Yellowstone cutthroat numbers continue to fall

BILLINGS – Yellowstone cutthroat trout, a source of food for grizzly bears and at least 40 other species, continue to decline in Yellowstone National Park.

Surveys along tributaries to Yellowstone Lake indicate a population lower than it has been seen since the 1950s. The fish has been harmed by predatory lake trout, whirling disease and drought.

Besides its importance to grizzlies, eagles, otters and other wildlife, the Yellowstone cutthroat helps support a $36 million sport fishing industry in the park and communities nearby.

At Clear Creek on the east side of Yellowstone Lake, 1,438 migrating cutthroat were counted in 2004, the lowest number since record keeping began in 1945 and a 58 percent decrease from 2003. More than 70,000 cutthroat were counted at Clear Creek in 1978.

At Bridge Creek, on the lake’s west side, only one cutthroat was counted during the 2004 spawning season. Eighty-six were seen there in 2003, and in 1999 the number topped 2,300.

Officials estimate that perhaps 1 million spawning-age cutthroat in remain in Yellowstone Lake.

“It’s probably really unlikely that those cutts would ever be extinct,” said Todd Koel, lead fisheries biologist at the park. “But without lake trout removal, without our help, they could be driven to the point where they don’t have any ecological significance.”

For grizzly bears, “Anytime you lose one of the important foods, it’s a big deal,” said Chuck Schwartz, head of the Interagency Grizzly Bear Study Team.

Researchers plan a study, beginning in 2007, of the relationship between bears and Yellowstone cutthroat trout. One recent study found only a small percentage of the estimated 600 grizzlies in the Yellowstone ecosystem rely on the trout.

The upcoming study “will give us a better picture if we lose this resource, what the overall effect ecosystem-wide will be,” Schwartz said.

During the past four years, park workers netted and killed more than 75,000 lake trout, introduced fish that consume cutthroat at a rate of 50 or more a year. Biologists are tracking the progress of whirling disease, which can kill trout or make them easy targets for predators.