True's Beaked Whale

True's Beaked Whale: Mesoplodon mirus

IUCN Status: Data deficient

Status and distribution summary:

Very poorly known. Two populations known, one in the North Atlantic including Biscay, the Azores, Canaries, Bahamas and Nova Scotia; the other from eastern South America east to Australia. These are likely to be isolated and so may be genetically distinct.

Exploitation: not known to be hunted

Other threats: as with all beaked whales, is vulnerable to loud under-sea noise from military sonar or seismic survey. Known to have died following ingestion of plastic bags, which could be a significant issue.

Where it is seen:

Over deep waters in southern Bay of Biscay, from 430-460 N.

Frequency of sightings:

Only recorded from ferries on 3 occasions.

Recognition:

Small to medium sized (c5m). Significantly smaller and less bulky than Cuvier's beaked whale.

  • Potentially variable paleage
  • Grey blue upper parts with some minor but diagnostic parallel gouge scarring in males (acquired during dominance fights - males have a pair of narrow set teeth at the tip of the lower mandible).
  • Small triangular slightly falcate dorsal fin set 2/3 back to the tail.
  • A medium length beak that smoothly blends to the small melon, with a slight notch where the blow hole is situated.
  • In adult males two small teeth are visible at mid point of beak, though  not a good feature unless seen very well.

Behaviour:

Little known. Recorded singly and in pairs in Biscay. Breaches.

Confusion species:

  • Other mesoplodon Beaked Whales look very similar, and great care is needed in separating them. Photographs are probably essential.
  • Gervais' Beaked Whale is the closest in appearance that occurs in the North Atlantic.