Yellowstone Lake Invaders: Boots on the ground

YELLOWSTONE -In 1994 it was discovered that nonnative, predatory lake trout had made their way into Yellowstone Lake and as a result began to wreak havoc on the population numbers of the lake's native species, the Yellowstone cutthroat trout.

Since the discovery efforts have been underway to restore the cutthroat as the dominant species of Yellowstone Lake many have stepped up and answered the call for the restoration of the cutthroats like Julia and George Argyros.

The Argyroses established a $500,000 grant through the National Park Foundation that goes to the Yellowstone Forever organization to help with their Native Fish Conservation Program.

The NFCP already receives an annual $1 million grant and the Argyros' grant is another step forward in restoring the cutthroat.

Helping lead the NFCP in their mission to restore the cutthroat is Todd Koel, Yellowstone's chief fisheries biologist. Koel and his team have put the money sent their way to excellent use and have seen the cutthroat numbers increase as a result.

But how do Koel and company battle the lake trout and other nonnative species? Yellowstone Lake isn't exactly small - it is North America's largest high elevation lake sitting above 7,000 feet, and stretching 20 miles long and 14 miles wide with a surface area of 132 square miles. And when you consider the average depth of the lake is 139 feet, with the deepest part at 390 feet, there is a lot of ground to cover.

Koel and his team at the NFCP have come up with some straightforward and ingenious ways of rooting out lake trout and other nonnative species from Yellowstone Lake.

Gillnetting is, as of now, the most effective way for the NFCP to remove nonnative species and has been ongoing since 1995. But it wasn't until 2008-09 when the Yellowstone Park Foundation (Yellowstone Forever wasn't formed until the merger of the Yellowstone Park Foundation and Yellowstone Association in 2016) chipped in that the results went to the program's liking.

"We started gillnetting in 1995 and increased the netting program annually. Around 2008, 2009, we were behind the population of the lake trout and weren't netting enough. That's when the foundation stepped in and started supporting the effort," said Koel.

"What we have now is a large-scale lake trout suppression program using contracted netting boats and crews ... This grant we just got will go directly to cutthroat restoration on Yellowstone Lake, not only for restoring the cutthroat trout but even beyond that the ecology of the whole system. We're already seeing good signs of that."

Another means of removal of the lake trout and their ilk is getting them at their spawning beds. To do this the fish are tagged and, appropriately, designated "Judas Fish." The Judas Fish then lead those at the NFCP to spawning sites.

Knowing where the spawning site is, is of great value not only for the location itself but what kind of setting the lake trout prefer when they spawn.

"We're getting close to developing new methods to kill the eggs at the spawning sites. They spawn within the lake itself and in really specific habitat types, so it's this clean angular rock and those places only occur in certain areas within the lake. We use tagged fish, we call them "Judas Fish," to lead us to those sites in the fall. Then we focus on netting and killing the large fish and using egg suppression methods on those sites," said Koel.

Once at the spawning beds those at the NFCP came up with another brilliant idea to snuff out the eggs. Rather than trying to smash each and every egg, the NFCP teams simply takes a lake trout carcass and lays them on top of the spawning beds; and lets nature do the rest.

"The best method we've come up with so far and what we're moving forward on is taking the dead lake trout carcasses and putting them over the top of the spawning sites in the fall. Within a few days the decomposition of the carcasses reduces the dissolved oxygen in the water to basically zero and kills the eggs," said Koel, "Essentially, we're using the lake trout to kill the lake trout."

Along with gillnetting this method has proven quite effective in removing the lake trout from Yellowstone. Yet, while the promise is there, Koel said researching is ongoing to make absolutely sure this method of removal won't have any unintentional side effects.

"We're still in research mode. We're still really carefully evaluating the ecology related to this work. We don't want any unintended consequences to this work but so far everything is looking really, really positive," said Koel.

INTRODUCTION OF NONNATIVE SPECIES IN YELLOWSTONE

Lake trout have been in Yellowstone Lake before but it was a small population. So when it was discovered their numbers had taken a dramatic leap up theories how that happened began to roll in.

One such theory was during the wildfires of 1988, fish were accidentally picked up when helicopters used water from Lewis and Shoshone lakes and some of that water was dropped by Yellowstone Lake tributaries.

