By MIKE STARKOf The (Billings) Gazette Staff
Native Yellowstone cutthroat trout are losing their fight for survival in the heart of Yellowstone National Park.
Non-native lake trout patrolling Yellowstone Lake are eating so deeply into the population that biologists last year found just 471 cutthroats at a spot where there were more than 70,000 in the 1970s.
The downward spiral has been particularly noticeable at that spot - Clear Creek on the eastern edge of Yellowstone Lake - over the last several years. After biologists counted 6,613 cutthroats in 2002, the number dropped to 3,432 in 2003, 1,438 in 2004, 917 in 2005 and 471 last spring, according to numbers released Wednesday.
They are the lowest numbers since record keeping began in 1945.
"We're deeply concerned," said Todd Koel, Yellowstone's chief fisheries biologist, "but we're working hard and trying to hold the line."
Last year, a record number of lake trout, more than 60,000, were caught and killed in Yellowstone Lake by Park Service crews. Since 1998, about 198,000 of the non-native trout have been removed.
Those efforts, which cost around $400,000 a year, are scheduled to continue this summer.
It is hoped that the work will give enough of an edge for the cutthroat to start rebounding, Koel said.
"That's what we're looking for," Koel said.
Yellowstone cutthroat are an important fish in the West both culturally and ecologically. Some 40 other species, including grizzly bears, bald eagles and otters, feed on the cutthroat.
Though drought and whirling disease have played a role, much of the cutthroat's decline has been attributed to lake trout, a predatory fish that can consume 50 to 60 smaller cutthroats each year.
Park officials have said the lake trout have reduced the cutthroat population to a fraction of what it once was. One of the best ways to gauge the damage is by counting fish that spawn in the lake's tributaries.
Some of the most significant dropoffs have been at Bridge Creek on the western edge of the lake. Seven years ago, 2,300 cutthroats were counted there. In 2005, none were found, and a counting station wasn't set up in 2006.
Crews also spent eight weeks visiting nine streams looking for cutthroats. They found just 27 fish and only twice saw signs that bears were looking for food there.
It's possible that parts of the Yellowstone River drainage above the lake may provide a reservoir of healthy cutthroat trout, Koel said. So far, that area appears to be free from whirling disease, though more work needs to be done to assess those populations.
"That hopefully will be part of the system that holds the line," Koel said.
Though Yellowstone cutthroat are struggling to survive in and around Yellowstone Lake - long one of the population's strongholds - the U.S. Fish and Wildlife Service declined last year to put the species on the federal endangered species list.
The fish, named for the reddish slash under its jaw, still survives in about 6,300 miles of streams in Montana, Idaho, Wyoming and smaller portions of Utah and Nevada, the agency said. Despite threats in some areas, there's no evidence that the overall population will go extinct in the next 20 to 30 years, the agency said.
Some environmental groups, though, have said the federal government is underestimating the magnitude of the threats facing the fish.
Contact Mike Stark at email@example.com or 657-1232