Federally slowly. However, as of 2013, the
Federally listed as vulnerable, theRoanoke logperch (Percina rex) is a freshwater fish found in the Roanoke andChowan drainage in Virginia, United States (Nature Serve,2013).
Generally, the Roanokelogperch dwell in small to medium rivers which have moderate water gradient (Pageand Burr 2011). Barriers such as dams have helped specify eight separatepopulations of the logperch, although the total adult population size is stillunknown. According to a report by the U.S. Fish and Wildlife Service in 2007,over the past 200 years, the occurrence and a population density of the Roanokelogperch has declined slowly. However, as of 2013, the population size of thelogperch is increasing. The Roanoke logperch experiencesfluctuations in its population size.
These Fluctuations are dependent onvarious environmental factors and are consequences of human activities. Severalstudies have been conducted to understand the relation between quality of waterthat the population inhabits and the decline in the Percina rex population.Roanoke logperch population in a water body is an indicator of low turbidity. Thepresence of suspended particles in water because of which the water loses itstransparency is called turbidity. These suspended particles include but are notlimited to sediments like clay and silt, fine organic and inorganic matter,soluble organic compounds and microscopic organisms like phytoplankton. Human activitiessuch as construction, agriculture, land disturbance and change in sedimentlevels due to surplus water entering water bodies also contribute to theturbidity of water (USEPA 2005). During the Roanoke River Flood ReductionProject in the late 1980s, the objectives mapped out for flood control includedremoval of items causing hindrance to streamflow like woody debris and lowbridges, substantial widening of the floodplain along the river channel andstabilization of water flow using training walls. Training walls could help inproviding better navigation of water, improved quality and flood mitigationservices, but also causes erosion due to interruption of longshore drift.
According to USACE’s 1989 Environmental Assessment, the environmental impact ofthese activities would be silt generated during these modifications. If carriedinto the river, this sediment could increase turbidity and silt depositionrates. High turbidity is an indicator ofbad water quality, which could be a cause of the decline of the Roanokelogperch population.
Although, according to a much recent study, the long-termdecline of the logperch population probably occurred due to creation of reservoirand the expansion of land and agricultural practices which resulted in extensivesiltation (USFWS 2007). Till the time threats like urbanization, industrial development,agricultural runoffs, flood control projects continue to prevail in the RoanokeRiver drainage, the logperch population will stay endangered (USFWS 1991, 2007).There arethree different age classes of the Roanoke logperch, the adult, the subadultand the young. These classes show evidence of habitat selectivity. Adultlogperch primarily preferred gravel areas of the deep water with medium to highwater velocities. The subadults were observed in somewhat shallow water with lowvelocity and moderately embedded gravel as compared to the adults. Youngerlogperch, in contrast, was found in nearly still areas such as backwaterhabitats, secondary channels, and the shallow edges of pools, riffles, andruns. One reason for habitat selectivity could be predation risk.
The differentpreference for habitats associated with the predator-prey interaction could bean integral factor in the diverse variety in habitatuse over body size. For habitat selection, predation is an immediate cause ofconcern than food for the fish because they can manage a level of starvation toavoid predators (Angermeier, 1992). Although, the logperch can deliberatelychange their feeding rates to avoid predation risk. Relating habitat use topredation highlights that the risk in shallow habitats is from predators likediving birds, while the risk in deep habitats is mostly from predators likepiscivorous fishes. It is rare to find large predatory fishes in shallow waterbecause they face possible danger from exposure to aerial predator.
Also, itlimits their mobility (Angermeier, 1992). Eventhough the younger logperch is vulnerable to different aquatic predators, they areless probable to the risk of predation by aerial predators. These habitatpreferences for the different class of Roanoke perch could very well be relatedto heavy silt depth and velocity of water.
In the Roanoke River, adult logperch selected deep, high-velocityriffles and runs, which provide loosely embedded substrate for feeding andpotential spawning habitat (Angermeier, 1992) and Subadults, however, werefound in habitats with intermediate depth, lower velocities, greater silt coverand a relatively embedded substrate. The adult Percina rex prefers deep and turbulent habitat with riffles andruns to keep safe from the predators in water and above ground. Whereas, thesubadult logperch due to their restricted swimming ability cannot takeadvantage of these high velocity water areas. Water bodies with slow velocitiesare generally heavily silted. Since the predators in water also dwell in theseareas, it is hard to segregate between the effect of predation and theinfluence of heavy silt on the specific preferences of the subadult Roanokelogperch.