Another, and one of the more popular theories, was environmental terrorists, sounds like the villains in Dwayne "The Rock" Johnson's next movie, collected a bunch of lake trout from Lewis and Shoshone lakes and dumped them into Yellowstone Lake.

"When the lake trout were first found in Yellowstone Lake – pretty quickly – people believed it was an illegal transport from Lewis Lake to Yellowstone Lake. That would have taken quite a concerted effort to do that and establish a population," said Koel.

Recently though, Koel has developed another theory that's far more plausible than the enormous effort it would take a person, likely persons, to catch and transport lake trout to Yellowstone Lake.

The continental divide separates Lewis and Shoshone lakes from Yellowstone Lake and acts as a barrier.

"Yellowstone Lake is in the Yellowstone River drainage, which flows northward out of the park. But we also have big lakes in Yellowstone on the south end of the park that are in the Snake River drainage, which drains south and over to the Columbia Basin. Those two lakes are Lewis and Shoshone. They're in a completely different watershed and in fact, it's across the Continental Divide between Yellowstone Lake and Lewis Lake. So fish can't get cross that," said Koel.

But there is a passage that lake trout could have taken advantage of, that passage being Two Ocean Pass. And it's believed that's how the cutthroat came to be in Yellowstone Lake, so it's certainly within the realm of possibility the lake trout used the same passage.

Nevertheless, how the lake trout made their way to Yellowstone Lake is beside the point because the bottom line is they have to go.

"I've recently come out with an idea that the lake trout swam to Yellowstone Lake over a natural connection south of Yellowstone Park called Two Ocean Pass. That's just another idea how they got to the lake, but the bottom line is it doesn't matter how they got there.

"In Yellowstone, we have a really strong, clear mission of preserving our native species and these lake trout are nonnative and really causing some ecological damage. We're on the right track to correct that and a big part of that is due to these private gifts coming in," said Koel.

PROGRESS TO THIS POINT

Increased gillnetting and new methods of removal have shown great success. The cutthroat population is rebounding and their size is increasing as well, 20-plus inches is the average size of the cutthroat being caught.

"We're seeing the numbers rebound but again the numbers need to come a long way. A lot of the recovery of the cutthroat is going on in the humongous, remote upper Yellowstone River system," said Koel. "The Yellowstone River flows into the south end of Yellowstone Lake, but the origin of the river is way south of the park in the Teton Wilderness.

"We've done telemetry studies and tracked the cutthroat; they move 30, 40 more miles up into the backcountry south of the Park in the Wilderness and spawn back there in these tiny tributaries."

The primary focus for Koel and his team is on Yellowstone Lake but as he said the Yellowstone River system is very large and getting to every tributary the cutthroat spawn would be an enormous undertaking. This is where help from anglers comes into play.

From time to time Koel will ask anglers he knows that travel to these tributaries to record data for the NFCP and this data has actually helped the group quite a bit.

"A lot of our recovery we're seeing within the lake is actually the recruitment of those fishes coming from this giant wilderness system that we can't monitor it and the best information we have is from anglers."

"We've had a lot of help from volunteer anglers over all the years I've been here. We've had a really coordinated volunteer fly fishing program for a long, long time. The anglers go out and collect data for us, essentially, and it's worked out pretty good," said Koel.

Cutthroat numbers are on the uptick but that doesn't mean restoration is complete. There's still work to do for Koel and the NFCP.

"Our indicators are counts within a big spawning stream we have, monitoring them by using a standardized netting program and the angler catch. In the 90s, angler catch was two fish per hour on the Lake. Right now we're just over one fish per hour," said Koel. "We have these multiple lines of evidence that tell us whether the population is going up or down."

Added Koel, "We have specific goals, benchmarks that we're trying to reach for the cutthroat trout. We're using an adaptive management to attain what we call desired conditions. We know we're never going to be able to get rid of all the lake trout, there always going to be there and we're always going to have to suppress them by either netting or killing their eggs. But we want to get the cutthroat back to where they were in the mid-1990s, just after the lake trout were discovered."

If you'd like to donate to the NFCP or another Yellowstone Forever conservation project you can donate at http://www.yellowstone.org/what-we-do/current-projects/wildlife-wonders-wilderness/.