URBANA, ILL. -- Wherever round gobies turn up in large numbers in the Great Lakes and nearby waterways, mottled sculpin-a fish that is the major part of the yellow perch's diet--disappear. The gobies, an alien nuisance fish species similar in size and appearance to the native sculpins, are clearly out-competing them, but how?
One critical factor is that round gobies can interfere with mottled sculpin spawning, according to a study funded by Illinois-Indiana Sea Grant. In effect, the round gobies appear to evict defending mottled sculpins from spawning shelters.
"We tested this theory in an artificial stream and found that when round gobies were added to successful mottled sculpin nest areas, they ate the sculpin egg masses, changed to their spawning coloration and began to defend the sites," said John Janssen, biologist at the University of Wisconsin-Milwaukee.
"By interfering with mottled sculpin reproduction, the round goby may have a negative impact on the food supply of yellow perch, an important sport fish in Lake Michigan. At this point, we don't know whether the round goby will be a part of the yellow perch diet," Janssen added. Yellow perch populations have declined in recent years.
The round goby is native to the Black and Caspian Seas and was probably brought to the Great Lakes in the ballast water discharged from transatlantic ships. Gobies were first spotted in 1990 in the St. Clair River, the channel connecting Lake Huron and Lake St. Clair. Since then, the aggressive, robust fish has expanded its population throughout most of the Great Lakes. Now, experts are concerned that the goby will spread from the Great Lakes water basin to the Mississippi water basin, further affecting North American native species and ecosystems.
Round gobies look very similar to mottled sculpins. Gobies have large heads (as do sculpins) and so they slightly resemble large tadpoles. They are typically about 5 inches long, but can grow to 10 inches. Gobies can most easily be distinguished from sculpins by their fused pelvic fins (the front pair underneath the body) that form a suction cup. The pelvic fins on sculpin are separate.
There may still hope for future generations of mottled sculpin even in the face of nest-raiding round gobies. By studying their nesting needs and preferences, Janssen, along with Martin Berg, a biologist at Loyola University of Chicago, found that while there are similarities in the two species' spawning areas, there are also differences. These differences might be used to minimize goby spawning habitat and encourage sculpin spawning.
"Both fish are bottom-dwellers that nest in rock cavities, but round gobies prefer sites with larger rocks and more surface area because unlike the sculpin, they lay their eggs in a single layer, said Janssen. "It may be possible to discourage goby breeding by removing larger rocks from areas that are prime spawning sites.
"We can also create artificial spawning shelters for the sculpins that would be too small for the gobies to use," added Janssen. For example, when bank protection, weirs and other rock structures are placed in rivers or streams it provides an opportunity to put in rocks small enough to suit the sculpins nesting needs, but not the gobies.
Next, Janssen looks to further study control methods that may reduce the risk of round goby populations eliminating the mottled sculpin.
Anglers should note that it is illegal in Illinois and Indiana, and most other Great Lake states, to possess live gobies. If one catches a goby, dispose of it in the trash or on land far away from the waterbody. To prevent the spread of invasive species, all leftover bait should also be disposed of in this fashion.
The Illinois-Indiana Sea Grant College Program is one of 30 National Sea Grant College Programs. Created by Congress in 1966, Sea Grant combines university, government, business and industry expertise to address coastal and Great Lakes needs. Funding is provided by the National Oceanic Atmospheric Administration (NOAA), U. S. Department of Commerce, Purdue University at West Lafayette, Indiana, and the University of Illinois at Urbana-Champaign.
Goby Illustration Available at: Sea Grant's Nonindigenous Species Site at http://www.sgnis.org where you'll find additional information and a 3-D rotatable goby image.
For more information about round gobies, visit the Illinois-Indiana Sea Grant Web page at http://www.iisgcp.org./pubs/br where watch cards and a free fact sheet are available.
The above story is based on materials provided by National Sea Grant College Program. Note: Materials may be edited for content and length.
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