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Why is Alaska's largest caribou herd seeing a steady decline?

Riley Woodford
Photo courtesy U.S. Fish and Wildlife Service

Alaska‘s largest caribou herd continues to shrink as challenges on its huge range in Northwest Alaska continue to pose problems.

The Western Arctic Herd numbered about 325,000 animals, according to the most-recent census by the Alaska Department of Fish and Game. Although that's just 5 percent less than the previous census in July 2009, it's about a third smaller than the herd's peak in 2003.  Since then, the population has steadily declined 4 to 6 percent a year.

State wildlife biologists believe their counts are accurate. Caribou bunch up in tight groups in summer in response to harassment by flies and mosquitoes. Radio-collared caribou within the herd help biologists flying aerial surveys locate these groups. The number of known collared animals relative to the number actually found is an indicator of completeness.

“Out of 97 collared caribou, we found 96 of them during the census,” said area biologist Jim Dau, who has worked with the herd for decades. He said 97th collared caribou was located later, too.

Animals are photographed from the air with a special mapping camera and then counted on 9-by-9-inch contact prints. In a process that takes months, photos are laid out and overlap lines are drawn so animals are not counted twice or missed. In this recent count, the photographs were very clear, suggesting the 2011 census was reasonably accurate.

Vital food staple, cultural link

The Western Arctic Herd ranges over a 140,000 square-mile area bounded by the Arctic Ocean, the lower Yukon River and the trans-Alaska pipeline. About 40 communities and 13,000 people live within its range. For the indigenous people of these communities, the herd is both a vital link to their cultural heritage and a food staple. The Western Arctic Herd is also important to visiting resident and nonresident hunters, and is an important source of income for commercial operators that selling hunting trips.

Because of its tremendous size, the ecological importance of the Western Arctic Herd to Northwest Alaska is incalculable. Although they are important prey for wolves and bears, Western Arctic caribou directly and indirectly impact the entire food web through nutrient cycling — affecting organisms from bacteria to vegetation to moose.

Caribou populations fluctuate in response to a variety of factors that fall into two categories:

• “Density dependent” factors such as range condition, predation and disease, which exert a negative force on a growing caribou herd.

• “Density independent” factors such as weather or resource development.

Both seem to be influencing the decline of the Western Arctic herd. Icing events between 2005 and 2007 meant some animals starved. Subsistence users, other hunters and commercial operators report that the numbers of wolves and grizzlies in the herd’s range are high.

The Western Arctic Herd has hovered around or above 300,000 caribou since 1988, and reports from hunters indicate that the body condition of caribou from this herd remains good.

Harvest limits coming?

There is no indication that the population decline will reverse soon. The U.S. Bureau of Land Management has documented long-term changes in winter range condition, and the demand for food and recreation by hunters has remained stable despite the declining number of caribou. Although the herd is still large, the department is cautioning residents that it may become necessary to reduce future harvests if the decline continues.

“Harvest has been pretty liberal for the past 20 years, but if the trend continues the state is definitely going to respond,” Dau said. “We’re not anticipating restricting any hunting right now though.”

Dau said subsistence harvest has been between 14,000 and 16,000 caribou per year for a long time. Harvest by others who don’t live within the range of the herd has been less than 800 per year for many years.

“Caribou harvests from this herd by nonlocal hunters are very small compared to the subsistence harvest,” Dau said.

A management plan is in place if it becomes necessary to limit harvest opportunities, thanks to the work of the Western Arctic Caribou Herd Working Group. The group includes subsistence users, other Alaska hunters, reindeer herders, hunting guides, transporters, conservationists, biologists, and natural resources managers. The group meets once each year, with additional sub-committee meetings as specific needs arise.

“We just spent over two and a half years updating a management plan that outlines how we would recommend restrictions in the future should that become necessary,” Dau said.

More scrutiny?

Part of that plan recommends additional scrutiny of the herd as numbers decline. Some types of surveys are conducted annually while others only need to be repeated every two or three years.

“As soon as we saw the first evidence of a population decline, we decided to census this herd more often,” Dau said. “Regardless of how frequently we census this herd, we estimate calf survival and adult cow mortality annually. That fills in the gaps between censuses and also helps explain what’s going on with census numbers — is the population declining because adults are dying or because calves aren’t surviving?”

In this case, it appears both things are factors. The next census is scheduled for 2013.

Riley Woodford is the editor of Alaska Fish and Wildlife News, a publication of the Alaska Department of Fish and Game.