Prespawning Movement of Wild and Hatchery Fall Chinook Salmon Adults in the Snake River

Abstract

We used radiotelemetry to describe the prespawning movement of adult fall Chinook salmon Oncorhynchus tshawytscha (5 wild males, 4 wild females, and 27 hatchery females) in the Snake River. We characterized the migratory phase as consecutive detections made in an upstream direction after radio-tagging and release. A transition from the migratory phase to the search phase was usually observed after wild adults passed their natal rearing areas and after hatchery adults passed the locations where they were released as subyearlings. This provided evidence for successful imprinting. A similar level of exposure to riverine habitat during a sensitive period coinciding with the parr–smolt transformation was a plausible explanation for this imprinting. The search phase was usually characterized by a series of downstream and upstream excursions ending with spawning site selection. Hatchery females moved an average of four to five times farther and two to three times more frequently than wild fish during these excursions. Available measures of genetic lineage, environmental conditions, and competition did not fully explain this pattern. We hypothesize that hatchery females moved farther and more frequently than wild adults partly because hatchery females had difficulty locating and identifying suitable spawning habitat as a result of hatching and early rearing in captivity.