Fremont, Ohio — Scientists said 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.
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.
The Sandusky River has about 15 miles of flowing waters accessible to the grass carp – a shorter stretch than experts previously believed necessary for spawning.
“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 project.
Grass carp eat aquatic vegetation, and there is concern that should the species spread, they could impact fish and waterfowl habitat through aquatic plant removal. The Ohio DNR Division of Wildlife is actively engaged in discussions with the Asian Carp Regional Coordinating Committee, U.S. Fish and Wildlife Service (USFWS), USGS, Great Lakes states, as well as Fisheries and Oceans Canada and the province of Ontario about next actions to address knowledge gaps about grass carp population status in the Great Lakes, evaluate risk from this species and potential to develop integrated pest management strategies to control impacts of feral, naturally reproducing grass carp.
“Grass carp are considered an Asian carp but should not be confused with bighead and silver Asian carp,” said ODNR Division of Wildlife Fish Administrator Rich Carter.
Grass carp have been stocked across the U.S. since the 1960s. Feral (wild) grass carp have been documented from numerous locations in the Great Lakes and Lake Erie since the mid-1980s, but ploidy status (sterile versus fertile) has not been tested until recently. Feral grass carp have been collected in the Ohio River watershed since 1980. Reproducing populations exist in the lower Ohio River. Recent research documented fertile (diploid) grass carp in Lake Michigan and Lake Erie at Monroe, Mich.
Ohio and 42 other states allow the sale of sterile (triploid) grass carp that are used for controlling aquatic vegetation in ponds. Ohio law does not allow importation or stocking of fertile (diploid) grass carp. Ohio law has allowed importation and stocking of certified sterile (triploid) grass carp since 1988. A certification program is administered by USFWS.
ODNR has developed an Ohio Asian Carp Tactical Plan that provides detailed approaches to address the threats by bighead, silver and grass carp. The plan is currently being finalized, incorporating stakeholder comments. ODNR’s strategies to address grass carp outlined in the plan include:
- Statewide testing of fish collected in ODNR assessments to determine fertility.
- Random testing of certified triploid grass carp for fertility status in Ohio shipments.
- Enforcement of prohibitions on diploid grass carp importation.
- Engaging regional partners in discussions on grass carp use.
The ODNR in its assessments is on the right track, said Kristy Meyer, managing director of agricultural, health and clean water programs at the Ohio Environmental Council.
“This goes to show that the outreach and education that the Ohio Division of Wildlife has been doing is paying off,” said Meyer.
“Anglers could have been catching grass carp for years and throwing them back, not knowing whether or not they were diploid carp and not fully understanding the potential devastating impacts they can cause to native habitat and therefore wildlife,” she said. “But, now, more anglers are turning suspect fish over to state game officials.”