Wildlife biologists Kalin Kellie and Craig Gardner caught 56 grizzly bears last summer in the Fortymile country and didn't lay a finger on a single bear.
Kellie and Gardner, who work for the Alaska Department of Fish and Game in Fairbanks, conducted a DNA-based mark and recapture study on grizzly bears in the upper Yukon-Tanana Bear Control Area east of Tok.
But instead of actually trapping and handling bears, biologists caught hair samples from bears by using bait surrounded with a single-strand, barbed wire fence. When the bears came into the bait, they rubbed against the fence and left tufts of hair resembling miniature tumbleweeds on the barbs.
"It's like a murder mystery," Gardner told members of the Alaska Board of Game on Friday during a presentation on study. "You can use DNA to uniquely identify an individual (bear). All you need is some roots of hair."
The technique has been widely used in Canada and the western U.S., but this was the first time wildlife biologists in Alaska have employed it.
"You've got to be part trapper because you have to know where you're going to catch the most bears, and you've got to be part rancher because you have to know how to string a barbed-wire fence," Gardner said.
The fence was strung 20 inches off the ground, high enough so that a cub crawling under it will scrape its back on the fence and low enough so that an adult that steps over it will scrape its belly. For bait, biologists used a liquid concoction that was two parts rotted fish and one part rotted pig's blood. They used liquid bait so the bears didn't get a reward, he said.
"We'd come back after a two-week soak, and this is what the bears would leave us," Gardner said, showing a close-up photo of a clump of brown bear hair on a barb.
The $100,000 study was aimed at figuring out how many bears are in the control area, which was created in 2004 and expanded by the Board of Game in 2006. Fish and Game initiated the DNA study last summer after the game board passed several proposals aimed at increasing the harvest of grizzly bears in the area, which included use of bait stations, selling of grizzly hides and no bag limit on bears.
"We needed a better number when those were put in place," Gardner said.
Over the course of the six-week study from May to July, the biologists set out more than 100 traps, which they checked and moved every two weeks. They collected almost 1,500 hair samples, of which more than 1,000 were from grizzly bears and 400 were black bears.
Using DNA analysis, biologists were then able to identify 56 individual grizzly bears from those samples - 28 males and 28 females. Figuring in the size of the area where they set their traps, biologists were able to calculate the estimated grizzly population in the control area, which they figure is about 150 bears, slightly lower than they had perceived.
"We have a very precise estimate of the bears in this area," Gardner said.
Not only were biologists able to get a firm handle on the grizzly bear population in the area, which can now be used to estimate populations in similar country, they also uncovered some revealing information about bear behavior.
For example, Gardner said bears spent little time in a large area that burned in a wildfire in 2004. Biologists caught hair from only one bear in the burn area.
"That 2004 burn turned out to be a big lake," Gardner said. "It was a total barrier to bears. They liked the edge of it but didn't use the center of the burn. That fire has made a significant change in how bears are distributed in the control area."
Judging from samples caught at traps on both sides of the burn, male bears were willing to travel back and forth through the burn but females were not.
"Basically, female bears avoided the burn," Gardner said. "We didn't have a single female cross the burn."
That's a significant development in terms of management, Kellie said. While biologists already knew that wildfire plays a key role in rejuvenating moose habitat and can produce increases in moose populations, they didn't know it could also reduce bear predation on moose calves, which they know is one of the main sources of moose calf mortality in the Interior.
"This is the first time we've seen habitat manipulation where it could improve moose calf survival for a low density moose population in a bear limited system," she said.
Biologists studied two older burns in unit 20E and found similar evidence. The Teslin and Ladue wildfires, both of which occurred about 25 years ago, had - and still have - much higher moose densities in the years following the burns than adjacent areas that didn't burn. While part of that may be due to better and more food, decreased bear predation could also play a role in the increase of a moose population, biologists said. |
