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 fish."
The European perch, she said, could out-compete 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.
By Paul Recer