TRAVERSE CITY, Mich. (AP) - 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.
“It’s bad news,” Chapman said. “It would have been a lot easier to control
these fish if they’d been limited in the number of places where they could
spawn. This makes our job harder. It doesn’t make it impossible, but it
makes it harder.”
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. Critics say more is needed and
are pressing to physically separate the two systems.
The U.S. Army Corps of Engineers is scheduled to release a report in coming
months on a long-term solution.
John Goss, who heads the White House Council on Environmental Quality’s
Asian carp program, said sterile grass carp have been found in the Great
Lakes for years. But the discovery that they can reproduce within the
watershed “reinforces why we must continue to execute the aggressive
strategy to keep silver and bighead carp out of the Great Lakes that we have
been pursuing for the past three and a half years,” he said.
A commercial fisherman captured four small grass carp from the Sandusky
River in 2012. Chapman and his colleagues determined they were at least a
year old and could become spawning adults.
The scientists also examined bones in the fishes’ heads called “otoliths”
that indicate the chemistry of the waters they’ve inhabited, and they
compared them with otoliths of farmed fish. The analysis confirmed the grass
carp were hatched through natural reproduction in the river.
To spawn successfully, Asian carp need rivers of a certain length with
currents that keep their eggs drifting long enough to hatch. Researchers are
fine-tuning computer models that can determine the likelihood that a
particular river is suitable.
A few years ago, scientists believed that perhaps two dozen rivers in the
Great Lakes watershed offered good spawning habitat. But the grass carp
analysis and other recent findings suggest the number may be considerably
higher, Chapman said. He and others are developing a list.
“It also means that many more reservoirs in the United States are at risk of
Asian carp establishment,” he said.
The Sandusky River has about 15 miles of flowing waters accessible to the
grass carp - a shorter stretch than experts previously believed necessary
“This is further evidence that we can’t underestimate the flexibility that
Asian carps have to become acclimated to and even adapt to environments
outside their native range,” said Reuben Goforth, a Purdue University
scientist who has studied the carp but wasn’t involved with the USGS