Dimorphic Beaked Whale

Unclassified Cetacean of the eastern Pacific Ocean.

Etymology: From its two distinct color forms.

Scientific name: Mesoplodon species A.

Variant name: Unidentified beaked whale.

Physical description: Length, 16-18 feet. Long, wide beak. Relatively flat head with a small but distinct melon. Low, triangular dorsal fin. Males have a broad, white swath across the body; the head and beak are reddish-brown or tan, while the back and flanks behind the swath are black-brown or chocolate-brown. Females and young are gray-brown, fading to pale gray on the underside.

Behavior: Usually seen traveling in tight groups at a moderate pace. Feeds on squid.

132 dientudo

Distribution: Eastern Pacific Ocean from central Mexico to Peru. Favors deep water.

Significant sightings: Known from about sixty-five sketchy sightings at sea, as well as a series of aerial photographs taken by a helicopter in November 1999.

Present status: Classification is pending, until a stranded specimen can be examined. Possible explanations:

(1) This animal is assumed to be an unknown species of beaked whale.

(2) Longman's beaked whale (Indopacetus pacificus) is known only from two skulls; there have been no live observations.

(3) Bahamonde's beaked whale (Mesoplodon bahamondi) is known from a single skull.

(4) The Lesser beaked whale (Mesoplodon peruvianus) was officially described in 1991 after a male specimen was found on a deserted beach north of Lima, Peru. Its range overlaps with the Dimorphic, but it has been thought to be smaller, at 11-12 feet long. Robert Pitman and Morgan Lynn consider that it is a good match and that Dimorphic sizes have been overestimated. Sources: Robert L. Pitman, Anelio Aguayo

L., and Jorge Urban R., "Observations of an Unidentified Beaked Whale (Mesoplodon sp.) in the Eastern Tropical Pacific," Marine Mammal Science 3 (1987): 345-352; Mark Carwardine, Whales, Dolphins, and Porpoises (New York: Dorling Kindersley, 1995), pp. 112-113; Robert L. Pitman and Morgan S. Lynn, "Biological Observations of an Unidentified Mesoplodont Whale in the Eastern Tropical Pacific and Probable Identity: Mesoplodon peruvianus," Marine Mammal Science 17 (2001): 648-657.

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