accurately assess freshness and predict shelf life for fish fillets and recommend this study be expanded to a larger number of species in the future.

Infectious agents and their physiological correlates in early marine Chinook salmon (Oncorhynchus tshawytscha).

Abstract The early marine life of Pacific salmon is believed to be a critical period limiting population-level survival. Recent evidence suggests that some infectious agents are associated with survival but linkages with underlying physiological mechanisms are lacking. While challenge studies can demonstrate cause and effect relationships between infection and pathological change or mortality, in some cases pathological change may only manifest in the presence of environmental stressors; thus, it is important to gain context from field observations. Herein, we examined physiological correlates with infectious agent loads in Chinook salmon during their first ocean year. We measured physiology at the molecular (gene expression), metabolic (plasma chemistry) and cellular (histopathology) levels. Of 46 assayed infectious agents, 27 were detected, including viruses, bacteria and parasites. This exploratory study identified: Importantly, our study provides the first evidence that the molecular activation of viral disease response and the lesions observed during the development of the PRV-related disease jaundice/anemia in farmed Chinook salmon are also observed in wild juvenile Chinook salmon.

Restrictions on leader length in an in‐river sport fishery reduce catch of threatened wild chinook salmon Oncorhynchus tshawytscha and increase harvest of hatchery origin chinook

AbstractTo achieve conservation and harvest objectives associated with Chinook Salmon, fisheries managers have relied on mark‐selective and anti‐snagging rules in freshwater whereby anglers are required to release wild Chinook and fish hooked in anatomical locations other than the head and mouth. However, in some cases these regulations have resulted in increased mortalities due to the number of fish (hatchery and wild) that require release. Regulations effective at increasing the number of fish hooked in the mouth have the potential to decrease total encounters (number of fish caught) of both hatchery and wild fish while increasing the total number of fish harvested; however, this has not been tested. A roving creel survey and a test fishery were used to describe the effect leader length and bait under a bobber has on catch rate and hooking location and simulate how a variety of restrictions on gear type would affect catch and harvest on wild and hatchery origin Chinook salmon. Results indicate that a 6‐foot leader length restriction would result in the highest catch of hatchery fish harvested and reduce exploitation rate on wild fish by greater than 20%. Regulations limiting leader length to 3 feet are expected to result in the greatest reduction (75.7%) to total encounters on wild fish; however, this method was unpopular and resulted in few hatchery fish harvested. The use of bait suspended under a bobber resulted in intermediate results with a reduction of 60.0% to catch of wild Chinook and the smallest number hooked outside the mouth (0/30). These results provide the first evaluation of the effect of leader length in a mark‐selective hook and line fishery and suggest that a 6‐foot leader length restriction would be expected to reduce encounters on wild Chinook, increase harvest of hatchery fish and extend the fishing season.

Parentage-based tagging and genetic stock identification applied to assessment of mixed-stock fisheries and hatchery broodstocks for Chinook salmon in British Columbia, Canada

Genetic stock identification (GSI) and parentage-based tagging (PBT) are being increasingly applied to salmon fisheries and hatchery broodstock management and assessment in Canada. GSI and PBT with single nucleotide polymorphisms (SNPs) were applied in assessment of 2020 Chinook salmon fisheries and hatchery broodstocks in British Columbia (BC), Canada, with 9234 individuals successfully genotyped in fishery samples and 2250 PBT identifications made (24.4% individual identification rate). As PBT identifications provided age of the individual and sex was determined from a SNP in the SNP panel, it was possible to evaluate sex ratios by age observed in the fishery sampling. Fishery catch sex ratios at age two and three years were male-biased, whereas those at age four and five years were female-biased. The combined age and sex information derived from genetics-based fishery sampling illustrates the ancillary information that becomes available relative to coded-wire tag (CWT) sampling if biological sampling of the catch is not conducted. There were 20,342 individuals genotyped in 65 hatchery broodstocks from which 6080 PBT identifications were made. Population-specific contributions to mixed-stock fisheries and exploitation rates were estimated with CWTs and GSI-PBT technologies for 13 populations, and close agreement of estimated population-specific exploitation rates between CWT and genetic methods for the 13 populations was observed (r2(11)= 0.951, P < 0.001). We conclude that a genetic approach can improve upon the results available from the current CWT program for assessment and management of Chinook salmon fisheries and hatchery broodstocks in BC, as well as provide ancillary information to improve wild Chinook salmon assessment and conservation by providing fishery impacts by conservation unit for any fishery in Canada.

A nonfunctional copy of the salmonid sex-determining gene (sdY) is responsible for the "apparent" XY females in Chinook salmon, Oncorhynchus tshawytscha.

