The number of animals in the Western Arctic Caribou Herd, the largest in Alaska, has declined modestly, according to a revised population estimate released by the state Department of Fish and Game.
The department counts caribou by photographing herds when animals bunch up in summer. A count of animals based on photos taken in July 2009 initially estimated the herd had increased from 377,000 to 401,000 animals over two years.
The revised estimate puts the population at 348,000 animals.
The population peaked at 490,000 caribou in 2003, which means the herd declined 4 percent to 6 percent annually over six years. The revised total is within a range of acceptable count variation, and the herd is considered stable, state biologist Jim Dau said Friday from his office in Kotzebue.
"We're not seeing any health issues," he said. "We're not pushing the panic button."
The revised estimate will not result in any immediate changes to management activities or hunting, he said.
Caribou are counted by human eyes, and the census was revised after Dau gave photographs a second look and found errors. The pictures are notoriously hard to read, with herds photographed sometimes on mountainsides or brush or in low light. It's easy to mistake a shadow for a second animal or misinterpret a tussock or a rock as a caribou.
"It's not like counting marbles on your floor," Dau said.
The herd ranges over the northwest quarter of Alaska. Caribou in the Porcupine Herd in northeast Alaska and Canada's Yukon Territory migrate farther -- an 800-mile round-trip between calving and wintering grounds.
The western herd's outer range covers 140,000 square miles -- roughly the size of Montana -- in a wide swath from Norton Sound to the Beaufort Sea.
The heritage and traditions of 40 subsistence-based Alaska Native communities have been shaped by the availability of caribou from the herd, according to the department.
In the winter, the caribou reside in the Seward Peninsula and land south and east. The herd in summer migrates to the northern foothills and mountains of the Brooks Range, using mountain passes and the coastal plain. The caribou seek relief from insects in the mountains and coastal areas from Point Lay to Cape Lisburne.
The Western Arctic Herd fell to a low of 75,000 caribou in 1976. The cause has not been determined, but many people at the time blamed village hunters, and hard feelings persist today.
"People felt wrongly accused, and they still feel that way," Dau said.
The department had far fewer tools to assess the herd back then, he said. For instance, radio collars are used today.
Herd numbers can fluctuate naturally. The herd itself can have an effect on the range by growing large and trampling lichens. Predator numbers go up. In December 2005, the winter range had four days of thaw and rain. When freezing temperatures resumed, caribou had difficulty finding food.
"The ice layer was almost impenetrable," Dau said. He remembers breaking a grain shovel retrieving radio collars from a caribou carcass. Many animals that survived into spring were in poor condition.
The herd rebounded steadily after 1976 to the 2003 peak. When biologists detected a decline in the 2007 census, they stepped up monitoring. The herd is counted every two years instead of three. Biologists also make more trips into the field to evaluate individual animals.
Hunting does not appear to be a cause for the decline. Subsistence harvest has held steady at 14,000 to 15,000 caribou. Non-local hunters kill another 1,000 or so, Dau said. The area does not have a good predator count, but people in the field say there's no shortage of wolves and grizzly bears, Dau said.
"After exceeding a population size of 400,000 caribou for over 20 years, a period of slow decline is probably preferable to continued growth and the possibility of an eventual, abrupt decline," Dau said.