Mortality of yearling chinook salmon prior to arrival at Lower Granite Dam, on the Snake River. Progress report

摘要

Efforts have been initiated to develop a research plan that will provide insight into causes of, and ultimately solutions to, the apparent excessive mortality of juvenile chinook upstream from Lower Granite Dam on the Snake River. In the context of the proposed salmon stock listings under the Endangered Species Act, issues that potentially affect wild stocks of spring chinook salmon probably warrant immediate consideration and resolution. Mark-recapture data at Lower Granite Dam indicate that few yearling chinook salmon (Oncorhynchus tshawytscha) smolts survive to that site after release from various hatcheries. Upriver stocks of yearling spring and summer chinook exhibit pronounced losses en route to the dam. In 1989 and 1990, only about 8 to 18% of PIT-tagged representatives from McCall or Sawtooth hatchery were detected at the dam. General survival indices for these stocks indicate that perhaps only 15 to 35% of the yearlings survived to that site. This suggests these stocks may sustain as much mortality traversing this unobstructed reach of river as the general population would passing through the entire hydroelectric complex.