Environmental Factors Associated with the Upstream Migration of Fall-Run Chinook Salmon in a Regulated River

AbstractWe examined upstream migration patterns of adult Chinook Salmon Oncorhynchus tshawytscha in relation to environmental factors and two management actions (installation of a rock barrier at a distributary and managed pulse flows). Data was collected using a portable resistance board weir and a Vaki Riverwatcher system that provided accurate daily counts of fall-run Chinook Salmon on their spawning migration. Akaike’s information criterion and multimodel inferential approaches, as well as generalized additive models, were used to assess the relative influence of water temperature, flow, moon illumination, weather, operation of a rock barrier, and managed pulse flows to explain the magnitude of daily counts and proportions of Chinook Salmon observed at the weir. Over the 12-year study period (2003–2014), we observed 38,206 Chinook Salmon. The installation of a rock barrier in the lower reaches of the San Joaquin River had positive and consistent influences on daily counts in the years it was installed...