General Technical Reports (CNRE)
Permanent URI for this collection
Browse
Recent Submissions
- Population ecology of variegate darter (Etheostoma variatum) in VirginiaArgentina, Jane E.; Angermeier, Paul L.; Hallerman, Eric M. (2013-08-12)Variegate darters (Etheostoma variatum) were listed as endangered in Virginia in 1992. Reasons for listing included habitat degradation and concerns about current and future impacts of coal mining throughout their Virginia range. Prior to this research, little was known about variegate darter distribution, habitat use, or populations in Virginia. Two primary goals of this research were to gain knowledge about the current population ecology and the relationship between landscape-level factors (e.g., land cover changes, watershed size, isolation from other populations) on current and past variegate darter population sizes. We investigated distribution, habitat suitability, population genetics, and population size and structure of variegate darters in the upper Big Sandy River drainage, Buchanan, Dickenson, and Wise Co., Virginia. Our results indicate variegate darters are primarily found in the Levisa Fork, with highest densities and abundances between its confluence with Dismal Creek and the Virginia-Kentucky border. Sporadic occurrences in smaller tributaries to the Levisa and Tug forks indicate they do exist more widely in low numbers, especially near the confluence with the Tug and Levisa mainstems. Detection of variegate darters in smaller tributaries was inconsistent, with reach-level occupancy varying among years. We detected young-of-year variegate darters every year we sampled. However, age 1+ darters were indistinguishable from older darters based on standard length. Variegate darter population size and stability in Virginia were estimated via multiple methods, including site occupancy surveys, mark-recapture studies, and population genetic analysis. Using mark-recapture methods at five sites, we estimated overall population size in 2011 to be approximately 12,800 individuals in the 35-km reach between the Levisa Fork - Dismal Creek confluence and the Virginia-Kentucky border. Age structure appeared stable, with breeding adults and young-of-year collected annually during 2008-2011. Population genetic analyses indicated that variegate darters in the Levisa Fork and its tributaries are part of a single genetic population. Historical and current genetic stability were seen in our analysis of the variegate darter population, with no genetic differentiation among riffles across the upper Levisa Fork watershed, indicating dispersal among these sites is enough to overcome random genetic drift. This population is genetically isolated from downstream variegate darter populations by the dam at Fishtrap Lake, Pike Co., Kentucky, and is beginning to show genetic isolation from other nearby populations. As expected, the Virginia population is most closely related to those in the Russell Fork and Levisa Fork downstream of the dam. Regular monitoring of variegate darters in the Levisa Fork mainstem from the Dismal Creek confluence to the Virginia-Kentucky border would facilitate better understanding of normal fluctuations of population size and distribution, as well as assessments of population status. This reach encompasses the core of the variegate darter population in Virginia, and its persistence will determine long-term viability of this species. Given that little is known about long-term population trends, we suggest that annual site-occupancy and population size estimates be made at ten randomly selected riffles for at least ten years to understand normal levels of variability. Thereafter, these population parameters could be monitored bi-annually as a way to detect changes in distribution or abundance, especially after any fish kill or other pollution event in the Levisa Fork. We further suggest that the sites upstream and downstream of the saline diffusor pipe be monitored to detect changes in the extent of the impact zone. Overall, the variegate darter population in Virginia appears stable, although primarily confined to the lower 35 km of the Levisa Fork. Nevertheless, variegate darters in Virginia do remain susceptible to extirpation due to catastrophic events, both physical (chemical spill) and biological (disease outbreak or invasive species introduction).
- Assessing impacts of the Roanoke River Flood Reduction Project on the endangered Roanoke logperch (Percina rex): Summary of Construction-Phase MonitoringRoberts, James H.; Anderson, Gregory B.; Angermeier, Paul L. (2013-08-12)The United States Army Corps of Engineers (USACE) has partnered with the City of Roanoke to carry out the Roanoke River Flood Reduction Project (RRFRP), a suite of floodplain modifications to the Roanoke River. The incidental take permit issued to USACE requires that USACE monitor populations of the federally endangered Roanoke logperch (Percina rex) prior to (Phase A), during (Phase B), and after (Phase C) construction, to estimate effects of incidental take during the course of the project. This report summarizes logperch relative abundance, suitable habitat, and water quality conditions across Phase B and compares these data to Phase A. We also conducted additional research in 2011 to assess the representativeness of permanent monitoring sites, estimate the sampling efficiency of the electrofishing methodology, and evaluate the statistical power and appropriateness of alternative impact-detection methods. Despite substantial fluctuation of the relative abundance of adult logperch over the course of monitoring, we found no statistical evidence for an impact of RRFRP construction. Thus USACE has maintained compliance with its incidental take permit during Phase B. Young-of-year logperch density, habitat availability, and water quality conditions also varied considerably over time and space during Phase B, but not in ways that could be attributable to the RRFRP. We found that permanent sites were representative of reach-wide conditions, suggesting that our findings can reasonably be extrapolated to the entire study area. The sampling efficiency of our standard electrofishing method was estimated to be low (~ 11%), yet our assessment method produced indices of abundance that were strongly correlated with true population estimates. Herein we demonstrate a new, generalized linear modeling approach to impact assessment that should provide greater insight and statistical rigor than the traditional t-test approach.