WASHINGTON -- More than 20 fish common
in the Caspian and Black Seas could accidentally be introduced
into the Great Lakes from ship ballast water and become
threats to native species, a study suggests.
Researchers at the U.S. Geological
Survey and the University of Notre Dame assessed the characteristics
that alien fish need to thrive in the Great Lakes. They
found that types of shad, carp, goby and minnow in the
Caspian area could quickly establish themselves in North
America if introduced.
At least five of the 22 fish identified
could become nuisances and disrupt the current balance
of fish in the Great Lakes, said Cynthia S. Kolar, a research
fishery biologist for the U.S. Geological Survey Upper
Midwest Environmental Sciences Center. She is first author
of a study appearing Friday in the journal Science.
"A lot of fish in the Caspian can
live in marine salinities all of the way up to fresh water,"
said Kolar. This means they could
easily adapt to the Great Lakes.
Alien fish are common in the United
States. Some are used as bait by sport fishermen, while
others were pets that were released into U.S. waters.
For instance, the northern snakefish, a voracious predator
that can live out of water and quickly multiply, was introduced
into a Maryland pond by a pet owner. State biologist poisoned
the pond last summer to wipe out the invader.
Kolar said most of the alien species
introduced into the Great Lakes arrive in the water that
ships carry in ballast tanks. Ships take on tons of water
in the Caspian or Black Seas for stability while crossing
the Atlantic, and larvae or baby fish are sucked in. When
the ships dump their ballast in the Great Lakes, they
also dump the alien species.
Some introduced species have been
devastating. The United States and Canada spend about
$15 million a year to control the lamprey, a snakelike
bloodsucker that attaches itself to larger fish. The lamprey
almost drove the native lake trout to extinction when
it first expanded into the Great Lakes, said Kolar.
Another introduced species is the
zebra mussel, a fast growing filter-feeder that clings
to boats and pilings and jams water intake pipes. Combatting
the pesky mussel in the Great Lakes costs the United States
about $100 million a year, said Kolar.
Some alien species were at first
a nuisance and then a benefit, she said. The alewife,
a small forage fish, invaded the Great Lakes and exploded
in population. Some Pacific salmon species were then introduced
to control the alewife, and now fishing for the salmon
has become a recreational industry, said Kolar.
Until now, scientists could only
guess which alien fish were likely to be introduced into
the Great Lakes and which would thrive there.
The study by Kolar and by David M.
Lodge of Notre Dame identifies the Caspian and Black Sea
species that may become a nuisance in the Great Lakes.
Among the likely nuisances are the
tyulka, a shad-like fish already invading European rivers;
the Eurasian minnow; the Black Sea silverside; the European
perch; and the monkey goby.
"No one knows for sure if the forage
fish would be ideal or have a long-term negative effect,"
said Kolar, "but these potential bait species (such as
the silverside and minnow) could really hurt the native
The European perch, she said, could
outcompete the native yellow perch and change the ecology
of the Great Lakes. The round goby, a trash fish which
is a relative of the monkey goby, is already troublesome.
"They are really abundant and are
considered a nuisance by fishery managers because they
are constantly being caught on hooks" intended for other
species, said Kolar.
Kolar said that understanding which
fish could represent threats to the Great Lakes could
help policy-makers draw up new regulations controlling
ballast dumping by ships. Right now, ships bound for the
Great Lakes are required to make a mid-ocean exchange
of ballast water, a measure aimed at reducing the transfer
of alien species. More stringent measures may need to
be considered, she said.