North America's largest caribou herd is continuing a decade-long population slide, a drop for which there is no easy explanation or solution, a veteran state biologist told a wildlife working group last week.
The Western Arctic Caribou Herd has been declining at a rate of 4 to 6 percent a year since the population peaked in 2003 at 490,000 animals, said Jim Dau, a Kotzebue-based biologist with the Alaska Department of Fish and Game. "I don't see any indication that that's about to turn around," Dau told the Western Arctic Caribou Herd Working Group at its annual meeting in Anchorage.
The last official population estimate, released in 2011, put the herd at 325,000 animals. An updated estimate is expected next spring, Dau said. Biologists are examining aerial photos and other data to come up with a number for the size of the herd, which roams over much of northwestern Alaska.
Population could slip to about half its 490,000 animal peak
So far, biologists have documented increased mortality for adult females and decreased survival for calves, a combination that bodes poorly for population numbers, Dau said.
"Maybe even this year, we could slip below 265,000 animals," triggering more conservative management and more hunting restrictions, he said.
Such a drop would mean the herd had lost 60,000 animals, or almost 20 percent of its population, since the last count two years ago.
Some factors appear ruled out as causes for the decline, Dau said. The number of animals hunted has been stable over several years, so overharvesting should not be a big factor, he said. Still, even though the total harvest has not increased, hunters are now taking about 5 percent of the herd, compared to 3 percent in past years, he said.
The road and other facilities associated with the Red Dog Mine -- the world's largest zinc producer and the only industrial development in the caribou habitat -- also seem blameless, as caribou have easily migrated across that area, he said. There is no sign of significant disease outbreaks or parasite infestations, he said.
Freezing rain may be factor
But some potential culprits have emerged -- too little lichen and too much ice.
The Bureau of Land Management has documented an incremental shift from lichen -- the caribou's preferred food -- to grasses and shrubs in the animals' winter range, Dau said. But at the same time, starvation does not seem to be a major problem for the caribou. "We're seeing fewer skinny caribou now than we used to see," Dau said, but those animals that are malnourished seem to be much more vulnerable to wolf predation, he said.
Weather oddities, possibly resulting from climate change, could also be taking a toll on the caribou, Dau said. There is more freezing rain falling in the region, creating hazardous conditions for the animals. Just three weeks ago, Kotzebue endured four to six days of a rain-snow mix that coated the area with ice.
"Icing events seem to be more common now that fall weather is more mild," Dau said. Effects can be seen on caribou bodies, with white patches of accumulated ice forming between the eyes and areas of shorn fur cut by sharp ice edges.
Past icing events have hurt animals around Alaska, including the Western Arctic caribou.
Movement across the land became difficult, and ice on the ground was a barrier to food sources.
Amid the extremely mild fall of 2013, the caribou migration south was late and unusually crowded, with "a very discrete leading edge," Dau said. "If you were south of that leading edge, you wouldn't know there was a caribou in northwestern Alaska," he said. "If you were below that edge, you were surrounded by tens of thousands of caribou."
The population information is sobering, said members of the Western Arctic Caribou Herd Working Group, an advisory group representing village residents, hunters, reindeer herders, environmentalists and guides.
Roy Ashenfelter, chairman of the working group, said members should let villagers and hunters elsewhere know about the declines "so that when changes come about, it's not a surprise." Though hunting did not cause the problem, hunters should prepare to be part of the solution, he said. "One of the things we've learned is to not wait until the last minute and tell the public, 'Hey, here are some restrictions,'" he said.
Contact Yereth Rosen at yereth(at)alaskadispatch.com