INDIVIDUAL VARIATION IN DISPERSAL BEHAVIOR OF NEWLY EMERGED CHINOOK SALMON (ONCORHYNCHUS-TSHAWYTSCHA) FROM THE UPPER FRASER-RIVER, BRITISH-COLUMBIA

Immediately after emergence from spawning gravels, fry of stream-type chinook salmon (Oncorhynchus tshawytscha) populations from tributaries of the upper Fraser River, British Columbia, distribute themselves do wnstream from the spawning areas, throughout the natal stream, and int o the Fraser River. We tested the hypothesis that this range in disper sal distances is caused by innate differences in nocturnal migratory t endency among individuals. Using an experimental stream channel, we fo und repeatable differences in downstream movement behaviour among newl y emerged chinook fry. Fish that moved downstream were larger than tho se that held position in the channel. However, the incidence of downst ream movement behaviours decreased over the first 2 weeks after emerge nce. We propose that the variation among individuals in downstream mov ement behaviour we observed leads to the dispersal of newly emerged fr y throughout all available rearing habitats. Thus, between-and within- population variation in the freshwater life history observed in these populations may be caused by small differences in the behaviour of ind ividuals.