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Biologists swarm Sandusky River in search of grass carp invaders

09/03/2017, 12:09am EDT

Species damaging to ecosystem; fish zapped, collected for testing

Janice Kerns, left, and Anne Marie Gorman, both with the Ohio Department of Natural Resources, net fish on the Sandusky River after a brief electric shock is sent into the water. THE BLADE/JETTA FRASER

FREMONT — A flotilla of boats was on the lower Sandusky River this past week, doggedly searching for what biologists hoped they would never find there — grass carp — one of the invasive Asian carps that present an ominous threat to the Great Lakes.

But grass carp, which devour aquatic plants and have the potential to degrade habitat essential to many native species, have been present in the waterway for several decades in what is believed to be very low numbers.

Teams of biologists from the Ohio Division of Wildlife, Michigan Department of Natural Resources, Department of Fisheries and Oceans Canada, U.S. Geological Survey, New York Department of Environmental Conservation, and the University of Toledo engaged in an intensive two-day hunt for grass carp on the river, while crews from the U.S. Fish and Wildlife Service scoured Sandusky Bay for the invasive fish.

It was a scavenger hunt in electro-fishing boats, a search for an elusive needle in a muddy, massive, water-filled haystack. But it also was a critical exercise to test various methods and determine the best techniques for capturing grass carp in the future. 

During its two days of work on the water, the group found eight adult grass carp, also known as white amur, ranging from 6 to 28 pounds, and those fish were sent to the U.S. Geological Survey lab in Sandusky for extensive testing that will determine their age, origin, and ability to reproduce.

“These fish have been in the system for some time, but we need to know more about them, so that’s why all of these agencies and personnel are here,” said Travis Hartman, Lake Erie Program administrator for the Division of Wildlife. “With more knowledge and information, we can be better equipped to hopefully prevent them from becoming established in greater numbers.”

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.

The primary threat from grass carp is damage to the ecosystem, because their vegetarian diet and vigorous feeding habits can result in the degradation of marshes and shallow areas vital to waterfowl and many other fish species.

It is critically important to make the distinction between grass carp and two other Asian carp species — silver carp and bighead carp — that have had a much more destructive impact on waters in the Mississippi River watershed. Bighead and silver carp are filter feeders that consume plankton essential to native fish species in their early stages of life.

Keeping silver carp and bighead carp out of the Great Lakes has been a top priority since these two species are believed to hold the potential to severely degrade the $7.2 billion fishery on the lakes.

“Grass carp are a problem and we need to keep on top of this, but anytime the words ‘Asian carp’ come up, people start to panic. But this is not the same critter as the silvers and the bighead,” said Dave Spangler, Lake Erie charter-boat captain and the president of the Lake Erie Waterkeeper organization.

“This study will help us learn the very specific spots that they go to spawn and where they like to congregate. We are gaining pieces of knowledge on them, and every bit of it is important.”

The grass carp brought to Ohio for stocking in ponds to control problem plant growth are required by law to be triploid — (sterile — fish incapable of reproducing. One of the most critical examples of information that should come from this past week’s sampling exercise is the reproductive capability of the captured fish.

“It will be interesting to see if those fish are triploid or not,” said Jeff Tyson from the Great Lakes Fisheries Commission in Ann Arbor, who was on hand for the research on the Sandusky River. “It is kind of a biological soup in the river here — it makes fish.”

The teams used electro-fishing boats that send a current through the water and temporarily stun fish, bringing them to the surface. Technicians netted the shocked fish to determine the species, immediately releasing unharmed all but the few grass carp found. The teams also use various nets and electro-fishing boats to drive fish toward the nets.

“With their body shape and size, grass carp are a little tougher to shock, plus they have a tendency to run from the electricity,” said Mike Wilkerson, fish management supervisor for the Ohio Department of Natural Resources, Division of Wildlife, for the northwest district.

In the summer of 2015, University of Toledo graduate student Holly Embke found the eggs of grass carp in the Sandusky River, providing the first direct proof that this type of Asian carp was reproducing in a Great Lakes tributary. Her work intensified the focus on the Sandusky watershed.

“Outside of this week’s work, we’ve spent quite a bit of time up here on the Sandusky doing a lot of electro-fishing and sampling, just looking for these fish,” Mr. Wilkerson said.

Nicole King, an aquatic ecology research technician at the Lake Erie Center working with the UT Department of Environmental Sciences, took part in the testing. She said the multiagency effort on the Sandusky River will help the group fine-tune its efforts and identify the best ways for dealing with grass carp in the future.

“This wasn’t about just removing these fish that were caught from the system, it was more about learning what habitats they prefer, and what gear to use when we set out to capture them,” she said.

Ms. King added that it is essential to stay in front of the grass carp situation in the river, on the bay, and in the lake, as the full measure of their impact is uncertain.

“We are spending a lot of time and resources in planting and rehabbing our wetlands, which provides habitat for a lot of other species, so if these grass carp end up damaging those habitats then their potential impact could be pretty widespread,” she said. “At this point we don’t really understand what all of the impacts could be.”

Tammy Newcomb, senior water policy adviser with the Michigan Department of Natural Resources, said the Sandusky River field work was a follow-up to a similar multiagency exercise that was conducted in the Michigan waters of Lake Erie off Monroe in 2014. The MDNR had one of its electro-fishing boats and personnel on hand for the Sandusky River work, which was based out of Memory Marina.

“This was much more strategic and targeted since it took place in a river,” she said. “We hope this produces an understanding of what types of steps we can take moving forward to reduce or eradicate grass carp in Lake Erie. Everyone’s resources are finite, and we could waste a lot of money chasing these fish around, so we want to build up our science-based approach and be strategic in going after these fish. We are all in this together and the goal at the end of the day is to protect the future of Lake Erie.”

Contact Blade outdoors editor Matt Markey at or 419-724-6068.

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