To look at it, the round goby doesn’t seem like much. A small fish the approximate size of an average pickle, it seems like the sort of creature that’d be the dominated in the aquatic universe, not the dominator.

But like an ecological David in reverse, the voracious goby has used strength of numbers to wreak serious damage on the gentle Goliath that is the Great Lakes food web. Sometimes found in groups of several hundred or more, round gobies have made short work of the key food sources that sustain the young of a lengthy list of Great Lakes sport fish: bass, walleye, and yellow perch. Round gobies also dine on sport fish eggs when the opportunity arises. These species are fighting back, feeding heavily on gobies, but goby populations are usually too large to be affected.

Worse, in what some researchers have dubbed a “classic ecological surprise,” the gobies haven’t limited their invasive ways to the Great Lakes: Over the past decade, they’ve also migrated to Wisconsin’s streams and rivers, where researchers are very concerned they could have a similar devastating effect on the ecosystem.

Beginning in 2007, using funding provided by University of Wisconsin Sea Grant, UW-Madison ecologist Jake Vander Zanden and UW graduate student Matt Kornis set out to discover just what kind of impact the gobies might be having. Using nets and a portable electro-fishing system, Kornis and a team of student researchers sampled and analyzed goby populations at 150 different stream locations along Wisconsin’s Lake Michigan coast.

“When we discovered round goby in some small streams in Wisconsin, it made us start to ask the question, what kind of impacts are they going to have?” stated Vander Zanden, the project’s principal investigator. “How many miles of stream in Wisconsin are going to be invaded, and is this something we need to be concerned about?”

Kornis and his team spent several months sampling from a variety of stream habitats—sandy, temperate and rocky—as well as areas where goby populations were either absent, low or prevalent. Of the 75 streams Kornis’s team sampled, 26 contained gobies. In more than 80 percent of those sample sites, the goby population was deemed small, with the remaining 10 percent described as “superabundant.”

The most surprising finding? At most of the sites, gobies have yet to devastate the ecosystem the way they have in the Great Lakes.

“Over the last three years, at most of our sites and streams, we haven’t seen the population level declines in the native species we would have expected based on what we know from the Great Lakes,” said Kornis.

That doesn’t mean it couldn’t eventually occur. Kornis and Vander Zanden remain focused on tracking the inevitable progress of the goby. They’ve identified and mapped 1300 kilometers of Wisconsin streams that are at risk for goby invasion, based on habitat suitability and natural migration projections from areas where the fish have already become established. Both researchers caution that if fishermen and boaters aren’t cautious about preventing the spread of invasive species like the goby, the number of invaded streams in the Lake Michigan basin could expand dramatically.

“Streams are different enough from lakes in terms of the amount of habitat and type of food available that maybe round gobies can’t reach the same densities as in the Great Lakes,” said Kornis. “Nonetheless, goby populations are growing in most streams. Since 2007, we’ve observed at least a doubling of round goby abundance at 65 percent of our sites.”

Vander Zanden agrees that further vigilance is critical to goby containment and habitat preservation. “This species is on the move, their inland spread is really rapid, and there is a lot of suitable habitat for them,” he said. “We’re worried about them making their way into inland lakes all around the state. We expect that they will have big impacts in these systems. Anglers and boaters need to be aware and not transport these fish into new waters.”

By Aaron R. Conklin