Since 1994, Yellowstone has eliminated the threat of nearly 3 million invasive lake trout from the native Yellowstone cutthroat trout’s habitat. Two million of those invasive fish have been removed since Yellowstone Forever donors started supporting this work.
Native Fish Conservation Program
Grants made by Yellowstone Forever continue to provide significant resources to Yellowstone National Park and their Native Fish Conservation Program.
The history of native fish conservation in Yellowstone
The Greater Yellowstone Ecosystem is home to the largest concentration of wildlife in the lower 48 states. But a dangerous threat to the ecosystem and its inhabitants lurks deep beneath the surface of Yellowstone Lake: lake trout. This non-native fish is a tenacious problem to the ecosystem, but thanks to escalating efforts through the Native Fish Conservation Program, progress is being made.
A lake trout was first discovered in Yellowstone Lake in 1994 by a fishing guide boat that was out with clients. They brought the fish to rangers to be examined, prompting the park to start netting in the area and subsequently finding more. The microchemistry was examined from some of the fish, and they were found to have come from Lewis Lake, near the park’s south entrance.
The U.S. Fishing Commission intentionally introduced lake trout to Lewis Lake in 1890 from Lake Michigan. Federal agencies, including NPS, used to stock fish for sport-fishing reasons, without much attention to the consequences. It is possible that someone brought lake trout from Lewis Lake to Yellowstone Lake, but we will likely never know for sure.
The negative effects of the invasive lake trout
It’s astounding what harm a single invasive species can have on the Yellowstone ecosystem. Lake trout are predatory and one mature lake trout can eat approximately 41 native cutthroat trout per year. Lake trout threaten the survival not only of the cutthroat but also the many species that depend on the cutthroat, including grizzly bears, osprey, otters and bald eagles.
Most predators can’t catch lake trout as a substitute food source, because these trout live in deep water and are quite large. So the lake trout have no natural predators in the park’s ecosystem, and can potentially live to their 30s and 40s in Yellowstone Lake if they are not removed by netting. The life span of cutthroat is typically 10-12 years.
By the early 2000s, just a few years after the first lake trout was discovered in Yellowstone Lake, there was evidence that the cutthroat trout population was on the decline. By 2008 the cutthroat were in a very bad state. For comparison, the population of cutthroat trout in the late 1970s was estimated at around 3.5 to 4 million fish. The low was estimated to be in the mid-to late-2000s at merely 5-10% of the numbers in the late 70s, roughly 500,000 fish.
Why this work matters
The primary activity of Yellowstone’s Native Fish Program is removal of the lake trout from Yellowstone Lake. Gill nets are used for this process: panels of net extend upward from the bottom of the lake about six to eight feet high and for many miles. These nets are lifted twice a week, pulling and killing lake trout.
Yellowstone National Park and contract crews removed 282,960 fish between May and October in 2019 compared to 297,110 in 2018, and 396,950 in 2017, a 29% decline over three years. Additionally, the catch of large adult fish continues to decline dramatically each year. These are likely indicators that the lake trout population is on the decline, which is great news for the native cutthroats.
In total, gillnetting has removed over 3 million lake trout since 1994, of which roughly 2 million have been removed over the past six seasons, during the period Yellowstone Forever has supported the increased effort.
All indicators—such as an increase in spawning fish in tributaries, a three-fold increase in juvenile fish within the lake, and higher catch rates by cutthroat anglers throughout the lake ecosystem—are all strong evidence that cutthroat trout numbers are up. Angling on the lake has been increasingly good over the last five years, especially after spring thaw.
However, despite the massive removal effort, lake trout are still in Yellowstone Lake in large quantities, and NPS employs adaptive management to continue to improve the approach. All of the data collected is put into models, which are then reviewed by a scientific panel each year to help better understand the present situation and inform decisions for future years.
How your support helps
Your gift to protect Yellowstone’s ecosystem and wildlife will help fund gilknetting efforts in Yellowstone Lake, continued research on alternative (complementary) methods to suppress the lake trout population by causing mortality of lake trout eggs on spawning sites and longterm monitoring of the native cutthroat trout population. By supporting this project, you ensure the continued decline of the invasive lake trout and restoration of an ecosystem dependent on the native cutthroat trout as a vital food source.
The health of Yellowstone’s native trout population has a direct impact throughout the ecosystem. The continued decline of the park’s native fish could be particularly devastating for birds of prey, the magnificent grizzly bear, and other wildlife species that specifically depend on native cutthroat as a vital food source.