Yellowstone Lake cutthroat trout may be increasing ever so slightly, and that is welcome news. But efforts to decimate lake trout must continue with dogged determination, experts say.

According to rough estimates, between 300,000 and 400,000 non-native adult lake trout dwell in Yellowstone Lake. To save cutthroats, the lake must be rid of the intruding lake trout and their spawn.

Before lake trout, an estimated 4 million cutthroats lived in the Yellowstone River system. Now the estimate has dwindled down to 10 percent of that, or perhaps as low as 1 or 2 percent, according to a 2012 Save the Yellowstone Cutthroat Trout brochure from Trout Unlimited.

There are a number of theories of explaining lake trout’s uninvited arrival, first noted in 1994, but there is no conclusive evidence supporting any particular hypothesis. To date, approximately 800,000 lake trout have been captured using gill nets since 1995.

Cutthroats are crucial to the Yellowstone ecosystem, providing food for large birds, small mammals and grizzly bears that fish the tributaries in the spring for spawning cutthroats.

At an East Yellowstone chapter of Trout Unlimited meeting in Cody earlier this month, member Dave Sweet provided an update of the telemetry study at Yellowstone Lake. Sweet is chairing the cutthroat preservation campaign for Trout Unlimited.

A telemetry study was launched last year to monitor lake trout movement patterns, particularly leading to spawning beds, Sweet said.

Last summer, 141 hydroacoustic tags were surgically implanted in lake trout bellies. Forty receivers were attached to buoys around the lake to track signals from the tags.

Roughly two-thirds of the tagged fish are males, because they visit multiple spawning beds while females tend to stick to one bed, Sweet said.

With a computer image, Sweet displays a map of Yellowstone Lake. Red dots around the lake indicate receiver locations. At a relatively narrow corridor entering West Thumb, red dots appear in three rows like a naval blockade.

The intent is to install a curtain of receivers to ascertain the lake trouts’ direction of travel, Sweet said.

The transmitters can lead to the beds. If spawning beds are found and the eggs destroyed, the lake trout population can be substantially reduced.

The receivers also can record lake trout locations, thus directing locations for gill nets that snag lake trout by the thousands. The scientific panel also recommended more gill-netting, which the service has done.

On an average day, 11 miles of gill nets were laid last summer by a commercial fishing boat and two boats manned by Park Service employees, Sweet said.

Approximately 220,000 lake trout were caught in 2011. Of those, 103,000 were netted by a commercial fishing boat. Although many of the 220,000 were juvenile fish, it nonetheless took a big bite from the population, Sweet said.

Preliminary data shows a lot of lake trout activity near Wolf Point, which is located roughly at the entrance to West Thumb.

One dot bounces around the map just outside West Thumb, indicating the travels of a male lake trout. Sweet said he believed the trout was a spawner.

“He is on the prowl,” said Unlimited member Duane Anderson, drawing chuckles from his colleagues.

Beneath Yellowstone Lake’s ice, the receivers are still collecting data.

Scientist Jackson Gross of the U.S. Geological Survey is developing ways to destroy eggs. One method, electroshock, was recently tested. Gross still is trying to evaluate its effectiveness, Sweet said.

The amount of data downloaded from the receivers is massive. At a February meeting in Bozeman, Mont., Robert Gresswell, a research biologist at the U.S.G.S., who initiated the telemetry study, said he did not have time to analyze it. Gresswell suggested hiring an individual to analyze the data would cost $100,000, Sweet said.

Yellowstone Park Superintendent Dan Wenk has said he would provide money from a Yellowstone Park Foundation grant.

“That’s the kind of commitment Dan Wenk is making,” Sweet said.

The foundation committed $1 million to help the park launch a comprehensive native fish conservation program, which is based on a service plan approved in 2011. The top priority of the program is to take proactive steps to restore the Yellowstone Lake cutthroats by removing lake trout.

The project to rid Yellowstone Lake of lake trout is a joint effort by the National Park Service, Trout Unlimited, U.S. Geological Survey, Greater Yellowstone Coalition, National Parks Conservation Association and the Yellowstone Park Foundation.

Trout Unlimited donated $40,000 last year to get the project started. This year they are seeking $85,000. A portion of that has been raised, Sweet said.

Yellowstone Park fishing licenses include a postcard asking anglers to report the location, number of fish caught, the species and the amount of time spent fishing. Survey results from thousands of anglers over the years said they caught on average 1.5 to 2 cutthroats per hour on Yellowstone Lake in the 1970s and ’80s. By the early to mid 2000s, anglers were catching 0.5 cutthroats per hour. However in the last two years, anglers were landing 0.7 to 0.8 cutthroats per hour. A small, but heartening cutthroat rebound. “It’s an indication that maybe things are getting a little better in the lake,” Sweet said.