The Common Carp was introduced a century ago and has been causing havoc in rivers, ponds and lakes ever since. (Image by Duane Raver, courtesy of the U.S. Fish and Wildlife Service)
In thousands of lakes and ponds across the country, there’s a fish messing up the water.
Some biologists say we’ve never seen these lakes the way nature intended due to the
common carp. The usual method to get rid of the common carp is to kill everything in
the lake and start over. Some biologists think there’s got to be a better way. Joel
Grostephan reports:
Transcript
In thousands of lakes and ponds across the country, there’s a fish messing up the water.
Some biologists say we’ve never seen these lakes the way nature intended due to the common carp. The usual method to get rid of the common carp is to kill everything in
the lake and start over. Some biologists think there’s got to be a better way. Joel
Grostephan reports:
Common carp are like underwater pigs. They root up aquatic plants. They constantly stir
up the mud in the bottoms of lakes, making them murky. And in some lakes, common
carp make up more than half of the total weight of fish. Peter Sorensen is a fisheries
professor at the University of Minnesota:
“With their habit of rooting around night and day, they will completely destroy the
bottoms of lakes, so they become cesspools.”
And it ruins the habitat for many birds and fish too:
“The fact is they are doing enormous damage. At a level that I don’t think people
fully realize. They are living with us, and we don’t know in many cases, what
these lakes and streams and rivers should be like and could be like.”
Common carp have been in U.S. lakes and ponds for more than a century. They came
from Europe and Asia. At the request of new immigrants, the United States government
stocked carp in lakes and rivers in the late 1800’s. Sorensen says it didn’t take long before
there were problems.
By the early 1900’s, it clicked this was a huge mistake, and they started to remove
them. Good records were not kept, and Sorensen says the overall impression is that
removal efforts didn’t work. Most attempts to control the fish are still unreliable. The fish
is very tough. It spawns every year, and females produce nearly a million eggs.
Fisheries managers try to control carp the best they know how. Some hire commercial
fisherman to net the carp. They also use poison — killing all the carp and all the other
fish in the lake and then start over.
Fisheries managers currently use a chemical called Rotenone, which they say is not toxic
to humans. Lee Sundmark is with the Minnesota Department of Natural Resources:
“If we see that a lake that a lake way out of balance, might have a lot of carp,
bullheads, tried biological means, and they aren’t working. Sometimes we get to the
point where we use Rotenone to treat it. We basically clean a lake out, and then we
might restock it.”
The trouble is sometimes not all the carp die. And just a handful of them can reproduce
and dominate that lake within a few years. Peter Sorensen and his team of researchers
believe there’s a better way. Sorenson says he does not object to Rotenone poisoning out-
of-hand but, he says, it’s expensive, heavy handed. He and his team have been studying
carp-infested lakes for the past three years to see if they can come up with a new method
to control the fish.
On this cold day, the biologists are surgically implanting radio tags in carp. The
scientists will be tracking these fish so they can find weak points in their lifecycle.
Prezmyslaw Bajer and his colleague Mario Traveline are about to operate on a fish they
caught:
“She will be collecting data that we will then use to remove carp from the lake. She
will be our carp spy.”
The researchers say if they can figure out the habits, and the instincts of the Common
Carp, they will able to control them in way that’s both — effective, and doesn’t kill all the
other fish in the lake. The study’s lead investigator, Sorensen, says this is important
work:
“Something must be done. This is our first, and most damaging species, and if we
don’t do something with this, that like I said, we can do something about — I wonder
what hope there is for any of them. This is to me, the one you got to take out.”
Sorensen says he hopes he can create a model that can be replicated in different parts of
the country. If he’s successful, the ponds, lakes and rivers that have been assaulted by the
carp for the last century might once again be able to host fish and other wildlife that were
forced out.
For the Environment Report, I’m Joel Grostephan.