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Mesoplodon sp. "A"(unidentified)

Distinctive Characteristics

An unidentified whale of the genus, referred to as Mesoplodon species “A,” has been described from the eastern tropical Pacific, based on many sightings at sea. Two morphs exist, a scarred black and white form that is easily identified in the field (presumably adult males), and a smaller uniformly brown one (probably females and subadults). These animals have moderately long beaks, and low triangular dorsal fins with slightly falcate or straight trailing edges. They do not match with descriptions of any known whale, and may represent an undescribed species.

Can be confused with

Adult males may be distinguishable by the presence of a broad swathe that runs from the head and down the sides, on the otherwise black body. Females and immatures are not readily distinguishable from other species of Mesoplodon.


Maximum length estimates for these animals are about 5.5 m.

Geographical Distribution

Mesoplodon species “A” is the most frequently sighted Mesoplodon whale in the offshore eastern tropical Pacific, and may be endemic to these waters.

Biology and Behaviour

Most groups have been of 2 animals, but have ranged up to 4. The behaviour of these animals appears to be similar to that of other species of mesplodonts, but during a sighting of a single male in the eastern tropical Pacific, the animal breached 3 times.


This animal is known only from sightings at sea, and no human exploitation is known.

IUCN Status

Not listed.

Mesoplodon sp. 'A'