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.

Impact/Purpose

Fish species richness is an important indicator of ecological condition in streams and rivers. In the western United States, collecting representative samples of the fish assemblage from larger streams and rivers can be challenging because of areas of swift water and remote access prohibit the use of motorized watercraft as sampling platforms. Sampling in these rivers can be conducted using electrofishing gear mounted on rafts controlled using oars. Using rafts could require sampling for longer distances to obtain a representative sample of the fish species present. In this study, we used rafts to collect fish from 10 river sites across the western USA over a distance equal to 300 times the mean channel width of each river. We found that 90% of the fish species present at a river site were collected after sampling river lengths of between 80 and 210 mean channel widths (mean=150 mean channel widths). Longer distances were required if a river contained a higher proportion of uncommon species. These distances are longer than studies in other regions of the USA using motorized watercraft have found. Monitoring programs intending to adequately estimate fish species richness in nonwadeable rivers should assess the sampling effort that will be necessary given the intended sampling platform and the level of interest in rare or uncommon species.

Citation

Hughes, R., A. Herlihy, AND Dave Peck. Sampling Efforts for Estimating Fish Species Richness in Western USA River Sites. Elsevier B.V., Amsterdam, NETHERLANDS, 87:125859, (2021). [DOI: 10.1016/j.limno.2021.125859]

DOI: Sampling Efforts for Estimating Fish Species Richness in Western USA River Sites