By Matt Walker
Editor, Earth News
A large group of a rarely sighted, mysterious species of whale has been seen off the coast of Antarctica.
Approximately 60 Arnoux's beaked whales were seen and photographed frolicking on the surface in the Gerlache Strait.
Few sightings of this enigmatic species are made in the wild, and even fewer in waters near to shore.
The sighting, of the largest group ever recorded, is also the first time this species of whale has been seen socialising at the water surface.
Marine biologists have published details of the sighting in the journal Marine Mammal Science.
"There was a fair bit of incredulity and excitement throughout the sighting," says Dr Ari Friedlaender of Duke University's Marine Laboratory, based in Beaufort, North Carolina, US.
As a group, beaked whales are among the least understood large animals on the planet.
Around 20 species belong to the family Ziphiidae, with several only having been discovered in the past couple of decades.
Typically, beaked whales are deep divers, and they are the only whales to have tusks, which are teeth that erupt from the lower jaws of the males.
Together with its close relative, the Baird's beaked whale (Berardius bairdii), the Arnoux's beaked whale (Berardius arnuxii) is among the two largest of all beaked whale species.
Member of a superpod
"Arnoux's are quite cryptic, and like most other beaked whales, are thought to have oceanic distributions," says Dr Friedlaender.
"Very little is known about their ecological requirements, or features around which their distribution is based."
The whale is best known from occasional sightings made by survey boats cruising circumpolar waters around Antarctica.
On 5 May this year, a team of Duke University researchers including Dr Friedlaender sighted approximately 60 Arnoux's beaked whales near the entrance to the Schollaert Channel between Brabant and Cuverville Islands, which lie in the Gerlache Strait, Antarctica.
"What made the sighting atypical and noteworthy was the size of the group of animals and their surface activity," says Dr Friedlaender.
"There were over 60 animals spread out linearly and over a few kilometres."
Each whale was dark-slate coloured, around 5-8m long with a small dorsal fin back toward the tail.
"The animals remained at the surface socialising in ways more befitting of dolphins."
"The whales were very tactile with each other, slapping the water with their tails, surfacing rapidly."
The researchers, who were aboard the research vessel ARSV LM Gould surveying humpback whales, approached the beaked whales in an inflatable boat, photographing them and observing their behaviour.
After the bout of socialising, the whales then dived in synchrony, remaining below the surface for 15 to 20 minutes at a time, with five minutes between dives.
On 7 June, the research team made a second sighting of Arnoux's beaked whales in the same region, this time of a group of at least 25 animals.
Preparing to dive
"We really know very little about their natural history," says Dr Friedlaender.
For example, this species of whale has never before been seen socialising at the surface, nor a group this large.
"The Arnoux's were a unique and amazing experience. Hopefully, this brief glimpse will spawn further work to better understand the species, their distribution and behaviour, and how these animals fit into the larger ecology of the southern ocean."
Being sighted in the Gerlache Strait, which contains channels and canyons up to 1,500m deep and is more than 150km from the edge of the continental shelf, suggests the whales may prefer to reside near to shore as much as in the open ocean.