Ageing whales: Scars reveal social secrets
Scientists studying one of the ocean's most mysterious whale species have found they form long-term alliances.
Baird's beaked whales, sometimes called giant bottlenose whales, seem to prefer the company of specific individuals.
Researchers who identified the whales by scars on their bodies, are calling for hunting of the species to be halted while more information is gathered about their complex social structure.
Currently, they are hunted by whalers off northern Japan.
The new findings have been published in the journal Marine Mammal Science.
Erich Hoyt, from Whale and Dolphin Conservation and co-director of the Russian Cetacean Habitat Project, who led the research, said his team had followed the animals from spring to early autumn over four years.
"We were trying to piece together the social behaviour," he told BBC News.
The whales spend relatively little time at the surface and make regular dives of up to 30 minutes, reaching depths of 1km (3,300ft).
This makes them difficult to study. But by following them over four years and cataloguing them based on each individual's numerous scars, the scientists were able to reveal new social insights.
Most striking were the long-term relationships the whales appeared to form.
The team, mostly made up of Russian research students, discovered one alliance of two whales that were together four times - the animals were apparently repeatedly meeting up with one another over a period of more than three years.
Of the scars on the whales' bodies, the team concluded these had been caused by drift nets, killer whale attacks and cookie cutter sharks.
As their name suggests, these sharks attack larger animals by biting a circular chunk out of their flesh. That indicated that the whales migrated from cold waters in eastern Russia to much warmer, subtropical waters, where the sharks feed.
Mr Hoyt told BBC News: "They're getting caught in nets, they're getting harpooned, so there's an international responsibility [for this species] that is getting overlooked at the moment.
"And the fact that we're seeing these animals ranging [so far] means the hunting of Baird's beaked whales is something that should be managed internationally."
The International Whaling Commission - the global body charged with the conservation of whales and management of whaling - said that despite their great size of up to 13m (40ft), Baird's beaked whales fell into "the category of small cetaceans (or toothed whales) rather than the so-called 'great whales'".
This means that, currently, they do not come under the commission's obligations - Japan's hunting of the species is subject to the country's own national regulations.
An IWC spokesperson told BBC News that member governments had been "debating for several years whether the organisation's regulatory mandate should be extended to small cetaceans".
New research shedding light on their social structure is likely to contribute to the ongoing discussion of whether and how this species is conserved.
Prof Ari Friedlaender, a marine ecologist from Oregon State University, said that the animals' long-term associations and complex social structures could mean that the impacts of "disturbing them or removing individuals might have significant consequences".
Dr Patrick Miller, from the University of St Andrews, added that more research was needed to clarify how the animals' associations might affect their breeding and feeding.
"But the study provides important data, which will improve our ability to understand how whaling and other [man-made] stressors like underwater noise might affect this species."