Underwater vehicles help solve mystery of Lake Michigan lake trout

Comments sought on plan to restore lake trout to Lake Michigan

MILWAUKEE – An underwater reef in deep water 40 miles off Sheboygan figures to play prominently in future efforts to restore native lake trout to Lake Michigan.

Research led by University of Wisconsin-Milwaukee Professor John Janssen using remotely operated underwater vehicles is finding that lake trout are spawning on this reef and that some eggs survive to hatch. Biologists say that is a hopeful sign following decades of stocking lake trout that have failed to successfully reproduce.

“John’s research gives us a ray of hope – Sheboygan Reef and East Reef appear to be promising spawning sites that may finally help restore populations of this native species to Lake Michigan,” says Bill Horns, Department of Natural Resources Great Lakes specialist.

Lake trout were a mainstay of commercial fishing in the early 1900s but had declined in all of the Great Lakes by the 1930s due to factors including invasion by sea lampreys, an invasive fish species that attaches to the sides of a host fish and sucks its body fluids out, overfishing, and possibly contaminants. By the 1950s, lake trout were extinct in Lake Michigan, Horns says.

Efforts to restore lake trout across the Great Lakes by the states, the federal government, tribal governments, and Ontario began in the mid-1950s with stocking. Starting in the 1960s, the sea lamprey control program carried out by the Great Lakes Fishery Commission suppressed sea lamprey.

Stocked lake trout survived well in Lake Michigan and the other Great Lakes, but with the exception of lake trout in Lake Superior, were not able to reproduce, Horns says. In Lake Michigan, spawning by stocked lake trout has been documented over the past few decades, and DNR netting surveys in recent years have shown that sexually mature lake trout from several year-classes are abundant in the Mid-Lake Reef area, but there’s been no documentation during the past decades that eggs have survived to adulthood to help rebuild naturally reproducing populations.

Janssen, whose position is jointly funded by UW-Milwaukee's WATER Institute and DNR, is starting to unravel that mystery with the help of submersibles. These remotely controlled vehicles are able to plumb the depths of the deep water reefs that appear to be acting as refuges for the fish from the variety of invasive species, including alewives, that dominate shallower water areas with reefs.

Equipped with a video camera, suction sampler, and electroshocking device designed to stun trout egg predators, the remotely operated vehicles are being used to locate lake trout spawning habitat, recover eggs and days-old fish called “fry,” and identify what fish may be preying on lake trout eggs and fry on the reef complex.

The researchers have focused their study on Sheboygan Reef and East Reef, which are parts of the Mid-Lake Reef Complex. East Reef lies about 25 miles out from Milwaukee and is 171 feet deep at its shallowest point. Sheboygan Reef is a little farther north and farther from shore. It reaches up to a depth of 121 feet.

The direct observations and collections made with the remotely operated vehicles have provided biologists much greater insight into the complex processes that affect lake trout reproduction and survival, Janssen says.

The underwater studies found that the Sheboygan Reef has abundant shrimp-like creatures (Mysis relicta), which are a major prey for very young lake trout. The reefs also provide good physical spawning habitat with rocky slopes that protect eggs during the months between spawning in the fall and hatching in late winter.

But the reefs also have been shown to have an unexpected abundance of burbot, a fish that may consume many lake trout eggs, but may also be able to control the other predator of lake trout eggs, the sculpins.

Burbot and sculpins are mostly unstudied factors in the Great Lakes and apparently will be a factor in understanding lake trout spawning at deep reefs. Future studies will address these issues more directly, Janssen says.

While the submersible is showing the Sheboygan Reef as good spawning habitat, Janssen is concerned about the future of the Mid-Lake Reef Complex because it is being invaded by quagga mussels, a non-native relative of zebra mussels. The quagga mussels, also filter feeders like the zebra mussels, are increasing rapidly.

Horns hopes that continued research using the submersible can continue providing essential information about the distribution and fate of hatched lake trout, particularly as the new invaders proliferate. It can also help identify which of the several genetic strains of lake trout are able to successfully use the Mid-Lake Reef Complex for reproduction.

