Their goal is to provide the best possible sport fishing, Hallac said.
Non-native lake trout stalking Yellowstone Lake are a major concern, because they eat cutthroats and thus cause an ecological chain reaction: birds and mammals no longer have the fish to feed on, he said.
Lake trout were stocked in Lewis Lake in 1890 because the lake had no fish, said Todd Koel, supervisor for the Yellowstone fisheries program. It is possible an angler may have illegally stocked Yellowstone Lake with those same lake trout, he said.
And park employees said it is possible Yellowstone Lake was stocked with lake trout by park employees sometime in the past. The lakers also may have been from a hatchery next to the lake that closed in 1955.
However the vertebrate interlopers arrived, park staff are determined to remove the lake trout so cutthroats can make a comeback.
“It doesn’t matter how they got there,” Hallac said.
“We’d be doing the exact same thing even if we put them there,” Koel said.
Few cutthroats are traveling the streams around the lake to spawn now.
It is essential to remove lake trout that prey on cutthroats, because the native fish are a keystone species, meaning other wildlife depend on cutthroats, such as bears, eagles and osprey.
Now there are no bears fishing the streams during spring spawning, Hallac said. An average of 40 osprey nests once surrounded Yellowstone Lake. Now the average is five nests.
The No. 1 means to eliminate the lake trout is gill-netting the fish by the thousands as a scientific review panel recommended in 2008, according to the YNP staffers.
Of the nearly 11,000 public comments received during a 2011 environmental assessment, a majority favored the preferred alternative of large scale suppression of the Lake trout, Hallac said.
Gill-netting has been the primary tool for lake trout elimination.
Nearly 1.5 million lake trout have been removed from the lake with nets since 1994, according to the National Park Service.
Park Service boats and commercial fishermen are netting Yellowstone Lake every year. On any given day in the summer, 25 miles of gill nets are not uncommon, Hallac said.
Unfortunately, those nets don’t discriminate.
Fifty percent of cutthroats caught in gill nets die, but staff can take preemptive measures, such as placing nets in deep water where only lake trout swim, or netting areas cutthroats don’t frequent, said Pat Bigelow, park fishery biologist.
Still, it’s not all gloom and doom for the fishery that once likely held the largest population of genetically pure Yellowstone cutthroats in the West.
Despite low counts of spawning cutthroats, some are spawning, and the nets catching small cutthroats prove it. (See accompanying story).
“There are obviously fish out there spawning,” Bigelow said.
Drought, whirling disease and fires — which diminish habitat, as well as reducing shade over water, which raises water temperature — have hit cutthroats hard, but lake trout are definitely the No. 1 menace, Koel said. If they can decimate the lake trout, cutthroats should persist, because they have coped with drought and fire in the past, Hallac said.
The perception is the Park Service is moving toward native fish only, said Dave Sweet of Trout Unlimited. But that is not entirely correct.
Their goal is not to kill all non-native fish. There are lots of streams where non-indigenous fish can be caught, Hallac said, using the Madison, Firehole and Gibbon rivers as examples.
In the regulations the area a few miles east and west of Madison Junction to the West Gate and south past Old Faithful is called a “Non-native Trout Tolerance Area.”
Yellowstone lake trout hit the skids
10-year effort to rid Yellowstone Lake of unwanted lake trout panning out
The illicit lake trout population is taking a dive in Yellowstone Lake and the indigenous cutthroat trout there are no longer just treading water.
Although firm population numbers are not available, Yellowstone Park officials believe lake trout are in a steep decline and native Yellowstone cutthroat trout are recovering.
For the last two years, distribution nets cast overnight have snared more cutthroats and young cutthroats, indicating natives are spawning in the lake’s tributaries thus producing young. Seeing young cutthroats in the net also suggests there are fewer lake trout that prey on the young natives, said Dave Sweet, Trout Unlimited member from Cody.
The National Park Service maintains the fish were illegally introduced 20 years ago, but not discovered until 1994. Evidence suggests the lake trout were illegally stocked from Lewis Lake.
Since 1994, about 1.5 million lake trout have been snared from the lake and destroyed. In 2012 and 2013, 300,000 lake trout were netted by both a commercial fishing contractor and National Park Service employees each year, Sweet said.
Cutthroat trout are considered a keystone species because grizzly bears, bald eagles and river otters prey on them. Predators can’t reach lake trout lurking in the lakes depths.
Scientific evidence indicates grizzlies, now unable to catch cutthroats spawning in the lake’s tributaries in the spring, are dining on elk calves, said Trout Unlimited.
High cost of death
Killing lake trout has been a costly endeavor.
Annually, $2 million is spent in lake trout suppression. About half is federal funding, and the other half arrives from donations, said Al Nash, Yellowstone Park spokesman.
The $2 million is for gill-netting, monitoring and management, Sweet said.
Add to that $500,000 raised by the National Park Service, Trout Unlimited, U.S. Geological Survey, Greater Yellowstone Coalition and National Parks Conservation Association for studies to track lake trout to spawning beds and develop a device to kill eggs and fry (infant fish) in spawning beds, Sweet said.
Wyoming Wildlife and Natural Resource Trust ponied up $150,000 last year, and the Wyoming Legislature gave $621,000 this year for tracking the trout, as well as researching and implementing the means to kill eggs and fry from 2014-16, Sweet said.
Telemetry tracking has shown the waters off Carrington Island to be a hotbed of lake trout spawning. There are seven other suspected spawning beds, and several more that will be pinned down this year from gleaning telemetry data gathered last fall, Sweet said.
Divers will confirm the spawning grounds. One suspected spawning bed, at 190 feet under the surface, is too deep for divers, so this spring a ROV will survey the site. This ROV, or remote operated vehicle, is similar to the ROV used to search for Malaysia Airlines Flight 370 in the Pacific Ocean, Sweet said.
An electro-shock grid device will be used to kill eggs off Carrington Island this fall. The grid was to be tested last fall in Yellowstone Lake, but the federal government’s temporary shutdown in October scrapped the project.
Instead, it was tested on Swan Lake east of Flathead Lake in Montana.
About 8 inches into the lakebed gravel, the grid, on average, killed 98 percent of the lake trout eggs, Sweet said.
At 16 inches into the “substrate” — the lakebed gravel — the grid was about 50 percent effective. It is not known how deep the eggs filter down the substate at Yellowstone Lake.
But, by adjusting the grid’s electrical current, voltage and other variables, the device can be made more effective, Sweet said.
This spring, they will ascertain how long fry remain in the substrate. If the lake trout hatchlings stick around after the lake’s ice breaks, the eggs could be shocked in the fall and the fry in the spring, Sweet said.
As the lake trout population dwindles, fewer lake trout will be caught in nets, while the increasing cutthroat population are. So using egg suppression, rather than nets, to keep the lake trout population at bay becomes more crucial, Sweet said.
A lake trout snagged in net a few years ago weighed 33 pounds. Park Service photos of disemboweled lake trout often display stomachs filled with cutthroats.
Park Service employees are seeing a decline of lake trout in all sizes, further suggesting the population is taking a header. “That’s good news,” Sweet said.
For anglers bemoaning the loss of lake trout because they are a popular sport fish elsewhere, there is no possession limit for non-native fish caught in Yellowstone Lake and its tributaries. All lake trout caught in Yellowstone Lake must be killed, according to the park’s fishing regulations.
According to Trout Unlimited, estimates in the early 1990s indicate the economic value of Yellowstone Lake cutthroats likely exceeded $10 million annually.