Abstract
Steelhead are anadromous Oncorhynchus mykiss that are ecologically and culturally important throughout their native range in western North America. In the past several decades, returns of Snake River steelhead have been low, so Snake River steelhead were listed as threatened under the Endangered Species Act. Steelhead are produced in hatcheries and released as juveniles throughout the basin to provide harvest opportunities for tribal and recreational anglers. Management of steelhead is complicated because of potentially conflicting goals to preserve natural-origin steelhead and to promulgate a fishery. Essential aspects of management are to monitor the status of each stock, evaluate the impacts of the fishery, implement regulations that balance multiple objectives, and to plan for future production of stocks. A management model exists to estimate fishery-related mortalities and escapement for stocks within the Snake River basin. However, the outputs of the model do not have estimates of uncertainty such as standard errors or confidence intervals. In Chapter 2, I extend the model in two different ways to estimate uncertainty, and I conduct a sensitivity analysis on the model. Estimates of escapement are robust to model assumptions when they are reported at large spatial scales. In Chapter 3, I evaluate the effects of bag and length limits on the steelhead fishery in the Clearwater River, which is in the Snake River Basin. Bag and length limits can effectively modulate harvest and catch-and-release mortalities, where more restrictive regulations substantially reduce total mortalities from harvest and catch-and-release mortalities. In Chapter 4, I investigate the potential effects of climate change on juvenile steelhead by evaluating the influence of extreme flows and stream temperature on juvenile steelhead abundance and size structure in montane streams and rivers in Idaho. The effects of flow and temperature on steelhead are complex and depend on the life history strategy of steelhead, suggesting the importance of conserving broad habitats to sustain broad life histories and the species’ resilience to climate change. Together, these three chapters evaluate three important aspects of steelhead management, from monitoring to planning for the future.