Sea Grant Research
Goby vs. Goby
Gobies Compete With Each Other When Crowded,
Sparing Native Fishes
By Marie Zhuikov
It seems counter-intuitive, but Wisconsin Sea Grant researchers have found that an invasive fish, the round goby, may have greater impacts on native fish populations when there are fewer of them. The reason? The round goby (Neogobius melanostomus) is so pugnacious and aggressive toward its own kind that when numbers are high, they compete among themselves to a greater extent than against native fishes.
University of Wisconsin-Madison Professor Jake Vander Zanden and former Ph.D. student Matthew Kornis (see facing page) and their team published their findings last year in the journal Oecologia. They stocked 18 enclosures in Little Suamico River, a tributary of Lake Michigan in northeastern Wisconsin, with gobies and three species of native fishes (creek chubs, white suckers and Johnny darters).
The enclosures contained the same amounts and types of natural food. The only difference was the number of gobies: from “no goby” to “low goby” (2.7 fish per square meter) to “high goby” (10.7 fish per square meter). The fish lived in enclosures made from PVC pipe and plastic mesh for 52 days and were weighed at the beginning and end of the experiment.
The lowest growth rates in the native fishes were in the low-goby enclosures, with Johnny darters and white suckers faring worst. Native fish growth in the high-goby enclosures was no different than in the enclosures without gobies.
“Gobies are super-territorial and they beat up on other gobies in these experimental settings,” explained Vander Zanden. “We believe that because they’re spending their time competing with other gobies, their impact on other species is reduced at high densities.”
Vander Zanden and his team were surprised by this result “because there’s an implicit assumption that presence corresponds with impacts, and that if you increase an invasive’s abundance, its impact would increase.”
Kornis explained “Although this type of finding isn’t entirely new, it has not been shown for an invasive species before in terms of its effect on native species.” He said that in addition to competing for food, gobies, which can spawn up to six times per season, are also intense rivals for mates.
Although the finding is specific to round gobies, Vander Zanden said it addresses broader issues in invasion science. “Don’t always assume that just because something is more abundant that it’s going to have more impact. Understanding how species have different impacts on different ecosystems is helpful in determining where to put our increasingly limited resources so that we get the most bang for the buck,” Vander Zanden said.
This experiment was part of a larger project that looked at the presence and impacts of round gobies in Great Lakes streams. Several years ago, Vander Zanden’s students found gobies in streams that drain into Lake Michigan.
“We were just shocked that this species that lives in huge lakes was moving into these tiny little streams because they’re such a different habitat,” Vander Zanden said. “Even in their native range in the Black and Caspian seas in Europe, they only live in large rivers and lakes.”
He set Kornis on the case, who confirmed that the gobies were living and expanding their range upstream every year by a third to a half of a mile.
“For a fish that normally has a small home range—like the size of a person’s living room—this is a very rapid range expansion,” Kornis said. He suspects the pressure of living in the higher stream temperatures and finding food, which is relatively less abundant in streams, may be the causes of their spread. “Unlike many native species, round gobies are built to feed on zebra mussels and quagga mussels, which are plentiful in the Great Lakes but usually absent in streams. Gobies in streams must compete with every other fish for the same food,” Kornis said. He used this information to develop a simulation model that predicts the gobies’ range expansion in streams.
Former Sea Grant Student Now Works With Millions of Fish
Matt Kornis’s mother likes to tell the story of how they would walk in the neighborhood when Matt was two and he would pick up a stick to “fish” for leaves in puddles. Later, in college, his love for water, fish and the outdoors won out over his interest in molecular biology, leading to his current job with the U.S. Fish and Wildlife Service (USFWS) in Green Bay, Wis.
Kornis was working on his undergraduate degree in biology at Lawrence University in Wisconsin when he applied for several internships in molecular biology or fisheries. As fate would have it, he received a fisheries internship with University of Wisconsin-Milwaukee’s John Janssen to look at alewife diets and habitat selection in Lake Michigan.
“I loved being outside every day during the summer, looking at different fish, analyzing data and using it to answer questions,” Kornis said. And his fisheries career began. Kornis pursued both his master’s and Ph.D. in limnology and marine science at UW-Madison with the help of Wisconsin Sea Grant funding. He worked with Professor Jake Vander Zanden at the Center for Limnology on projects that explored the expansion of the invasive round goby into streams that enter Lake Michigan.
This led to a post-doctoral fellowship with the Smithsonian Environmental Research Center in Maryland. Kornis looked at how land use in the Chesapeake Bay watershed combined with shoreline alteration to impact fish and shellfish. A major finding of his work was that wetland loss and shoreline hardening (construction with cement, rock or other hard materials) have negative effects on the abundance of many species. Kornis also explored how phragmities, an invasive wetland plant, affects nearshore fish communities.
After three years at the center, Kornis, a native of Glendale, Wis., moved back to Wisconsin to work for the Great Lakes Mass Marking Program. With the help of an automated process that can handle more than 8,000 fish per hour, USFWS biologists have inserted tiny coded wire tags into the snouts of 16 million Chinook salmon and 28.5 million lake trout stocked into lakes Michigan and Huron since 2010. The tags, which look like small pieces of mechanical pencil lead, rest in the cartilage of the fish’s snout and contain numerical codes that denote what hatchery the fish are from and where they were stocked. The fish’s adipose fin (the small fleshy fin located behind the dorsal fin on the top of each fish) is clipped as a visual marker that the fish is tagged.
The tags are retrieved later by fisheries managers, sport anglers, commercial fishermen and “head hunters”—USFWS tag recovery technicians who haunt fishing tournaments and fish cleaning stations to assess fish caught by anglers willing to participate in the program.
Each tag is painstakingly extracted from the fish’s snout by hand and read under a microscope for its code. Nearly 50,000 tags have been recovered since the program’s inception, providing information on two important Great Lakes fisheries.
“Chinook salmon and lake trout fisheries contribute to a 7-billion-dollar-per-year industry,” said Kornis. “The importance of these fisheries to the Great Lakes region can’t be understated, and we’re processing information to help enhance our understanding of that fishery.”
The boy who used to fish in puddles has come a long way.