In the continual battle to confront the serious threat that invasive species pose to the Great Lakes, and specifically to Lake Erie and its adjoining river systems, dogged surveillance and early detection of any level of infiltration have been essential elements.
Asian carp have usually been at the top of the most-feared and most-studied list, since they could potentially be the most destructive invasives to date. While the primary focus has been on the Chicago waterway and its close proximity to Lake Michigan, there are multiple fronts in this biological war.
Locally, the Sandusky and Maumee rivers and their bays have been closely scrutinized for the presence of grass carp or white amurs, one of the four species commonly referred to as Asian carp – bighead carp, silver carp, black carp and grass carp. Grass carp are primarily herbivorous and they consume large amounts of aquatic vegetation, and therefore present a threat to the habitat in the rivers, lake and bays that is essential for native fish and waterfowl. Here’s a picture of where fish live:
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Fisheries biologists from multiple state, federal and provincial agencies as well as conservation groups conducted an extensive search for grass carp on the Sandusky and Maumee rivers last week, hoping to assess their ability to capture grass carp, study some captured specimens, and release others after implanting tracking devices to follow their future movements.
The effort included crews from the ODNR Division of Wildlife, Michigan DNR, U.S. Fish and Wildlife Service, the Department of Fisheries and Oceans Canada, Ontario Ministry of Natural Resources and Forestry, Minnesota DNR; Great Lakes Fishery Commission, The Nature Conservancy, U.S. Geological Survey, Quebec Ministry of Forest, Wildlife, and Parks, New York State Department of Environmental Conservation, Michigan State University; The Ohio State University and the University of Toledo using multiple boats, nets and shocking systems in the search.
Over three days of searching, they collected 28 grass carp from the Sandusky River and three from the Maumee River. Biologists have been aware for some time that grass carp were present in the river systems, but these are believed to be very small populations.
Travis Hartman, the Lake Erie Program Administrator for the Division of Wildlife, said a similar search conducted last year was less successful, primarily since the water level was low and the fish were likely much more scattered. A high flow in the river can trigger spawning activity and concentrate the fish, but with no such conditions, last year’s effort captured just eight fish.
“Last year we intended to sample during a high-flow spawning event, and we didn’t get one in the time frame we had scheduled, so we had to scramble,” Hartman said. “This year the date showed up and we got a high flow event. We learned a lot about how to catch them last year, and we utilized that information this year.”
Grass carp were imported and stocked in private ponds throughout the country as far back as the early 1970s, to control vegetation. Some are believed to have escaped during flood events, while others might have been accidentally or intentionally released into the rivers and streams that flow into Lake Erie, where rogue fish have been detected since the mid-1980s. Efforts to capture grass carp have resulted in low catch rates, which biologists hope indicates low densities.
Ohio pond owners can still stock grass carp, but only triploid or sterile specimens are allowed to be brought into the state and sold for stocking. Michigan forbids the sale or stocking of all grass carp. The sterile variety sold in some states today was not available until the 1980s. Grass carp can grow to more than 100 pounds and over six feet long. The fish captured in the recent work on the two area rivers were all adult grass carp, Hartman said, with most in the 30-40 inch range.
“When you get large, adult, fertile fish that are spawning, it tells you that they have been in the system for a while,” Hartman said. “Grass carp have been in Lake Erie for many years, in very low numbers, and we are much more aware of them now.”
He said that of the 31 fish captured in the study, nine were outfitted with tracking devices and released, 21 will be studied to determine their age, origin and if they were sterile stock or not, and one fish that had been captured previously and already had a tracking device was released.
“From those 21 fish we’ll be looking at, we will look for evidence that they came from the Sandusky River system,” he said. They will also study scale samples that were taken from the fish that were released.
“With everyone partnering in this manner, we’re learning so much more about these fish and looking at how we can control or eradicate them,” Hartman said. “It is tough to assume that we can eradicate them, but now we know that if there is a high-flow spawning event, we can successfully remove them from the waterway.”