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Biologists struggle to estimate grizzly population in Interior Alaska
Grizzly bears are sparsely distributed around Alaska’s Interior, but figuring out exactly how rare they are continues to challenge researchers.
A population estimate remains elusive despite an ambitious project to count bears in an area south of Fairbanks in May.
New study
One of the most extensive state projects to estimate Interior bears is based on 25-year-old surveys. Biologists estimated that between 120 and 160 grizzlies roamed the Alaska Range and Tanana Flats in Game Management Unit 20A, based on surveys that Alaska Department of Fish and Game Biologist Harry Reynolds did between 1981 and 1991. The game management unit is a Hawaii-sized area bounded by the Tanana, Delta and Nenana rivers and to the south by a line marking the boundary with Game Management Unit 13.
This May, 10 biologists aboard five Super Cub airplanes spent a week trying to get a new estimate for the same area covered by Reynolds. They used a technique called a line transect method.
Bear population studies like this are rare, according to Kerry Nicholson, the Alaska Department of Fish and Game furbearer biologist who led the study. It’s expensive to survey bears, and there’s less demand for it than for moose and caribou studies.
“Logistically and financially, bears are probably the most difficult species (to survey),” she said. “Some of it has to do with what the public feels worthy of us focusing on. Political issues drive research directions. No one really cares about muskrats, for instance, even though they’ve vacated nearly three-quarters of their historic range.”
Estimating bear populations is difficult because the bears are so spread out and are hard to detect. In general, Alaska biologists consider North Slope grizzlies the most spread out, followed by Interior grizzlies. The same species of bears are known as brown bears in coastal Alaska and are larger and much more common there because they have access to salmon runs, Nicholson said.
Grizzly bear density is generally believed to be greater south of Fairbanks in GMU 20A than around Fairbanks in GMU 20B because the mountains and the foothills of the Alaska Range make for better grizzly habitat than the small heavily-forested Interior hills. But this isn’t known for certain because bear surveys are so rare and 20A is one of the best-understood Interior regions.
To estimate the number of bears in GMU 20A this year, the researchers spent about eight hours a day flying randomized patterns around the unit while looking for bears. They planned to spend 10 days on the project and to use a statistical model to extrapolate the total number of grizzly bears.
The research was carefully timed to take place before snowmelt and greenup in order to make the bears easier to see from the air. But it had to occur after bears came out of their dens for the spring.
“Within the first week we realized it was not going to work. We were not seeing enough bears to even make an estimate of how many there were,” said Area Wildlife Biologist Don Young at a meeting this fall of the Fairbanks Fish and Game Advisory Committee.
Over the course of a week, the researchers spotted a total of 22 grizzly bears. They cut the research off three days early because of scant bear sightings. They would have needed about 150 observations over multiple years in order to develop a statistically meaningful estimate. Their project had a $120,000 budget and they were able to save more than half of it by ending the project early, Nicholson said.
The lack of bear sightings is hard to explain and doesn’t necessarily mean there are fewer grizzlies in the area than previously expected, Young said.
“We thought we had good conditions in the mountains. It could have just been that the bears are just hard to see. It could be that there’s not as many bears there as we think,” he said. “Honestly we just don’t know. We’re going to have to come up with a different technique.”
Future counts
Because of the expense, the department isn’t likely to put five more planes in the area for another Interior grizzly bear study, Nicholson said.
One future method could produce a population estimate from genetic bear data collected from the carcasses of grizzlies that hunters bring to the Department of Fish and Game office.
But it won’t be easy. The method was created by an Australian researcher to estimate fish populations, so it will have to be adjusted for bears.
“They’ve been using harvest-only information and looking at genetic relatedness of individuals,” Nicholson said. “It’s probably not a smoking gun. It still needs a lot to be fleshed out because the original study was done on bluefish tuna. If you actually translate that fish species to terrestrial species, caribou are much more similar.”
Bear harvest numbers alone don’t tell biologists how many grizzlies are in the field because the amount of energy people put into bear hunting varies from year to year. The new method would combine genetic information from the harvested bears and information about how long Interior grizzlies live and how many cubs they have.
Biologist returned to the mountains of 20A in June with the narrower mission of collaring bears to gather some of this data.
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