Effects of Hydroelectric
Operations on Fish-eating Birds
For years I have enjoyed fly-fishing. When I lived
in
Arkansas, I fished in the tailwater fisheries below dams on the White
River.
Wading in the water below Bull Shoals dam in the middle of summer when
the air
temperature is over 90 degrees, the water in which I was standing
rarely topped
50 degrees as my wadered, but numb legs would testify. This was my
first
realization of how hydroelectric operations could affect life below
dams.
<>Probably because hydro operations are highly regulated by
the federal government, much research has been devoted to the effects
of dam
operations on water quality, invertebrates and fish.
Virtually no research, however, has been
conducted to determine the effects of hydro operations on birds and
mammals
that eat fish. I am currently conducting research to determine the
effects of
altered flow regimes on foraging of great blue herons. Herons are
visual
feeders and they forage on fish near the surface. Also, they most often
stand
or walk in the water to find fish, thus water depth is critical to
their
foraging success. In coastal areas where water depth changes with the
tide,
great blue herons feed primarily at low tide when water depth allows
better
access to fish.
<>The Lancaster area is an excellent place to study the
influence of dams on wildlife. The Catawba River is one of the most
intensely
regulated rivers in the country. There are six dams within a 30-mile
radius of
Lancaster and one of the only free-flowing parts of the river is within
5-10 miles
of the USC Lancaster campus. Dams differ in their pattern of generation
and, consequently,
in the amount and timing of water they release, but changes in water
depth and
velocity can be striking. Water depth can vary a meter or more within
and hour.
For a heron, high water can virtually eliminate the possibility of
catching fish
and, as with the tide, likely will determine when herons can forage—or
at least
when they can forage on the main stem of the river. Thus, for herons
foraging
below a dam, the operations of the dam determine daily patterns of
foraging
which influence when and how often nestlings get fed, and possibly even
the
group size of heron colonies.
<>My study currently focuses on great blue heron foraging
patterns at various points below the Lake Wylie Dam south of Charlotte,
North
Carolina. I am also looking for heron colonies in that area to get an
idea of
where and how much the herons move during the day to find food. I
believe that
herons follow the falling water downstream after generation is shut
off. If
this is true it opens up more questions such as how far do herons
travel down
the river? If they don’t stay on the river during high water, where do
they go?
This system may also be valuable in addressing some ecological and
behavioral
theory related to foraging and predation, and also the reason that
herons nest
communally. Future research may also focus on other species of
piscivorous
birds, such as other herons and egrets or the small but bold kingfisher.
<>This research lends itself well to student involvement at
many levels; from being a field assistant to developing an independent
project.
Please contact me if you are interested.
