Alaska's two largest caribou herds, the Western Arctic and Porcupine herds, appear to follow the Arctic trend of declining population, and the Mulchatna herd west of Anchorage is especially hard hit.

But the news isn't all bad for Alaska caribou.

The Teshekpuk, Central Arctic and Fortymile caribou herds are all significantly on the upswing, according to the Alaska Department of Fish and Game.

The department reported this spring that the Central Arctic herd had doubled from about 32,000 animals in 2002 to about 67,000 in 2009. "The herd is growing rapidly," said Fort Yukon area biologist Beth Lenart.

Geography can play into the survival of a herd. For example, the declining Western Arctic herd is close to the Bering Sea. When rain comes off the sea and falls on frozen ground, it creates a problem.

"Precipitation on frozen ground creates a glaze; caribou can't deal with that at all," said Lincoln Parrett, a state caribou biologist.

He said climate change appears to be a factor in caribou declines, although it could be a cyclical phenomenon rather than a result of long-term global warming.

Caribou populations were also at high levels worldwide and "can't go on like this forever," he said.

Find Sean Cockerham online at adn.com/contact/scockerham or call 257-4344.

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