A new method for counting grizzly bears in the Greater Yellowstone Ecosystem could boost the known population by 100 to 150 animals.
“Our previous count was always super conservative,” said Chris Servheen, grizzly bear recovery coordinator for the U.S. Fish and Wildlife Service, in Missoula. “This is a new method, and it allows us to be more accurate in estimating population size.”
The agency is taking public comment on its proposal to implement the new counting method for bears in the ecosystem. The method was developed over several years and was peer reviewed by bear specialists as well as mathematicians before being released to the public.
“The initial methods used to calculate the population and mortality estimates for the Yellowstone Ecosystem were designed to address a sparse population in need of recovery,” Servheen said in a statement. “The proposed changes allow us to use the best data available to carefully measure the health of a larger, more robust population.”
Servheen said the new method increases the science of the counts based on better technology.
“It’s a better way to estimate the size of the population because we’ll be less biased,” he said.
In addition to new ways to count bears, the Fish and Wildlife Service is proposing that bears outside of the region where the population estimate is made no longer be counted as dead bears within the recovery population.
“As bears move outside into the periphery, onto private land, they have been counted against the mortality limits,” Servheen said.
The grizzly bear population in and around Yellowstone National Park has been estimated at about 600 animals for the past few years.
“We have a lot of bears on the landscape,” Servheen said.
As part of its search for a better method to count bears, cooperators reviewed the past survival and cub productivity of bears and found in preliminary data that the population growth of the animals has slowed since 2001. The initial findings point to a lower survival rate among yearlings and possibly cubs while adult male survival has grown. Female survival has remained steady but the number of females giving birth to cubs declined slightly.
To address the change, the Fish and Wildlife Service is proposing to lower the acceptable mortality rate from 9 percent to 7.6 percent for female grizzlies at least 2 years old and dependent offspring.
Last year, the Interagency Grizzly Bear Study Team recorded 56 bear deaths in the Yellowstone region, an increase from 44 in 2011 and 50 in 2010. Seventeen of the bear deaths in 2012 were cubs of the year, almost double the number of cubs that died in 2011.
Reducing the number of bear deaths caused by humans is the main focus of Defenders of Wildlife, said Erin Edge, the conservation group’s grizzly bear specialist in Missoula.
She said Defenders is still analyzing the Fish and Wildlife Service proposal, but noted the new method appears to have a higher confidence level than the old one.
Grizzly bears are still listed as an endangered species. The Fish and Wildlife Service proposed delisting the animal in 2007. That was challenged in court and the agency won on all but one point — consideration of the effect of the decline in whitebark pine on grizzly bears. The trees provide a high-protein food source for bears and have been recognized as an endangered species, but precluded from listing because of other priorities.
Servheen said the Fish and Wildlife Service is examining a number of scientific studies on grizzly bears’ adaptability to changing food supplies in the Yellowstone ecosystem. When that is completed this fall, the agency will make a decision on whether or not to try and convince the 9th Circuit Court of Appeals to overturn their earlier ruling.