Alaska oil fields and caribou

Published May 1, 2001

There is growing interest in the possibility of increasing domestic U.S. oil production by beginning exploration in the Arctic National Wildlife Refuge (ANWR). But many Americans are concerned that oil exploration and development will hurt the wildlife, particularly caribou, that make their home in the refuge.

The public’s concern is due in large measure to misinformation they’ve been given about the impact existing oil fields in the Prudhoe Bay region of Alaska have had on the caribou population there.

Misinformation need not reign on this issue, however. A great deal of research has been conducted this question, and the results generally show that caribou have fared quite well since Prudhoe Bay oil field development began in the late 1970s. What government agencies, environmental groups, and the media have reported, however, is a one-sided and largely incorrect view of the relationship between caribou and oil fields.

A series of scientific papers published since 1992 consistently show that the caribou population has increased dramatically during the period of oil field development, and caribou herds regularly use ranges in the oil fields. In 1998, the journal Arctic published a paper documenting that caribou do in fact use ranges in and around the oil fields at Prudhoe Bay. The paper’s publication was reported in The Yukon News, a Canadian newspaper, but not in Alaskan or other U.S. media.

Another paper published in 1998, in the journal Biological Conservation, showed the size of the caribou herd that uses the oil fields has increased dramatically (from about 5,000 animals to more than 23,000) since the oil fields were first developed.

Bad news, good news

In 1995, Congress considered opening ANWR to oil exploration, but the initiative failed. That same year, an important census was taken of the caribou herd that uses the existing oil fields. Caribou numbers were found to have declined from 23,000 in 1992 to about 18,000 in 1995.

Most notably, the numbers of caribou in the western part of the range (with the oil fields) fell from 14,842 in 1992 to 6,327 in 1995, while numbers in the eastern part of the range (without oil fields) increased from 8,602 to 11,766 during the period.

The results of the census were heralded in a front-page headline in the Anchorage Daily News, “Oil field caribou decline.” The story focused on speculation that something about the oil fields had caused the decline.

Senator Frank Murkowski (R-Alaska) was quoted, though not on the front page, as suggesting the decline in caribou numbers was due to natural factors and not the oil fields. A handful of wildlife biologists, too, began to consider whether factors other than oil field impacts could have affected the herd numbers.

In 1997, a team of wildlife biologists published a paper in The Journal of Wildlife Research showing that population density–simply movements of caribou between the ranges with and without oil fields–explained the changes in caribou numbers between 1992 and 1995 better than oil field impacts.

The herd was counted again in 1997, and the caribou numbers were found to have increased from the 1995 levels, to over 19,000 caribou. The number of caribou in the western range (with the oil fields) increased to 10,669 between 1995 and 1997, while the numbers in the eastern range (without oil fields) fell to 9,061 caribou.

The year 2000 caribou census showed the herd population had increased to 27,128 animals. The number of caribou in both the western (oil field) and eastern (no oil field) ranges increased (to 14,295 in the western range and 12,833 in the eastern range). This provides strong evidence that the oil fields did not cause the decline in caribou numbers between 1992 and 1995.

Incredibly, these dramatic reversals of the negative results of 1995’s census were not reported to the public.

It seems clear that the numbers of caribou in the eastern and western summer ranges of the herd fluctuate for reasons other than impacts from the oil fields. As suggested in the 1997 Journal of Wildlife Research paper, movement of animals between the eastern and western ranges is a plausible explanation. Caribou are highly mobile and regularly make dramatic changes in spatial distribution. These observations were confirmed more recently in a paper in the Wildlife Society Bulletin published last year.

Other data help support the conclusion that the oil fields have had no adverse effect on caribou populations. Between 1997 and 2000 the number of calves per 100 cows in the western (oil field) range was higher than or equal to the number of calves per 100 cows in the eastern (without oil fields) range.

If you don’t agree with it, ignore it?

The 1995 to 1997 increase in the caribou population in the western range was reported in federal government agency documents, but not in the Environmental Impact Statement for the National Petroleum Reserve-Alaska (NPRA) . . . or in the media. Senator Murkowski’s 1995 explanation for the decline in the herd was supported by the 1997 census, but no one noticed or reported it.

Caribou numbers in the Central Arctic Herd
Year Eastern Range Western Range Total
1992 8,602 14,842 23,444
1995 11,766
(increase 36.8%)
(decrease 57.4%)
(decrease 22.8%)
1996 9,061
(decrease 23.0%)
(increase 68.6%)
(increase 9.0%)
2000 12,833
(increase 41.6%)
(increase 34.0%)
(increase 37.5%)
Census counts of the number of caribou in the Central Arctic caribou herd including ranges without oil fields (Eastern Range), ranges with oil field development (Western Range), and the entire herd. The percent increase or decrease from the previous census is indicated below the census number.

The caribou census data noted here, and the lack of reporting of positive results by the media, are paralleled in the scientific literature. Papers by University of Alaska researchers Nellman and Cameron don’t cite the several papers that have appeared in peer-reviewed scientific journals and document the health of the oil field caribou population. Nor do those researchers entertain the possibility that the oil fields haven’t affected the herd numbers.

This refusal to recognize the positive is not universal. The Alaska Department of Fish & Game, for example, has acknowledged in its Wildlife Notebook Series ( and memos that the oil fields and pipelines have had no significant impact on caribou populations.

The experience in the Prudhoe Bay oil fields is actually one of the great success stories in wildlife management. Other species besides caribou, including grizzly bears, have increased in numbers since the oil fields were developed. Clearly, the ANWR could be explored and developed without seriously affecting the wildlife populations. It will just take dedicated planning and management . . . and a commitment to fair dealing and honesty by all participants in the policy discussion.

Matthew Cronin, Ph.D. is an analyst with Alaska Research Associates, a private environmental consulting firm, and affiliate professor in the School of Agriculture and Land Resources Management at the University of Alaska. He has published extensively in the wildlife-related research journals on the relationship between the Prudhoe Bay oil field and its caribou herds.