Many salmonids have a male heterogametic (XX/XY) sex determination system, and they are supposed to have a conserved master sex-determining gene (sdY) that interacts at the protein level with Foxl2 leading to the blockage of the synergistic induction of Foxl2 and Nr5a1 of the cyp19a1a promoter. However, this hypothesis of a conserved master sex-determining role of sdY in salmonids is challenged by a few exceptions, one of them being the presence of naturally occurring “apparent” XY Chinook salmon, Oncorhynchus tshawytscha, females. Here, we show that some XY Chinook salmon females have a sdY gene (sdY-N183), with 1 missense mutation leading to a substitution of a conserved isoleucine to an asparagine (I183N). In contrast, Chinook salmon males have both a nonmutated sdY-I183 gene and the missense mutation sdY-N183 gene. The 3-dimensional model of SdY-I183N predicts that the I183N hydrophobic to hydrophilic amino acid change leads to a modification in the SdY β-sandwich structure. Using in vitro cell transfection assays, we found that SdY-I183N, like the wild-type SdY, is preferentially localized in the cytoplasm. However, compared to wild-type SdY, SdY-I183N is more prone to degradation, its nuclear translocation by Foxl2 is reduced, and SdY-I183N is unable to significantly repress the synergistic Foxl2/Nr5a1 induction of the cyp19a1a promoter. Altogether, our results suggest that the sdY-N183 gene of XY Chinook females is nonfunctional and that SdY-I183N is no longer able to promote testicular differentiation by impairing the synthesis of estrogens in the early differentiating gonads of wild Chinook salmon XY females.

Field assessments of heart rate dynamics during spawning migration of wild and hatchery-reared Chinook salmon.

During spawning, adult Pacific salmonids (Oncorhynchus spp.) complete challenging upriver migrations during which energy and oxygen delivery must be partitioned into activities such as locomotion, maturation and spawning behaviours under the constraints of an individual's cardiac capacity. To advance our understanding of cardiac function in free-swimming fishes, we implanted migrating adult Chinook salmon (Oncorhynchus tshawytscha) collected near the mouth of the Sydenham River, Ontario, with heart rate (fH) biologgers that recorded fH every 3 min until these semelparous fish expired on spawning grounds several days later. Fundamental aspects of cardiac function were quantified, including resting, routine and maximum fH, as well as scope for fH (maximum-resting fH). Predictors of fH were explored using generalized least-squares regression, including water temperature, discharge, fish size and fish origin (wild versus hatchery). Heart rate was positively correlated with water temperature, which aligned closely with daily and seasonal shifts. Wild fish had slower resting heart rates than hatchery fish, which led to significantly higher scope for fH. Our findings suggest that wild salmon may have better cardiac capacity during migration than hatchery fish, potentially promoting migration success in wild fish. This article is part of the theme issue 'Measuring physiology in free-living animals (Part I)'.

Population Dynamics and Temporal Trends of Bull Trout in the East Fork Salmon River, Idaho

AbstractBecause of their long‐term listing under the Endangered Species Act, much interest has been placed on estimating population vital rates for Bull Trout Salvelinus confluentus, but the biotic and abiotic factors that influence the interannual variability in those vital rates have rarely been evaluated. We used mark–recapture data to estimate fish growth, survival, and trends in abundance for fluvial adult Bull Trout in the East Fork Salmon River, Idaho. Over an 8‐year period, a total of 1,205 individual Bull Trout were collected at a weir on the East Fork Salmon River (29 km upstream of its confluence with the Salmon River) during June–September, of which 420 were recaptures from prior years. Bull Trout varied in length from 215 to 756 mm and achieved a slightly larger asymptotic length and a slightly lower rate of growth relative to other fluvial and adfluvial Bull Trout populations. Apparent survival averaged 0.42 across all years, which was similar to previous studies estimating apparent survival for Bull Trout. The number of emigrating anadromous salmonid smolts in the upper Salmon River basin positively influenced East Fork Salmon River Bull Trout growth and survival, and survival was higher in years with lower annual discharge. Assessment of population growth via linear regression analysis indicated that the Bull Trout population was increasing during the study period (λ = 1.08; 95% confidence interval = 1.03–1.14). Our findings highlight the ecological link between the abundance of wild and hatchery Chinook Salmon Oncorhynchus tshawytscha, Sockeye Salmon O. nerka, and steelhead O. mykiss smolts and growth and survival of adult Bull Trout in systems where these species occur in sympatry.

Differential impacts of freshwater and marine covariates on wild and hatchery Chinook salmon marine survival.

