Sampling Efforts for Estimating Fish Species Richness in Western USA River Sites
Fish species richness is an indicator of river ecological condition but it is particularly difficult to estimate in large unwadeable rapidly flowing rivers. Intensive multi-gear sampling is time consuming, logistically complex and expensive. However, insufficient sampling effort underestimates species richness and yields inaccurate data about the ecological condition of river sites. We raft-electrofished 10 river sites in 10 ecoregions and six western USA states for distances equal to 300 times their mean wetted channel widths (MCWs) to estimate the effort needed to approach asymptotes in fish species richness. To collect 90% of the fish species at the sites, we found that 80-210 MCWs or an average of 150 MCWs were needed, with the number of MCWs increasing in rivers with a higher proportion of spatially rare species. Frequently, the second or third additional 100 MCWs produced only one or two additional singletons or doubletons. Before initiating sampling programs for adequately estimating species richness, we recommend assessing sampling effort, particularly if rare or uncommon species are expected or desired.