Arctic bowhead whales have lost a significant portion of their genetic diversity in the past 500 years, according to a new study to be published online Friday in the journal Ecology and Evolution.
Scientists drew on hundreds of DNA samples from both living whales and samples obtained from vessels, toys and housing material made from whale baleen and preserved in pre-European settlements in the Canadian Arctic.
The bowhead -- which can span up to 65 feet in length and weigh as much as 100 tons -- gets its name from its enormous bow-shaped head, which it can use to break through ice up to 23 inches thick in order to breathe.
The researchers found that the whales were not deterred by ice-covered inlets and straits separating the Atlantic and Pacific populations, and exchanged genes.
Some unique maternal lineages from the past have been lost since the 1500s, most likely because of whaling and climatic cooling between the 16th and 19th centuries -- known as the little Ice Age -- which reduced the whales' summer habitat, according to the study.
Howard Rosenbaum, a co-author and director of the Wildlife Conservation Society's Ocean Giants Program, said in an interview that the loss of the female lines were important because "the cultural knowledge associated with maternal lineages" guides whales in their migrations to certain areas.
"You are potentially losing a significant, discrete component of the population," he said. "We looked at this not just through space but through time."
Researchers say there are four or five stocks of bowheads, two of which, the Okhotsk Sea and Spitsbergen populations, are identified by the International Union for Conservation of Nature as "endangered" and "critically endangered," respectively.
The species was commercially hunted throughout the Arctic and sub-Arctic starting in Labrador around 1540 until the International Whaling Commission banned the practice in 1946; bowhead whales are still hunted for subsistence by some indigenous Arctic communities.
Stanford University marine sciences professor Stephen R. Palumbi, who has also conducted genetic analyses to gauge the impact of commercial hunts on global whale populations, said the study helps show "the stories about early whalers scrubbing the ocean of whales were true." It also draws distinctions between bowheads and other high-Arctic whales such as blue, humpback and gray whales.
These other whale species, Palumbi wrote in an email, "have been stymied by the sea ice in the Northwest Passage, and populations in the Atlantic and Pacific are quite distinct genetically."
The study's immediate policy implications remain unclear. Randall Reeves, who chairs the IUCN cetacean specialist group, wrote in an email that the biggest threats bowhead whales face include an increase in subsistence hunting, environmental changes such as shrinking sea ice, and the ongoing industrialization of the Arctic spurred by climate change.
Patrick Ramage, whales program director for the International Fund for Animal Welfare, said that the paper helps capture the "cumulative impact human activities have on bowhead whales" across hundreds of years. "For policymakers facing a bonanza of proposals for Arctic drilling, shipping and industrial development, this should be a cautionary tale," he added.
Palumbi wrote that the research sheds light on how bowheads can thrive in the icy Arctic but that it is difficult to project "whether the coming Ice Free Age will be a huge ecological problem for them."
Since "specialized creatures tend to lose in competition to environmental generalists" in less-extreme conditions, he wrote, "for bowheads, the future may see them crowded out by other whales which do not have the bowhead's ice breaker heads."