The pygmy beaked whale is one of the most recently described members of the genus, and appears to be the smallest of the species of Mesoplodon. 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 tend to be dark gray above and lighter below, apparently with relatively little scarring. They have small, triangular, wide-based dorsal fins that are shaped like those of harbor porpoises.
The most distinctive characteristic is the teeth, which are extremely small and egg-shaped in cross section (although generally they are not visible in at-sea sightings).
This is the smallest known species of Mesoplodon; maximum known length is only 3.9 m, apparently with males larger than females. At birth, these animals are about 1.6 m long.
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 juveniles are not readily distinguishable from other mesoplodonts.
The pygmy beaked whale is known only from a handful of specimens and several sightings from the eastern tropical Pacific and Gulf of California, as well as off Peru and Chile. There is a single record of a stranding in New Zealand, suggesting that this species may have a more extensive distribution than previously believed. This is the most frequently sighted Mesoplodon whale in the offshore eastern tropical Pacific.
Ecology and Behavior
Most groups have been of two animals, but have ranged up to four. The behavior 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 three times.
Feeding and Prey
The diet consists of small midwater fishes, oceanic squid, and shrimps.
Threats and Status
Little is known of the pygmy beaked whale’s status or threats; the IUCN classes them as “Data Deficient” and they are “Not Listed” under the United States Endangered Species Act.
Dalebout, M.L. 2002. Species identity, genetic diversity, and molecular systematic relationships among the Ziphiidae (beaked whales). Ph.D. dissertation, University of Auckland, New Zealand.
Pitman, R.L. 2002. Mesoplodont whales Mesoplodon spp. pp. 738-742 in W.F. Perrin, B. Würsig and J.G.M. Thewissen, eds. Encyclopedia of marine mammals. Academic Press.
Pitman, R.L., A. Aguayo-L. and J. Urban-R. 1987. Observations of an unidentified beaked whale (Mesoplodon sp.) in the eastern tropical Pacific. Marine Mammal Science 3:345-352.
Pitman, R.L. and M.S. Lynn. 2001. Biological observations of an unidentified mesoplodont whale in the eastern tropical Pacific and probable identity Mesoplodon peruvianus. Marine Mammal Science 17:648-657.
Reyes, J.C., J.G. Mead and K. Van Waerebeek. 1991. A new species of beaked whale Mesoplodon peruvianus sp. n. (Cetacea Ziphiidae) from Peru. Marine Mammal Science 7:1-24.