Large-scale atmospheric conditions in the Northeast Pacific Ocean affect both the freshwater environment in the Columbia River Basin and marine conditions along the coasts of Oregon, Washington, and British Columbia, resulting in correlated conditions in the two environments. For migrating species, such as salmonids that move through multiple habitats, these correlations can amplify the impact of good or poor physical conditions on growth and survival, as movements among habitats may not alleviate effects of anomalous conditions. Unfortunately, identifying the mechanistic drivers of salmon survival in space and time is hindered by these cross-habitat correlations. To address this issue, we modeled the marine survival of Snake River spring/summer Chinook salmon with multiple indices of the marine environment and an explicit treatment of the effect of arrival timing from freshwater to the ocean, and found that both habitats contribute to marine survival rates. We show how this particular carryover effect of freshwater conditions on marine survival varies by year and rearing type (hatchery or wild), with a larger effect for wild fish. As environmental conditions change, incorporating effects from both freshwater and marine habitats into salmon survival models will become more important, and has the additional benefit of highlighting how management actions that affect arrival timing may improve marine survival.

Farm to Fish: Lessons from a Multi-Year Study on Agricultural Floodplain Habitat

Large areas of California’s historic floodplain have been separated from adjacent river channels by levee construction, allowing the development of an extensive agricultural industry. Based on successful partnerships between agriculture and conservation groups to support migrating waterfowl, we examined whether seasonally flooded rice fields could be modified to provide off-channel rearing habitat for juvenile Chinook Salmon Oncorhynchus tshawytscha. During winter and spring of 2012-2017, we conducted a series of experiments in Yolo Bypass and other regions of California’s Central Valley using hatchery Chinook Salmon as a surrogate for wild Chinook Salmon, the management target for our project. Overall, we found that seasonally flooded fields are highly productive, resulting in significantly higher levels of zooplankton and high Chinook Salmon growth rates as compared to the adjacent Sacramento River. We found similar results for multiple geographical areas in the Central Valley, and in different cover types, such as non-rice crops and fallow areas. Although field substrate type did not detectably affect fish growth and survival, connectivity with upstream and downstream areas appeared to drive fish occupancy, because rearing young salmon were generally attracted to inflow in the fields, and not all of the fish successfully emigrated off the fields without efficient drainage. In general, we faced numerous logistic and environmental challenges to complete our research. For example, periodic unmanaged floods in the Yolo Bypass made it difficult to schedule and complete experiments. During severe drought conditions, we found that managed agricultural habitats produced low and variable salmon survival results, likely because of periodically high temperatures and concentrated avian predation. In addition, our project required substantial landowner time and effort to install and maintain experimental fields. Recent and future infrastructure improvements in Yolo Bypass could substantially improve options for experimental work and broaden efforts to enhance salmon habitat.

Investigation of the nutritional composition of different types of salmon available to Canadian consumers

Salmon is regarded as an excellent source of nutrients and there are numerous choices in the types of salmon available. In North America, nutritional labelling for fresh seafood is not required. The lack of nutritional information may be confusing to some consumers when selecting a product for specific health benefits. The aim of this study was to examine the nutritional composition of different types of salmon fillets that are commonly available to Canadian consumers, which included different species, wild and farmed, organic, and environmental sustainability certifications. Six types of salmon were analyzed: farmed Atlantic, farmed organic Atlantic, farmed organic Chinook, wild Chinook, wild Pacific (pink), and wild Sockeye. Protein, fat, fatty acids, amino acids, potassium, iron, cholesterol, and mercury were analyzed. Wild Pacific was the most dissimilar salmon type, due to high moisture content (79%), and lowest fat (0.8%) and fatty acid content, compared with all salmon types. Protein and fat were highest wild Sockeye, wild Chinook, and farmed Atlantic salmon. DHA and EPA were highest in wild Sockeye (81 mg/g) and wild Chinook (79 mg/g), and lower in farmed organic Chinook (23 mg/g), farmed Atlantic (20 mg/g), farmed organic Atlantic (16 mg/g), and wild Pacific (10 mg/g). Mercury was highest in farmed organic Chinook (0.3 μg/g) and lowest in farmed Atlantic (38% lower) and farmed organic Atlantic. Considering nutrient profiles as multivariable, PERMANOVA revealed significant differences due to salmon type, and whether it was wild or farmed, organic or non-organic, certified or not certified. Wild Sockeye and Chinook were found to be the most nutrient-dense and have the highest omega-3 content. However, for frequent consumption, farmed Atlantic salmon is an excellent option due to nutrient density, low mercury, affordability, and availability. This study is important as an indicator of the current nutritional status of various salmon products. • This study examined nutrient content of different types of salmon in Canada. • Fatty acids, amino acids, potassium, iron, cholesterol, mercury were measured. • Wild Pacific was the most dissimilar salmon type, due to high moisture, low fat. • Wild Sockeye and Chinook were most nutrient-dense, with the highest omega-3s. • Farmed Atlantic good option for nutrient density, low mercury, cost, availability.

