|Feb. 22, 2006
Raleigh, North Carolina — It’s tough being a mussel — particularly
one living in the Roanoke River in Halifax County. Ever since a dam altered
the river’s flow in 1963, water has bypassed a significant portion of the
original river channel, leaving a river bed that, until two years ago, was
virtually dry and devoid of all but the most tenacious aquatic wildlife.
But through a relicensing agreement, Dominion Virginia Power Co. began
releasing water back into the original river channel, or bypass reach, in
May 2004. Biologists with the N.C. Wildlife Resources Commission hope the
water’s steady flow will prompt the return of greater numbers and varieties
of mussels and other aquatic species to an area where they once flourished.
To assess what animals will eventually recolonize the reach, wildlife
biologists had to know what species were present before the water release.
In June 2004, they conducted a survey in a 1.5-mile stretch of river to
determine the distribution and abundance of mussels, snails and crayfish in
the upper and lower sections of the reach.
By comparing these data with information they’ll collect after completing
the next survey in five to seven years, biologists will know what species,
if any, recolonized the reach on their own.
The initial survey yielded encouraging results in the lowest section of the
reach, which is basically the backwater of the river. There, biologists
found nine mussel species, two crayfish and five snail species. Biologists
had expected to find a diverse aquatic community given that the habitat in
the lower reach was similar to the current river channel, with comparable
substrate and water depth.
Conversely, they found little aquatic wildlife — only one or two mussel
species, a few snails and a couple of crayfish — in the upper section. This
discovery was not surprising since the area lacked the water flow necessary
to sustain large numbers of wildlife.
Biologists hope that with the water flowing continuously, mussels and other
aquatic species now present in the lower reach will recolonize the upper
reach in greater numbers, if given time. How much time they don’t know for
sure, although they expect the presence of fish in the reach will expedite
mussel movement upstream.
“In order to complete their life cycle, larval mussels attach themselves to
the gills of certain kinds of fishes and then are carried by the fish to
different parts of the river,” said Angie Rodgers, eastern aquatic nongame
coordinator for the Commission. “Eventually, the larvae drop off the fish
and onto the river bottom. If the habitat is suitable, that location
becomes the mussels’ new home.” [see life cycle here]
The Commission has no plans to restock any species in the upper section. It
may consider reintroduction strategies if biologists don’t see any signs of
recolonization after the next survey.
Species recolonization is the most appealing prospect for two reasons: it
indicates that a species can survive and thrive without human intervention;
and it shows that water quality in the reach is suitable to support even
the most finicky of aquatic fauna.
“Being sedentary filter feeders, mussels are extremely sensitive to changes
in water quality and will not survive if the water quality is poor,”
Rodgers said. “Because of their sensitivity, mussels are often referred to
as ‘biological indicators of water quality.’”
Diverse mussel populations, as biologists found in the lower reach,
indicate that the water is clean enough to support other aquatic wildlife.
In addition to serving as water-quality monitors, mussels act as a natural
water filter by straining out suspended particles and pollutants. They also
are a vital link in the aquatic food web, serving as a food source for a
variety of wildlife, including muskrats, otters, raccoons, herons and some
Among the nine mussel species that the Wildlife Commission detected in its
survey, five of them are state-listed as either threatened or endangered.
Their presence in the lower reach is particularly encouraging because they
often are less tolerant of poor water quality than their hardier, more
Although more than 60 species of freshwater mussels call North Carolina
home, 50 percent are state-listed as endangered, threatened or special
concern. Funding for this survey comes from the Nongame and Endangered
Wildlife Fund, the primary source of state funds for the Commission’s
Faunal Diversity and Aquatic Nongame programs. The Wildlife Commission uses
this fund, which supports nongame species research and management, to
generate matching money from federal grants.
You can support this effort as well as other nongame species research and
management projects in North Carolina through the Tax Check-off for Nongame
and Endangered Wildlife. This tax check-off allows taxpayers to designate
part or all of their state tax refunds to this fund. Since 1984, taxpayers
have given more than $7 million for wildlife conservation through this