Biologists went to the north shore of Yellowstone Lake last year to look for spawning Yellowstone cutthroat trout.
Six years earlier, they had counted more than 2,300 at Bridge Creek.
But at the same spot in 2005, they didn't find one.
On the eastern shore, where more than 70,000 spawning cutthroat were counted in the late 1970s on Clear Creek, only 917 were seen — the lowest number since record keeping began in 1945.
The situation was similar at other places along the shore of Yellowstone Lake, long considered an important stronghold for the cutthroat trout.
"It's dismal," said Todd Koel, lead fisheries biologist in Yellowstone National Park.
Drought, whirling disease and predatory lake trout continue to take a toll on the national park's resident population of Yellowstone cutthroat. The population has been on a steady decline for years, and recently released 2005 data point in the same direction.
But there are subtle signs of hope.
The increasing number of young cutthroat spotted in Yellowstone Lake in recent years should be getting old enough to spawn in the next year or so, Koel said, which could help rebuild the population.
A decent snowpack in Yellowstone this winter, closer to long-term averages than the last several years, should increase the flow of the park's waterways, possibly reconnecting some drought-stricken streams with the lake again and lowering water temperatures, which might impede the advance of whirling disease.
And an aggressive gillnetting program that kills thousands of lake trout each year at Yellowstone Lake may also be paying dividends, as evidenced by declining numbers of the non-native trout being hooked by anglers.
"We're encouraged. That's what we need to see," Koel said.
There are still probably tens of thousands of Yellowstone cutthroat trout in Yellowstone, Koel said. It's a fraction of the population that once numbered in the millions, but anglers are still catching and releasing cutthroat, Koel said.
The biggest trouble has been the invasive lake trout, first found in Yellowstone Lake in 1994. One lake trout can eat 50 to 60 cutthroat a year.
Since 1994, more than 100,000 lake trout have been caught in gillnets on Yellowstone Lake and killed. Several thousand have been caught already this year, Koel said.
Fish biologists are hoping to refine their methods in the coming years, including learning more about where the lake trout are during certain times of the year so gillnetting operations can target those areas.
Biologists are also discussing the possibility of researching synthetic pheromones to attract lake trout so they can be caught, Koel said. Such a discovery would also help reduce lake trout numbers elsewhere in the West, including at Swan Lake, Lake McDonald in Glacier National Park and Lake Pend Oreille in northern Idaho.
Unless the lake trout are controlled, the cutthroat population could continue to decline precipitously in the coming decades.
"Right now, we're in a situation where we can't let up," Koel said.
The loss of cutthroat could affect other species in the park, including grizzly bears, eagles and other animals that feed on the spawning fish and thrive on the protein.
Earlier this year, the U.S. Fish and Wildlife Service denied a petition to protect the cutthroat under the Endangered Species Act. The agency said that despite shrinking habitat and threats to the fish, there wasn't enough evidence to indicate the fish will disappear in the next 20 to 30 years in the West.
Contact Mike Stark at firstname.lastname@example.org or 657-1232.