Researchers trying to explain declining elk numbers in the Yellowstone National Park (YNP) placed part of the blame Wednesday on a previously unlinked phenomenon—a predatory trout invasion.
The lake trout eat the bears’ traditional prey, native cutthroat trout, and spawn in deeper waters where the grizzlies cannot reach them.
The bears, in turn, have started feeding more heavily on newborn elk calves—shifting the balance in their formerly fish-heavier diet.
“This synthesis suggests that even in core wilderness areas like Yellowstone, a human blunder in the aquatic system many years ago can have far-reaching impacts by forcing an omnivorous predator to seek new foods in the terrestrial landscape,” said study leader Arthur Middleton of the University of Wyoming.
The researchers arrived at their conclusions from a synthesis of over 20 studies of bear diet and elk populations conducted between 1985 and 2012, as well as recent elk counts.
Most of the elk decline had hitherto been blamed on successive droughts and the reintroduction from 1995 of wolves that were extinct in the park by the 1970s.