How are giant bighead carp getting into ponds?
Chicago — Asian carp turning up in small urban ponds in and around Chicago have been somewhat of a mystery to those trying to keep the invasive fish out of nearby Lake Michigan.
But many have a hunch.
A 2011 study by DNR became reference material in recent weeks after an 82-pound carp was pulled from Flatfoot Lake, a pond in Beaubien Woods Forest Preserve, adjacent to I-94 on the south side of the city.
According to “Bighead Carp in Illinois Urban Fishing Ponds,” a report by the Division of Fisheries Aquatic Nuisance Species Program dated December 2011, “there is building evidence that young bighead carp may have been unintentionally stocked in urban fishing ponds with shipments of desirable fish species.”
In other words, the carp slipped in during stocking of sport fish such as channel catfish.
During netting and electrofishing for the study in Flatfoot, DNR reported catches of more than a dozen adult bighead carp ranging from 48 to 80 pounds, and three adult bighead carp ranging from 56 to 62 pounds from Schiller Pond in Schiller Park.
DNR noted in its reports that “Typically, no bighead or silver carp are captured during sampling responses.”
A growing body of evidence suggests that bighead carp likely were introduced accidentally in contaminated shipments of channel catfish made during the late 1990s and early 2000s, the report noted.
Kevin Irons, Aquaculture and Aquatic Nuisance Species Program manager for DNR, said all signs point to stocking.
“We have a theory that this could have been there historically, as a result of catfish stocking that has taken place there over the years,” he recently told The Associated Press.
For many years leading up the discovery of the carp, urban ponds in the Chicago area were annually stocked with catfish and sunfish. Irons and other DNR biologists believe Asian carp could have “blended
in” with small catfish and panfish while at hatcheries in Arkansas, the source of many fish stocks for Illinois.
It was noted that potential sources for the carp are no longer in business.
Flatfoot Lake, just 19 acres in size, is only a few miles from Lake Michigan, and only three football fields from the Little Calumet River. The lake is in the DNR Urban Fishing Program and has been stocked with catchable-sized channel catfish and hybrid sunfish annually for more than a decade.
When local fishermen reported a very large fish suspected of being Asian carp in the lake in September of 2011, DNR biologists sampled the lake with electrofishing gear and nets. A total of 14 bighead carp and four large grass carp also were captured and removed. Biologists observed three additional bighead carp that avoided capture.
The pond was sampled again two weeks later, and DNR biologists captured and removed two bighead carp each weighing 76 pounds.
Biological samples of the carp were taken, and it was determined that the fish captured in the urban ponds were not connected to Asian carp found in the state’s river system, giving more credence to the belief that they were accidentally stocked in the ponds.
“The fact that all bighead carp obtained from Chicago area ponds to date have been very large fish of similar size and age also points towards stocking as a potential source,” the 2011 report stated. “These demographics indicate that stocking probably occurred during a limited number of events sometime before 2005 and likely before the State of Illinois banned transport of live bighead carp in 2002-2003. This corresponds to a time when bighead carp were raised for market in ponds with channel catfish in certain regions of the U.S.”
DNR has noted that shipments of channel catfish “may be the most likely source of contamination in Illinois urban fishing ponds because catchable-sized catfish are stocked frequently and extensively in these waters throughout the state.”
Stocking records of DNR’s Urban Fishing Program indicates that channel catfish have been purchased from in-state and out-of-state suppliers over the years.
According to the Aquatic Nuisance Species Program report, “Any producers rearing catfish and carp together in culture ponds could be a potential source of bighead carp in Chicago area urban fishing ponds.”
The Associated Press contributed to this report