In 1990, a small stowaway was dumped from the ballast tank of an ocean-going freighter into the waters of the St. Clair River, joining more than 180 other non-native species in the Great Lakes. Two decades later, the round goby, an aggressive, voracious, bottom-dwelling fish has invaded all five Great Lakes and has had profound impacts on other fish populations. As is the case with most aquatic invasive species, the lakes were only the first stop of the goby invasion. Now new research out of the Center for Limnology (CFL) shows that the fish is rapidly spreading into Wisconsin streams.
Reporting in the February issue of the journal Diversity and Distributions, a team of CFL-affiliated researchers shows that, between 2007 and 2010, goby populations in already invaded streams increased more than ten-fold. And that’s just the average increase, says Matt Kornis, the study’s lead author and a postdoctoral fellow at the Smithsonian Environmental Research Center. In some cases, the goby population boom was much more pronounced. Take, for example, the Ahnapee River in Door County, Wisconsin. “At one site we caught a single round goby in 2007,” Kornis recalls. “In 2010, using the same sample method, we caught upwards of 60.”
What’s more, it appears gobies are just getting going. Working out of the CFL’s Vander Zanden lab at the University of Wisconsin-Madison, Kornis documented round goby invasions in 170 miles-worth of Wisconsin waterways. That’s only about 20% of the 850 miles of Wisconsin streams and rivers that feed into Lake Michigan that, he says, is likely suitable habitat for gobies. And that number is a mere fraction of the tens of thousands of miles of tributaries accessible to the goby in the Great Lakes Basin.
Kornis says another surprising finding of the study was that the gobies were most prevalent in sites that had a high number and diversity of native fish species like mottled sculpins, logperch and Johnny darters. Traditionally, studies on invasive species have indicated that invaders do best in degraded ecosystems that have low numbers of native species and, presumably, less competition for resources. While many of those studies have focused on invasive plants, Kornis says, the results indicate that, “communities that have more diversity can be more resistant to invasion.” Gobies, however, do just fine in ecosystems with balmy temperatures, lots of food sources, and a ton of competition. Considering gobies compete with native fish for food like benthic invertebrates and can also predate on the eggs and larvae of sportfish such as bass and trout, their expansion into habitats already occupied by natives is worrisome.
In Lake Erie, for example, fisheries managers have had to restrict bass fishing during spawning season because bass recruitment was low due to round gobies competing for spawning beds and eating eggs. While no one has documented the same effect in rivers or streams, Kornis says, it’s not hard to imagine gobies out-competing fish like darters and sculpins for food, while also hurting sportfish populations by predation on eggs and larvae.
Currently, it appears that Wisconsin’s native fish populations are holding their own with their aggressive new neighbors. And it’s conceivable that the gobies won’t be able to sustain their current exponential population growth if Wisconsin’s rivers and streams prove less hospitable than the Great Lakes, where part of the goby explosion can be credited to their ability to take advantage of a plentiful food source untouched by other fish – zebra and quagga mussels. In streams, Kornis says, “A lot of species are as well adapted as gobies at feeding on benthic invertebrates.”
Of course it’s far too soon to tell which way the story of the goby will go. “While we didn’t see any negative responses in native fish populations [from 2007 to 2010],” Kornis warns, “it’s definitely going to merit keeping an eye on, because it looks like they’re continuing to increase in abundance and there is usually a pretty tight link between the abundance of invasive species and the amount of impact they have on a native ecosystem. Just because we haven’t seen any eye-popping severe affects yet doesn’t mean it won’t happen.”
A video about Kornis’s work, produced by the University of Wisconsin Sea Grant is below.
For more information, contact:
Matt Kornis, firstname.lastname@example.org or Adam Hinterthuer, email@example.com