Electrofishing Distance Needed to Estimate Consistent Index of Biotic Integrity (IBI) Scores in Raftable Oregon Rivers

Abstract An important issue surrounding assessment of riverine fish assemblages is the minimum amount of sampling distance needed to adequately determine biotic condition. Determining adequate sampling distance is important because sampling distance affects estimates of fish assemblage condition at both local and regional scales, and oversampling is costly. We examined the sampling distance question by sampling 45 raftable Oregon river reaches for an entire day and then assessing the minimum distance needed to obtain index of biotic integrity (IBI) scores in those reaches that varied by less than 10% from the 1‐d samples. An electrofishing raft was used to collect fish, and physical and chemical habitats were sampled to aid in reach description. We found that a sampling distance equal to 50 times the mean wetted channel width, or a catch of more than 120 individuals, produced IBI scores that met our criteria.