Yellowstone Revealed: Swans and Fishes

(Editor’s note: This year marks Yellowstone National Park’s 150th anniversary. In honor of this historical milestone, we bring you a new series entitled Yellowstone Revealed. These reports offer a glimpse into the park’s colorful history and the Stories you’ve probably never heard before. Part three – “Swans and Fish” – explores the delicate relationships between some wild animals in the world’s first national park.)

YELLOWSTONE NATIONAL PARK – What do lake trout gillnets have to do with trumpeter swans? The answer is our country’s national bird: the bald eagle.

When Europeans first arrived in the Americas, trumpeter swans, native water slugs with eight-foot wingspans, lived across the continent. Now a population of hundreds of Trumpeters winters at two lakes in northern Arkansas. State biologists say they’re likely coming south from Iowa, not Yellowstone.

Now there are around 63,000 Trumper Swans in the lower 48 states. But America’s swans were nearly wiped out of the Lower 48 by 1930 through hunting and habitat loss. At that time only 70 swans survived in Yellowstone.

Now, park biologists have observed a new threat to Yellowstone swans: a newcomer to Yellowstone Lake.

Non-native lake trout were discovered in Yellowstone Lake in the mid 1990’s. The voracious deep-sea predators ate the native cutthroat trout, reducing their populations in Yellowstone Lake tributaries by an estimated 90%.

So park officials began fishing for lake trout with gillnets, and have so far killed nearly four million of the non-native fish. But cutthroat populations are growing but are still depressed and animals that eat cutthroat, such as grizzlies and bald eagles, are affected.

Doug Smith, senior wildlife biologist at Yellowstone Park, said in 2016, “Bald eagles have greatly altered their feeding habits due to the loss of cutthroats. But they also take loon chicks and swan tails, and we don’t have a lot of those left.”

Anglers catch and kill as many lake trout as they can while the gill nets continue to affect the predator population. Smith hopes cutthroat populations will rebound to feed bears, ospreys, and bald eagles.

But what about the swans?

In 2019, biologists counted just 27 resident trumpeter swans in Yellowstone.

The 2022 Yellowstone Resources and Issues Handbook says decades of drought and warmer weather are drying up the wetlands where swans used to breed. While more swans migrate to the park during the winter, Trumpeter Swans are a species of concern in Yellowstone.


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