Population Estimate of the State and Federally Threatened Spotfin Chub Using Underwater Observations

Abstract

AbstractDetermining the population demographics of threatened or endangered species can be difficult if the methods that are used must be minimally invasive. However, knowing the population status of species that are of conservation interest must be understood for successful management. We used underwater observations (i.e., snorkeling) to determine population estimates for Spotfin Chub Erimonax monachus in the Cheoah River in North Carolina, a species that is listed as threatened at both state (North Carolina) and federal levels. Seven sites were randomly selected between the Santeetlah Dam and the confluence with the Little Tennessee River. Each site was surveyed by three snorkelers who completed multipass snorkeling from July 17 to 25, 2019. The population estimates were generated with an N‐mixture model and incorporated site‐specific habitat. Four hundred and sixty‐six observations of Spotfin Chub were recorded across all of the sites and passes. The simple model without covariates of abundance estimated a total population size of 12,139 (95% credible interval [CRI] = 9,821–15,453). Incorporating site‐specific percentage of bedrock improved model fit and indicated that the percentage of bedrock was positively related to site‐specific abundance. The total population size as estimated with the covariate model was 13,905 (95% CRI = 11,620–22,181). Our results yielded new insight into the status of a threatened species while confirming previous knowledge about its microhabitat use. Locally, the results of this work suggest that Spotfin Chub are well established in the Cheoah River and maintain a substrate affinity to bedrock. Broadly, the field methods that were used here are logistically feasible, cost efficient, and minimally stressful for the fish. We suggest that this methodology be considered when total and site‐specific population estimates are needed to manage species of concern. Additionally, more detailed site‐specific habitat can improve model estimates by explaining site‐specific variability in abundance, resulting in more precise total population estimates.