Chinook Salmon Oncorhynchus Tshawytscha Populations Research Articles

Paradigm Shift: Applying Capture–Recapture Techniques to Electronic Licensing System Data to Estimate Chinook Salmon Harvest

Implementing creel surveys that produce robust and unbiased estimates of harvest can be complicated, expensive, and labor intensive. Additionally, field personnel often face safety risks associated with traversing roads and highways, occasionally under inclement travel conditions. Here, we develop an alternative method to estimate recreational fish harvest using a hybrid creel that employs capture–recapture techniques in conjunction with data collected from the Oregon Department of Fish and Wildlife's electronic licensing system. We evaluated the method by comparing harvest estimates between the new approach (e-creel) and estimates from a traditional roving creel conducted on four of Oregon's coastal Chinook Salmon Oncorhynchus tshawytscha populations in 2019. Our results indicated that Chinook Salmon harvest estimates derived from our hybrid creel approach were more precise than estimates using traditional creel methods. Both methods generated statistically equivalent estimates of Chinook Salmon recreational harvest, differing by only 3.4%. Estimated mean harvest was 1,264 Chinook Salmon based on the e-creel approach versus 1,258 based on the traditional creel approach. On average, the e-creel estimates reduced the SE by 41% relative to traditional creel estimates. Post hoc assessment of spending associated with creel projects in 2019 suggested that a total savings of US$74,525 in personnel and operational cost, corresponding to an average 15% budget reduction per investigation, could be realized by transitioning from a traditional creel design to an e-creel design.

Two‐Way Trap and Haul as a Conservation Strategy for Anadromous Salmonids

Dams are ubiquitous in the United States and have disconnected migratory fishes from important historical habitat. Trapping fish and moving them around dams (trap and haul) is a common strategy to manage Pacific coast salmonids. Usually, juveniles or adults are moved in one direction, but there is growing interest in two‐way trap and haul (TH2), where both adults and out‐migrating juveniles are captured and transported over dams. Despite recent technological advances, no TH2 program is an unequivocal success. Our review indicates that uncertainties associated with TH2 programs exist and include delayed effects from transportation, maintenance of above‐dam populations, out‐migrant capture efficiency, and the role of hatchery supplementation. Two‐way trap and haul programs should (1) clearly define measurable and objective success metrics, such as the 10 we provide; (2) proceed experimentally under an adaptive management framework to determine risk–benefit trade‐offs; and (3) be part of comprehensive conservation strategies that consider the entire life cycle of each species. Two‐way trap and haul is proposed as a high‐priority recovery strategy for Chinook Salmon Oncorhynchus tshawytscha populations in California. Our findings indicate that any such TH2 program should proceed with extreme caution.

Trophic Ontogeny of Fluvial Bull Trout and Seasonal Predation on Pacific Salmon in a Riverine Food Web

AbstractBull Trout Salvelinus confluentus are typically top predators in their host ecosystems. The Skagit River in northwestern Washington State contains Bull Trout and Chinook Salmon Oncorhynchus tshawytscha populations that are among the largest in the Puget Sound region and also contains a regionally large population of steelhead O. mykiss (anadromous Rainbow Trout). All three species are listed as threatened under the Endangered Species Act (ESA). Our objective was to determine the trophic ecology of Bull Trout, especially their role as predators and consumers in the riverine food web. We seasonally sampled distribution, diets, and growth of Bull Trout in main‐stem and tributary habitats during 2007 and winter–spring 2008. Consumption rates were estimated with a bioenergetics model to (1) determine the annual and seasonal contributions of different prey types to Bull Trout energy budgets and (2) estimate the potential impacts of Bull Trout predation on juvenile Pacific salmon populations. Salmon carcasses and eggs contributed approximately 50% of the annual energy budget for large Bull Trout in main‐stem habitats, whereas those prey types were largely inaccessible to smaller Bull Trout in tributary habitats. The remaining 50% of the energy budget was acquired by eating juvenile salmon, resident fishes, and immature aquatic insects. Predation on listed Chinook Salmon and steelhead/Rainbow Trout was highest during winter and spring (January–June). Predation on juvenile salmon differed between the two study years, likely due to the dominant odd‐year spawning cycle for Pink Salmon O. gorbuscha. The population impact on ocean‐ and stream‐type Chinook Salmon was negligible, whereas the impact on steelhead/Rainbow Trout was potentially very high. Due to the ESA‐listed status of Bull Trout, steelhead, and Chinook Salmon, the complex trophic interactions in this drainage provide both challenges and opportunities for creative adaptive management strategies.

