The Aggression and Progression of Round Gobies
by Sharon Moen
In the life-and-death scramble for food and shelter, Great Lakes bottom-feeders like gobies, sculpins, and logperch may find themselves lunging for the same benthic insect or scrapping over real estate. A recent study funded by Sea Grant and published in the Transactions of the American Fisheries Society suggests that success in these tussles might be more about copping an attitude than physical prowess.
"Round gobies are like playground bullies," said Margot Bergstrom, the study's lead author. "In our artificial stream trials, when one round goby was housed with a fish of a different species, the other fish fared worse. The goby would aggressively chase the other fish."
Reintroducing slimy sculpins ainít easy
In addition to playing a part in round goby research, slimy sculpins are the focus of another Sea Grant project. Loren Miller, research associate in the department of fisheries, wildlife, and conservation biology at the University of Minnesota Twin Cities and his colleagues wonder if genetics plays a role in whether populations of the small fish can be successfully reintroduced in Southeast Minnesota trout streams.
Over a year ago the researchers reintroduced sculpin at six sites. They checked for surviving adults in the spring and decided that either stocked sculpins didn't survive or they were hard to recapture. This autumn the researchers looked for sculpin offspring. Miller reports that early results suggest that relatively few individuals seem to have contributed genes to the next generation. A project highlight was when the researchers developed the first microsatellites specifically for slimy sculpin. The microsatellites provide sufficient genetic diversity to accurately determine parentage and will play an essential part in deciphering source ancestry of slimy sculpins reintroduced to streams from multiple source populations.
JR 565. Fujishin et al. 2009. Isolation of 13 polymorphic microsatellite loci for slimy sculpin (Cottus cognatus). Conservation Genetics Resources DOI 10.1007/s12686-009-9099-3
Bergstrom, who is pursuing a Ph.D. at the University of Rhode Island, recently earned a Masterís degree while working with Allen (Al) Mensinger, an associate professor in the department of biology at the University of Minnesota Duluth. Bergstrom and Mensinger spent countless hours studying resource competition between the invasive round goby and three fish species (slimy sculpin, spoonhead sculpin, and logperch) that are native to the Duluth-Superior Harbor and that have similar ecological preferences.
Bergstrom and Mensinger found when a round goby spent 21 days in confinement with a spoonhead sculpin or logperch "cellmate," the goby gained about as much weight (up to 15% of original weight) as the other fish lost. Only slimy sculpins were able to maintain their weight in the presence of gobies. Even then, the round gobies gained weight.
Thinking that the round gobies might be gaining weight because they were better at finding and capturing food than their competitors, the researchers proceeded to study the fishesí ability to sense and strike at potential prey. They designed predator-prey trials to examine how vision and the lateral line systems of the fish species might differ. A fishís lateral line, sometime referred to as "a touch at a distance", responds to subtle changes in water pressure within one to two body length of the fish.
"What I expected to see, I didnít," Bergstrom said. "I thought the round gobies would have an edge, but it turned out that the native species have the visual advantage."
Bergstrom and Mensinger found that in the dark, a round goby has as much chance of catching a meal as sculpins do. (Without light, logperch are inactive.) However, even a small increase in light intensity was sufficient to give the native species, including logperch, a significant advantage in reaction and strike distances.
Although studying aggressive behavior was not part of the research, Bergstrom anecdotally reports that round gobies exhibited "continual antagonistic behavior toward other fish." She suggests that aggressive behavior allows round gobies to dominate a limited food supply, and that related stress could exacerbate the observed weight loss in the native species.
In a related study, Bergstrom, Mensinger, and their U.S. Geological Survey collaborator (Lori Evrard) report that round gobies exhibited a five-fold increase in abundance in the Duluth-Superior Harbor from 1998 to 2004. Logperch and slimy sculpins occupy the benthic habitat favored by round gobies but seem to have all-but-vanished from round goby infested areas of the Duluth-Superior Harbor. Round gobies are relative newbies to the harbor. They arrived around 1995, presumably by way of ballast water released from ships.
During last seasonís minnow-trap studies, Mensinger was impressed by the number of round gobies they were pulling up from the heart of the infestation. "We got over 30 gobies in one minnow trap," said Mensinger. "That's a lot of fish! Itís almost unheard of."
Watch the Research
Ever wonder what the researchers see? A video from Al Mensingerís laboratory shows how logperch, sculpin, and round goby strike at prey. See the research clip at: www.seagrant.umn.edu/video/bergstrom.mov (this video has no sound).
Fisheries managers and anglers are concerned about the spread of round gobies in Lake Superior and the invaders' ability to compete with native species. To date, round gobies are reproducing in the Duluth-Superior Harbor and at least one was pulled from the Amnicon River, 10 miles to the east along Lake Superiorís south shore.
Bergstrom and Mensinger's work adds to a growing body of information defining the characteristics that allow round gobies to be successful and documenting their distribution. The journal articles are available online. They are also available through Minnesota Sea Grant (See JR 542 and JR 542A).
JR 542. Bergstrom, M.A. and A.F. Mensinger. 2009. Interspecific resource competition between the invasive round goby and three native species: Logperch, slimy sculpin, and spoonhead sculpin. Trans. Am. Fish. Soc. 138: 1009-1017
JR 542A. Bergstrom, M.A., L.M. Evrard, and A.F. Mensinger. 2008. Distribution, abundance, and range of the round goby, Apollina melanostroma, in the Duluth-Superior Harbor and St. Louis River Estuary, 1998-2004. J. Great Lakes Res.