Researchers recording whale songs in frigid Southern Ocean waters around Antarctica have discovered a unique echolocation signal that may belong to a previously unknown species of beaked whale, BBC reports. The findings were published in Marine Mammal Science earlier this month.

Beaked whales make up the second-largest family of cetaceans, but being such cryptic, deep foragers, they’re also some of the most poorly understood. For example, just last year, two Cuvier’s beaked whales broke the mammalian records for dive depth and duration: 2,992 meters (1.8 miles) below the surface and 2 hours, 17 minutes, 30 seconds.

Beaked whales are also the only cetaceans known to use FM signals called upsweep pulses to echolocate—and these signals appear to be species specific. So, an international team led by Jennifer Trickey from Scripps Institution of Oceanography recorded these sorts of signals using a hydrophone array towed behind a research vessel sailing near the South Scotia Ridge, South Orkney Islands, South Shetland Islands, and Antarctic Peninsula.

The team recorded one signal, called Antarctic BW29, more than 1,000 times during 14 separate recordings, and the timing and type of sound make it rather unique: Its structure doesn’t quite fit any known beaked whales, BBC explains.

With a new discovery confirmed just one year ago, we now know of 22 beaked whale species. And of these, at least five reside in the Southern Ocean south of the South American continent. So far, the team has ruled out Arnoux's beaked whales, the largest of the Antarctic beaked whales, as well as Cuvier's beaked whales. The signal definitely doesn’t match those produced by these two deep divers.

That leaves Gray’s beaked whale, southern bottlenose whales (pictured), and strap-toothed whales. Unfortunately, we don’t have a full description of the FM pulses they produce, though strap-toothed whales aren’t typically spotted at this latitude in the Southern Ocean, unlike the other two. However, if there exists a relationship between body size and the frequency of calls, then Antarctic BW29 likely didn’t come from a Gray’s beaked whale. And if southern bottlenose whales vocalize like their cousins to the north, then the calls wouldn’t match these whales either.

Additionally, a second unique, higher frequency call (dubbed Antarctic BW37) was recorded on six other occasions, and the team is unsure who this call belongs to as well. It’s possible—based on the relationship between whale size and call frequency—that the smaller Gray’s beaked whale made the higher frequency Antarctic BW37 pulse type while the southern bottlenose whale made the Antarctic BW29 call. Or... they were made by an altogether new species!

[BBC]

Images: shutterstock.com (top), Southwest Fisheries Science Center/NOAA (middle)