Percina jenkinsi, Conasauga Logperch
The Conasauga logperch is one of the rarest darters in North America, known only from a 27-mile reach of the mainstem Conasauga River in Georgia and Tennessee. The species, when described in 1985, typically was observed at low densities in swift riffles over gravel and cobble substrate. Recently, however, population size appears to have declined substantially -- over the past ten years, numbers of Conasauga logperch observed during surveys in suitable habitat have decreased from 1-6 individuals/riffle to 0-3 individuals/riffle; only 7 Conasauga logperch were collected during surveys at 17 high quality riffles in 2008 (Megan Hagler, University of Georgia, pers. comm.. Nov. 2008). Census estimates indicate the population currently has less than 200 adults (Anna George, Tennessee Aquarium Research Institute, pers. comm.. Nov. 2008).
Reasons for this apparent decline in population numbers are unknown but may be related to recent changes in agricultural practices in the basin, including a shift to Round-Up Ready crops, conversion of pasture land to row crop production, and/or increased use of chicken litter fertilizer, that have increased sediment, nutrient, and herbicide loads in agricultural runoff. The 2004 hurricanes and 2007-2008 drought may have further jeopardized this species. Similar recent declines have been observed in other, often common, species in the basin. Georgia and Asheville Ecological Services personnel currently are coordinating with the Natural Resources Conservation Service, the Georgia Soil and Water Conservation Service, The Nature Conservancy, the University of Georgia, and others to identify and address stressors that may be affecting water quality and fish, macroinvertebrate, and aquatic vegetation communities.
The Conasauga logperch is highly vulnerable to extinction due to stochastic or human-induced events, since it occurs only in small numbers in a short reach of a single river system. Captive propagation to augment numbers may be vital to prevent the species’ extinction until the Service and partners can identify and implement measures to mitigate recent stressors. CFI’s attempt to captive rear Conasauga logperch in 2002 was unsuccessful, despite our extensive experience in propagating closely-related species. Recent genetic analyses have revealed unusually high genetic diversity in the Conasauga logperch population, a situation unusual in a species with such low numbers. Statistical tests of these genetic data support the existence of balancing selection in Conasauga logperch mate selection. Balancing selection is a form of natural selection that acts to maintain genetic variability in a small population – individuals choose mates with different genes than their own to avoid the negative effects of inbreeding. Further genetic analysis to support the hypothesis of balancing selection in Conasauga logperch is necessary. Learning more about how mates are selected will help to insure successful captive propagation efforts.
This study will examine both genetic diversity and sexual selection in the Conasauga logperch to create a successful captive breeding program. This project is critical because recent declines in logperch numbers already have reduced the number of individuals available for mating; it is imperative that we learn about mate choice patterns now, before the effective population size drops below a critical threshold for survival.
Partners include TNARI, CFI, the Tennessee Aquarium (TNAQ), and the University of Tennessee at Chattanooga (UTC). Staff from these agencies will collect Conasauga logperch for captive breeding and genetic analysis. Additional samples may be provided by Georgia Department of Natural Resources, University of Georgia, and USGS personnel working in the basin. Genetic analysis will be conducted by TNARI personnel using lab space and equipment at UTC. Three Conasauga logperch collected in late fall 2009 are currently held in captivity at CFI to begin captive propagation efforts spring 2010. CFI has considerable experience propagating closely –related darter species, including the threatened goldline darter (P. aurolineata), endangered boulder darter (Etheostoma wapiti) Roanoke logperch (Percina rex), and imperiled blotchside logperch (P. burtoni).