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GLIN==> Invasive Gobies Prevent Sculpin Spawning in the Great Lakes

Posted on behalf of Irene Miles <miles@uiuc.edu>

Invasive Gobies Prevent Sculpin Spawning in the Great Lakes

Contact: Irene Miles
Extension Communications Specialist
(217)333-8055; miles@uiuc.edu

August 27, 2001

Invasive Gobies Prevent Sculpin Spawning in the Great Lakes

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

"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.

For more information about round gobies, you can visit the Illinois-Indiana
Sea Grant Web page at http://www.iisgcp.org./pubs/br and order a copy of the
book "Round Goby: A Review of European and North American Literature." Also
available are watch cards and a free fact sheet. You can also learn to
identify the round goby by visiting Sea Grant's Nonindigenous Species Site
at http://www.sgnis.org where you'll find information and a 3-D rotatable
goby image.

Anglers should note that it is illegal in Illinois and Indiana to possess
live gobies. If you catch 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

Source: John Janssen (414)964-6542

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