Svalbard’s Bowhead whales winter under the ice
Svalbard Bowhead whales (Balaena mysticetus) are still endangered, but little is known about their distribution, which makes an accurate assessment of their risk status impossible. With a new study, Norwegian scientists have now provided important data for an evaluation.
The population of Bowhead whales which lives in the region between East Greenland and Svalbard has been hunted so intensively since the early 17th century that their numbers were estimated to be only a few dozen animals in the early 1990s. And because they have been so severely decimated, it is not an easy task for scientists to learn more about the habits of the cold-loving ocean giants. Nevertheless, a few years ago, researchers succeeded in demonstrating a year-round presence of the endangered Bowhead whales in the Fram Strait between Svalbard and Greenland using acoustic methods. In the winter months, they even recorded the whales’ song for 24 hours a day, suggesting that this region is the mating ground of the Svalbard population.
In a recent study published in the journal Biology Letters, scientists from the Norwegian Polar Institute in Tromsø studied the year-round movement patterns of Svalbard Bowhead whales and their habitat use to provide important data for conservation measures. For this purpose, the researchers attached satellite transmitters to 16 animals from a helicopter, 13 of which reliably provided location information.
The data delivered remarkable results: First, they confirmed previous observations that Svalbard’s Bowhead whales are found in cold water and in close contact with sea ice at all times of the year. Second, the data showed that this population moves south in summer and north in winter — in contrast to its relatives in the Bering-Chukchi-Beaufort region and the population between Eastern Canada and Western Greenland, which move northward in summer and south in winter.
The animals of the Svalbard population spend the winter in deep, cold waters which are almost completely covered with sea ice, often more than 100 kilometers away from large, open water areas relying on a few cracks in the sea ice. During summer, they use the food supply at the ice edge, where productivity is high due to upwelling and melting processes.
The authors suspect that this behavior cannot only be explained by food availability but is also related to the intense hunting in past centuries. Animals that stayed further north during winter, were protected by the ice and spared by the whalers while those in open water were killed.
Bowhead whales are the only baleen whales that reside year-round in the Arctic and have adapted perfectly to life in the ice over the course of evolution: this includes having no dorsal fin and having a slow life-history strategy that involves extreme longevity of up to 200 years, late sexual maturation at 20 years and long intervals between births. In addition, their four meter long baleen permit high ingestion rates allowing them to maintain a blubber layer that can be up to 50 centimeters thick.
Bowhead whales do not belong to the deep-diving whales and mainly go hunting in the upper 200 meters for copepods, krill and amphipods.
The populations in the Bering-Chukchi-Beaufort region and eastern Canada/Western Greenland are recovering from historic whaling and the Svalbard population is also showing signs of an upward trend.
However, the loss of habitat and thermal stress due to rising water temperatures and the associated loss of sea ice could counteract the positive population development.
According to the authors, Svalbard’s Bowhead whales would retract north to offshore, deep water areas in the future where they would be forced to rely on zooplankton production. They assume that such a situation is likely to prevent recovery of the population.
Source: Nature, Kovacs et al. 2020
