TRAVERSE CITY (AP) - Foreign species that slipped into the Great Lakes in ballast tanks of oceangoing cargo ships cost the regional economy at least $200 million a year, said a University of Notre Dame study released Wednesday.
But a separate report issued by the National Research Council rejected the proposal of some activists and politicians to stem the species invasion by closing the St. Lawrence Seaway or declaring it off-limits to oceangoing freighters.
Instead, the U.S. and Canada should work together to make sure that saltwater ships exchange their ballast water - or rinse their tanks if empty - while still at sea, said the report by the council's Transportation Research Board.
The reports come as environmentalists are prodding the U.S. Senate to approve a bill ordering ships to install systems for killing invasive fish, mussels and other critters that can disrupt the Great Lakes ecosystem. The measure has cleared the House but supporters say its prospects will be dim unless the Senate acts before its August recess.
''Politics are holding up our ability to stop the next invader,'' said Jennifer Nalbone, invasive species campaign director for Great Lakes United.
Of the 185 exotic animals and plants that have established populations in the lakes, 84 have arrived since the St. Lawrence Seaway opened in 1959, providing a navigational link between the lakes and the Atlantic.
Fifty-seven of the newcomers likely caught a ride in ballast water scooped up in foreign ports and dumped into the lakes when ships took on cargo, the Notre Dame report said. Among them: the round goby, the spiny water flea and the Eurasian ruffe.
They also include zebra and quagga mussels, which have been especially damaging to the regional economy by clogging water intake pipes and gobbling algae at the base of the aquatic food web.
Estimates of their cost to the economy have varied widely. The Notre Dame scientists suggested a price tag of $300 million last spring. But their latest report, using a different analytical method, pegged the loss at $200 million.
