Yellowstone Cutthroat Rebounding

Feb 5, 2016

Yellowstone biologists are winning the war against invasive Lake Trout, and bringing back native Yellowstone Cutthroat.

Yellowstone Lake is a cold place. If you’re out on the lake even in the middle of the summer, you’ll need a jacket. So, when we went out in a boat with Yellowstone’s leader of the Cutthroat Trout restoration project, it was chilly.

Credit National Park Service

Yellowstone Lake is the largest fresh water lake above 7000 feet in north America. It is also very deep, and cold. That is why non-native Lake Trout have thrived here. They evolved in the Great Lakes. 

Three netting boats on Yellowstone Lake every day all summer long, catching and killing Lake Trout. Yellowstone’s Fisheries biologist Dr. Todd Koel looked out on the lake from his boat.

Koel remarked, “Any given day there will be upwards of thirty or more miles of gill net in Yellowstone Lake fishing for Lake Trout. And they are long monofilament mesh panels of net that extend along the bottom of the lake where, on the deeper waters where lake trout generally reside within Yellowstone Lake.”

Biologists here believe Lake Trout were illegally introduced into Yellowstone Lake decades ago. Lake trout eat Yellowstone Cutthroats, and by 2008, the natives numbers were at their lowest level in decades.

He said, “And the monitoring suggested that the cutthroat at that time were at levels that had occurred previously in history. Back in the 1950’s there was a hatchery operation here in Yellowstone Lake where cutthroat trout eggs were harvested. Also there was a lot of angling harvest of cutthroat back in the early years of the park.”

We asked Yellowstone’s wildlife biologist Dr. Doug Smith about the effects on other animals.

He answered, “Ospreys have declined  precipitously. They went from over thirty breeding pairs to under four.”

Smith says there is one area on the lake where some birds nest. But that area is quiet now, because the birds weren’t getting enough of their favorite food: Cutthroat Trout.

He pointed out, “Breeding of white pelicans and cormorants is down.”

Worse yet, the bald eagles that used to eat cutthroat, are killing the other birds chicks…

Smith said, “They’ll also take loon chicks and swan signets, and we don’t have a lot of those to spare.”

But things are changing. Koel says the netting boats are killing more Lake Trout now.

From his boat controls, he said, “You know some of these boats will kill thousands of Lake Trout within a given day. Already in four weeks of netting we’ve killed about a hundred thousand Lake Trout have been killed to save the native Yellowstone Cutthroat Trout.”

The park reports it killed more than a million Lake Trout since 1994. Half of those were taken from 2012 to 2014. 

We found Koel in his office in Mammoth in the middle of the winter. His desk was covered with papers from the research from the Lake last summer. He had more good news.

He reported, “In 2015, we removed 315,000 non-native Lake Trout, and that’s a record year for us. That’s more Lake Trout than we’ve ever removed before.”

And, Koel said they’re seeing more and more natives now.

“Cutthroat trout continue to see rebound in Yellowstone Lake. And we again saw an abundance of young juvenile fish recruiting back to the ecosystem.”

Koel said private donations through the Yellowstone Park Foundation helped put more boats and crews on the lake since 2012, and that helped turn the corner on Lake Trout.

He remarked, “So for four straight years now, the population modeling that we do on our removal program suggests that the lake trout are in a significant population decline.”

And now, biologists are researching a new suppression method.

Koel revealed, “We are applying electroshocking methods to kill the embryos on these spawning sites.

Koel said  killing the Lake Trout before they hatch is the long term solution, “Because Lake Trout are always going to exist in Yellowstone Lake and we need efficient ways to keep them at low levels or low densities.”