BACKGROUND

Juvenile fall chinook salmon Oncorhynchus tshawytscha listed for protection under the Endangered Species Act mostly have an ocean-type life history.  Fry emerge in the spring, grow rapidly, and migrate from the Snake River during summer.  However, some of the later emerging and slower growing juvenile fall chinook salmon fail to leave the Snake River as subyearlings, overwinter in the reservoir, and then resume seaward migration the following spring as yearlings (hereafter, holdover smolts).  This is especially prevalent in the lower Clearwater River, which produces the latest emerging fry of present-day production areas.  In recent years as part of other studies, researchers have compiled moderate amounts of unpublished data that suggests that wild juvenile Snake River fall chinook salmon that holdover in the lower Snake River reservoirs contribute up to 30% to adult production.  Existing data cannot be used to determine the specific time holdover fall chinook salmon smolts pass dams in the Snake and Columbia River, but there is a good chance that passage occurs during late winter when fish bypass facilities are shut down.  This means holdover smolts pass through the turbines and are susceptible to blade strike.  Our new project will refine existing methods for determining the age and genetic lineage of holdover fall chinook salmon, compile and publish the existing data on holdover fall chinook salmon, and then document passage timing of holdover fall chinook salmon smolts at Lower Granite Dam.



COORDINATION

Coordination with the agencies and tribes is necessary to avoid duplicating work and to make efficient use of existing resources and personnel.  We will coordinate our research with the Bonneville Power Administration, Environmental Protection Agency, Fish Passage Center, Idaho Fish and Game, Idaho Power Company, National Marine Fisheries Service, Nez Perce Tribe, Oregon Department of Fish and Wildlife, Pacific States Marine Fisheries Commission, U. S. Army Corps of Engineers, U. S. Fish and Wildlife Service, U. S. Geological Survey, University of Idaho, and Washington Department of Fish and Wildlife.



GOAL

Our research goal is to provide fishery managers with a complete description of holdover by juvenile Snake River fall chinook salmon, so that the management implications of this atypical migrational behavior can be understood.

OBJECTIVES AND RATIONALE

Objective 1:   Determine if holdover wild fall chinook salmon pass Lower Granite Dam during the winter when the fish bypass systems are shut down.

Rationale: If holdover wild fall chinook salmon pass Lower Granite Dam in the winter, it is likely that a high percentage of the fish are killed by turbine blade strike.  Starting fish bypass operations in March, rather than in April, might lead to large increases in fall chinook salmon adult returns to the Snake River.  Objective 1 of our study will provide mangers with the data to decide if earlier operation of the fish bypass system at Lower Granite Dam should be considered.