An unhelpful current for unwanted fish

Unable to stop the relentless spread of the lowly zebra mussel from the Great Lakes into the Mississippi River, scientists and federal officials are drawing a line in the water against a new menace, a tiny bottom-feeder known as the round goby.

Their line is a proposed underwater electric barrier capable of emitting a current strong enough to repel the goby from migrating into the Mississippi--yet weak enough so the invader and other fish are not fried in the process.

The barrier, now being analyzed in lab tests and not expected to be ready for at least a year, will need to work quickly. Gobies were found last June in the Cal-Sag Channel, a shipping lane 12 miles south of Chicago. The channel leads into the Illinois River, a Mississippi tributary.

“We knew it was moving fast, but we were surprised it was that far downstream,” said Philip B. Moy, a fisheries biologist here with the U.S. Army Corps of Engineers, the federal agency planning the nearly $1-million barrier project.

The goby is a speckled 5 1/2-inch-long nuisance that clings to the rocky depths of lakes and rivers. It hogs the habitats of other tiny fish, often devouring them and their eggs. Native to the Caspian and Black seas in the Baltic region of Eurasia, the goby was apparently introduced into the Great Lakes over the last seven years, hitching rides across the Atlantic Ocean in the ballast water of long-distance freighters.

Gobies cluster in such dense, cloud-like formations that their sheer numbers drive away smaller bottom-dwellers, such as darters and mottled sculpin. Scientists have found as many as 50 gobies in a square meter of water.

“That’s a heck of a lot of fish,” said Jeffrey Gunderson, director of the Sea Grant Program at the University of Minnesota at Duluth.

The worry among river experts is that if the gobies invade the Mississippi water system, they might displace dozens of smaller species.

The effect on the river’s food chain is uncertain, scientists say, but one concern involves the zebra mussel, another invader that has multiplied by the tens of thousands in the Mississippi, displacing local shellfish varieties.

The goby, it turns out, loves nothing more than to feast on zebra mussels. “It would be great if we could just unleash them on the mussels,” Moy said.

But there is a catch: Even though they clog river channels, zebra mussels have had one beneficiary effect--filtering out toxic metallic traces, such as PCBs from waterways. If the gobies devour tainted mussels and are in turn eaten by bass and other larger fish, anglers could begin hauling up toxin-soaked fish--a problem that environmental laws have mostly cured in the Great Lakes and Great Plains rivers over the last 30 years.

The gobies have to be stopped, scientists say, before they spill into the Illinois River. So river and aquatic experts are collaborating with federal officials in a proposal to stop the fish with pulsing electric cables. The concept has worked in smaller settings, Moy said.

“The trick here,” said Jackie Savino, a U.S. Geological Survey scientist who is testing a model of the barrier at the Great Lakes Science Center in Ann Arbor, Mich., is to ward off the gobies without stunning them. If the barrier’s current is too strong, the fish may be briefly rendered unconscious but revive downstream to spawn and multiply.

Scientists are optimistic, Savino said. They have refined the barrier’s steady electric pulse to a low level, “enough to drive the gobies crazy. But if a human put their hands in the water, all they would feel is a tickle.”

Once the barrier is dug into the recesses of Chicago’s Sanitary and Shipping Canal, near where the gobies were last spotted, some scientists believe that its tickle could be the cure for the aquatic invasions that have plagued the Great Lakes and the Mississippi for a half-century.

If it fails, they might have to consider sound barriers, fish poisons, even dams or a system of locks. A dam would be expensive and likely force engineers to consider reversing the course of the Chicago River--a prospect likely to outrage the city’s politicians and business community.

“The science behind [the barrier] is sound,” Moy said. And if not? “We won’t have a lot of time to go to Plan B.”