Evaluating the Accuracy and Precision of Multiple Abundance Estimators Using State‐Space Models: A Case Study for a Threatened Population of Chinook Salmon in Johnson Creek, Idaho

AbstractOver the last century, Chinook Salmon Oncorhynchus tshawytscha populations in the Pacific Northwest have experienced dramatic declines, leading to many of them being listed as threatened under the Endangered Species Act. The abundance of these threatened populations relative to the thresholds for delisting remains the primary metric for assessing recovery, yet determining the true population abundances from multiple survey types with unknown levels of accuracy and precision remains difficult. The abundance of the spring–summer Chinook Salmon population in Johnson Creek, Idaho, has been measured using a mark–recapture survey and three different redd count surveys (RCSs) that vary temporally and spatially. Using a state‐space model, we determined the accuracy and precision of each survey type by decoupling the observation error of the survey from the process error describing the annual variability in the true population abundance. We then extended the results of the model to determine the risk of managers’ incorrectly delisting the population (a type I error) or incorrectly keeping it listed (a type II error). Finally, we show that salmon managers with data‐limited populations (primarily those with only single‐pass index RCSs) might use the results of our risk analysis to determine whether expanding survey efforts to minimize management risks is appropriate when they are confronted with dwindling financial resources. For example, we determined that although both the multiple‐pass extended RCS (CV = 0.06) and mark–recapture surveys (CV = 0.14) provide unbiased estimates of salmon abundance in Johnson Creek, the mark–recapture study can have annual costs that are 30–100 times greater. Managers may determine that directing research funds toward acquiring information unique to weir‐based mark–recapture surveys (i.e., migration timing, good genetics samples, etc.) may not be justified for all populations.Received October 7, 2013; accepted March 5, 2014

Bayesian decision analysis for status of Snake River spring?summer Chinook salmon Oncorhynchus tshawytscha populations at extinction risk

The viability of populations was assessed using population trend data and the Diffusion Approximation (DA) model. Various extinction risk metrics for a population are functions of the DA model parameters, and thus, estimates of the DA model parameters are key quantities. Using Bayesian methods, we showed uncertainty in those estimates, and further proceeded to a decision analysis to assess viability of populations. These methods were demonstrated using population trend data from return years since 1980 on naturally produced Snake River spring-summer Chinook salmon Oncorhynchus tshawytscha populations. Of 19 populations examined, the Catherine Creek population was assessed at serious risk, Tucannon River Spring and Grande Ronde Upper Main stem populations were assessed at minor risk, and the other populations were not at risk. This assessment helps managers to prioritize populations at risk for recovery management.

Snake river spring and summer chinook salmon: Can they be saved?

AbstractSpring and summer chinook salmon Oncorhynchus tshawytscha populations from the Snake River have declined precipitously from historical levels. Declines initially were the result of overfishing, but since the late 1950s they have been primarily the result of hydroelectric dams that blocked access to spawning areas, created slack water, and caused mortalities of juvenile outmigrants. Mitigation hatcheries and juvenile collection and bypass systems at dams, transportation of juveniles from upriver dams to a release site on the lower Columbia River, a water budget, allocated spill for fish at main‐stem dams have not increased these populations appreciably. Ocean conditions may have been a factor in the low returns from 1976 through 1984, but the factors currently considered as controlling the viability of the run are the low genetic variability, lack of stress tolerance, and incidence of bacterial kidney disease inherent in the stock. With control of disease, reduced stress at main‐stem projects, and continued efforts to maintain genetic variability, the chinook salmon populations should increase and their long‐term viability should be assured.

Age, Morphology, and Biochemical Genetic Variation of Yukon River Chinook Salmon

Abstract We examined Chinook salmon Oncorhynchus tshawytscha populations in the Yukon Territory for variation in age and size of spawning adults, juvenile morphology, and biochemical genetics during 1985–1987. Yukon River Chinook salmon spent at least one winter in fresh water as juveniles; about 6% of the returning adults had spent two winters in fresh water as juveniles. Males matured at younger ages and generally at smaller mean lengths at age than did females. We observed differences in juvenile morphology among populations: juveniles in habitats with faster water velocities had larger fins and thicker bodies than those in habitats with slower water velocity. We also observed genetic differentiation among populations; the greatest difference was between those populations in the Yukon River drainage and an Alsek River population. Within the Yukon River drainage, Chinook salmon from the Whitehorse fishway and Takhini River were distinct from other populations surveyed. We noted some variation in allelic...