Volume 1 2012

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Sea Grant Research

Little Fish. Big Problem. 

By Aaron R. Conklin

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 among the dominated in the aquatic universe, not the dominator.

However, the voracious goby has used strength of numbers to inflict serious damage on the Great Lakes food web. Sometimes found in groups of several hundred or more, round gobies have made short work of the food sources that sustain the young of many Great Lakes sport fish—bass, walleye and yellow perch—and they also dine on sport fish eggs when the opportunity arises. The sport fish are fighting back, feeding heavily on gobies, but goby populations are usually too large to be affected.

Unfortunately, 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 they could have a similarly devastating effect on the ecosystem.
Beginning in 2007, using funding provided by Wisconsin Sea Grant, UW-Madison ecologist Jake Vander Zanden and graduate student Matt Kornis set out to discover what kind of effects the gobies were 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.

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 populations 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 notes that goby numbers are still rising.

“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 vigilance is critical.

“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.”

The Aquatic Sciences Center is the administrative home of the
University of Wisconsin Sea Grant Institute & University of Wisconsin Water Resources Institute.

©2011 University of Wisconsin Board of Regents