Outmigration survival of wild Chinook salmon smolts through the Sacramento River during historic drought and high water conditions

Populations of wild spring-run Chinook salmon in California’s Central Valley, once numbering in the millions, have dramatically declined to record low numbers. Dam construction, habitat degradation, and altered flow regimes have all contributed to depress populations, which currently persist in only a few tributaries to the Sacramento River. Mill Creek (Tehama County) continues to support these threatened fish, and contains some of the most pristine spawning and rearing habitat available in the Central Valley. Despite this pristine habitat, the number of Chinook salmon returning to spawn has declined to record low numbers, likely due to poor outmigration survival rates. From 2013 to 2017, 334 smolts were captured and acoustic tagged while out-migrating from Mill Creek, allowing for movement and survival rates to be tracked over 250 km through the Sacramento River. During this study California experienced both a historic drought and record rainfall, resulting in dramatic fluctuations in year-to-year river flow and water temperature. Cumulative survival of tagged smolts from Mill Creek through the Sacramento River was 9.5% (±1.6) during the study, with relatively low survival during historic drought conditions in 2015 (4.9% ± 1.6) followed by increased survival during high flows in 2017 (42.3% ± 9.1). Survival in Mill Creek and the Sacramento River was modeled over a range of flow values, which indicated that higher flows in each region result in increased survival rates. Survival estimates gathered in this study can help focus management and restoration actions over a relatively long migration corridor to specific regions of low survival, and provide guidance for management actions in the Sacramento River aimed at restoring populations of threatened Central Valley spring-run Chinook salmon.

Fluctuating asymmetry of adult Chinook Salmon (Oncorhynchus tshawytscha) otoliths from wild and hatchery origins

Fluctuating asymmetry is the non-directional deviations from bilateral symmetry and occurs across organisms. Fish otoliths are often used to test for differences in symmetry as otoliths aid in hearing, homing, and balance. Here, we evaluated the symmetry of otolith pairs in adult Chinook Salmon between wild and hatchery-origin stocks. Pacific salmon are economically and ecologically important to the Pacific Northwest, USA. Chinook Salmon are widely distributed throughout the North Pacific Ocean, yet several wild populations are federally listed as endangered or threatened due to depleted stocks, loss of genetic diversity, and hatchery contribution to wild stocks. As such, fishery managers are concerned with the health and condition of hatchery-origin fish and their impacts on wild populations. We included both hatchery and wild-origin Chinook Salmon from the Coast Mountain and Willamette regions in Oregon as well as hatchery populations from southeast Alaska. We evaluated several metrics to test shape variation and symmetry between the left and right sagittal otoliths. We found consistently more asymmetry in otoliths from hatchery origin than wild Chinook Salmon within seven out of eight total metrics. These results could have conservation and management implications as hatchery-origin Chinook Salmon can reduce pressure from wild stocks while continuing to support commercial and recreational industries.

Examining the potential of otolith chemistry to determine natal origins of wild Lake Michigan Chinook salmon

Previous research has demonstrated a large movement of hatchery-reared Chinook salmon (Oncorhynchus tshawytscha) from Lake Huron to Lake Michigan, suggesting the potential for wild fish to exhibit similar movement patterns. We assessed the feasibility of using otolith microchemistry to estimate the natal source composition of wild Chinook salmon in Lake Michigan and evaluate interbasin movement. Otolith pairs were extracted from juvenile and adult fish collected in 2015 and 2016 from Great Lakes tributaries. Otoliths were analyzed using laser ablation inductively coupled plasma mass spectrometry to determine trace element concentrations, and four multivariate classification algorithms were evaluated for classification accuracy. Juvenile data reclassified to their natal regions with up to 89% success on a basin level, with a random forest approach performing the best among all models. Assigning adults to their natal origins resulted in more success on a basin-wide scale (74% to 88%) compared with a regional scale (32% to 51%), but success was still below juvenile reclassification accuracy. Our findings suggest that otolith microchemistry can be used to estimate wild Chinook salmon interbasin movement and that classification accuracy can be improved by matching juvenile and adult year classes in our assessment samples. Ultimately, we intend to use these models to assess the effects of wild Chinook salmon interbasin movement on Lake Michigan predatory demand and evaluate the risks of various stocking alternatives.