UVM research documents
fish eating zebra mussels
By LISA RATHKE
Article Courtesy of the Associated Press
August 16, 2001
ABOARD THE MELOSIRA, Vermont (AP) -- University of
Vermont researchers have discovered that fish are feeding
on zebra mussels in Lake Champlain and are investigating
whether that diet could reduce the population of the nuisance
species that has infested lakes across the country.
" We don' t believe that they' re going to
get rid of zebra mussels by any stretch but if they can
make a dent that would be pretty incredible in itself,
" said Mary Watzin, head of the University of
Vermont' s Rubenstein Ecosystem Science Laboratory.
With an underwater, remote-controlled video camera,
Watzin and her team of researchers have filmed sheepshead
and other fish eating zebra mussels off a sunken railroad
barge near Port Henry, N.Y. The barge is scattered
with broken mussel shells.
" The sheepshead fish in Lake Champlain seem to be
learning that zebra mussels are food, " she said
from the deck of the Melosira, the university'
s research boat.
Sheepshead, also known as freshwater drum, apparently
crush the mussels with their jaws and spit out the shells,
she said. Other fish, such as yellow perch and pumpkinseed,
feed on the smaller, younger zebra mussels, digesting
them whole or spitting out the thinner shells.
Zebra mussels, native to Europe, have infested
freshwater lakes and rivers from the Mississippi River
east. They can choke out native species, clog water
filtration systems and sewage plants, and create hazards
to swimmers and boaters.
This week, Watzin spent three days on the Melosira
to gather more evidence.
She filmed fish pecking at the mussels and spitting out
the shells. The crew set out gill and trap nets at night
to catch fish to take back to the lab. There they will
analyze their contents to see how much of their diet is
zebra mussels and how that could affect their health.
By the second of the three days, they hadn' t
seen or caught any sheepshead. Plenty of sunfish,
however, hovered over the barge, and ingested
smaller mussels, while the remote controlled camera,
which Watzin operates with joy sticks from the boat,
watched. The gritty image of a school of fish floating
over beds of crushed shells played above board on a monitor.
The research is funded by a $50, 000 grant from the
Watzin said she doesn' t think the fish will control
the mussels but their feeding behavior could help reduce
the zebra mussel population.
" One of the really interesting things when you see
zebra mussels in their native habitat is that their densities
aren' t anything like we see over here because so
many birds and fish eat them, " she said. "
So the more things in Lake Champlain or any place in North
America that learn how to eat zebra mussels and recognize
them as food they' ll have some impact on the population
and they won' t be quite as devastating."
Although Watzin is encouraged by the research, she
emphasized that the discovery will not solve the spread
of the mussels.
" I don' t hold out a lot of hope for anything
controlling them, " she said. " I think we
just have to get used to the fact that the ecosystem is
going to be different. It' s going to be a different
lake in 10 years than it is now."
The zebra mussel arrived from Europe on ships that unloaded
in the Great Lakes in the late 1980s. They have since
invaded every major water body east of and including the
They were first spotted in Lake Champlain in 1993 and
have infested the entire lake since then, encrusting
rock ledges, shipwrecks and docks. And the population
continues to grow.
The mussels block water intakes and sewer lines. They
also choke out native mussels by growing on top of them.
They eat plankton and filter algae and other food sources
The result is clearer water " at the expense of the
food chain, " said Watzin.
A diet of zebra mussel can be detrimental to some fish.
White fish in Lake Michigan are eating the mussels,
and their health is declining, said Tom Nalepa,
a research biologist with the Great Lakes Environmental
Research Lab in Ann Arbor, Mich.
" The population is going down, their weight
is going down, " he said. " While their stomachs
are full of shells, they are not getting nutrition,
" he said.
Watzin' s research is not the first discovery of
fish eating zebra mussels but its significance will depend
on the extent of the feeding.
" We find zebra mussels in the diet of sheepshead,
" said Jeffry Miner, associate professor of biology
at Bowling Green State University in Ohio, who does
zebra mussel research in the Great Lakes. " It'
s perfectly expected that they would (eat them.) They
are bottom feeders."
He has studied whether the round goby fish, which
feeds on zebra mussels in the Great Lakes, could reduce
the population there.
" We find in experiments we can reduce the number
of zebra mussels, " he said.
The gobies eat the smaller mussels, which may reduce
the number of adults, he said.
The ecosystem of Lake Champlain could have different
effects on zebra mussels. Because the lake has less calcium
than the Great Lakes, zebra mussel shells are weaker.
" There could be a slight combined effect, "
said Miner. " There' s not enough minerals for
the shells to be strong. That might allow sheepshead to
have just enough advantage. What might happen in Lake
Champlain is predators that aren' t effective in Lake
Erie could be effective in Lake Champlain. In Lake Champlain
the sheepshead may succeed."