2013 Arctic Report Card: Reindeer and caribou numbers low, winter ranges small

Aerial image of the Western Arctic Caribou herd, 2011. Jim Dau / ADF&G

Caribou and reindeer—members of theRangifer genus—are hunted and herded by many Arctic and Subarctic societies, which is why it’s natural to imagine that reindeer would be tasked with pulling Santa’s sleigh to and from the North Pole. Rangifer populations have fluctuated in number historically, but currently many wild herds have unusually low numbers and their winter ranges in particular are smaller than they used to be.

The map shows the current status of 24 major migratory tundra reindeer and caribou herds. Green indicates increasing populations; red indicates decreasing numbers; black and yellow indicate populations have remained stable either on the high or low end of their historic numbers. Only a few herds are increasing or are stable at high numbers; the most recent population estimates indicate that most herds continue to decline or remain at low numbers after severe declines.

Just as scientists try to figure out the causes behind climate cycles, wildlife experts are trying to understand what is behind cycles in herd populations. Local and traditional knowledge indicates that caribou go through periods of abundance and scarcity every 40-60 years. The size of individual herds has varied greatly since 1970 when population estimates began. Since it is normal for herds to vary in size over time, scientists are still uncertain whether the current low numbers are natural or perhaps driven by some of the rapid changes in the Arctic environment. For some herds, their current ranges are approaching the low end of their historic extent.

In the United States, there are four distinct herds of caribou in Alaska—two that are decreasing in number and two that are increasing. The Western Arctic herd—the state’s largest—reached a population low of 75,000 in the mid-1970s, and then rebounded during the 1980s and 1990s to reach a peak of 490,000 in 2003. The herd then declined to 325,000 in 2011. While the herd is still very large, the Alaska Department of Fish and Game says it may become necessary to reduce harvests in the future if this decline continues.

Many countries are attempting to stabilize population numbers through harvest management. Beginning in 2000, Greenland began to allow hunting to reduce caribou populations. Despite this, surveys indicated that the largest herd, the Kangerlussuaq-Sisimiut, remained at around 98,000 animals. The second largest, Akia-Maniitsoq, decreased from an estimated 46,000 in 2001 to about 17,400 in 2010. One possible cause might be differences in topography: hunting access is easier in the Akia-Maniitsoq territory compared to the rough, mountainous terrain that the Kangerlussuaq-Sisimiut inhabits.

Between the 1950s and 1970s, Russia’s Taimyr Herd—one of the largest in the world—increased from 110,000 to 450,000 in 1975. Even after commercial hunting increased, the herd held to a size of about 600,000 animals. When subsidies to commercial hunters were removed, hunting declined and the herd grew rapidly by 2000 to 1 million animals. Currently the herd is assumed to have declined to about 700,000 animals.

More information about individual migratory Rangifer herds in the Arctic can be found in the Migratory Tundra Rangifer chapter of the Arctic Report Card: Update for 2013.

Map by NOAA Climate.gov, based on rangifer migratory range data provided by Don Russell. 

The Western Arctic Caribou Herd has been declining at a rate of 4 to 6 percent a year since the population peaked in 2003 at 490,000 animals, said Jim Dau, a Kotzebue-based biologist with the Alaska Department of Fish and Game. “I don’t see any indication that that’s about to turn around,” Dau told the Western Arctic Caribou Herd Working Group at its annual meeting in Anchorage.

The last official population estimate, released in 2011, put the herd at 325,000 animals. An updated estimate is expected next spring, Dau said. Biologists are examining aerial photos and other data to come up with a number for the size of the herd, which roams over much of northwestern Alaska.

Population could slip to about half its 490,000 animal peak

So far, biologists have documented increased mortality for adult females and decreased survival for calves, a combination that bodes poorly for population numbers, Dau said.

“Maybe even this year, we could slip below 265,000 animals,” triggering more conservative management and more hunting restrictions, he said.

Such a drop would mean the herd had lost 60,000 animals, or almost 20 percent of its population, since the last count two years ago.

Some factors appear ruled out as causes for the decline, Dau said. The number of animals hunted has been stable over several years, so overharvesting should not be a big factor, he said. Still, even though the total harvest has not increased, hunters are now taking about 5 percent of the herd, compared to 3 percent in past years, he said.

