5,000 Miles Of Netting Cast In Battle Against Yellowstone National Park Lake Trout

Since National Park Service crews started pulling non-native lake trout out of Yellowstone Lake in 1995, they've hauled in more than 4.9 million 'lakers." And they're still hauling more than 250,000 of the fish out of the lake each year.

By the time this year's effort ends in October, it's estimated that the crews will have tossed, and retrieved, 5,000 miles of netting.

While more than a few anglers treasure the ability to catch a big, fat lake trout, the fish are not supposed to be in Yellowstone Lake. It's believed someone purposely dumped a buck or more of the fish into the lake back in the late 1980s or early 1990s, apparently unaware that the big fish would prey on the lake's native Yellowstone cutthroat trout.

By the early 2000s, the lake trout had made their presence known:  Yellowstone Lake’s population of spawning cutthroat trout had plummeted to just 5-10 percent of what it was in the late 1970s, according to the Park Service.

The loss goes beyond a decline in cutthroat trout, as they are essential to the park’s food web, serving as an important food source for grizzly bears, osprey, river otter, and other wildlife.

Yellowstone biologists say an adult lake trout "can eat up to 41 cutthroat trout per year and can consume cutthroat trout up to 55 percent their own size." At the same time, a 12-pound female lake trout can produce roughly 9,000 eggs per year, they add.

The impact to the native cutthroat trout has been significant. Six years ago grizzly bears that used to pull spawning cutthroats from the lake's tributaries had to look elsewhere for a meal, as did osprey, which can't normally dive deep enough to snare a lake trout. The lake waters also have become more clear because the downfall in cutthroat trout numbers led to a boost in zooplankton. The fallout of that, according to researchers, has been a slight increase in water temperature.

Even local economies outside the park benefit from a healthy population of Yellowstone cutthroat trout, which has lured fly fishing tourists to the area for generations.

“Anglers from all over the world come here to try and get a chance to catch these big, beautiful fish,” said Drew MacDonald, a native fish conservation technician for NPS in an online webinar about the program.

Fortunately, the aggressive netting program is producing results.

After decades of dwindling numbers, the Yellowstone cutthroat trout are coming back in numbers. “And they’re beautiful,” adds Todd Koel, leader of the park's Native Fish Conservation Program.

Koel attributes their return to the park’s ambitious gill-netting program, considered one of the largest and longest-running non-native fish suppression projects in the country.

“It's amazing—the cutthroat are running up spawning streams again, and we're having bear activity like we haven't seen in quite a long time on these streams, because they're feeding on these cutthroat,” said Koel, who notes that bald eagles are back and that ospreys are starting to return too. “From an angler's perspective, the fishing is unbelievable. The fish are huge and numerous."

Helping to make the netting program a success has been Forever Yellowstone, the park's charitable partner that has been raising about $1 million a year for the Yellowstone's native fish program.

“The results are incredible, as noted by biologists who are once again seeing an abundance of Yellowstone cutthroat trout and other native fish species," said Lisa Diekmann, Forever Yellowstone's president and CEO.

As long as lake trout remain in Yellowstone Lake, the park will continue its gill-netting operations and researchers will continue studying the impacts of invasive fish suppression.

“At this point, it almost becomes like maintaining roads, fixing the boilers in the buildings, rebuilding the walkways and trails—all this kind of stuff that goes on in Yellowstone, the suppression of lake trout is kind of like that,” said Koel. “We will continue in the future to maintain the ecosystem.”