Leeches getting a grip on Lake Erie's Central Basin walleye

Anglers are not the only ones basking in the glory of the walleye gold rush in Lake Erie’s Central Basin.

So too are leeches, parasitic invertebrates that Central Basin anglers who are dragging their rigs close to the lake’s silt-sand and mud bottom are encountering. This is where the leeches live, unable to swim. Here, a leech finds a walleye the perfect place to seek attachment and fulfill its blood meal needs.

Just which species of leech is being found remains something of a minor mystery, however. There is scant scientific data on the subject: and not much more in the way of speculation.

And given that scientists say there could be from 700 to as many as 1,000 leech species worldwide, that leaves some margin of error in determining which one is finding Lake Erie walleye the perfect host.

One known, though, is that the leeches almost certainly do not harm their walleye hosts. More importantly, the leeches do not threaten people’s health when eating the prized fish.

What is understood also is that as the summer heated up and the water temperature rose, the walleye started to hug the bottom. It was than Central Basin fishers also began encountering leeches of one-half to as long as one inch in length.

Most of these leeches were being found at the bottom of ice chests, the creatures having left their respective hosts once the walleyes were deposited into the containers.

“The last time (fishing pal) Larry and I cleaned our fish we must have had eight or 10 leeches on the bottom of the cooler. When I pulled one loose it went for my finger,” said Bob Ashley of Mentor.

Ashley typically fishes for walleye off Lake County’s Mentor Lagoons. He and his fishing buddy were employing directional divers set to allow their attached lures to move just above the lake’s floor in about 40 to 45 feet of water, Ashley said.

None of the gullets of any cleaned walleye showed the fish were feasting on the leeches, however, Ashley added.

Marv DeGreen of Huntsburg Township and captain of Evil Eye charters, operates out of the Grand River and said his parties also encountered leeches. But that was earlier in the year when the operation was plying shallower water, DeGreen said.

“We’re now running out to 70 and 72 feet of water so we’re not seeing the leeches any more,” DeGreen said.

Scientists with both the Ohio Division of Wildlife and the Ohio Sea Grant Agency say because of certain factors they are not terribly surprised that leeches are being found in shallow water, though the experience is not particularly well documented.

A 1994 paper noted incidence of a particular leech species attached to Lake Erie Western Basin freshwater drum. This report was prepared by Michael T. Bur, then with the National Biological Survey’s Great Lakes Science Center in Ann Arbor, Michigan and provided by Ohio Division of Wildlife fisheries biologist Tim Bader with the agency’s Fairport Harbor Research Station.

Bur’s report stated the appearance of the leeches appeared to be associated with three factors. Among them were “above-average water temperatures” that could have sparked increased leech activity; increased water clarity making it easier for leeches to locate their respective host; and an aggressive drum collection program that may have brought on more observations.

Yet not much else is stashed in scientific literature, a detail noted by Bader, Wildlife Division Lake Erie fisheries supervisor Travis Hartman, as well as Kristen M. DeVanna Fussell, the Ohio Sea Grant program’s assistant director of administration and research.

DeVanna Fussell said that while leeches may be common in Lake Erie and most often – when encountered – seen on freshwater drum, they are parasitic invertebrates. Thus if a leech can locate a large enough host it will attach itself for a blood meal before dislocating itself, not harming the fish, the scientist said.

“My first thought is that the increased occurrence on walleye is really just due to current densities of the fish. Leeches are opportunistic, and now there are just more walleye for them to attach to,” DeVanna Fussell said.

That is a point that both Bader and Hartman are suggesting with equal accord.

“I wouldn’t say it’s common occurrence, but there are a lot more walleye out there for the leeches to find,” Hartman said.

Then, too, DeVanna Fussell says, “there is more than enough decomposing organic matter at the bottom of the lake that I bet leech populations are also doing really well.”

As for concerns about whether a walleye that attracts one or more leeches is safe to eat, all three scientists were likewise in one accord.

“No, they’re perfectly fine to eat,” Bader said.

- Jeffrey L. Frischkorn
JFrischk@Ameritech.net