Are Polar Bears Really Endangered?
The technical answer to this question is no. Polar bears (Ursus maritimus) were declared to be a threatened species by the U.S. Fish & Wildlife Service in May, 2008. The threatened classification means that the species is vulnerable to becoming endangered in the future. Perhaps the more interesting question is – how many of the world’s 19 polar bear populations may become endangered in the near future by climate change?
In Canada, polar bears are listed as a species of “Special Concern.” Polar bear hunting was banned by the Soviet Union in 1956 and the species is also a species of concern in Russia. The Russian Prime Minister, Vladimir Putin, recently banned the hunting of polar bears even by indigenous groups in Russia. International attention on the species has been so prominent that one of the few agreements that could be signed by Canada, Norway, Denmark (Greenland), Russia, and the U.S. during the Cold War was the 1973 Oslo Agreement for conservation of polar bears.
We think and talk a lot about bears at Washington State University because of the work of our Dr. Charles T. Robbins, Director of the WSU Bear Center, and Dr. Lynne Nelson, and other research colleagues working on bears. Our Bear Center is the only such facility in the world to house adult grizzly bears (Ursus arctos) for research emphasizing their nutritional ecology, hibernation physiology, behavior, and conservation.
Dr. Robbins and associates are now working on polar bears as well, for which nutritional ecology, linked to habitat changes in the Arctic, is emerging as a major factor influencing their reproductive success, survival, and population status. Let’s look at some of the recent scientific evidence on factors related to polar bear populations.
The Arctic ecosystem has been experiencing rapid warming due to global climate change, resulting in less ice persisting over relatively shallow continental waters through the summer months. These relatively shallow coastal waters have higher biological productivity and support larger populations of seals, the foundation of polar bear diets.
The extent of sea ice in the summer has been declining about 8-9% every 10 years in many Arctic regions since 1979. That’s a major problem for polar bears, classified as one of the most ice-dependent marine mammals – meaning they require ice pack for travel, mating, some denning by females, and to provide optimal conditions to hunt for ringed seals (Phoca hispida) and bearded seals (Erignathus barbatus).
[Projected changes in polar bear habitat from 2001-2010 to 2041-2050 by the U.S. Geological Survey. Red illustrates areas losing optimal bear habitat, while blue areas indicate areas projected to gain habitat. Source: Wikipedia.]
Studies conducted in the Beaufort Sea show that when more sea ice melts in summer, more bears are forced to stay out on thicker, permanent ice farther away from the continental shelf, where productivity and foraging success is lower. Part of the population, perhaps 4-8%, stay on land with some attempting to survive off of whale carcasses washed up on beaches or killed by subsistence hunters.
The evidence indicates that longer ice-free periods over the continental shelf results in lower foraging success, nutritional stress, lower reproductive success, less body mass of cubs, fewer yearlings observed per female, and even starvation and cannibalism. In years when rapid melting of sea ice combined with severe storms, polar bears were observed drowning in the southern Beaufort Sea.
Scientists use samples of marked and radio-collared bears to estimate survival and growth rates in polar bear populations. Data collected from over 600 polar bears from the Beaufort Sea population predict that reproductive success and survival will decrease with projected increases in temperature and longer periods of ice-free conditions in the Arctic summer. And given that the polar bear population of about 7,500 bears in the Beaufort Sea region represents about one-third of the world’s polar bears, there is indeed good reason to be “concerned” about the future of polar bears in the Arctic.
The Polar Bear Specialist Group (PBSG) for the International Union for the Conservation of Nature (IUCN) estimates that there are about 20,000 – 25,000 polar bears in the world. Of the 19 identified polar bear populations in the world, 8 are declining, 3 are stable, and 7 have insufficient data to make any determination about population trends. Only 1 population appears to be increasing. If you are at all curious about the raw data behind projections about the potential future status of polar bears, the following two graphics from the PBSG are quite informative: 1) Polar bear map (interactive), 2) Table of Population Status and Trends.
[Female polar bear with cubs. Source: adressa.no]
Humans are extremely efficient at extirpating large predators and polar bears are exceptionally vulnerable, even in the seemingly remote regions of the Arctic. With more nutritionally-stressed bears coming ashore, and with the certainty of increasing mineral and oil exploration in a thawing Arctic, the potential for increased human-bear conflicts is obvious.
Some native communities around the Arctic region contend that polar bear populations have actually increased, perhaps not realizing or being willing to admit that more bears coming ashore actually may mean that summer sea ice conditions are worsening for polar bears, driving them onto land. When you see more bears, certainly it’s easy to believe there are more bears, when the reality and trends for the population as a whole may be just the opposite.
So are polar bears endangered? Technically, no, not yet. But all the ecological signs, climate models, and the best scientific data in hand point to a declining future for most polar bear populations.
Sources & Additional Reading:
Regehr, E.V., C.M. Hunter, H. Caswell, S.C. Amstrup, and I. Stirling. 2010. Survival and breeding of polar bears in the southern Beaufort Sea in relation to sea ice. J. Animal Ecology. 79:117-127.
Wikipedia: Polar Bear
[Lead Photo: Polar bear in Alaska. Source: Wikipedia.]