Some researchers fear oil drilling in the Arctic refuge could threaten the survival of caribou calves.

PETER MATHER/MINDEN PICTURES

Drilling in Arctic refuge could put North America’s largest caribou herd at risk

A push by lawmakers in Congress to open parts of Alaska’s vast Arctic National Wildlife Refuge to oil drilling is rekindling a fierce, decades-old conservation battle. A major point of contention: how drilling in the refuge’s coastal plain might affect a main calving ground for the Porcupine caribou herd, one of North America’s largest and healthiest.

Last week, the Senate’s energy committee moved a step closer to allowing drilling in the refuge, voting 13–10 to advance legislation that orders the federal Bureau of Land Management to make two major oil lease sales in the 635,000-hectare coastal area over the next 7 years. If the bill becomes law, Republican lawmakers will have achieved a goal they have sought since the 1980s.

Drilling proponents, including Senator Lisa Murkowski (R–AK), who leads the energy panel, say the plan will minimize environmental impacts by limiting the total footprint of oil infrastructure to no more than 809 hectares. And they argue that, elsewhere on Alaska’s oil-rich North Slope, predictions that drilling would harm caribou proved to be unfounded. 

Environmental groups dispute that claim. And they say that the development limit won’t apply to roads and pipelines that could sprawl across the landscape, fragmenting habitat. The plan also could allow drilling on an additional 40,000 hectares of refuge that is controlled by Native Alaskan corporations, says Mark Salvo, vice president of land conservation at Defenders of Wildlife in Washington, D.C. “You’re talking potentially about direct and indirect impacts on tens of thousands of acres,” he says.

With distinctive antlers that reach a meter tall, so-called barren-ground caribou are a linchpin of Arctic ecosystems, and a key food source for subsistence hunters and other predators. Forming sizable herds that can cycle between boom and bust—the refuge’s Porcupine herd has had between 120,000 and 200,000 animals since 2001—caribou can migrate 500 kilometers across rugged terrain beset by frigid winters.

In the past, those conditions made it difficult to study how caribou responded to development. But more recently, researchers have reached a “pretty strong” consensus that industrial activity disturbs the animals, says Chris Johnson, a wildlife ecologist at the University of Northern British Columbia in Prince George, Canada. In Canada’s Northwest Territories, for example, researchers found that caribou spent less time than expected in areas as far as 14 kilometers away from diamond mines. To the west of the Arctic refuge, in the heart of the North Slope oil fields, researchers with the U.S. Geological Survey (USGS) found that, in the 1980s and 1990s, the Central Arctic caribou herd shifted calving areas away from well concentrations. And in longterm studies of the Porcupine herd (named after the Porcupine River in the Yukon and Alaska), Johnson found that even decades after oil development in the Canadian portion of its range, caribou were still avoiding areas within 6 kilometers of roads and wells. 

Contested ground

The Porcupine caribou herd often concentrates its calving on the Arctic refuge’s coastal plain, which would be opened to oil development under a Senate bill.

U.S. DEPARTMENT OF INTERIOR/BIOLOGICAL SCIENCE REPORT USGS/BRD/BSR-2002-0001, P. 22, FIGURE 3.2 ADAPTED BY J. YOU/SCIENCE

But it is not clear how those behavioral changes might affect population size. “We get into a more nuanced conversation: ‘Does this mean there are going to be a lot fewer caribou, [or] a little fewer?’” Johnson says. “What [development] means for population dynamics is the million-dollar question.”

Drilling proponents have long emphasized that uncertainty. They note, for example, that the Central Arctic caribou herd ballooned during the North Slope oil boom, growing from 3000 animals in 1969 to 70,000 in 2010, before falling to 22,000 in 2016. “We have seen anything but the catastrophic predictions” of herd declines, Alaska Lt. Gov. Byron Mallott told the Senate energy panel earlier this year.

But that herd might have grown even bigger without the drilling, says Brad Griffith, a USGS wildlife biologist and head of the Alaska Cooperative Fish and Wildlife Research Unit in Fairbanks. He notes that a nearby herd not affected by oil development grew even faster during the same period.

One factor that might determine how development affects a herd is its habitat, says Don Russell, a retired Canadian Wildlife Service biologist in Whitehorse. Pregnant females, he notes, tend to seek out high-quality forage to meet the energy demands of nursing. But they are skittish of humans. In herds with relatively large calving areas—such as the Central Arctic herd—females have more room to avoid industrial sites. The Porcupine herd, however, often calves on a slice of the Arctic refuge’s coastal plain that narrows to 14 kilometers in places, sandwiched between the Brooks Range mountains and the Arctic Ocean. “They don’t really have options to expand,”Russell says. “We think they’re much more vulnerable in that very small area.”

A 2002 USGS modeling study estimated that if drilling on the coastal plain were as extensive as on the North Slope, the survival rate of caribou calves would drop by as much as 8%, depending on where most calving occurred, in part because of greater exposure to predators and lower-quality forage. Such mortality could ultimately cause herd numbers to fluctuate more dramatically, and make it harder to recover from declines, the study concluded.

That worries conservationists. The Porcupine herd is one of the few in North America to have avoided major losses in recent years; others have shrunk by up to 90%, likely part of a natural cycle that some fear could be exacerbated by development, climate change, and hunting. But concerns about caribou may not be enough to derail the Senate plan, which Republican leaders in Congress plan to add to a fast-moving tax bill. So, after decades of debate, predictions about how the refuge’s caribou will respond to drilling might get a real-world test.