Habitat Suitability for Roanoke Logperch in Streams near Philpott Reservoir.
August 2009 - March 2012
- U.S. Army
PROJECT DESCRIPTION: The entire known range of the endangered Roanoke logperch (Percina rex) comprises 4 disjunct areas in Virginia, including the upper Roanoke, Pigg, Smith, and Nottoway river drainages. Developing an effective conservation strategy, including implementation of the Endangered Species Act, requires accurate knowledge of the species’ distribution and abundance. The U.S. Army Corps of Engineers (USACE) is responsible for protecting and recovering logperch associated with their water projects, including Philpott Reservoir on Smith River. In particular, the USACE must survey their waters for logperch and suitable habitat, and monitor and manage populations therein.An important conservation tactic is to ensure that survey information allows accurate descriptions of species distribution, abundance, and population trends. Roanoke logperch were recently discovered to be relatively common throughout Smith River upstream of Philpott Reservoir. Additional surveys are warranted to monitor logperch abundance and to assess habitat suitability. OBJECTIVES: Project objectives are as follows: 1) estimate population density and distribution of Age-1+ Roanoke logperch in the project area; 2) measure and map, by suitability class, the distribution of habitat suitable for Roanoke logperch in the project area; 3) assess water quality relative to Roanoke logperch habitat in the project area; 4) use the data on logperch abundance, habitat suitability, and water quality to test the general validity of correlates of logperch abundance from other locations; 5) identify opportunities and threats related to protecting and enhancing Roanoke logperch habitat; and, 6) provide recommendations on the necessity and scale of future studies and monitoring related to logperch in and near USACE waters. PROGRESS: We captured a total of five Roanoke logperch in fall 2010, of which three were Age-1+ and two were Age-0. Population density ranged from 0.0 to 83.3 total individuals ha-1 at individual sites and averaged 20.0 total individuals ha-1 over all sites. This was the lowest density recorded since the present monitoring protocol began in 2006. Population density of Roanoke logperch also was lower in 2010 than in 2006-2009 in the Roanoke River, though the overall density of logperch always was higher in the Roanoke than the Smith River during this time period. Spatial peaks and troughs of Age-1+ logperch density do not seem to coincide with peaks and troughs of Age-0 logperch density. Age-0 density tends to be high at Sites 1 and 5 and low at Sites 2, 3 and 4, whereas Age-1+ density tends to be high at Site 4 and low at Sites 1 and 5. This lack of correlation is not surprising, given that adult and juvenile logperch exhibit preferences for different habitat configurations. On average, 41.4% of the area of sites provided “high-quality” (i.e., good to excellent) habitat for Roanoke logperch in fall 2010, whereas only 18.2% of the area of sites provided “low-quality” (i.e., poor to unsuitable) habitat. High-quality habitat was less common in 2010 than in 2009, but within the range previously observed. Annual variation in habitat suitability may be related to annual variation in the streamflow of the Smith River, as estimated by the U.S. Geological Survey gauging station near Woolwine, VA. The estimated percentage of high quality habitat is strongly positively correlated with the mean streamflow during habitat sampling, as well as with the mean and variance of streamflow during the spring (1 April to 30 June) leading up to the sample. Elevated spring streamflows may scour away previously-deposited silt, thereby increasing habitat suitability, whereas elevated streamflows during sampling may increase habitat suitability by increasing the depth and velocity of microhabitat cells. Habitat conditions appear to exhibit greater fixed temporal than fixed spatial variability. The availability of high-quality Age-1+ habitat at sites varies consistently among years, whereas no sites seem to consistently maintain more high-quality habitat than others. However, Site 3 exhibits less annual variability than other sites, possibly because of its deep morphology and prevalent unsuitable bedrock substrate, which make habitat suitability calculations at the site less sensitive to hydrologic variation. Furthermore, spatial variation in habitat quality does not clearly relate to spatial variation in Age-1+ or Age-0 logperch density. This lack of spatial correlation between habitat and logperch density also has been observed in the upper Roanoke River and suggests that logperch migrate among sites over their lifetimes. Water quality exhibited only minor between-site variability. Based on published accounts and data from the Roanoke River, water quality in the Smith River during fall 2010 was well within ranges acceptable for use by Roanoke logperch. Based on bivariate correlations, logperch density does not appear to be strongly related to streamflow. Estimated Age-1+ logperch density is weakly negatively correlated, and Age-0 density weakly positively correlated, with the mean and variance of streamflow during spring (1 April through 30 June) and with the mean of streamflow during fish sampling. In contrast, Age-1+ density is strongly negatively correlated with the percentage of high quality habitat. Because habitat quality itself is collinear with streamflow, we regard the latter relationship as spurious. This same, presumably spurious, negative correlation between fish density and habitat quality has been observed in the Roanoke River. In the 2009 Smith River report, bivariate correlations suggested stronger relationships between hydrologic variability and logperch density. This change in results given a single additional observation indicates the danger of placing too much emphasis on such findings and underscores the need for additional annual samples.