Population ecology of variegate darter in Virginia
May 2008 - May 2012
- Virginia Department of Mines, Minerals and Energy
PROJECT DESCRIPTION: The variegate darter (Etheostoma variatum) is listed as endangered in Virginia. The species is known to occur in Virginia at only four sites in four streams of the Big Sandy River drainage (BSRD) in Buchanan and Dickenson counties, and has suffered population declines and range contractions due to resource extraction, non-point source pollution, and habitat alteration. Specific threats include coal mining, logging, urban development, road construction, sewer and waterline construction, and associated land uses. In April 2007, CONSOL Energy installed a diffuser pipe to discharge high-chloride waste water from their Buchanan No.1 mine into Levisa Fork, Buchanan County, Virginia. The pipe will discharge >1000 gal/min; environmental impacts are expected to occur for several hundred meters downstream. Because variegate darters are known to occupy this reach, longterm monitoring is necessary to determine the effects to this species.An important conservation tactic is to ensure that information is sufficient to accurately describe species distribution, abundance, and status and to assess current human impacts. Although some sites in the BSRD have been surveyed, additional potentially suitable sites remain unsurveyed in recent years. Furthermore, neither habitat quality nor population status for any Virginia population of VD has been rigorously assessed, and the biotic impacts of the diffuser discharge are unknown. The proposed research will address Priority Actions 1, 3, and 4 in the variegate darter recovery plan and will establish a study design to assess biotic impacts associated with the diffuser discharge.
OBJECTIVES: 1) Document the geographic extent of variegate darter distribution in Virginia; 2) Assess the habitat suitability for variegate darter at all survey sites; 3) Estimate population size and age structure of variegate darter in Virginia; 4) estimate genetic distinctiveness and effective population sizes of variegate darter populations in Virginia; and 5) develop a protocol to monitor status and trends of variegate darter in Virginia.
PROGRESS: We sampled 20 sites in the BSRD in Virginia between May and October 2010, and we collected variegate darters at nine of the 13 Levisa Fork sites and at zero of seven Russell Fork sites. Detection probability across all sites was high (0.95), and site occupancy did not vary among years at any site. Variegate darters preferentially used habitat with water depths > 0.41 m and velocity > 0.16 m/s2. Water quality in the Levisa Fork generally met Virginia Department of Environmental Quality standards for pH, temperature, and dissolved oxygen, but conductivity and salinity exceeded standard levels across both Levisa and Russell fork watersheds. We identified three year classes in 2010, including young-of-year, age 1+ and age 2+, indicative of successful spawning in 2010. Fish growth appeared to be slower in 2010 than 2009 given the smaller average and maximum length in age 1+ and 2+ year classes. Mark-recapture sampling indicated density at two riffles was 0.17 to 0.18 individuals/m2. Calculated abundances were 216 and 201 darters at these sites. We measured total habitat availability (riffle area) and we used CPUE from sampled sites to extrapolate an estimate of population size; we estimated variegate darter population size is 16,950 in Levisa Fork from the Virginia state line to the mouth of Dismal Creek. We assessed genetic size and structure of variegate darters in Virginia, and we identified a moderate-sized, genetically stable population in Virginia, though this population is isolated from downstream populations and has begun to differentiate through random genetic drift. Despite isolation, Virginia populations are more closely related to downstream Levisa Fork individuals than to those in Tug Fork, as expected. These data and future collections will allow for on-going monitoring of status and trends of variegate darter populations in Virginia.