Lake Trout Threaten Cutthroats Park Biologists Fishing For Solution To Illegally Introduced Mackinaw In Yellowstone Lake

Summer snowflakes spit in the morning air as waves on Yellowstone Lake rock the 30-foot boat like a toy in a bathtub.

At the controls, Jeff Lutch, a biologist with the National Park Service, fights to keep the craft from passing over a 300-foot-long net that Eric Reinertson, Brian Hertel and Meredith Burnett are hand-reeling on board.

They hope the net will contain Mackinaw, or lake trout as they are more commonly called. Big ones - 10, 20 pounds or more - are full of eggs. But this isn’t for sport.

The Park Service crew seines the lake because macs have been illegally dumped into what once was the premier inland cutthroat trout fishery in North America.

Someone released the exotic lake trout apparently hoping to “diversify” the fishery. The presence of the fish wasn’t confirmed until two years ago. Since then, six age classes have been found, leading experts to believe the sabotage may have happened 20 years ago.

“We patted ourselves on the back for decades that we kept Yellowstone Lake pure,” said John Varley, the park’s science director. “Now the sport fishing for cutthroats is in jeopardy.”

When they get to be 15 or 16 inches long, lake trout switch diets from plants and crustaceans to fish - and the cutthroat is one of the least competitive trout around.

In fact, researchers already have taken 12-inch cutthroats from the stomachs of some lake trout in Yellowstone Lake.

The net had been set three days earlier in 118 feet of water. When totally pulled in, 10 more fish are found - nine cutthroats and a sucker. No mackinaws.

“Right now we’re doing a lot of experimenting trying to figure out exactly where the lake trout hang out,” Lutch explained.

“It’s going to start getting more critical as we head into the spawning season this fall because we really want to determine what areas those big females with thousands of eggs will be in to spawn.”

Jack McIntyre, a retired U.S. Forest Service fisheries project leader, heads a group of U.S. and Canadian experts to determine what might be done about the lake trout.

“We had been receiving reports from anglers since 1985 that there were lake trout, but you hear all sorts of things and we doubted it,” he said.

Then, on July 30, 1994, a fishing guide came to rangers with a 19-inch lake trout one of his clients hooked in the lake.

News hit the papers, and people started calling in with other stories.

A fisheries expert from Wyoming said the cutthroat population at Jackson Lake had dropped 90 percent this century because of lake trout.

A prediction was made that within 30 years, the number of cutthroat in Yellowstone Lake could drop from 2.5 million to 250,000 if nothing is done.

The recommendation: Determine the areas where the mackinaws spawn and use gill nets to drag them out. Also, remove limits on the number of lake trout anglers are allowed to catch and make it unlawful to return a mackinaw to the lake.

Varley, the park science director, said more than recreation is at stake.

“There are 42 species that rely on cutthroat spawning in the lake’s 126 tributaries, including the grizzly bear, bald eagle, white pelican, otter, black bear, mink, osprey and loon,” he said.

Because mackinaws spawn in cobble, rubble, or boulder substrates in the lake itself, they would not serve as a replacement food source for mammals and birds because they don’t go up into the streams.

“We looked at options,” Varley said, “and one was simply to leave the lake trout and start stocking cutthroats, but that’s very costly.

“Another would be to poison the lake, which would cost $28 million, and even then we couldn’t be certain we were totally successful. One pair in the lake and it all starts over again.”

He said the experts from the Great Lakes who deal with the lake trout say commercial fishing is the only way to control them.

For now, gill netting and angling are considered the most effective ways to handle the situation.