Under a threatening sky, two Federal biologists trawling in the Thunder Bay River last September made a catch that sent shivers up the spine of commercial fishermen. The flapping mass they hauled in included 23 silver-scaled marauders known as the Eurasian ruffe.

Feared as perhaps the most dangerous threat to Great Lakes fisheries since the arrival of the sea lamprey 160 years ago, the little infiltrater has shown its formidable knack for pushing trout, perch, and other important species out of their habitats, raising the specter of big losses for the region’s recreational fishing industry. Notices of the catch were flashed to fish and game departments in eight states and Canada. The ruffe (pronounced rough) was multiplying in Lake Huron!

It’s not often that a creature that a fits on a child’s palm prods governments into action. The ruffe, however, has turned into a poster fish of sorts. It’s the focus of a joint state and Federal campaign to convince the public that biological threats to the Great Lakes are at least as important as the toxic ones. In July, Governor John Engler announced a $1 million grant to develop technology to intercept "dangerous foreign organisms and diseases from ships entering the Great Lakes."

G. Tracy Mehan III, director of the Michigan Office of the Great Lakes, praised the governor’s action, calling it far-sighted. "Exotic species disrupt ecosystems and create natural and economic havoc," said Mehan. "They are the most immediate and potentially catastrophic threat to the Great Lakes."

While acknowledging the severity of the problem, some environmental leaders nevertheless remarked that Governor Engler was mustering unusual energy to attack the invaders. "I just wish he would pound the pulpit just as hard for other serious Great Lakes concerns," said Dave Dempsey, policy director for the Michigan Environmental Council.

Somehow it’s hard to imagine that a little fish can disrupt an entire ecosystem. Non-native plants and animals — so-called exotic species — cause harm by rearranging the relationships between the home grown critters. In especially severe cases, such as the proliferation of the thumb-nail size zebra mussels, they appear to be establishing whole new ecosystems, say scientists.

Few regions of the world provide quite as grand a welcome mat as the Great Lakes. Since 1830, nearly 140 exotic species have established new homes here. Some are deliberately introduced, like the Coho salmon in 1933, to invigorate the sport fishery. Others, like the sea lamprey, which attaches to game fish and literally sucks the life out of its prey, migrated in on their own.

Most exotic species, however, are now arriving in the ballast water of cargo ships. The zebra mussel, a stowaway in a ship coming from eastern Europe, was discovered in 1988 and is now clogging intake pipes throughout the Mississippi River basin.

Two years before the zebra mussel was discovered in Detroit, the Eurasian ruffe was found in the St. Louis River in Duluth, Minn. According to Tom Busiahn, a Federal fisheries biologist in Ashland, Wisconsin, ruffes now make up nearly 80 percent of the fish now found in the river.

Until 1994, the furthest the ruffes had gotten in the United States was the Ontonagon River, about 180 miles east of Duluth. But last year, biologists found three ruffes in Alpena, and theorized they’d been picked up in the ballast water of a ship that left Duluth. With the discovery of 23 more in September, there’s no longer any doubt that the outlaw population has thrived.

Six years ago, Congress took a swipe at the problem, calling for vessels entering the Great Lakes to voluntarily empty their ballast tanks at sea. The Alpena situation only served to confirm how ineffective the federal prevention program really is. The guidelines do not apply to many classes of ships, nor do they require ships to take precautions with their ballast while enroute within the Great Lakes. This year, Congress had an opportunity to strengthen the law, but in October a new version was approved that did almost nothing to fix the basic weaknesses.

With no legislative relief forthcoming, the region’s governors turned to technology. Money from the Great Lakes Protection Fund is being invested in an experimental ballast treatment system designed to filter out foreign agents. The system is being installed on a Great Lakes ship, and if works, it’s hoped that other carriers will retrofit their vessels.

What’s really needed, though, is mandatory rules. Without them, the risk of the ruffe’s migration to Northwestern Michigan only grows more pressing. After all, like every other living organism, the ruffes’ basic nature is to expand it range.