FAIRBANKS — State wildlife biologists don’t know why the populations of
two of the state’s largest caribou herds have jumped significantly in the
past seven years while numbers in larger surrounding herds have declined,
but nobody is complaining, especially the people who eat the caribou.
The Central Arctic Caribou Herd has more than doubled from 32,000 to
67,000 animals since 2002, becoming the state’s third-largest herd. The
Teshekpuk Caribou Herd has similarly increased from 45,000 to 64,000
animals during the same time and now ranks as the state’s fourth-largest
herd, based on photo censuses completed last summer.
At the same time, the Western Arctic and Porcupine herds, the state’s
largest two caribou herds that range on either side of the Teshekpuk and
Central Arctic herds, appear to be decreasing, according to a press
release issued by the Department of Fish and Game on Monday.
“It’s very curious,” ADF&G information officer Cathie Harms said.
But it’s a good thing, Harms said. The two herds account for nearly
one-quarter of Alaska’s annual caribou harvest, which last year was about
20,000 animals.
“People that use those herds are pleased,” Harms said.
The Teshekpuk herd, which roams the western North Slope, is the state’s
second most-hunted caribou herd behind the Western Arctic herd, the
state’s largest at 375,000 animals. The herd provides meat for
subsistence hunters in several North Slope villages such as Barrow,
Nuiqsut, Wainwright, Anaktuvuk Pass and Atqasuk. They kill about 4,000
Teshekpuk caribou a year, according to state harvest statistics.
The Central Arctic herd roams between the Brooks Range and Beaufort Sea
and attracts resident and non-resident sport hunters — many of them
bowhunters — who hunt off the Dalton Highway. Last year, about 1,500
hunters killed approximately 900 Central Arctic caribou, biologist Beth
Lenart said.
As to why those two herds are faring better than other arctic herds is a
mystery biologists are trying to solve, Harms said.
“We don’t have an answer yet,” she said.
Caribou herds are famous for their fluctuating populations, and the
Central Arctic herd is a prime example. It numbered only about 5,000
animals when it was identified as a separate herd in the early 1970s. It
increased to about 24,000 in the 1980s before starting another decline.
It began increasing again in the 1990s and has been growing ever since,
Lenart said.
Judging by the high pregnancy rates they had documented combined with
high calf survival and a relatively low harvest rate, biologists figured
the Central Arctic herd was growing but Lenart was surprised by how much.
“We expected them to increase but we didn’t guess it would be that high,”
she said of the 13 percent annual growth rate.
Both herds will likely continue to grow “as long as the habitat is
there,” Harms said.
“Caribou herds tend to grow and decline,” she noted. “Smaller herds tend
to be governed by predation, and larger herds tend to be governed by
habitat.”
Food availability drives caribou populations in herds the size of the
Teshekpuk and Central Arctic, Lenart said. Pregnancy rates go up when
caribou are healthy, resulting in bigger calf crops.
“I think range use is what effects these big cycles,” she said.
The Central Arctic herd has been expanding its winter range bit by bit in
recent years and the animals appear to have plenty to eat, Lenart said.
“They’re healthy, fat, good-conditioned caribou,” she said. “They’re
doing really, really well. You look at them, and they look fat and
healthy.”
Based on radio-tracking data, biologists are confident the increases are
not a result of caribou from neighboring herds joining the Teshekpuk and
Central Arctic herds.
No radio-collared animals from neighboring herds were found within the
Teshekpuk herd during the photocensus and only four collared caribou —
two from the Teshekpuk herd and two from the Porcupine herd — were found
in the Central Arctic herd.
“Even if each collared animal represented a thousand caribou, it wouldn’t
be enough to explain the increase in Central Arctic herd size,” she said.
Biologists are confident their counts are accurate. In a photo census,
biologists radio-track collared caribou to locate groups of animals,
which are then photographed by a large-format camera in the belly of
another plane. The photos are examined under magnifying glasses and
individual caribou are counted. Ideally, biologist do a photo census
every two or three years, Lenart said. However, conditions haven’t
allowed a count of the Teshekpuk or Central Arctic herds since 2002.
 
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