THE INFLUENCE OF HABITAT COMPLEXITY AND FISH SIRE ON OVER-WINTER SURVIVAL AND GROWTH OF INDIVIDUALLY MARKED JUVENILE COHO SALMON (ONCORHYNCHUS-KISUTCH) IN BIG BEEF CREEK, WASHINGTON

Wild juvenile coho salmon (Oncorhynchus kisutch) were individually mar ked in October 1990 and 1991 to evaluate the effects of habitat comple xity and fish size on over-winter survival in Big Beef Creek, Washingt on. Habitat complexity was quantified for the habitat unit where the f ish were collected and, in 1991, also for the 500-m reach downstream f rom the collection site. Survival, estimated from recovery of marked s melts at the stream's mouth, differed between years (25.4 and 46.2%) a nd also varied among habitat units and reaches within years. Survival was at most weakly correlated with complexity of the habitat units but was strongly correlated with the quantity of woody debris and density of habitat units in the 500-m reach, and distance from the estuary. B ecause distance covaried with habitat complexity, we could not ascerta in which factor had the primary influence on survival. In addition, la rger fish generally survived at a higher rate than smaller individuals . However, fish tagged above William Symington Lake were smaller in th e fall but larger as smelts and had higher survival rates than those t agged below the lake. Taken together, these results reveal complex rel ationships between size, habitat, and growth that may affect over-wint er survival and subsequent life-history events.