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Predicting Oil Development Impact on PCH
The United States Congress is debating whether or not to allow North Slope oil development to expand onto the
coastal plain of the Arctic National Wildlife Refuge. The potential lease area lies within the calving grounds
of the Porcupine Caribou Herd. This large, migratory herd moves between the U.S. and Canada is vital to the traditional
subsistence cultures of numerous native villages in both countries. To help us to understand the effects of oil
development on the Porcupine caribou herd (PCH) we can look at the Central Arctic herd (CAH) whose traditional
calving grounds are within the operating oilfields near Prudhoe Bay and other oilfields on the North Slope.
Map showing range of Central Arctic caribou herd:
There
are some problems in comparing the Central Arctic and the Porcupine herds. In addition, because of the lack of
scientific study in this area, the data from the Central Arctic studies are somewhat ambiguous.
Caribou Abandoning Preferred Habitat
One confounding issue is that although the calving grounds of the CAH lies within the area of oil development,
their population has increased significantly since the 1970s when development first began. The current population
stands around 23,000, up from 5,000 in the mid 1970s. Long time population studies are not available and this growth
in population could be part of a natural population cycle.
There are now indications that the caribou which spend more time on or near oilfields are not faring as well as
other members of the CAH that seldom encounter development. Avoidance of roads and pipelines during calving may
be causing caribou to abandon preferred habitats and possibly to overuse some undisturbed habitats. It is possible
that chronic disruption of summer movements forces caribou to use habitats with less nutritious forage and prolongs
their exposure to biting insects.
Herd Sizes Differ Dramatically
The PCH is a much larger herd. The 2001 census of the PCH showed that population at 123,000 although over the past
25 years, the Porcupine Herd has fluctuated between about 100,000 and 180,000 animals. The Porcupine Caribou Herd
is much more concentrated on its calving ground than the smaller Central Arctic Herd and may therefore be more
vulnerable to disturbance. Although calving has occurred historically over a fairly large area of the North Slope
in Alaska and the Yukon Territory, most calves are usually born in a smaller region that includes much of the area
being considered for oil development. During late June and early July, essentially all cows and calves and many
bulls of the Porcupine Herd use the potential development area every year.
Porcupine caribou normally herd in much larger groups than Central Arctic Herd caribou. Studies in the Prudhoe
Bay and Kuparuk oilfields show that larger groups (100 or more caribou) have difficulty crossing roads and pipes
(Smith and Cameron 1985). Groups of several thousand caribou occur throughout the summer in the Porcupine Herd,
and from mid-June through July, group sizes in the tens of thousands are common.
Shift in Calving Area
There is fairly strong evidence that pregnant cows and cows with new-born calves tend to avoid developed areas.
However, when calves get to be about 3-4 weeks old, and especially when warm weather brings out insects, then
this avoidance behavior disappears. At times, caribou may even seek out roads, gravel pads, pipelines, or other
structures where insect harrassment may be less.
There is very strong evidence that, since the Kuparuk Field was developed, the main concentration of calving caribou
has shifted to the south of the field, and that this has brought the caribou into less-productive habitat. However,
we cannot say whether this shift was due to development or simply a result of the increase in herd size, because
some caribou continue to use the areas within the developed field. Biologists including Dr. Arthur are currently
working on a study of growth rates and weight gain of calves in the area just south of the Kuparuk field. The area
will likely be developed during the next 5 years, and scientists hope to determine if caribou continue to shift
away from development, and if this has an effect on calf growth rates and survival.
Literature Cited:
Cameron, R.D. 1995. Distribution and productivity of the Central Arctic Herd in relation to petroleum development:
case history studies with a nutritional perspective. Fed. Aid in Wildl. Rest. Final Rept. Ak. Dept. Fish and Game.
Juneau. 35pp.
Nellemann; C., and R. D. Cameron. No date. Terrain preferences of calving caribou exposed to petroleum development,
Submitted to Arctic.
Smith, W. T., and R. D. Cameron. 1985. Reactions of large groups of caribou to a pipeline corridor on the arctic
coastal plain of Alaska. Arctic. 38:53-57
Personal research gathered from Dr. Stephen Arthur.
Copyright 2002 Journey North. All Rights Reserved.
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