The road and other facilities associated with the Red Dog Mine — the world’s largest zinc producer and the only industrial development in the caribou habitat — also seem blameless, as caribou have easily migrated across that area, he said. There is no sign of significant disease outbreaks or parasite infestations, he said.

Male caribou in Alaska

Male caribou in Alaska (Photo credit: Wikipedia)

But some potential culprits have emerged — too little lichen and too much ice.
The Bureau of Land Management has documented an incremental shift from lichen — the caribou’s preferred food — to grasses and shrubs in the animals’ winter range, Dau said. But at the same time, starvation does not seem to be a major problem for the caribou.  “We’re seeing fewer skinny caribou now than we used to see,” Dau said, but those animals that are malnourished seem to be much more vulnerable to wolf predation, he said.

Weather oddities, possibly resulting from climate change, could also be taking a toll on the caribou, Dau said. There is more freezing rain falling in the region, creating hazardous conditions for the animals. Just three weeks ago, Kotzebue endured four to six days of a rain-snow mix that coated the area with ice.

“Icing events seem to be more common now that fall weather is more mild,” Dau said. Effects can be seen on caribou bodies, with white patches of accumulated ice forming between the eyes and areas of shorn fur cut by sharp ice edges.

Past icing events have hurt animals around Alaska, including the Western Arctic caribou.

Movement across the land became difficult, and ice on the ground was a barrier to food sources.

Amid the extremely mild fall of 2013, the caribou migration south was late and unusually crowded, with “a very discrete leading edge,” Dau said. “If you were south of that leading edge, you wouldn’t know there was a caribou in northwestern Alaska,” he said. “If you were below that edge, you were surrounded by tens of thousands of caribou.”

The population information is sobering, said members of the Western Arctic Caribou Herd Working Group, an advisory group representing village residents, hunters, reindeer herders, environmentalists and guides.

Roy Ashenfelter, chairman of the working group, said members should let villagers and hunters elsewhere know about the declines “so that when changes come about, it’s not a surprise.” Though hunting did not cause the problem, hunters should prepare to be part of the solution, he said. “One of the things we’ve learned is to not wait until the last minute and tell the public, ‘Hey, here are some restrictions,’” he said.

Sources: https://www.alaskadispatch.com/article/20131209/alaskas-western-arctic-caribou-herd-numbers-continue-slide


Spatio-temporal dynamics in the response of woodland caribou and moose to the passage of grey wolf

  • Predators impact prey populations not only by consuming individuals, but also by altering their behaviours. These nonlethal effects can influence food web properties as much as lethal effects. The mechanisms of nonlethal effects include chronic and temporary anti-predator behaviours, the nature of which depends on the spatial dynamics of predators and the range over which prey perceive risk.
  • The relation between chronic and ephemeral responses to risk determines predator–prey interactions, with consequences that can ripple across the food web. Nonetheless, few studies have quantified the spatio-temporal scales over which prey respond to predation threat, and how this response varies with habitat features.
  • We evaluated the reaction of radio-collared caribou and moose to the passage of radio-collared wolves, by considering changes in movement characteristics during winter and summer. We used an optimization algorithm to identify the rate at which the impact of prior passage of wolves decreases over time and with the predator’s distance.
  • The spatial and temporal scales of anti-predator responses varied with prey species and season. Caribou and moose displayed four types of behaviour following the passage of wolves: lack of response, increased selection of safe land cover types, decreased selection of risky cover types and increased selection of food-rich forest stands. For example, moose increased their avoidance of open conifer stands with lichen in summer, which are selected by wolves in this season. Also in winter, caribou increased their selection of conifer stands with lichen for nearly 10 days following a wolf’s passage. This stronger selection for food-rich patches could indicate that the recent passage of wolves informs caribou on the current predator distribution and reveals the rate at which this information become less reliable over time.
  • Caribou and moose used anti-predator responses that combine both long- and short-term behavioural adjustments. The spatial game between wolves and their prey involves complex and nonlinear mechanisms that vary between species and seasons. A comprehensive assessment of risk effects on ecosystem dynamics thus requires the characterization of chronic and temporary anti-predator behaviours.

Latombe, G., Fortin, D., Parrott, L. (2013), Spatio-temporal dynamics in the response of woodland caribou and moose to the passage of grey wolf. Journal of Animal Ecology. doi: 10.1111/1365-2656.12108

Available in: http://onlinelibrary.wiley.com/doi/10.1111/1365-2656.12108/abstract