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In “Grizzlies of Pilgrim Creek,”

photographer Thomas Mangelsen tracks Yellowstone grizzly sow 399 through a decade of motherhood, and its attendant joys and sorrows.

As the Interagency Grizzly Bear Committee moves toward a possible removal of its namesake animal from federal protection next year, the way it counts those bears gets intense scrutiny.

Just less than 2,000 bears roam the continental United States, according to the latest research done by the IGBC’s study teams. That’s far from the estimated 100,000 that used to be found south of Canada before hunting and habitat loss put the grizzly under U.S. Endangered Species Act protection in 1975. But it’s also at or beyond what some researchers think is how many grizzly bears the Rocky Mountains can hold.

In particular, the IGBC is focused on the Greater Yellowstone Ecosystem, which this year contains 717 bears, according to the statistical models used by the U.S. Fish and Wildlife Service. That number could be 75 bears low or high. It’s high enough that the committee proposed delisting grizzlies in that area in 2013. The move was blocked by a court order, and now IGBC officials expect to have a new delisting plan ready for debate in early 2016.

Yellowstone National Park encompasses about 4,000 square miles, mostly in Wyoming. But the suitable grizzly habitat in the Greater Yellowstone Ecosystem totals more than 22,500 square miles, drawing in the Beartooth and Wind River mountain ranges, along with swaths of southwestern Montana and eastern Idaho.

Interagency Grizzly Bear Study Team ecologist Frank Van Manan said the more important point was that the rate of growth was slowing down. That’s because the ecosystem appears to be filling up, and young grizzlies are having a harder time competing for space with older, more established bears.

“Some have referred to this as voodoo science,” Van Manan said Tuesday. “Let’s not confuse policy with science. We’re not just making this stuff up. As a population reaches carrying capacity, you see a drop in the survival of young and suppression of reproduction.”

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However, a number of critics of the IGBC maintain its numbers are unreliable and its targets unrealistic.

As the committee was meeting in Missoula this week, members of the Center for Biological Diversity, Western Watersheds Project and others argued for slowing down or stopping the delisting process. They also objected to proposed population targets now being discussed between FWS and the wildlife management agencies of Montana, Wyoming and Idaho.

“It’s simply far too soon to remove protections for these grizzly bears,” CBD attorney Andrea Santarsiere wrote in an email. “The Endangered Species Act has done a great job of helping to recover grizzly bears in Greater Yellowstone, but isolation, declining food sources and an increase in human-caused mortality have caused the population to decrease from 757 to 714 bears just this year.”

(The CBD number is different because Van Manan adjusted the 2015 total after new data was received just before the conference started this week.)

“Recovery isn’t a math equation, it’s a geography question,” added Josh Osher, Montana Director for Western Watersheds Project. “The states’ tentative agreement with the Service fails to ensure connectivity throughout the species’ range and fails to address the livestock operations that are the root cause of lethal conflict for the grizzly bear.”

Louisa Willcox, who publishes critiques of grizzly bear management in her newsletter, “Grizzly Times,” said the GYE needed a population of at least 2,000 bears to be viable in isolation. She argued that declines in critical food sources in the Yellowstone area made it unlikely the bears could survive without continued federal protection.

Matt Hogan, deputy regional director of the U.S. Fish and Wildlife Service Denver office, said the current counting system actually addresses the criticisms leveled at the delisting effort. Improvements in the techniques have made it harder to show increases in bear numbers.

“I think we’re doing the opposite,” Hogan said. “We’re relying on the more conservative estimator, that underestimates the population by 30 (percent) to 40 percent. I could see the criticism if we were using a method that went the other way around with higher estimates than we thought were there.”

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Van Manan said one unusual statistic was the number of bears captured each year that had never been handled by humans before. That figure has stayed around 60 percent for several years.

“If this was a population on the verge of decline, this would not be possible,” Van Manan said. “You couldn’t get that many new animals in the system.”

A less happy data point was the continued absence of any sign that grizzlies outside the Greater Yellowstone Ecosystem had entered or bred with local bears. That shows grizzlies still haven’t found a comfortable way to travel between the Yellowstone area and the Northern Continental Divide Ecosystem, which holds at least 1,000 bears in the Rocky Mountains between Missoula and Glacier National Park.

However, a new research tool developed by the Northern Rocky Mountain Science Center appears to show the Yellowstone grizzlies’ isolation is far from troublesome levels. U.S. Geological Survey geneticist Pauline Kamath said a long-term look at grizzly DNA shows that in 2007, there was an “effective population” of at least 450 bears. The effective population only counts those bears of breeding age – excluding cubs and immature youngsters.

The analysis’ more important result highlighted how much genetic interchange was taking place in the population. A fear for isolated populations is how soon they get so small that inbreeding starts causing health dangers.

“The larger the effective population, the slower the loss of genetic diversity over time,” Kamath said. “That allows the population to respond to unforeseen environmental or habitat changes. The DNA study shows the Yellowstone grizzly population to be losing genetic diversity at such a low rate, it’s undetectable.”

Van Manan added that between 1982 and 2007, the effective population size in the Greater Yellowstone Ecosystem grew by a factor of four.

“That kind of surprised us,” he said. “The data also showed an increase in breeding adults over the same period.”

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