Janssen has recently received an additional grant to continue the research work, which to date has been funded by the National Undersea Research Center for the North Atlantic and Great Lakes, Wisconsin Sea Grant, and U. S. Fish and Wildlife Service through the Great Lakes Fish and Wildlife Restoration Act.

“This research is difficult and expensive because of the setting, but it’s vital,” Horns says. “Not only is it important to the future of lake trout, but in shedding light on the complex interactions in Lake Michigan, particularly with the arrival and proliferation of invasive species.”

Draft lake trout management plan available for public comment

Information from Janssen’s research has helped shape a draft plan for restoration of lake trout that is now available for public comment. People can view the draft plan through the DNR’s Wisconsin Fishing Web site <http://www.wisconsinfishing.org>. Click on Lake Michigan fisheries on the lefthand side, then select “management reports” and then “A restoration plan for lake trout” (pdf).

The draft plan, developed by a technical committee of Great Lakes fisheries biologists, calls for continued stocking of lake trout as a major restoration tool, but seeks more targeted stocking and better matching the strain of lake trout stocked with its habitat to boost natural reproduction and survival.

“Where the fish will be stocked and what strains will be used are questions that remain to be settled among the different agencies that have the management jurisdictions on Lake Michigan,” says Horns, who is Wisconsin’s representative to the Lake Michigan Committee, the interjurisdictional body that will consider the biologists’ plan.

Horns says Wisconsin will carry into its discussions with other committee members its interests in maintaining a viable sport fishery for lake trout; establishing a naturally reproducing lake trout population; sustaining the present multi-species salmon and trout sport fishery; sustaining a multi-species forage base; and sustaining a viable multi-species commercial fishery.

“Lake trout restoration is a central goal of Wisconsin fisheries management,” he says. “But we want to achieve that goal without compromising our salmon and trout fishery or other fisheries objectives.

“We also recognize that other states have interests that must be taken into account in developing a final lake-wide plan that works for everyone.”

The draft lake-wide plan recommends stocking lake trout in the most promising spawning habitat, away from alewives, which biologists now believe may have been a major barrier in the past to successful reproduction by stocked lake trout, Horns says. Alewives, a member of the herring family, were confined to the Atlantic Coast but were introduced into the Great Lakes and were first documented in Lake Michigan in 1952 and Lake Superior in 1954.

“One hypothesis that’s gained ground in recent years is that the adult lake trout are deficient in thiamin as a result of eating alewives, which contain a thiamin-destroying enzyme, thiaminase,” Horns says. “As a result, the eggs produced by the stocked lake trout may be deficient in thiamin and unable to survive.”

There’s also evidence that the alewives eat the lake trout fry during a brief period just after hatching.

The draft plan would avoid lake trout interactions with alewives by focusing much of future stocking on the mid-lake reef complex, a deep-water area where the alewives typically aren’t found. This area has been a site of stocking and a lake trout refuge for a number of years; it is off limits for commercial fishing and lake trout may not be possessed by anglers within its boundaries.

The draft plan would also seek to better match the strain of lake trout stocked with the shallow water or deep water into which it is stocked. Native lake trout in the Great Lakes adapted to a variety of habitats, and biologists believe that some were better adapted to deep water areas than others.

Because lake trout were never driven to extinction in Lake Superior, some of the original variety of Great Lakes strains remain there and one option proposed in the draft plan is to use a Lake Superior strain or strain that’s successful in deeper water.

Sustained control of sea lamprey populations is recommended as another essential component to help achieve the population densities required for sustained natural reproduction, Horns says.

Submit comments on the plan to Bill Horns via e-mail: <Bill.Horns@dnr.state.wi.us> or U.S. mail: Bill Horns, Wisconsin DNR, PO Box 7921, Madison, WI 53707-7921.

FOR MORE INFORMATION CONTACT: Bill Horns - (608) 266-8782; John Janssen, UWM (414) 382-1733

Reprinted by permission of the Wisconsin DNR