Estimating in-river survival of migrating salmonid smolts using radiotelemetry

A field study to estimate the survival of outmigrating steelhead (Oncorhync hus mykiss) smolts using radiotelemetry methods is illustrated. A paired re lease-recapture design was used to estimate pool (i.e., reservoir), dam, an d project (i.e., reservoir plus dam) survival at two mid-Columbia River hyd roprojects based on maximum likelihood estimation. The release and detectio n scheme was designed to minimize the possibility of detecting false-positi ve radio signals from smolts that might have died upstream during the hydro project passage. Model assumptions and possible violations are discussed. R eleases of radio-tagged and passive integrated transponder (PIT) tagged ste elhead smolts were also compared to assess the possible effects of tag type on migration behavior. Survival through the Rocky Reach project (P = 0.86) and Rock Island project (P = 0.41) and bypass diversion probabilities at R ocky Reach Dam (P = 0.39) were found to be similar between tag types. Small but significant differences in arrival patterns (P = 0.02) and travel time s (P = 0.01) were observed between radio-tagged and PIT-tagged smolts.