When the Alaska Department of Fish and Game last took a count in July 2002, the Central Arctic caribou herd was thriving. The results of an aerial photo census pegged the herd population at 31,857 animals, up from 27,128 animals in 2000, an increase of 4,729 animals or 17 percent.
The caribou count was made from aerial photographs taken in July, at the height of the Arctic summer, on the Arctic Ocean coast where the animals bunch in groups of several thousand each for relief from pestering insects, according to Beth Lenart, an ADF&G biologist.
In summer, the Central Arctic herd migrates north from the south side of the Brooks Range, where it winters, to the Arctic Ocean. When the herd gathers on the Arctic coast, the department rushes a belly camera-equipped single-engine DeHavilland Beaver airplane to the scene to nab a series of photos for later analysis. As temperatures cool and the wind picks up, the animals drift inland from the coast and fan out. The range of the herd is bounded on the west by the Colville River and on the east by the Canning River.
Most of the current oil activity on the North Slope, including the Prudhoe Bay and Kuparuk oil fields, is within the range of the herd. The trans-Alaska oil pipeline and the Dalton Highway snake southward from Prudhoe Bay through the center of the herd’s range.
Lenart said a healthy pregnancy rate and high calf survival contributed to the herd’s success. The greatest hazards the animals face on the North Slope are the bugs and an occasional bear, she said. The animals also face predation by wolves on their annual trek into the mountains of the Brooks Range for the winter.
Some winters, the herd can be found on the west side of the Dalton Highway, Lenart said. ADF&G tracks the herd via radio transmitters on some of the animals.
537 percent increase over 28 years
The Central Arctic herd has grown from 5,000 animals in 1974, the early days of oil development on the North Slope, to almost 32,000 today — an increase of 26,857 animals or 537 percent over 28 years. Biologists don’t know why the herd has grown so large.
Over the 28-year period of study, the herd size grew steadily with the exception of the 1995 count, when it dropped from about 24,000 animals to 18,000 animals in a three-year span.
When asked whether Alaska’s caribou herd numbers are part of a natural fluctuating cycle, Pat Valkenberg, an ADF&G research coordinator, said in 2000 that it is one of the issues that caribou biologists periodically debate.
“In Alaska, in North America, some of the herds do appear to go up and down — some on a 20-year cycle. … Other herds fluctuate fairly erratically. Other herds, such as the Porcupine, have been remarkably stable,” Valkenberg said. Biologists venture that the reasons are partly weather related. Predator cycles might also contribute to fluctuations.
Four herds share North Slope
The Central Arctic herd shares the North Slope with three other herds, the Teshekpuk herd, the Western Arctic herd and the Porcupine herd, which wanders back and forth from the Arctic National Wildlife Refuge into Canada.
The Western Arctic and Porcupine herds have larger ranges than the Central Arctic herd, to the west and east, respectively.
The Teshekpuk herd, located northwest of Kuparuk and encompassing the city of Barrow, wanders a range of about the same size as the Central Arctic herd. The ranges of each of the three other herds overlap the edges of the Central Arctic herd’s range. In recent years, the Central Arctic herd has occasionally crossed the Canning River into the Arctic National Wildlife Refuge, Lenart said.