Up to 2,737 Miles a Year: Alaska’s Western Arctic Caribou in Decline

Caribou make the longest land migrations on the planet, and individuals in Alaska’s Western Arctic Herd have travelled up to 2,737 miles (4,404 km) in a year. Yet the herd has been shrinking. It numbered nearly 500,000 in 2003, when it was the largest herd in Alaska and one of the largest on Earth. By 2016 it had declined to 201,000, according to the Alaska Department of Fish and Game.

Caribou are excellent swimmers; these two bulls are in Kobuk Valley National Park. NPS Photo / Kyle Joly.

A smaller range, but more travel

As the herd declined, its home range, roughly the size of Montana, shrank too, a pattern also documented in other herds. Even so, travel by individual caribou increased during the decline. One possible explanation, the article says, is that the quality of the herd’s range has declined.

What may be behind the decline

Habitat, climate, predators, human activity, crowding, insects, parasites, disease and competition with other species can all influence caribou numbers. The article says it is unclear which of them matters most in this decade-long decline, though particularly difficult winters may have contributed.

One pattern stands out. The herd’s crashes and surges have been linked to the Pacific Decadal Oscillation (PDO), a long-lasting, large-scale climate cycle. Declines go with its “negative” phase, the colder years, and increases with its “positive” phase, the warmer years. Caribou populations are known to rise and fall naturally over decades, so the article asks whether the strong positive PDO of the couple of years before it was written is a sign of recovery. Climate change and rapid industrial development, it adds, may hinder a natural recovery.

Hunting is part of the picture too. Subsistence hunters who live within the herd’s range take more than 90 percent of the harvest. Hunting likely had limited effect when the herd numbered 500,000, but its influence has grown as the herd has shrunk, and a high harvest of cows could speed the decline. The article calls for cautious management of the harvest until the herd’s trajectory reverses.

Caribou running on snow in winter. NPS / Kyle Joly.

Pressures ahead

Climate. Caribou tolerate an extreme range of temperatures, but a changing climate could affect them in many ways. Warmer weather could bring more wildfire, which would reduce lichens, their main winter food. The early successional habitats that fire promotes, together with warmth, may also allow more shrubs and moose, and with them more wolves, which could affect caribou. These conditions may also boost the insects that torment caribou during the short Arctic summer. Not every effect has to be harmful: warming could lengthen the growing season and increase summer forage.

Caribou often gather in large groups in July, in response to intense insect harassment; this herd is in Noatak National Preserve. NPS Photo / Kyle Joly.

Industry. Industrial development is spreading across the Arctic and is predicted to speed up as warming makes the region easier to reach. According to the article, the only major development in the herd’s range is the Red Dog Mine, with its port, related facilities and an industrial road joining the two. Early anecdotal evidence suggested its effects were limited, but later quantitative studies found otherwise. Dust from ore-hauling trucks is carried by the wind and affects habitat for miles, including in Noatak National Preserve. Disturbance from the road has also been implicated in altering the herd’s migration: substantial numbers of caribou can be delayed for more than a month on their fall journey south when they meet this single, well-controlled road.

The article says these effects need to be considered as agencies analyze a State of Alaska proposal for a 200-mile road from the existing road system through Gates of the Arctic National Park and Preserve into northwest Alaska, one of the largest roadless areas left in the world, to reach mining prospects in the Ambler region. Long-distance migrations are imperiled around the globe, it adds, so protecting the herd’s migratory corridors is critical.

It closes with an Inuit saying it calls millennia old: no one knows the way of the wind and the caribou.

Sources

• Kyle Joly, National Park Service, Caribou: Nomads of the North, Alaska Park Science, volume 16 (Science in Alaska’s Arctic Parks); rewritten in hubnx's own words.