Addressing Invasive Species: Yellowstone National Park Sees Progress and Setbacks in Efforts to Protect Native Cutthroat Trout | Local


Yellowstone National Park sees progress and setbacks in efforts to protect native cutthroat trout

Two summers ago, a gillnet team working to catch invasive lake trout on Yellowstone Lake hauled up their nets and found a small, hand-sized fish that sent shockwaves through the biologists of the fisheries working to save endangered cutthroat trout in Yellowstone National Park.

The little fish was a cisco, and it was far from its native waters, the Great Lakes. How the displaced fish got there is an estimate as there are no natural connections, but the implications of another invasive fish gobbling up the same food sources needed by native Yellowstone cutthroat trout are profound. .

“(The cisco) was a 3-year-old female,” said Todd Koel, a fisheries biologist from Yellowstone overseeing the lake trout removal project from the park. “We did the otolith microchemistry work, basically looking at the bone chemistry of the fish, and we determined that it was born in the lake, which means it has parents and has probably thousands of siblings.

The discovery comes at a time when Yellowstone is making significant progress in removing the invasive lake trout discovered about 25 years ago. As the lake trout population multiplied and fed on cutthroat, the native fish, which once numbered in the millions, saw its population collapse. The ecology of the park, especially around the lake, has been altered. These animals dependent on abundant cutthroat have disappeared or changed their diet. The tributary streams, once associated with the lake’s breeding cutthroat trout, were home to few or no migrating fish adult cam sites.

Since the turn of the century, the lake trout population has continued to grow, threatening to eliminate the burden. The park began spending nearly $ 3 million a year on suppression efforts and in 2012 the number of lake trout stopped increasing and fierce health began a slow rebound.

“I am very optimistic that the adult lake trout population has declined dramatically over the past six to seven years and as a result the burdens are returning,” said Dave Sweet, Yellowstone Lake Special Project Director at Trout. Unlimited. “We are seeing a higher number of burdens and, more importantly, we are seeing more young cutthroat, smaller sizes.”

Koel said the lake trout removal project will receive its annual review by an independent group of scientists next week. The group is made up of lake trout experts and people who know how to best fight them.

“They are interested in trying to help us,” Koel said. “They’re looking at our information for the year and our population modeling. They give us their feedback every year. Because of the scale of the program and the cost, we want to make sure that we don’t do things in a vacuum. ”

Koel said many scientists who have commented are familiar with the behavior of lake trout and cisco that have worked in lakes in the Midwest. He said his team focused primarily on lake trout, but after the cisco was discovered, they spent the last summer hunting the lake trying to find more.

“It’s not a good find at all,” Koel said. “We are trying to find out more. We are now making nets especially for Cisco just to try and find more. No suppression nets like we do with lake trout, but we are targeting the nets so that we can maybe catch another cisco.

Besides the nets, the park team has been opening lake trout stomachs to gillnets since 2019 “and we haven’t found another cisco yet”. Cisco is a preferred forage fish for lake trout. He admits, however, that it’s like playing the lottery as only a few thousand stomachs are checked against over 300,000 lake trout. “The benefit goes to the species when it comes to detection, especially new invasions,” he said.

A third method his team plans to use to detect cisco in the lake is environmental DNA sampling. This type of sampling tests the lake water for the DNA of specific fish.

Koel finds it irritating that his staff now have to worry about another invasive species after all the publicity about unwanted lake trout.

“The biggest crush on this one is that these cisco weren’t swimming alone towards Lake Yellowstone,” he said. “We’ve been in this battle with the lake trout all these years – this was a 25-year report I published last year – and then we still have stuff like that. It’s hard. It’s hard to swallow, that’s for sure.

Koel said he believed someone had carefully transported the fish to the lake thinking it might be a food source for lake trout.

Biologists have realized that lake trout must be suppressed on more than one front.

“We’re in a place where we have lake trout in a significant decline,” Koel said. “This means that since 2012, we have reduced the adult part of the lake trout population by over 80%. That’s a huge decline in adult breeding lake trout which is great, but they are also able to produce a lot of young despite this decline in adults.

Koel said he was successful in killing the lake trout eggs before they hatched.

The park hopes to crush the lake trout population, but Koel said it likely won’t happen for three to five years. The problem is that a few adults who escape gillnets can produce thousands of offspring, replacing those caught each summer through gillnet efforts. A female lake trout can produce up to 9,000 eggs each year.

Biologists using telemetry technology have identified at least 14 lake trout spawning sites. At one site near Carrington Island in the lake’s West Thumb area, Koel and his crew managed to kill lake trout eggs by spraying organic pellets from a helicopter over the spawning grounds. The granules break down and remove dissolved oxygen from the water long enough to kill the eggs. In a few weeks, the granules are eliminated and the water returns to normal.

“We have eliminated all recruiting at this site for the past two years,” Koel said.

The program plans to complete environmental assessments at some of the other spawning sites in the coming years to attack the fish before they become adults.

“If we can kill these embryos at these sites in the fall, when the entire lake trout population depends on the production of these limited sites, we can get to a point where we process the majority of them – suddenly what becomes. much easier than later trying to catch them as adult fish all over the lake and at all depths of the lake, ”Koel said.

Sweet and Koel report a trip to the park’s Thorofare area in 2019 as a sign that lake trout removal is bearing fruit. A group trip to this backcountry follows the lake’s main tributary, the Yellowstone River.

“It’s very encouraging,” said Sweet. “These burdens are back in the sources of the Yellowstone River. The ones we caught were almost certainly migrating fish out of the lake because they were big fish. … They were 18 to 20 fish even 22 inches. They were big, make-up adults moving up the system out of the lake. ”

Koel said before lake trout numbers were brought under control, spawners in the Yellowstone River were gone, along with outfitters and other anglers eager to catch them.

“When we were back there (in 2019) the camps were full of people, and there was a lot of traffic on the trails and people were fishing,” Koel said. “I’m glad to see it’s back.”

The park estimates that it costs between $ 2.5 million and $ 3 million per year to lead lake trout suppression efforts. Funding comes from three main sources: the park budget, Yellowstone’s nonprofit partner Forever, and Trout Unlimited. The pandemic and the recent restructuring of Yellowstone Forever caused the foundation to withdraw its funding, Koel said. Trout Unlimited has pledged approximately $ 1 million annually. The park takes the rest of the note by increasing fishing license fees, boating fees, and other fees.

“We’re here for the long haul,” Sweet said of Trout Unlimited’s support. “It has been a long process. We’ve been supporting them for over 10 years, I would say about 13 years now.

Yellowstone National Park Superintendent Cam Sholly recently announced a doubling of fees to help cover the shortfall.

“Efforts to restore native fish to Yellowstone Lake remain one of our highest conservation priorities,” Sholly said in a statement. “Our continued success will depend in large part on an ongoing and reliable income stream that will not only help us continue our efforts to restore native fish, but also increase our ability to detect and prevent new non-native species from entering. in the waters of Yellowstone.

In the past, three-day, seven-day, all-season Yellowstone fishing licenses were $ 18, $ 25, and $ 40, in 2021 the fees will increase to $ 40, $ 55, and $ 75.

The boating license fee also drops from $ 10 for a week-long non-motorized sticker to $ 20 and $ 30 for the season. Seven-day and annual motorized permits have gone from $ 10 and $ 20 to $ 40 and $ 60 respectively.

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