As ice is melting earlier in the year and forming later, the period of time with ice-free water in the Arctic Circle is lasting for longer and longer each year. It is already known that this is having a massive impact on polar bears, which are having to go for longer periods without eating as they need the ice to hunt seals. But how is it affecting the other marine mammals that inhabit this frozen world?
To investigate, a team of researchers from the University of Washington has been keeping track of whales and other underwater mammals during the dark and squally winter months – by eavesdropping on them. While traditional observations made by simply spotting whales from the shore or boats might not work during the dark Arctic winter months, underwater microphones have been able to show the researchers many surprising things. For example, male humpback whales were found to perform reproductive displays, which are normally associated with tropical waters and never before documented in the Arctic.
“The Arctic is still very dark and cold in the dead of winter, and can be stormy and foggy at other times,” explained Kathleen Stafford, who has presented the results from the survey during the Acoustical Society of America’s Fall 2015 Meeting. “And although we can't directly observe it, by eavesdropping under the ice, we can hear quite a lot of animal activity going on.” Using underwater microphones, known as hydrophones, they’ve been able to determine the seasonal movements of whales in and out of the gateway to the Pacific Arctic, through the Bering Strait.
In this region of the Arctic Circle, the stretch of water between the eastern coast of Russia and the western coast of the United States supports many communities that rely on marine mammals to survive in the harsh condition they endure. “Changes in the environment cause changes in animal distributions or seasonal occurrences that can affect access to subsistence species,” said Stafford.
From the acoustic patterns recorded from the waters around the Bering Strait, the researchers could determine what species of marine mammals were present at what time of year, and to a certain extent, what the whales were doing. Alongside the discovery of the humpbacks' reproductive displays in the Chukchi Sea, the same area, it’s worth noting, that Shell was planning on drilling for oil, they’ve also discovered that other whales which normally only enter the Arctic waters during the summer months are instead entering the Arctic for an extended period as the waters remain ice-free as late as November.
The researchers suspect that this could negatively affect the distribution and numbers of the whales that normally have the Arctic waters to themselves during the winter, such as Bowhead whales, due to increased competition for food. This in turn could have implications for Native Americans who use the whales for subsistence hunting.
“Summer whales have always occurred north of Bering Strait, although not in great numbers, and not in September, October, or November, when we hear them now,” said Stafford. The researchers want to continue tracking the whales’ movements between seasons, and then explore their relationship with other oceanographic data collected, such as sea ice, temperature, and current speed, in order to try and gauge these annual changes in their movements, and how they are impacted by a warming climate.