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Yellowstone's Grizzlies Are Devouring Elk Calves At Increasing Rates Due To Reckless Human Behavior: A Study

May 15, 2013 11:59 AM EDT

Yellowstone’s grizzlies are devouring the national park’s migratory elk at increasing rates and the reason appears to lie in the shrinking numberof cutthroat trout due in part to the introduction of nonnative lake trout, according to an article published in the Proceedings of the Royal Society B.

The number of native cutthroat in Yellowstone Lake and spawn in its tributaries has seen a dramatic drop over the last two decades, largely as a result of the illegal introduction of lake trout, which not only prey on cutthroats but spawn at depths inaccessible to bears, according to researchers.

Such a trend, they explain, could “permanently alter native species interaction” in the area and highlights that, while many recent ecological changes in the park “have been attributed to the recovery of large carnivores – particularly wolves," the phenomenon represents a "growing role of human impacts on the foraging behavior of grizzly bears.”

Traditionally, the spawning cutthroat served as an important seasonal meal for as many as 70 grizzly bears, though recent studies by researchers at Washington State University show the bears are turning to elk calves.

Sure enough, wildlife agencies in Wyoming, Montana and Idaho are all reporting a significant drop in some of the elk herds that spend their winters there, and in particular cow-to-calf ratios.

“This synthesis suggests that, even in a core wilderness area like Yellowstone, a fisherman’s blunder in the aquatic system many years ago can have far-reaching effects by forcing an omnivorous predator to seek new foods in the terrestrial landscape,” lead author Arthur Middleton said in a press release.

And while drought and an increase in both grizzlies and wolves have played a part in a decrease in elk numbers overall, the report shows that "important effects of human disturbance and grizzly bear predation on migratory elk are being overlooked” and that the shift in diet “is uniquely important to research and management because it represents a novel, human influence operating cryptically within core protected areas.”

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