Summer movement and growth of juvenile anadromous salmonids in small western Washington streams

Ahstmct: Movements of juvenile coho salmon (Oncorhynrhu,~ kisutch), cutthroat trout (Oncorhynchus clarki clarki), wd steelhead trout (Oncorhynchus mykiss) were studied by observalions and rccapturc of marked individutlls in three western Washington streams to test the hypotheses that few fish would move, downstream movement would predominate, movers would be initially smaller and grow slower after movement than residents, and habitat quality would influence movement. Contrary to predictions, from 2R to 60% of marked fish moved at least one huhitut unit, and immigration of unmarked fish also indicated considcrtiblc movement. Upstream movement predominated but thc stream with the stcp-pool/cascude channel rypc had fcwcr upstrcum movers and greatcr divtunces moved downstream. Coho movers were not smullcr than nonrnovers, as predicted based on assumptions that movement results from competitive exclusion. Habitat units that coho left were smdler and shallower but lowcr in density than units whcrc coho remained. Thus, movement is a common phenomenon rather than an aberration, and m n y t f l ~ ~ h n h ~ ~ . _ c @ i c e ether than .. . territorial . .," -. --eviction. voreover, movers grew faster than n o u n o ~ s , , s o the u ~ R k & & F t i o n ~ of the population wtu: not composed of comgfitively inferi&'hh but rather hdividuals that thrived. The phenomenon of small-scalc habitatw d growth-relatcd movements should be considered when planning and interpreting studies of juvenile salmonid ecology in strems.