Field Notes: Coaster Comeback?

Biologists are cautiously optimistic about signs that Lake Superior's coaster brook trout are slowly recovering after years of low population due to sportfishing and habitat loss. Coasters, which can commonly weigh 6 pounds, spawn in Superior's tributaries and reside in the big lake.

A 2002 population survey turned up larger coasters in several streams than did a similar survey in 1997, suggesting the fish are surviving longer. In addition, creel clerks, who survey steelhead anglers fishing Superior each spring, say the anglers report catching more coasters each year.

"It's not knock-you-over encouraging," said Don Schreiner, DNR Lake Superior fisheries supervisor, Duluth, "but taken as a whole, I think there's reason to be optimistic about the possibility of a limited self-sustaining population of coasters on the North Shore."

Notoriously aggressive and vulnerable to overfishing, coaster brook trout began to disappear almost immediately after anglers discovered concentrations of the fish 140 years ago in tributaries along the North Shore as well as in Michigan, Wisconsin, and Ontario.

Logging contributed to population decline. It cleared streambanks of shade-giving conifers, causing erosion and warmer water and thus hindering spawning.

By 1900 government, private, and tribal groups had initiated restoration programs that consisted largely of stocking hatchery-raised brook trout. While stocked brook trout have provided angling opportunities, they typically don't survive well in Lake Superior, where they become prey for numerous species of fish, says Schreiner.

In the past decade, biologists learned more about restoring the lake's native populations of coaster brook trout as well as walleye and lake sturgeon. The studies have been completed in the past three years by the Ontario Ministry of Natural Resources and the U.S. Geological Survey Great Lakes Science Center, in partnership with state agencies, including the Minnesota DNR.

Based on the studies, biologists think coaster brook trout are genetically similar to brook trout that reside entirely in Lake Superior streams. "It appears that coasters are an ecological variant-they are brook trout that found their way into the lake, where there was more food and more habitat," Schreiner said. "Like goldfish [which grow in proportion to the size of their bowl], coasters grow larger in Lake Superior than they do in tributaries."

In 2000 the DNR posted special regulation signs along some tributaries with coasters. Regulations in place since 1997 limit anglers to one brook trout 20 inches or longer from below barrier waterfalls in tributaries.

"A lot of the people who fish the tributaries below the boundaries are tourists and may not have been aware of the regulations," Schreiner said. "We hope that posting the regulations on the streams helped increase compliance."

Jason Abraham

For more information on trout, see MN DNR Nature Snapshots.