A new species of whale may be cruising the icy cold waters of the Antarctic.

Scientists have recorded a unique whale song, which they can’t identify, in the area.

Evidence for the species is tantalising, rather than strong, as the song could be from one of a few known species of beaked whale.

But it has a structure that doesn’t quite fit any known beaked whales; leaving open the possibility it is from a new species.

Although beaked whales comprise the second-largest family of cetaceans (the group containing whales and dolphins), they are one of the most poorly known groups of all large mammals.

Last year, Deraniyagala‘s beaked whale was confirmed as a new species, bringing the total known to 22.

All beaked whales are extremely elusive, diving deeply and spending very little time at the surface. That makes them difficult to spot. However, they do produce unique sounds that they use to echolocate in the depths, sounds that scientists can use to track and record their movements.

New species of beaked whale are still being discovered

The signal, known as the Antarctic BW29 signal, was recorded by a hydrophone array towed 200 metres behind a research vessel sailing the waters near the South Orkney Islands, South Shetland Islands, and Antarctic Peninsula.

The team of scientists on board comprised researchers from the US and Argentina, led by Jennifer Trickey of the Scripps Institution of Oceanography, at the University of California, in La Jolla, California, US.

They recorded the unique Antarctic BW29 signal more than 1000 times, during 14 separate recordings. It is unique in both its timing and the type of sounds making up the signal, the scientists report in the Journal of Marine Mammal Science.

Some whale species have been definitely ruled out – the signal doesn’t match those produced by Arnoux's beaked whales, the largest of the Antarctic beaked whales. Nor is it from a Cuvier's beaked whale.

It could yet be from a known species; either a strap-toothed whale, a southern bottlenosed whale or a Gray’s beaked whale.

The researchers also recorded a second unique call on six other occasions

But strap-toothed whales are generally not sighted south of latitude of 60°S, in the Southern Ocean.

Southern bottlenosed whales or Gray’s beaked whales are commonly sighted in the region.

Yet there is also a relationship between the size of a beaked whale and the frequency of its calls. The unique call isn’t at the right frequency to be a Gray’s beaked whale.

That leaves the southern bottlenosed whale as a candidate.

But even here, there is some doubt, as the sister species of the southern bottlenosed whale, the northern bottlenosed whale, makes very different calls, and its southern cousin might be expected to vocalise in a similar way. If so, they too would not match the Antarctic BW29 signal.

As well as signal Antarctic BW29, the researchers also recorded a second unique call on six other occasions, dubbed Antarctic BW37.

This second signal was produced at a higher frequency.

“It remains unknown whether this belongs to a different beaked whale species than the one producing  Antarctic BW29,” write the researchers.

If the relationship between the size of a beaked whale and the frequency of its calls holds true, then it is possible that the southern bottlenose whale produces the Antarctic BW29 pulse type, whereas the higher frequency Antarctic BW37 pulse type could belong to the smaller Gray's beaked whale.

Alternatively, say the researchers, it is possible that a single species could produce multiple signal types; however, to date this has not been shown for any species of beaked whale.

“Lastly, given that new species of beaked whale are still being discovered,” the researchers report “the source of these Antarctic signals might be a species that has yet to be identified.”

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