Less than a year after the U.S. Fish and Wildlife Service removed protection for Greater Yellowstone grizzlies under the Endangered Species Act, federal scientists say female grizzly mortalities are approaching the threshold that could trigger a review.

So far in 2007, research teams documented a near-record 50 females with cubs of the year, with an average litter size of 2.16 cubs.

But, those same researchers estimate that about 18 female grizzlies over 2 years of age have died from hunting accidents, management removals and natural causes.

Though the overall grizzly bear population is thriving with an estimated 571 animals, Interagency Grizzly Bear Study Team leader Chuck Schwartz said the female mortalities are approaching the sustainable limit of 9 percent.

If female mortality exceeds 9 percent of the population for two consecutive years, bear management officials from Idaho, Wyoming, Montana, Grand Teton National Park, Yellowstone National Park and the U.S. Fish and Wildlife Service must hold a management review that could put grizzlies back under the protection of the Endangered Species Act.

In all, officials tallied 25 known and probable grizzly mortalities. Twenty-two were human-caused, two resulted from natural causes, and the reason for one death was undetermined. Aside from management removals, for every bear that is reported dead, two more likely went unreported, according to Schwartz.

“This is not a good year for bears as far as mortality is concerned,” said Schwartz.

Schwartz reported this year’s results at the annual meeting of the Yellowstone Grizzly Coordinating Committee at Snow King in Jackson last week.

Nine female grizzlies over 2 years of age were among the reported dead: three from management actions, four from hunting incidents, and two from natural causes.

Wildlife managers say these so-called “independent-age females” have the biggest impact on the grizzly populations.

But Schwartz said the total grizzly population estimate of 571 bears is likely low. “As bears increase in this ecosystem, we’re likely underestimating what is out there,” he said. Statisticians and biologists are working on a new formula for counting the animals.

Further, Schwartz says one year of high mortality among females does not constitute a crisis.

“We have exceeded sustainable mortality limits in the past,” he said. “When we have a year like this, typically the mortality levels drop down again.”

Schwartz said his study team uses models that let researchers look at estimated female survival. “Through 2003, we’ve shown a very slight increase in female survival, which sort of shows that all of the programs to keep females alive are working,” he said. “Our major concern through all of this is that we don’t allow the bear population to decline because of humans.”

Louisa Willcox, director of the Natural Resource Defense Council’s wild bears project, said the high mortality among females is just one more reason why grizzlies should remain protected under the federal endangered species law.

“The very first year, just months after delisting, we have a problem,” she said.

A lack of natural food in 2007 has created a “perfect storm” for grizzly conflicts and mortalities, according to Willcox. Droughts and late frosts have hurt berry crops, mild winters have yielded fewer animal carcasses, mountain pine beetles and blister rust have robbed forests of whitebark pine trees, and lake trout have caused declines in Yellowstone’s cutthroat trout populations.

The Natural Resources Defense Council is one of several conservation groups that have filed a lawsuit against the grizzly delisting.

Schwartz agreed that a decline in natural food sources is cause for worry but said individual bears seem nutritionally sound. The study team uses electrodes placed on a captured bear’s nose and tail to measure body fat, similar to the system that is used on Olympic athletes.

“Bears going into the den in the autumn are around 30 percent body fat,” he said. “We’ve measured that every year since 2000. You let the health of the animal tell you about how healthy the environment is.”

“If food is limited, then you wouldn’t expect the bear to get fat,” Schwartz continued. “If the environment were to change and food were less abundant, then we can detect it. If we began to see a downward trend, that would be indicative that the bears are not meeting this nutrition requirement.”

Schwartz said most bears would spend more time eating alternative foods during years when their traditional fare is meager.

However, eating different foods doesn’t solve the problem. For example, a positive relationship exists between whitebark pine seed production and grizzly bear birth rates, Schwartz said.

Researchers with the Interagency Grizzly Bear Study Team and elsewhere are currently conducting habitat surveys to see how mountain pine beetles and blister rust are affecting the whitebark pine tree population.

Further, biologists are looking at other food sources like cutthroat trout, army cutworm moths, and elk carcasses.

For instance, cub and yearling survival seems to be a little better in years following winters with heavy snowfall. Last winter, which saw light snowfall, elk carcasses were only found every 0.14 kilometers on certain survey transcets.

Bears are attracted to carcasses in the spring. When there aren’t a lot, bears will congregate around those available. Since large male grizzlies are known to kill cubs, sharing carcasses could result in lower cub survival.

“Those offspring are a little more vulnerable than if she had her own carcass and he had another carcass off to himself,” he said outlining a scene of a mother with cubs sharing a carcass with an adult male.

As for Yellowstone cutthroat, fisheries biologists measuring spawning fish in Clear Creek, a tributary of Yellowstone Lake, found only 500 fish this spring compared to upwards of 60,000 fish in the 1970s.

“The bears aren’t using the streams the way the used to,” Schwartz said. Most bears have switched from streams to elk calving areas.

“It’s mostly male bears that are eating fish, not female bears,” he said.

Yellowstone officials are currently using gill nets to catch and kill lake trout in Yellowstone Lake. With more 270,000 fish harvested over the past several years, biologists expect the cutthroat population to rebound.

“If things hold, we can anticipate that there are going to be more fish available,” Schwartz said.

Army cutworm moth supplies, another important food source for grizzlies, seem to be holding steady. In 2007, researchers documented 253 bears in 172 groups at 51 confirmed and possible moth sites. Though not all of those 253 are different bears, Schwartz said the food source seems intact.

“As near as we can tell, moth numbers are probably holding up just fine,” he said. “We’re seeing a continued use of moth sites in this ecosystem.”