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When oil development began in the mid-1970s, the central Arctic herd numbered around 5,000 animals. Almost immediately, caribou movements and distribution were altered.
As a retired biologist who spent many years studying North Slope caribou, I would like to comment on what we have learned about caribou and oil in the Arctic, and how that information should affect decisions on whether to lease part of the Arctic National Wildlife Refuge.
The central Arctic caribou herd, which interacts with Prudhoe Bay and its associated oilfields, has grown about five-fold since development began. This increase has led many people to conclude that development hasn't affected caribou at all, or that mitigation measures used on the North Slope are highly effective and can be expected to work wherever else we go to extract oil in the Arctic.
Mitigation hasn't worked all that well, however. When oil development began in the mid-1970s, the central Arctic herd numbered around 5,000 animals. Almost immediately, caribou movements and distribution were altered. Calving within the Prudhoe Field had largely ceased by the time oil first flowed south. Cow caribou with young calves avoided the Trans Alaska Pipeline, and a dense network of production facilities blocked mid-summer movements along the Arctic coast. Nevertheless, disturbance was small relative to the total amount of range available, and caribou were able to thrive.
Newer oil fields at Kuparuk and Milne Point incorporated designs that allowed caribou to move more freely than at Prudhoe Bay. However, the expanding oil fields invaded more critical habitats than had been disturbed at Prudhoe Bay. Also, relatively large groups of caribou (a few hundred to a few thousand) had more difficulty negotiating oilfield structures. As even the state-of-the-art Kuparuk and Milne Point Fields became more heavily developed, caribou used them less and less freely.
By the late 1980s, the central Arctic herd stabilized at about 23,000 caribou. Radio-collared cows that spent more time in or near the oil fields gained less weight and had fewer calves than other collared cows that seldom encountered development. When weather turned bad, the herd declined to about 18,000 in 1995. With mild weather since 1997, the herd has increased to 27,000.
The central Arctic herd has been resilient enough to cope with development, so long as suitable alternative range was available and other environmental factors were favorable. We can't be certain that ongoing disturbance won't exacerbate effects of bad weather when it happens again, as it surely will. Nor can we be sure the herd will fare as well if continued displacement drives calving cows into areas with more predators.
The Porcupine caribou herd differs from the central Arctic herd in several important ways. Porcupine caribou migrate over a vast range in Alaska and Canada, but most calves are born on the narrow coastal plain of the Arctic Refuge. Unlike the area around Prudhoe Bay, there is no unoccupied habitat similar to areas already being heavily used. Historically, the Porcupine herd has grown more slowly than other herds. Once numbering as high as 180,000 caribou, the porcupine herd has been declining for the past 10 years and numbers about 120,000. Displacement from its calving grounds would put Porcupine herd cows into areas with poorer forage and more predators. Porcupine caribou regularly occur in groups numbering tens of thousands far larger than groups that have had trouble getting through existing oilfields. All these factors indicate that the Porcupine herd may be particularly vulnerable to disturbance.
In summary, we have been fortunate to develop the vast wealth of our current North Slope oilfields with no unacceptable effects on size of the relatively small resident caribou herd, so far. From what we've seen in the Prudhoe Bay area, we can assume that development in the Arctic Refuge would alter caribou movements and distribution. We cannot be sure that impacts on the much larger and apparently less robust Porcupine herd, on its smaller calving grounds, would not have much graver effects on calf survival. Any long-term decline in calf survival of the Porcupine herd could decrease population size over time, with serious consequences for many rural residents in both the U.S and Canada who depend on Porcupine caribou for subsistence. Should we risk the Porcupine herd to find out if oil development and caribou are truly compatible? National polls indicate that most Americans think we should not, and I agree.
Ken Whitten of Fairbanks was the state's chief research biologist for the Porcupine herd from 1978-98 and was research coordinator for the Division of Wildlife Conservation in Region III when he retired in June 2000.