Electrofishing and salmonid movement: reciprocal effects in two small montane streams

The effects of electrofishing on salmonid movement and of salmonid movement on electrofishing‐derived abundance estimates were studied in two streams in western Montana, U.S.A. Electrofishing increased emigration of salmonids from study reaches for 1 day, but not for succeeding days, whereas immigration to study reaches was unaffected. Movement of most emigrating fishes was downstream. On these small streams, electrofishing did not appear to cause fishes to flee during sampling. Numbers of salmonids migrating between mark and recapture runs were small relative to the fish abundance estimates in study reaches, usually much less than the 95% CL for those estimates, thus disregarding movements of marked fishes from the study reaches would have produced small positive biases in abundance estimates. Overall, for this suite of salmonid species in mid‐summer in these streams, the effects of electrofishing on fish movement and of fish movement on abundance estimates were minor.