Monitoring protocol for Sacramento River winter chinook salmon, Oncorhynchus tshawytscha: application of statistical power analysis to recovery of an endangered species*

The Sacramento River winter chinook sal mon is listed as an endangered species under the U.S. Endangered Species Act (ESA). The historical spawning grounds of the winter chinook salmon were in upper tributaries of the Sacramento River, including the Upper Sacramento, Pit, and McCloud Rivers (Fig. 1). The completion of Shasta and Keswick Dams in the 1940s blocked access to these spawning grounds, although populations had already declined from historic levels owing to habitat destruction in the upper tributaries (Fisher, 1994). Quantitative winter chinook salmon population size estimates began in 1967 when the Red Bluff Diversion Dam (RBDD), a fl ashboard dam with three fi sh ladders, was completed. Since the completion of RBDD, winter chinook salmon spawning runs have declined from over 100,000 adults to a few hundred adults in the 1980s (Fig. 2; Williams and Williams, 1991). The winter chinook salmon population re mains extremely depleted. The Cali fornia Fish and Game Commission listed the population as a “candidate” species under California’s Endangered Species Act in 1988 and declared it endangered under that Act in 1989. The National Marine Fisheries Service (NMFS) declared the species “threatened” under the federal ESA in the same year, and it was declared “endangered” in 1994. NMFS has taken numerous regulatory actions under the ESA to improve winter chinook salmon survival, including changes in the regulations governing California’s ocean salmon fi sheries.1 Monitoring protocol for Sacramento River winter chinook salmon, Oncorhynchus tshawytscha: application of statistical power analysis to recovery of an endangered species*