Yellowstone cutthroat trout numbers declining

published on Friday, November 25, 2005 10:45 PM MST

By SCOTT McMILLION, Chronicle Staff Writer

Yellowstone cutthroat trout numbers appear to have fallen by at least 60 percent in Yellowstone Lake, their largest refuge, and their future doesn't look rosy, according to a new scientific journal article by National Park Service scientists.

Yellowstone National Park's largest lake once held millions of members of the cutthroat trout subspecies that share the famous name.

Netting, testing and mathematical models suggest that "only a fraction of that population exists today," says the article, written by aquatic specialists in the park and published in "Fisheries," the magazine of the American Fisheries Society.

There is also some low-tech evidence: in 1998, anglers caught an average of two cutthroats an hour in the lake. Last year, that number fell to 0.8 fish per hour.

The Park Service is dedicated to "the preservation and recovery" of the fish, the article says, yet "it appears to be in peril."

The news could have implications both inside and outside the park.

In the park, a wide variety of species, from otters to pelicans, from bald eagles to grizzly bears, rely on cutthroats as an important food.

Outside the park, environmental groups have been trying for years to have the Yellowstone cutthroat listed under the Endangered Species Act. If they succeed, it could change how people irrigate, manage cattle and harvest timber in big parts of several states around the park.

The U.S. Fish and Wildlife Service, the agency in charge of endangered species programs, has cited Yellowstone Lake's abundant population as one major reason not to list the fish. Environmentalists point to loss of habitat and cross breeding with non-native fish outside the park as a reason to list it.

"The park's doing everything it can," said Steve Kelly, a Bozeman environmentalist who has pushed for the trout's listing. "If they can't make it happen there, maybe they can't make it happen. Normally, the park is a stronghold for a species."

The cutthroats face major threats from non-native lake trout and from whirling disease, a European malady that infests the lake and some of its major spawning tributaries.

And then there is lingering drought, which in recent years has left some tributaries so dry that by the end of summer, when tiny fish that hatch in the streams normally swim to the lake, they find themselves trapped in isolated pools and channels.

Lake trout were illegally introduced to the lake in the 1980s, the article says. After they were discovered in 1995, the Park Service began an aggressive gill netting program to try to reduce their numbers.

Lake trout, which feed voraciously on cutthroats, cannot fill the cutthroats' place in the food chain because they favor deep waters where they are unavailable to predators.

The nets have killed more than 100,000 lake trout, and technicians are growing increasingly skilled in their pursuit.

They are making progress but "control" of the lake trout cannot yet be claimed, the article says.

Kill rates might improve with the use of underwater photography and other technological advances to find lake trout spawning beds, but the gill netting program needs to continue "into the future" if Yellowstone cutthroat are to continue to play their key role in the "overall integrity of the greater Yellowstone ecosystem," the article says.

Scott McMillion is at scottm@dailychronicle.com

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