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updated 6/22/2009 5:23:07 PM ET 2009-06-22T21:23:07

In Alaska, Canada, Greenland and other Arctic regions, people depend on caribou and reindeer as both a food source and a spiritual anchor. A new study reports that the animals have declined dramatically in recent decades.

Overall, caribou and reindeer populations have dwindled by an average of nearly 60 percent, the study found. In some cases, dips have been far more extreme than that.

"I want to emphasize the negative effects this will have on Arctic people who rely on caribou for sustenance," said Liv Vors, a population ecologist at the University of Alberta in Edmonton. "If the situation continues at the rate it's going, it will have profoundly negative economic, social and spiritual consequences."

Caribou and reindeer belong to the same species. Their names simply refer to where they live: caribou in North America and reindeer throughout the rest of their range. Seven subspecies live in Arctic regions from Siberia to Scandinavia to Canada.

Throughout history, caribou numbers have naturally cycled up and down. Until now, though, groups of scientists have focused only on the status of one population at a time. Vors and colleague Mark Boyce wanted to know what was happening on a grander scale.

The researchers looked through government archives, previously published studies, wildlife management boards, and other sources to consolidate everything that was known about the animals and their population sizes over the last several decades. They ended up gathering data on about 58 major herds.

Of those 58, they reported in the journal Global Change Biology, 34 were in decline, eight were gradually increasing, and 16 were lacking enough data to tell for sure.

Among the herds that were suffering, the average dip was 57 percent since the most recent peak. Some populations were much harder hit. A herd in Labrador, north of Quebec, for example, had dropped from 750 animals to fewer than 100. In the Canadian High Arctic, a herd that was 50,000 animals strong 50 or 60 years ago now numbers fewer than 1,000.

Land development is one of the biggest threats to caribou and reindeer, especially for the subspecies that migrate long distances. Caribou are among the few species left that have retained their ancient migration routes, said Justina Ray, executive director of the Wildlife Conservation Society in Toronto.

Logging, warming factors
Even those that don't migrate need lots of space, and they're extremely sensitive to changes in their environment. Logging has changed much of their habitat from old-growth forests to leafier vegetation.

That habitat shift has also boosted the food supply for burgeoning populations of moose and deer, which in turn, has boosted the food supply for wolves. Caribou are easier to catch than deer or moose, though, and they're the ones suffering the brunt of a bigger wolf population.

Climate change is another problem, albeit an indirect one. For one thing, warming has increased mosquito populations to the point where caribou spend so much time running around and shaking off insects that they don't eat enough to make it through winter with a good supply of stored body fat.

With warming, whitetail deer have also spread further north — bringing along a parasitic disease that doesn't sicken the deer but does kill the caribou. At the same time, spring is getting greener earlier that it used to, but caribou haven't adjusted the timing of their migrations. As a result, birthing females are missing out on the freshest vegetation and the chance to build up the highest-quality milk for their calves.

"So goes the North, so go caribou. So go caribou, so goes the North," said Ray, whose book "Caribou and the North: A shared Future" explores the same theme. "The fates of the two are intertwined."

The new work suggests that conservationists can't save caribou on a herd-by-herd basis. The effort needs to be more widespread and focused on protecting large swaths of old-growth forest.

"I hope this puts a spotlight on this situation," Vors said. "We can't be complacent."

© 2012 Discovery Channel

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