Young Grizzly Bear Moved to Cabinet-Yaak Ecosystem to Help Boost Population
Augmentation program preserving population, genetic diversity
The augmentation program continues to be a success in an ecosystem that saw its grizzly bear population nearly vanish 30 years ago. In 1988, biologists estimated fewer than 15 grizzly bears remained in the Cabinet-Yaak, which spans approximately 1,000 square miles in the Yaak River drainage and 1,620 square miles in the Cabinet Mountains.
“Knowing what we know now from sampling, I think that was actually a very generous estimate. The number of bears were probably in the single digits,” Wayne Kasworm, grizzly bear biologist for the U.S. Fish and Wildlife Service Cabinet-Yaak Ecosystem Program, stated in the press release.
Today, thanks largely to the augmentation program that Kasworm helped establish, there is an estimated 55-60 grizzly bears in the Cabinet-Yaak Ecosystem, with a projected growth rate of 2.1 percent annually.
The 6 designated Grizzly Bear conservation areas created by the U.S. Fish & Wildlife Service
Today, thanks largely to the augmentation program that Kasworm helped establish, there is an estimated 55-60 grizzly bears in the Cabinet-Yaak Ecosystem, with a projected growth rate of 2.1 percent annually.
Illustrating the intent and success of the program, the third bear moved through augmentation, a female in 1993, is responsible for at least 25 descendants through three generations. That female produced at least 10 first-generation offspring, which gave rise to at least 14 additional grizzly bears, and among those at least one offspring and counting.
“We are trying to increase the genetic structure of the population by bringing in unrelated individuals with no history of conflict,” Kim Annis, FWP grizzly bear management specialist, stated in the release. “We have a really good family tree for the Cabinet Mountains that shows we might possibly have lost the population altogether without having continued this augmentation program.”
Wayne Kasworm/USFWS
The recovery goal is 100 grizzly bears in the Cabinet-Yaak and hopefully over time the animals will link with surrounding yet separate ecosystems, the Selkirk to the west, the Northern Continental Divide to the east, the Bitterroot to the south, and British Columbia to the north.
“The ultimate goal is to see bears move into the Cabinet Mountains and reproduce. We haven’t seen documented gene flow or reproduction, and only in the last few years have we seen minimal movement into the Cabinet Mountains,” Kasworm said. “That’s another step forward.”
The gender ratio of bears shows a slight preponderance of females in the Cabinet-Yaak, and while research shows that makes have been moving back and forth between the Yaak and Cabinets in recent years, the movement hasn’t resulted in reproduction.
“We don’t want to be moving bears with a pick-up truck forever. We want to encourage natural movement to help with gene flow and growing the population,” Kasworm told the Beacon. “That hasn’t really happened yet.”
Part of the problem is that the male grizzlies are moving between the main Cabinet Mountains and the Yaak during the fall rather than in spring, when breeding occurs. Another issue preventing reproduction could be the young bears aren’t yet competitive enough to successfully mate.
“Not only do you have to be there and be a competitive male, but you have to be there at the right time,” Kasworm said.
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