Federally to a much recent study, the long-term decline

Federally listed as vulnerable, the
Roanoke logperch (Percina rex) is a freshwater fish found in the Roanoke and
Chowan drainage in Virginia, United States (Nature Serve,2013). Generally, the Roanoke
logperch dwell in small to medium rivers which have moderate water gradient (Page
and Burr 2011). Barriers such as dams have helped specify eight separate
populations of the logperch, although the total adult population size is still
unknown. 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 Roanoke
logperch has declined slowly. However, as of 2013, the population size of the
logperch is increasing.

The Roanoke logperch experiences
fluctuations in its population size. These Fluctuations are dependent on
various environmental factors and are consequences of human activities. Several
studies have been conducted to understand the relation between quality of water
that the population inhabits and the decline in the Percina rex population.
Roanoke logperch population in a water body is an indicator of low turbidity. The
presence of suspended particles in water because of which the water loses its
transparency is called turbidity. These suspended particles include but are not
limited to sediments like clay and silt, fine organic and inorganic matter,
soluble organic compounds and microscopic organisms like phytoplankton. Human activities
such as construction, agriculture, land disturbance and change in sediment
levels due to surplus water entering water bodies also contribute to the
turbidity of water (USEPA 2005). During the Roanoke River Flood Reduction
Project in the late 1980s, the objectives mapped out for flood control included
removal of items causing hindrance to streamflow like woody debris and low
bridges, substantial widening of the floodplain along the river channel and
stabilization of water flow using training walls. Training walls could help in
providing better navigation of water, improved quality and flood mitigation
services, but also causes erosion due to interruption of longshore drift.
According to USACE’s 1989 Environmental Assessment, the environmental impact of
these activities would be silt generated during these modifications. If carried
into the river, this sediment could increase turbidity and silt deposition
rates.  High turbidity is an indicator of
bad water quality, which could be a cause of the decline of the Roanoke
logperch population. Although, according to a much recent study, the long-term
decline of the logperch population probably occurred due to creation of reservoir
and the expansion of land and agricultural practices which resulted in extensive
siltation (USFWS 2007). Till the time threats like urbanization, industrial development,
agricultural runoffs, flood control projects continue to prevail in the Roanoke
River drainage, the logperch population will stay endangered (USFWS 1991, 2007).

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There are
three different age classes of the Roanoke logperch, the adult, the subadult
and the young. These classes show evidence of habitat selectivity. Adult
logperch primarily preferred gravel areas of the deep water with medium to high
water velocities. The subadults were observed in somewhat shallow water with low
velocity and moderately embedded gravel as compared to the adults. Younger
logperch, in contrast, was found in nearly still areas such as backwater
habitats, secondary channels, and the shallow edges of pools, riffles, and
runs. One reason for habitat selectivity could be predation risk. The different
preference for habitats associated with the predator-prey interaction could be
an integral factor in the diverse variety in habitat
use over body size. For habitat selection, predation is an immediate cause of
concern than food for the fish because they can manage a level of starvation to
avoid predators (Angermeier, 1992). Although, the logperch can deliberately
change their feeding rates to avoid predation risk. Relating habitat use to
predation highlights that the risk in shallow habitats is from predators like
diving birds, while the risk in deep habitats is mostly from predators like
piscivorous fishes. It is rare to find large predatory fishes in shallow water
because they face possible danger from exposure to aerial predator. Also, it
limits their mobility (Angermeier, 1992). Even
though the younger logperch is vulnerable to different aquatic predators, they are
less probable to the risk of predation by aerial predators. These habitat
preferences for the different class of Roanoke perch could very well be related
to heavy silt depth and velocity of water. 
In the Roanoke River, adult logperch selected deep, high-velocity
riffles and runs, which provide loosely embedded substrate for feeding and
potential spawning habitat (Angermeier, 1992) and Subadults, however, were
found in habitats with intermediate depth, lower velocities, greater silt cover
and a relatively embedded substrate. The adult Percina rex prefers deep and turbulent habitat with riffles and
runs to keep safe from the predators in water and above ground. Whereas, the
subadult logperch due to their restricted swimming ability cannot take
advantage of these high velocity water areas. Water bodies with slow velocities
are generally heavily silted. Since the predators in water also dwell in these
areas, it is hard to segregate between the effect of predation and the
influence of heavy silt on the specific preferences of the subadult Roanoke