Assessing electrofishing effort required to estimate species richness of fishes in nonwadeable rivers of Alabama, USA

Abstract

AbstractObjectiveMuch of the fish biodiversity in the southeastern USA is found in lotic systems, but assessment of fish community structure in large nonwadeable rivers has lagged compared to streams. Sampling designs that adequately estimate species richness are a prerequisite to creating bioassessment metrics but thus far has not been attempted in highly biodiverse rivers in the southeastern USA east of the Mississippi River.MethodsFish communities in four nonwadeable rivers across Alabama spanning catchments of 2046–57,415 km2 were sampled using electrofishing in summer and fall of 2015 and 2016. All rivers were sampled during day; two rivers were also sampled at night to assess diel changes in species accumulation.ResultIn total, 55,239 fishes were collected across rivers, representing 106 species in 24 families. Species collected continued to increase as sampling increased in all river‐season combinations, rarely displaying an asymptote. Species generally accrued more quickly and accumulation curves showed more tendency to asymptote in fall than summer in all but the largest river. Species accumulated faster at night than during the day in both rivers during summer but was similar between diel periods in fall. On average, 95% of the species observed were collected in eight subreaches in fall but not until nine during summer; however, observed number of species was generally one to six species lower than mean estimates of true species richness. Sampling efforts collected approximately similar species assemblages across transects, years, season, and diel periods. Extrapolation of species accumulation curves suggested that 6–17 km of sampling distance would be required to collect all species present.ConclusionResults of this study demonstrate that assessing fish communities in species nonwadeable rivers requires an inordinate amount of sampling effort, which may be unattainable for many agencies. Further study is warranted to develop innovative solutions to overcome these logistical challenges.