http://ipraudio.interlochen.org/LakeTrout.mp3
For the last 25 years, fisheries biologists have tried to rehabilitate lake trout in Lake Michigan. Every year they've raised millions of fish in hatcheries and released them in special refuges set aside to protect the trout. Their goal is to restore the ecosystem's top predator that was wiped out by overfishing and the parasitic sea lamprey. But their efforts appear to have come up short.
A recent study by the Great Lakes Science Center in Ann Arbor shows virtually no lake trout are breeding in northern Lake Michigan. Every year for the past decade a team of researchers has used gill nets to catch lake trout in the northern refuge near Beaver Island. If they catch a fish with clipped fins, it came from a hatchery. If the fins are not clipped, the lake trout might have been born and raised in the wild.
"The percentage of wild fish in the northern refuge on average during the 2000's was only about 2 percent to 3 percent," says Primary Researcher Chuck Madenjian. "That's below the failure rate to clip fish at the hatchery. You could almost count that as a negligible amount.
There are several reasons researchers think they are finding few wild lake trout, but Madenjian thinks the alewife is key, a small invasive species not much bigger than a sardine. It affects lake trout in two ways. It eats eggs and newly hatched trout. And adult lake trout also eat alewives, but when they do, the alewives pass along a deficiency in the vitamin thiamine. And that deficiency makes it harder for lake trout to reproduce.
The politics of fish
Madenjian suggests stocking more lake trout in the refuges to improve the odds for survival.
"To build up a larger stock of spawners, because right now the spawner stock size within the refuge is very low," he says. But the decision to increase stocking is not based solely on biology. Resource mangers around the lake take into account many other factors, and some think that increasing stocks of lake trout may mess with the salmon fishery.
For years the agencies that manage Lake Michigan have discussed a plan to stock more lake trout, but it hasn't been approved. The group that oversees fishing for five northern Michigan tribes would like to see more lake trout stocked. The tribes have treaty rights to fish for trout commercially. But salmon is the most popular sport fish in the Great lakes, and some states aren't interested in putting more trout into the lake.
"Wisconsin is adamant about maintaining Chinook salmon stocking, says Mark Ebener, a researcher with the Chippewa Ottawa Resource Authority, or CORA. "They've got a big salmon fishery on their side. And they don't really want to increase lake trout stocking to the levels that are called for in the rehabilitation plan partly because Wisconsin doesn't get a lot of lake trout."
Wisconsin fisheries biologist Brad Eggold doesn't disagree with that. He says the salmon fishery is important to his state's tourism economy. Eggold thinks it's possible to support both lake trout and salmon. But he favors experimenting with where the lake trout are stocked, rather than stocking more. He says it's more than just alewives that are disrupting reproductive success for the trout.
"Any time you do an experiment in the natural environment there are so many variables that come into play," he says. "It gets real hard to nail down exact causes from each of those on whether rehabilitation is going to be successful."
And Eggold says the agencies could pay closer attention to the success or failure of the rehabilitation program. He hopes they don't wait another twenty years to adjust their strategy if it isn't working. But that raises the question of how much control resource managers have over the fishery. Ebener, from CORA, says not much. And he doesn't think it's possible to balance all the factors.
"I describe it as balancing on a knife edge," he says. "You don't want too many alewives because once you have too many alewives you know they inhibit reproduction and survival of native species: lake trout, emerald shiners, yellow perch stuff like that. But you don't want too few to where you start getting declines in growth rates of Chinook salmon and it starts affecting salmon abundance. Personal opinion, it's an impossible task to follow."
But the natural resource managers will adopt a strategy and try for some improvement in lake trout recovery, a goal that's largely been accomplished in Lake Superior and is starting to succeed in Lake Huron but has so far eluded them in the refuges of Lake Michigan.