JACKSON, Wyo. — Fewer lake trout are being caught per net in Yellowstone Lake, marking a turning point in the effort to knock the invasive species out of the big lake.
National Park Service and contracted fishing boats have caught more lake trout this year than any other.
But that’s because there are more nets being set. The number of lake trout per net, a key indicator of population, is falling, Yellowstone National Park spokesman Dan Hottle said.
“Our catch rate was down compared to this time last year,” Hottle said. “It’s about 6.3 fish per net night.”
The commercial fishing boats, now midway through the 11th year of operations, have caught and killed 200,000 lake trout since ice came off Yellowstone Lake this spring. Last year at this time they’d killed 180,000 fish. Carcasses are dropped back into Yellowstone Lake’s waters.
“We have a little bit better sense of where the fish are,” Hottle tells the Jackson Hole News & Guide (http://bit.ly/1338ivH), “so we’re fishing smarter.”
The park continues to mount a two-pronged attack against the large predatory trout, using both gill nets and trap nets in shallower waters where cutthroat are found.
Lake trout, also known as mackinaw, is a prized game fish in its native range of the Great Lakes, New England and much of Canada. In Yellowstone, however, the fish eaters, which commonly exceed 20 pounds, are believed to be the primary catalyst in a 90-plus percent drop in numbers of native Yellowstone Cutthroat Trout.
The cutthroat collapse has wide-ranging environmental implications, biologists say, and has been connected to everything from failing osprey nests to higher rates of grizzly bear predation on elk calves.
Officials with Trout Unlimited, a prominent fishing conservation group, were encouraged by news that lake trout catch rates are dropping.
“It’s really exciting for us,” said Scott Christy, Trout Unlimited’s Wyoming Coordinator. “That’s a heartening sign.
“The challenge is really that you have to keep doing that for a little while,” he said. “You need to keep the effort high even as the catch reduces to fully ensure that you’ll take down the population.”
One indication lake trout suppression is working as designed, Christy said, is that fish censuses on the lake are beginning to show small cutthroat.
Last year the numbers of cutthroat in the gill nets doubled relative to lake trout.
“Most years, it’s about four cut throat per 100 lake trout,” Pat Bigelow, a Park Service fisheries biologist, said. “This year, it’s double that.”
Yellowstone fisheries biologists did not return phone calls by press time.
Bob Gresswell, a U.S. Geological Survey research biologist closely involved with the lake trout campaign, said he forecasted the declining lake trout catch rate.
“From what we’ve seen the last couple years, I figured that either this year or next we’d see a decline,” Gresswell said.
“I’d hypothesize that (the decline) would increase again if they can afford to keep the effort at current levels.”
Boats on the Yellowstone Lake netted and killed 300,000 lake trout last year and 224,000 in 2011. The total cull the entire previous decade, however, was just 500,000.
Using mostly outside grants, the parks spends more than $2 million a year on the effort.
Yellowstone will begin targeting laker spawning beds this September, Gresswell said. Aided by 270 lake trout implanted with transmitters that send location information, biologists will attempt to kill eggs at two locations using two experimental methods: electrocution and suction.
Fisheries biologists hope that spawning bed treatments could hold Yellowstone Lake’s lake trout population at a low level at less cost in the long run. Entirely removing mackinaw from the 139-square-mile body of water is believed to be impossible.
Treatment of spawning beds all around the lake could come within the next several years, Gresswell said.
“The advisory panel that I’ve been head of is suggesting to the Park Service that they have something ready by 2016,” he said, “because we expect that the decline of lake trout will be fairly substantial by then.”