By Tom Pelton
s a rising sun burned mist from the
Potomac River, a group of scientists
launched a strange-looking research vessel in
pursuit of exotic predators.
The biologists with the Maryland
Department of Natural Resources were on
the hunt for blue catfish. Native to the
Mississippi River, blue cats owe their name
to their steely-blue skin color. They have
long whiskers, wide mouths, milky bellies,
and can grow up to 140 pounds and four-and-a-half feet long—twice the size of any
native Chesapeake catfish. They live as
long as 20 years.
Populations of blue catfish in the Potomac River and other Bay tributaries have exploded since the
invasive species was introduced in 1975. In fact, blue cats have been found in all of Virginia’s tidal
rivers and increasingly in Maryland’s rivers.
federal and state governments are investing
millions of dollars to protect and restore.
Mary Groves, Southern Regional Fisheries
Manager with the state agency, drove an
18-foot electrofishing boat with a pair of
metal arms trailing giant egg beaters. The
devices were wired to an electric
generator, designed to emit low
pulses that stun fish.
As Groves and her colleagues cruised along
the wooded shores of the Potomac River,
atop a bluff rose Mount Vernon, home of
the most famous shad fisherman: George
lusks and the remains of fish they could not
immediately identify, and so sent it to a lab
for DNA testing. If their study concludes
that blue cats consume large numbers of
American shad or river herring (another
declining species), fisheries managers will
feel more urgency to create a management
system to reduce blue catfish populations.
“Blue catfish are an invasive
species,” Groves explained, as seag-
ulls wheeled over the placid blue-
green river about four miles south
of Washington, D.C. “Blue catfish
don’t belong here, but over the last
10 or 15 years the population has explod-
ed. We are trying to learn as much as we
can about the fish, so we can come up with
a management plan for them.”
An alarm beeped on the boat, warning pas-
sengers that electricity was surging from the
egg beaters into the water.
One of the leading strategies for controlling blue catfish is to encourage
fishing for them—in other words, to
target predation on the predators,
which happen to be delicious. In this
sense, blue cats are like Asian snakeheads, another Potomac River invader that has now become a popular
sport fish. Scientists caution, however, that the very largest and oldest blue catfish
can accumulate contaminates from bottom-feeding, making the younger and smaller
blue cats better for eating.
In 1975, the Virginia Division of Inland
Fish and Game Fisheries began introducing blue catfish into Chesapeake Bay tributaries as a game fish. But ecologists now
regret the move, because the monster-sized catfish have voracious appetites for
native fish species.
Among the prey of blue cats appear to be
American shad, a declining species that
Suddenly, hundreds of blue catfish sur-
faced all around the boat, swimming fran-
tically in circles, their fins slicing the river.
The scientists used long-handled nets to
scoop up about a dozen of the fish, which
they plopped into a large metal tank on
The researchers later examined the stom-
achs of the blue catfish to discover what they
had been eating. The scientists found mol-
Introducing exotic species, no matter how
well intended, almost always comes back to
bite. It may turn out the best weapon
against them is a knife and fork.
Tom Pelton is Senior Writer and
Investigative Reporter for the
Chesapeake Bay Foundation.
Read his blog, Bay Daily, at