Omura’s Whale

Balaenoptera cf. B. omurai
Wada, Oishi, and Yamada, 2003 (nomenclature unresolved)

Order: Cetacea
Suborder: Mysticeti
Family: Balaenopteridae

The Omura whale was described in 2003. There is now profuse evidence from molecular genetic studies to confirm that Omura is a valid species. It is different from and not closely related to Bryde’s whales. Confirmation of the nomenclature is awaiting determination from a type specimen in the Calcutta Museum.

Specimens of this whale were included among pygmy/dwarf Bryde’s whales in some studies, but it is now known to be offshoot of the rorqual* line of whales, and perhaps more closely related to the blue whale.

The body shape of the Omura’s whale is streamlined and sleek. They apparently have only one prominent ridge on their rostrum, whereas most Bryde’s whales have three. The dorsal fin shape is not well known, but it is believed to be like that of Bryde’s and sei whales which is tall and falcate** and rising abruptly out of the back. They may be very falcate some evidence suggests. The flukes are broad with a relative straight trailing edge.

The Omura’s color pattern is not completely known, but it most closely resembles that of the fin whale with an asymmetrical lower jaw (which is white on the right and dark on the left). It appears that some animals have light streaks and blazes that extend up from the light ventral side onto the darker back. Anterior edges and inner surfaces of the flippers are white and so is the ventral surface of the flukes which have a black margin.

The 80-90 throat pleats reach beyond the navel. The 180-210 pairs of baleen plates are short and broad. In color, they are yellowish white to black and some may be two-tone.

Because the Omura has only recently been described and its physical appearance is not well known, care must be taken in identifying the species and ruling out other whales (small fin, sei, Bryde’s and minke whales).

The complex color pattern of the Omura should be easily identifiable when it is clearly observed. It has an asymmetrical lower jaw and light streaks and chevrons on its back. The dorsal fin may have a very hooked fin rising at a steep angle.

Three head ridges have for many years been a source of confirming a Bryde’s whale; however there is some suggestion that the Omura may sometimes also have accessory head ridges. Also, water rippling off the head of other species can be mistaken for accessory head ridges.

Omura’s whales can also be confused with minke whales but they are generally slightly smaller and have a sharper point to the head when viewed from above. The white bands on its flippers are indicative of common minkes. They also have symmetrical head coloration, unlike the Omura. To be absolutely certain of the whale’s identify, genetic samples may be required for confirmation.

Distribution: The limits of its range are not well known but they appear to be limited to the western Pacific and eastern Indian Oceans. Apparently, it is restricted to tropical and subtropical waters and appears over the continental shelf in relatively nearshore waters.

Ecology and Behavior: Little is known of the species’ ecology and virtually nothing is known about its reproductive biology. It is suspected that it does not have a precise breeding season unlike most rorquals. Generally seen in pairs, they may congregate in larger groups on feeding grounds.

Feeding and Prey: Omura’s whales are probably primarily schooling fish eaters. Like most other rorquals, they are lunge feeders.

Threats and Status: Omura’s whales have probably never been hunted as extensively as their larger relatives: the blue, fin, sei and Bryde’s whales. Because of this, it is probably not critically depleted, except possibly in the Philippines. The Japanese have hunted them under “scientific whaling” in the Solomon Sea and near the Cocos Islands in the Indian Ocean. They have also been killed by artisanal whalers from Philippine villages (and probably Indonesia).

IUCN Status: Not listed – International Union for the Conservation of Nature and Natural Resources, now the World Conservation Union (IUCN Red List).

Source: Marine Mammals of the World: A Comprehensive Guide to their Identification by Thomas A. Jefferson, Marc A. Webber and Robert L. Pittman

*Rorqual – A whale of the family Balaenopteridae which includes the blue, fin, sei, Bryde’s, minke and humpback whales.

**Falcate – Sickle shaped and curved toward the tail; recurved.