Studying steelhead (Oncorhynchus mykiss) populations in the rivers of California’s Central Valley has long challenged scientists and managers due to the species’ diverse and complex life history. Although recent initiatives such as the Central Valley Steelhead Monitoring Program (CVSMP) have sought to improve our understanding of steelhead in the Sacramento River Basin, no such concerted efforts have been developed for the San Joaquin River Basin. To begin addressing this gap, the Delta Science Program recently hosted a virtual workshop entitled Monitoring Steelhead Populations in the San Joaquin Basin. Over 200 participants, including experts from state and federal agencies, academia, NGOs, and private consultancies, came together to learn about current steelhead monitoring programs in other watersheds, assess the status of ongoing steelhead monitoring in the Central Valley, and identify opportunities for interagency and stakeholder partnerships to implement an efficient and sustainable steelhead monitoring plan for the San Joaquin Basin. By identifying key gaps in knowledge and defining current management challenges, the workshop outcomes will be used to help develop and design an improved approach to steelhead monitoring in the long overshadowed southern half of the Central Valley.

The first day of the workshop focused on management challenges and existing steelhead monitoring frameworks in other watersheds. Common “lessons learned” from ongoing monitoring in the Columbia and Russian River basins included that no one method or approach to sampling works perfectly all the time, but a suite of approaches such as weirs, rotary screw traps, snorkel surveys, PIT and acoustic tags, and genetic analyses can be used together to improve our understanding of steelhead populations. One presentation highlighted the homogenizing effect of 70 years of hatchery steelhead production, which has reduced variability in migration timing and, potentially, the ability of fish to adapt to environmental change. Another presentation discussed recent developments in the understanding of genetic control of migratory behavior. Although it isn’t possible to use genetics to definitively distinguish whether an individual fish is, or will become, a migratory steelhead or a rainbow trout (the resident form of the species), examining higher level genetic patterns can provide valuable insight into diversity, connectivity, and adaptation of populations. Finally, a discussion of statistical models of Central Valley steelhead life-history expression described an effort to explain variation in migratory behavior among different rivers, and discussed the need for studies to refine the relationships between temperature, flow, food, and growth, as well as model the effects of environmental change.