While several states fight in court to keep Asian carp out of the Great Lakes, Iowa officials have resigned themselves to the slow spread of the troublesome fish through state waters.
“They’re coming. It’s just a matter of time” before Asian carp spread through Iowa waters of the Mississippi River, said Department of Natural Resources fisheries biologist Mike Steuck.
“Physical barriers are the only thing we have to stop them, but dams work only until there is a flood,” said Kim Bogenschutz, coordinator of the DNR’s Aquatic Invasive Species Program.
The prolific and voracious bighead and silver carp — Asian imports that escaped commercial fish ponds in the South — eat plankton, threatening the food source that sustains most freshwater aquatic life. The silver carp, with its proclivity to leap from the water at the least provocation, also threatens physical harm to boaters and water skiers.
Michigan has sued the state of Illinois and the Army Corps of Engineers, seeking to close a century-old Chicago canal that connects Lake Michigan and the Mississippi River basin via the Illinois River. Wisconsin, Minnesota, Ohio, Indiana and New York have since supported the suit, intended to protect the $7 billion Great Lakes fishing industry from potential ruin by carp.
The Mississippi River lock and dam system has been impeding their progress, but the bighead carp and silver carp are slowly moving upstream, said Steuck, who heads the DNR’s Mississippi research station at Bellevue. Like a towboat, they have “locked through” the 38.2-foot-tall lock at Keokuk, which was once thought to prevent their upstream movement, he said.
Discussion of a barrier using sound, bubbles, electricity or possibly all three, at either Dubuque or the Quad Cities, “has gone nowhere,” he said.
Bogenschutz said the floods of 2008 enabled Asian carp to leapfrog what had been barriers to their expansion.
Bigheads surmounted the 5-in-1 Dam in Cedar Rapids and spread up the Cedar River to Black Hawk County, where several specimens were found in 2009.
Silver carp, which had been confined below the Des Moines River dam at Ottumwa, have moved upstream “in big numbers” to the Red Rock dam, said Bogenschutz.
DNR fisheries biologist Paul Sleeper said bigheads have been found in the Iowa River at Iowa City for most of the past decade and in the Cedar River as far upstream as Palisades-Kepler State Park since 2006.
The Skunk River in southern Iowa also has large populations of bighead and silver carp, Bogenschutz said.
Asian carp made a big splash in Cedar Rapids in June when archer Tracy Seaton of Shellsburg killed the state record bighead carp — a 79 pound 4 ounce monster — while bowfishing in a Cedar River backwater within the city limits.
Steuck said bigheads have been caught in Pool 12 above Bellevue, and both species have been captured in Pool 8 near La Crosse, Wis. Natural reproduction has not yet been documented in the Upper Mississippi, he said.
The prolific spawners will multiply rapidly if they are able to reproduce as they do in the Illinois River, which Steuck called “the worst-case scenario.”
“They eat so much and grow so fast that they are changing the bottom content of the Illinois River with their excrement,” said Asian carp expert Kevin Irons, a large river ecologist with the Illinois Natural History Survey.
Unlike most freshwater fish, which spawn annually, the Asian carp spawn almost every time the river rises.
“We have documented at least four spawns in one year on the Illinois River,” Irons said.
Researchers also have documented that filter-feeding fish, such as the bigmouth buffalo and gizzard shad, which compete directly with Asian carp for plankton, have become skinnier during the ascendancy of Asian carp, Irons said.
Researchers have not documented any decline in popular game fish, although they have not ruled out such declines.
Apart from Asian carps’ threat to other species, they have certainly impacted human recreation on the lower Illinois. “Who wants to water- ski or Jet Ski when you have 20-pound fish slapping you in the face?” Irons said.