TRAVERSE CITY, Mich. – Scientists said Monday they have documented for the first time that an Asian carp species has successfully reproduced within the Great Lakes watershed, an ominous development in the struggle to slam the door on the hungry invaders that could threaten native fish.
An analysis of four grass carp captured last year in Ohio’s Sandusky River, a tributary of Lake Erie, found they had spent their entire lives there and were not introduced through means such as stocking, according to researchers with the U.S. Geological Survey and Bowling Green State University.
Grass carp are among four species imported from Asia decades ago to control algae and unwanted plants in controlled settings such as sewage treatment lagoons. They escaped into the wild and have spread into the Mississippi and other rivers and lakes across the nation’s heartland.
Of greatest concern in the Great Lakes region are bighead and silver carp, prolific breeders that gobble huge amounts of plankton – tiny plants and animals that are vital to aquatic food chains. Scientists say if they gain a foothold in the lakes, they could spread widely and destabilize a fishing industry valued at $7 billion.
Grass carp are less worrisome because they eat larger plants instead of plankton and don’t compete with native species, although they could harm valuable wetland vegetation where some fish spawn.
But because all Asian carp species require similar conditions to reproduce successfully, the Sandusky River discovery suggests it’s likely that any of them could spawn there and in many other Great Lakes tributaries, said Duane Chapman, a USGS fisheries biologist and member of the research team.
The Obama administration has spent nearly $200 million to shield the lakes, focusing primarily on an electrified barrier and other measures in Chicago-area waterways that offer a pathway from the carp-infested Mississippi River watershed to Lake Michigan.
Among the waterways of concern is Eagle Marsh on Fort Wayne’s southwest side, which can offer such a pathway during a flood. The Indiana Department of Natural Resources built a temporary fence across the marsh in 2010, and the U.S. Army Corps of Engineers is considering spending millions on work at the marsh to block the carp.