A MULTIPLE-REACH MODEL DESCRIBING THE MIGRATORY BEHAVIOR OF SNAKE RIVER YEARLING CHINOOK SALMON (ONCORHYNCHUS-TSHAWYTSCHA)

A multiple-reach model was developed to describe the downstream migrat ion of juvenile salmonids in the Columbia River system. Migration rate for cohorts of fish was allowed to vary by reach and time step. A nes ted sequence of linear and nonlinear models related the variation in m igration rates to river flow, date in season, and experience in the ri ver. By comparing predicted with observed travel times at multiple obs ervation sites along the migration route, the relative performance of the migration rate models was assessed. The analysis was applied to co horts of yearling chinook salmon (Oncorhynchus tshawytscha) captured a t the Snake River Trap near Lewiston, Idaho, and fitted with passive i ntegrated transponder (PLT) tags over the 8-year period 1989-1996. The fish were observed at Lower Granite and Little Goose dams on the Snak e River and McNary Dam on the Columbia River covering a migration dist ance of 277 km. The data supported a model containing two behavioral c omponents: a flow term related to season where fish spend more time in regions of higher river velocity later in the season and a flow-indep endent experience effect where the fish migrate faster the longer they have been in the river.