The Muskellunge Esox masquinongy is a highly sought-after sport fish that is native to the Tennessee River drainage of western North Carolina. After the extirpation of Muskellunge from North Carolina in the 1950s, the North Carolina Wildlife Resources Commission began a stocking program to re-establish the species and produce viable Muskellunge fisheries in North Carolina. Although stocking efforts have created a Muskellunge fishery in, for example, the French Broad River (where the species was native), there is little evidence of success in North Carolina sections of the New River (where the species was not native). Possible mechanisms inhibiting stocking success are unclear because there is relatively little information available on the juvenile life stage of the Muskellunge, especially in the southern portion of its distribution. We addressed the perceived differences in recruitment between the two fisheries by using telemetry to investigate dispersal, mortality, and habitat use by stocked juvenile Muskellunge. Fifty hatchery-reared, age-0 Muskellunge (282-307 mm TL) were tagged prior to stocking in the New River (fall 2013) and French Broad River (fall 2014). Three months after stocking, known survival of tagged fish was 4% in the New River and 29% in the French Broad River; the survival probability after 3 months was estimated at 9% (range = 4-17%) in the New River and 37% (range = 25-56%) in the French Broad River. Extended survival in the French Broad River was 14% at 252 d poststocking. High dispersal was observed, with maximum individual dispersal of 67.4 km in the New River and 55.5 km in the French Broad River. Habitat suitability analyses indicated that juvenile Muskellunge in the FBR selected shallow nearshore areas with low water velocity, fine substrate, and substantial cover in the form of woody debris and overhanging vegetation. Information on the survival and behavior of stocked Muskellunge can facilitate efforts to successfully manage these fisheries.
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.
Endemic species are threatened by invasive species, habitat loss, and climate change. Endemic species are also an important group that maintains biodiversity. Understanding population dynamics of endemic species is needed to maintain or restore their populations. Advancements in models that describe population dynamics of endemic species and species of conservation need has been made possible by the application of novel quantitative methods. One such modeling tool is state-space modeling. These models provide a flexible framework to describe population dynamics using simple mortality models and more complex integrated population models. Here we develop a state-space model to describe survival and population size of the Sicklefin Redhorse (Catostomidae: Moxostoma sp.), a species of conservation concern from two rivers located in North Carolina, USA. This model is structured to combine information across similar rivers and to account for complex interactions of sex, time, variable sampling effort, and river discharge. Survival of Sicklefin Redhorse was found to vary by sex, and annual variability was not consistent across rivers. Discharge was negatively related to capture probability for males. Capture probabilities also differed across sex. Population estimates revealed a large difference between sex where males outnumbered females each year in both rivers. We conclude that electrofishing is not an efficient capture method but when used, should consider discharge. Discharge was not included in the survival model, however, the 3 years with the lowest survival in the Little Tennessee River coincided with the three lowest discharge years in the time series. Future work should investigate the difference in survival between the rivers.
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