Yellowstone Grizzly Population at Risk of Decline

September 2013: Yellowstone’s grizzly bear population is not as high as previously reported. That’s the hypothesis of a new study by researchers at the University of Colorado-Boulder and the University of California-Berkeley, which asserts that the park currently has 600 grizzlies, far fewer than the previously estimated 718 bears.

Grizzly counting practices involve heavy statistics in which biologists collect observations over the course of a year and then extrapolate a total. The tallies are important because totals determine whether or not the animal remains protected under the Endangered Species Act. The U.S. Fish and Wildlife Service plans to hold a vote in 2014 over whether or not to delist grizzlies. If the species is taken off of the list, then states become responsible for their protection. The Denver Post reports that “Wyoming, Montana and Idaho are eager to take over grizzly management and perhaps set hunting seasons, much as they have for gray wolves, which were returned to state control in 2011.”

However arguments that grizzlies must remain on the endangered species list largely surround the decline of critical food sources like cutthroat trout that have been overrun by the invasive lake trout species.

“The Yellowstone grizzly is at greater risk of decline,” Dave Mattson, a wildlife biologist who worked on the interagency grizzly bear team from 1974 to 1993, told the Post, “because we know less than we thought we did about population trends and the major deterioration of habitat and food sources.”

Bears looking for high-calorie meal replacements and additions to pine nuts and trout often munch on army cutworm moths, which are found on open, rocky slopes. So because the bears spend more time out in the open dining on moths, the CU researchers guess that grizzlies have been easier to count, and more than likely, to overcount, than before when the bears spent more time in the forest looking for nuts and fish. Plus, the number of aerial count flights has tripled since 1995.

“If you fish one hour a week,” Daniel Doak, one of the study’s authors, told the Post, “you get a rough idea of how many fish are in the pond.” However, doubling the time spent fishing makes it more likely to catch something, but it doesn’t affect how many fish are in the pond.

So are there enough grizzlies for the bears to be taken off the endangered species list? It’s hard to tell. But Gary Frazer, Fish and Wildlife’s assistant director for endangered species, makes a case that the bears should stay protected.

“The Yellowstone grizzly population (may not be) just stabilizing but declining, which would make a delisting decision even more difficult to defend,” he told the Post.