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Lessons from the Caribou of Milne Point

A familiar name caught my eye in the December issue of the journal Arctic: Fairbanks biologist Ray Cameron, collaborating with others in the Alaska Department of Fish and Game, published an article called Redistribution of Calving Caribou in response to Oil Field Development on the Arctic Slope of Alaska.

The hassles over how petroleum development affects caribou have been going on for decades, and show no sign of easing. Mostly they've been expressions of opinion backed by extrapolation from a scanty supply of fact. Cameron and colleagues confront that problem in their first paragraph. They note that calving caribou seemed to be avoiding the Prudhoe Bay area, "suggesting a causal relationship between oil field presence and low caribou abundance." But the authors make it clear that suggestions is as far as science can go because "comparable pre-development observations were lacking, and the data remained equivocal."

That's a nice choice of words, for indeed the few facts could be made to speak with equal voices for one side or the other of the controversy. Certainly fewer caribou cows were giving birth to calves near the Prudhoe Bay development than in other areas of the coastal plain, but caribou don't disperse evenly. Inappropriate food plants, predator density, even weather patterns could have produced a natural paucity of calving caribou there before industry arrived. To be reasonably sure of causal relationships, scientists need to collect lots of data over a long time. This is especially important when they deal with organisms as complex and apparently capricious as caribou, which can and do show large changes in population size and group behavior for reasons still under debate.

When surface oilfield development expanded across the Kuparuk River and into the area of Oliktok and Milne points, the biologists gained a chance for some real before-and-after comparisons. The biologists flew aerial surveys to check for caribou on 10 to 14 June of every year from 1978 through 1987. They pinpointed where the animals were found and, as possible, ascertained the sex and age of the caribou counted.

The results of their study might at first also seem equivocal. For example, the greatest number of caribou near the Milne Point road---1259, with 559 of them calves---were counted in 1984, well after the region had been built up. The lowest census, 232 animals, came in 1980, during the construction phase of activity, with the second lowest turning up in 1987. But a very clear pattern appeared in years of both high and low population: the caribou tried to keep their distance from the roads. They were always most scarce within a kilometer of a road, most numerous five to six kilometers away.

From the information they have gathered, the researchers draw some cautious conclusions. Because the caribou need a safety margin around roadways and cluster at that safe distance, the habitat near the roads is underutilized while that farther away is overexploited. If roads are built too close together, a whole area could become unsuitable as calving grounds.

Is this worth worrying about? After all, the size of the Central Arctic Caribou Herd has increased from an estimated 6000 animals in 1978 to about 19,000 in 1991, a pretty clear indication that development hasn't proved lethal to the population so far.

The biologists would stress that "so far." The need to avoid predators and insects leads the pregnant caribou cows to seek the coastal plain. Once on the windswept plain, they look for the best places to bear and nurture their calves. When other factors don't combine to put extra stress on the herd, the animals can deal with losing some of the best calving places. In tough years, second-best places may just not be good enough. And where roads and other facilities lie close together, as far as cow caribou are concerned, what's left is less than second best.