Growth of polar bear populations depends on sea ice

Growth of polar bear populations depends on sea ice

17 October 2013

The Marine Mammal Council (MMC) has completed the second field phase of the Polar Bear Programme, which in 2013 was sponsored by the Russian Geographical Society and involved the participation of the MMC and VNIIPrirody experts.


The expedition lasted from 29 August to 8 September off the coast of the East Siberian and Chukchi seas in the Chukotka Autonomous District. An aerial survey of 800 km of the Arctic coast of Chukotka provided important information about the distribution and relative abundance of polar bears on land. Skin microsamples were taken for genetic research.


Fifteen polar bear encounters, including a female with her yearling cub, were recorded. Several dozen high-resolution pictures taken during the encounters provide additional information about each animal.


A dead bear with a wounded left thigh was found. According to the experts, it was a well-fed animal. They believe that a gunshot wound is the most likely cause of death. Fleeing poachers, the bear likely jumped into the water and swam away from the shore, where it died from loss of blood. The carcass was washed up on shore during a storm.


On average, one bear was encountered per 150 km within the surveyed area. Researchers note that such a low number of encounters is a disturbing sign. Females give birth to cubs only on shore. Bears cannot hibernate in the unstable and unsafe ice of the Arctic Ocean. Most bears, including pregnant females, follow the ice as it recedes toward the pole during the summer and autumn. From there, the bears must swim to reach land.


The bears spotted by researchers during the aerial survey of the coast were predominantly males. It’s highly likely that only two of the 15 bears were females. The experts visually determined the gender of almost all the polar bears captured on film. They took biological samples from six of them and used genetic analysis to determine the gender. One of the females was with a cub.


Prolonged swimming in cold and often rough seas exhausts the bears. Pregnant females won’t swim as the stress could cause them to lose the fetus. Births of new cubs depend on how quickly the East Siberian and Chukchi seas are covered with ice, whether the females have time to reach the coast of the Chukchi Sea, and whether they have enough fat to be able to start hibernation in November. Currently, the ice is forming rapidly in the central part of the Russian Arctic, while waters in ​​the Alaska and Chukotka region are still free of ice.


Testing and refining methods of monitoring the Alaska-Chukotka polar bear population and assessing its numbers was another important part of the expedition.