Knowledge could help contain menacing fish
originally published in Sioux Falls Argus Leader
original link: http://bit.ly/fsvPOl
Monday, Feb. 14
by Cody Winchester
Abetted by last summer's record flooding, Asian carp are continuing their advance up the Big Sioux and other Missouri River tributaries, as researchers and wildlife officials gear up to deal with the invasion.
"They're here, so the big question is, how many are we going to get?" said Brian Graeb, an assistant professor in South Dakota State University's wildlife and fisheries department.
Graeb and a doctoral student, Cari-Ann Hayer, have been studying the Asian carp's incursion into eastern South Dakota for almost two years. Results of the population research so far has been encouraging: Sampling runs have netted only 18 carp, which include silver, black, grass and bighead species. It's uncertain how the population will swell from there, Graeb said.
Left unchecked, the fish devastate river ecosystems, reproducing prolifically and consuming up to 20 percent of their body weight in plankton and algae every day. They compete directly with native fish such as gizzard shad and emerald shiner, and in strong enough numbers can knock out the bottom link on the food chain.
"It just collapses that whole food web," said Mike Smith, the aquatic nuisance species coordinator at South Dakota Game, Fish and Parks.
Silver carp also can pose a hazard to humans. Known as flying fish, they leap like scaly missiles out of the water when startled, smacking rivergoers in the face with enough force sometimes to break bones.
Asian carp can grow to 100 pounds or more and 5 feet in length, depending on the species and the setting. They were first imported to clean up algae at fish farms in the 1970s but escaped during widespread flooding. They have been moving steadily up the Mississippi River ever since.
As part of their research, Graeb and Hayer are gathering baseline data for existing food pathways in the rivers. This puts them in a better position to predict how the Asian carp might affect the rivers' ecosystems and how best to manage a population boom, if it ever comes.
The carp have been in the Big Sioux and other tributaries of the Missouri River since at least 2006, when a fisherman caught a silver carp just below the Canton Dam, Hayer said. Presumably, they maneuvered upstream during last summer's flooding, Graeb said.
Found in Big Sioux near Sioux Falls dam
Last fall, for the first time, Hayer found juveniles in the Big Sioux River near the Sioux Falls dam - evidence that a second generation is establishing itself.
"It's evidence of successful reproduction," Graeb said. "We don't know if that reproduction happened in South Dakota."
If the fish do muscle farther into South Dakota, the experience of other states shows that managing carp populations can be like trying to unring a bell.
They have devastated the ecosystems of the Mississippi and Illinois rivers, where in some places Asian carp outnumber other species nine to one, according to an interagency committee tasked with keeping the fish out of the Great Lakes.
The problem has become so great that in September the White House appointed a "carp czar" to oversee $78 million in federal funding for efforts to halt the fish's advance.
2 million eggs found in a 40-pound bighead
"Asian carps are really successful because they're able to overpopulate an area very quickly - they're prolific spawners," Smith said.
The fish are broadcast spawners, floating to midstream to release a torrent of eggs into the current. Kevin Irons, the aquatic nuisance species program manager at the Illinois Department of Natural Resources, said one of his technicians once cut open a 40-pound bighead carp and found 2 million eggs inside, he said.
"They're very abundant (here)," Irons said. "There are probably more of them in the Illinois River than anywhere else in the world."
Illinois has had some success in keeping population numbers down by offering incentives to commercial fisherman - though bony, the carp's firm, white meat is reportedly quite tasty. The regional fishing industry nets at least a million pounds of Asian carp a month, Irons said.
"There is a standing order for 30 million pounds to China."
Gavins Point Dam a major barrier to carp
One thing South Dakota has going for it is the artificial barrier of Gavins Point Dam, which has prevented the carps from advancing farther into the state, Smith said. Because it's difficult to tell young Asian carp apart from bait fish, fishermen are prohibited from using bait caught below Gavins Point anywhere else.
Smith said preventing such "bait-bucket" introductions is one of his section's top priorities.
Another bright spot is the relatively harsh environment of South Dakota's waterways, which could depress carp populations, Graeb said.
Although the SDSU researchers don't have enough information yet to know how much the population will grow, Graeb said one thing is clear: "We're never going to get rid of them completely."
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