The Omura’s whale is a long and sleek baleen whale, with a body plan typical of rorquals and more slender than most. The external appearance of Omura’s whale was first described by Wada et al. 2003 based upon very limited information from the Japanese research whaling expeditions in the Solomon and Cocos Islands, and the Sea of Japan holotype stranding specimen. Our work in Madagascar resulted in the first detailed description of the external appearance and pigmentation pattern, adding substantially to what had been previously reported. Omura’s whales have an unusual pigmentation pattern in that they are laterally asymmetrical, similar to the fin whale, with the lower jaw being white on the right and dark on the left, along with a light blaze and chevron that is more prominent on the right. The ventral grooves extend beyond the umbilicus and number approximately 80-90, which is different in comparison to Bryde’s whales having 42-54 grooves. The top of the head, or rostrum, has a single prominent central ridge; the lateral rostral ridges that are prominent in Bryde’s whales are absent in Omura’s whales, however the head is not entirely smooth. Reported sizes are less than 12m, with physically mature individuals ranging from 10.3 to 11.5m for females, and 9.6 to 10.0m for males.
Images of several Madagascar Omura’s whales displaying details of pigmentation and external appearance. Visible features:
(A) Lower Jaw - asymmetrical coloration of the lower jaw, with lightly pigmented right jaw and darkly pigmented left jaw;
(B) Gape - asymmetrical coloration of the gape (inferred by inner lower lip), with lightly pigmented left gape and darkly pigmented right gape;
(C) Pectoral fin - leading edge of pectoral fin white from tip to shoulder;
(D) Head and rostrum - the apparent absence of lateral rostral ridges, with only faint indications detectable at some angles;
(E) Blaze - lightly pigmented blaze originating in front of the eye, present only on the right side, with dark eye and ear stripe, two additional dark stripes and a light inter-stripe wash;
(F) Chevron - lightly pigmented chevron in front of dorsal fin, present on both sides but asymmetrical, being most prominent on right where it displays a broad double-banded pattern, and a more narrow single-band on the left with different positions relative to the dorsal fin;
(G) Dorsal fin - highly falcate dorsal fin with gradual sloping insertion angle into the back, intermediate between fin whales (which have a more gradual slope) and Bryde’s and sei whales (which are more upright and have a sharper right angle insertion).