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

Abstract

Determining 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.

Long‐Term Population Dynamics and Habitat Association of the Federally Threatened Spotfin Chub in the Little Tennessee River

“…Nevertheless, variation across sites could be affecting our results. Our habitat analysis across three sites was consistent with known habitat use by Spotfin Chubs (Kano et al 2012; Doll et al 2020). For example, out of the three sites where habitat was measured, Needmore and Dean Island had the highest estimated relative abundances in 2015 (Table 3), corresponding to the sites with the highest percentage of bedrock.…”

“…For example, the Cheoah River contains a reestablished population developed from the Little Tennessee River broodstock. An estimate of the Spotfin Chub population in the Cheoah River in 2019 indicated that they are locally well established: the total population estimate was 13,905 fish (95% CRI = 11,620–22,181; Doll et al 2020). The current study, paired with the results of Doll et al (2020), highlights the importance of understanding the Little Tennessee River population dynamics.…”

“…An estimate of the Spotfin Chub population in the Cheoah River in 2019 indicated that they are locally well established: the total population estimate was 13,905 fish (95% CRI = 11,620–22,181; Doll et al 2020). The current study, paired with the results of Doll et al (2020), highlights the importance of understanding the Little Tennessee River population dynamics. Although population trends within the Little Tennessee River cannot be generalized to trends in populations rangewide, documenting a stable population within this river is a necessary step toward reestablishing the Spotfin Chub across its historical range.…”

Incorporating Batch Mark–Recapture Data into an Integrated Population Model of Brown Trout

“…Multiple observations of the population that are replicated over space and time are needed to estimate detection. Common approaches include tagging individual fish that are recaptured over multiple occasions (Bradshaw et al 2007;Conner et al 2015), depletion methods (Mäntyniemi et al 2005), and repeated surveys (Royle 2004;Webster and Pollock 2008;Coggins et al 2014;Doll et al 2020). Although informative, these sampling protocols can be costly because of the increased sampling effort at a single site or reliance on tracking individual fish.…”

Genomic and phenotypic divergence informs translocation strategies for an endangered freshwater fish

“…Captive propagation, translocation, and reintroduction of species to areas of extirpation are being increasingly deployed to combat declines in diversity and abundance (George et al, 2009). In North America, the translocation of nongame fishes has mainly been focused at the organismal level, with the goals of reintroducing individuals to historical habitats or increasing the size and stability of existing populations (Andreasen & Springer, 2001; Doll et al, 2020; Shute et al, 2005). Although some of these translocations have also sought to bolster genetic variation of the target populations (e.g., Shute et al, 2005) there has been relatively little focus on the hidden histories of genetic material being moved with the fishes.…”