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ELECTROFISHING DISTANCE NEEDED TO ESTIMATE FISH SPECIES RICHNESS IN RAFTABLE WESTERN USA RIVERS
Citation:
Hughes, R M. AND A. T. Herlihy. ELECTROFISHING DISTANCE NEEDED TO ESTIMATE FISH SPECIES RICHNESS IN RAFTABLE WESTERN USA RIVERS. Presented at American Society of Ichthyologists & Herpetologists, Manaus, Brazil, June 26-July 1, 2003.
Description:
A critical issue in river monitoring is the minimum amount of sampling distance required to adequately represent the fish assemblage of a reach. Determining adequate sampling distance is important because it affects estimates of fish assemblage integrity and diversity at local and regional scales. We addressed this issue by using a raft-mounted electrofishing unit to sample 105 nonwadeable river reaches (each for 100 times the mean wetted channel width) across the western USA. We assessed the minimum effort needed to collect 95% of the species obtained in 75% of the reaches sampled (our goal for sampling sufficiency). We also resampled 16 reaches to estimate measurement and sampling period errors, and we sampled 6 reaches for 3 days each to ensure what we thought would be an oversample. The observed species richness of these reaches ranged from 2-24 species. The observed numbers of species were typically 0-5 species fewer than predicted for true species richness by simulated species accumulation curves, nonparametric models, and the 3-day samples. Revisits produced the same number of species or changed by one species. We found no strong correlation between environmental conditions and sampling effort or accuracy. We concluded that a sampling distance equal to 100 times the mean wetted channel width produced repeatable results, could usually be completed in a single day, and that the additional species came at the rate of 2 species per day.