With sea ice receding in the Arctic, animals that rely on this ice to rest are being forced to find alternate places to haul out. Pacific walruses, like those pictured above, are retreating from their typical resting spots on ice in the Chukchi Sea and instead heading to land on Alaskan beaches to rest in the summer. With animals closer to shore, it is easier for researchers to study these populations and obtain data that was previously difficult to capture.
Flying over the herds in a helicopter, researchers took videos of walruses as they lay on beaches (see the clip below) and evaluated their demographics. Researchers looked for distinguishing features to identify males and females and used Fay’s method which considers head morphology and the ratio of an individual’s tusk length to snout width or depth to estimated age. They found that a majority of the herd was comprised of females and young less than two years old.
The walruses seemed to gather in much larger groups on land than they did at sea, perhaps simply because the space allowed but this may also be a strategy to protect from predators that is not possible on ice. Gathering in these large groups of up to 19,000 individuals, however, increases the risk of trampling calves. The researchers suggest this may be why young were found in greater numbers along the outer edges of the groups rather than within the herd. Being on the outside could possibly also allow a quick escape into the water should the herd be disturbed.
As sea ice continues to recede, populations of Pacific walrus, as well as other animals, will continue to adjust their behavior to survive. Monitoring their population dynamics could provide insight to how their habits may be influenced by climate change.
Citation: Monson DH, Udevitz MS, Jay CV (2013) Estimating Age Ratios and Size of Pacific Walrus Herds on Coastal Haulouts using Video Imaging. PLoS ONE 8(7): e69806. doi:10.1371/journal.pone.0069806
Image: Walrus 2 from U.S. Fish and Wildlife Service Headquarters http://bit.ly/19TeYMp