They determined the existence of the species by analysing the morphology and mitochondrial DNA of nine individuals – eight caught by Japanese research vessels in the late 1970s in the Indo-Pacific and an adult female collected in 1998 from Tsunoshima, an island in the Sea of Japan.

[9] The six specimens obtained in the Solomon Sea in 1976 were only noted to be smaller at sexual maturity than the "ordinary" Bryde's whales caught off New Zealand, whereas the two caught near the Cocos-Keeling Islands in 1978 were not differentiated from the 118 other "ordinary" Bryde's whales taken in the eastern Indian Ocean, south of Java.

Despite this declaration, the specific status of the Solomon Sea specimens was supported by a mitochondrial DNA study done by Hideyoshi Yoshida and Hidehiro Kato (1999).

[1][10][11][12][13] The identity of these eight specimens was finally resolved in 1998 when an unidentified whale, which had died after colliding with a fishing boat in the Sea of Japan and was towed to Tsunoshima, was examined by Tadasu Yamada, Chief of the Division of Mammals and Birds at the National Science Museum, Tokyo.

This specimen closely resembled the individuals caught in the 1970s in external appearance and allowed a complete osteological examination of the putative new species to be conducted.

As a result of external morphology, osteology, and mitochondrial DNA analysis of two of the harvested whales and the Tsunoshima specimen, Wada, Masayuki Oishi, and Yamada described Balaenoptera omurai in the 20 November 2003 issue of the journal Nature.

[5][12] The holotype is an 11.03 m (36.2 ft) adult female, NSMT-M32505 (National Science Museum, Tokyo), which stranded at Tsunoshima (34°21′03″N 130°53′09″E / 34.35083°N 130.88583°E / 34.35083; 130.88583) in the southern Sea of Japan on 11 September 1998.

In B. omurai and B. brydei, the posterior end of the ascending process of the maxilla widens to become squarish, whereas in B. edeni, it is slender and round throughout its length.

B. omurai has two small foramina "along the suture between the parietal and squamosal in the posterior wall of the temporal fossa", which both B. brydei and B. edeni lack.

B. omurai has an oblique ridge on the dorsal side of the maxilla near the base of the rostrum, which is absent in both B. brydei and B. edeni.

[5][14] Omura's whale has a total of 53 vertebrae, including seven cervical (the standard number among mammals), 13 thoracic, 12 lumbar, and 21 caudal.

The type specimen (NSMT-M32505) had 203-208 pairs of baleen plates that were "short and broad with uncurled, stiff, grayish-white fringes", while NRIFSF6 had an estimated 181–190 on the right side – fewer than any other species in its genus.

[3][5][17][18] Omura's whale seen off New Caledonia, the Solomon Islands, West Sumatra, and East Kalimantan showed extensive scarring from cookiecutter shark bites, indicating they had ventured into deep waters;[19] whereas those off Madagascar did not exhibit them.

They have been seen lunge feeding, defecating, and breaching off both Komodo National Park and northwestern Madagascar; they've also been seen rolling at the surface in apparent mating (the last of which allowed the identification of a male) off the former area.

A total of thirteen cow-calf pairs were observed between 2011 and 2016, including a female first seen in an aggregation in 2012, then with a calf in 2013, and alone again in 2015 and 2017, showing that individuals can exhibit strong site fidelity.

[31] The six paratypes taken in the Solomon Sea in 1976 reportedly only had krill (Euphausia diomedeae) in their stomachs,[1][32] while crustaceans and fish were found in a 7 m (23 ft) female from Japan.

[31] Omura's whale are found in the Indo-Pacific and the Atlantic Oceans, primarily in shelf waters between 35° N and 35° S, with the majority of records in the tropics (between 23° 26' N and 23° 26' S).

[19] Their range includes southern Japan (with strandings and entanglements recorded in March and from May to October; including the prefectures of Yamaguchi,[33] Miyazaki,[34] Kagawa,[35] Mie, Shizuoka, and Chiba),[19] South Korea[36] (December to January, from the provinces of South Jeolla and South Gyeongsang),[19] China[37][38] (with strandings from November to February and in August; including the provinces of Zhejiang, Fujian, Guangdong,[18] and Guangxi),[20] Taiwan (with strandings from November to March and in May; there are also sightings from April to May and July to August),[14][39] Hong Kong (March),[40][41] the Philippines[42] (Manila Bay, Busuanga,[19] and the Bohol Sea),[24] Vietnam (Quảng Ngãi Province),[19] Malaysia (Pahang),[43] Thailand (with sightings and strandings from February, May to June, and November to December; including the provinces of Phang Nga, Phuket,[14] Prachuap Khiri Khan, and Songkhla),[19] Indonesia (with sightings and strandings from February, April to June, and from September to November; with records from West Sumatra, the southern Java Sea, Bali,[19] Komodo,[30] the Solor Archipelago, Seram, Raja Ampat Islands, and East Kalimantan),[19] the Cocos (Keeling) Islands,[5] the Andaman Islands (April),[19] Australia (Western Australia from Exmouth[44] to north of Darwin in the Northern Territory at about 9° 30' S - 10° S, 130° E),[45] South Australia[46] (January, Gulf St Vincent), Queensland (November to December, Port Douglas and Mission Beach),[47] the Solomon Islands,[48] New Caledonia,[49] Sri Lanka (February),[50] the Chagos Archipelago,[19] Iran (September, Strait of Hormuz),[51] Egypt (April, the northern Red Sea)[19] northwestern Madagascar (12° 01' S to 19° 23' S, with sightings by researchers from August and October to December, by whale watch operators from April to December, and acoustically detected year-round),[31] Mauritania (November, Trarza Region),[52] Brazil (September, Ceará),[21] and in the vicinity of the Saint Peter and Saint Paul Archipelago.

At first, they were tentatively identified as a "pygmy or regionally distinct" form of Bryde's whale, which was confirmed when one was photographed and biopsied in October 2000 and its tissue sample sent to the Southwest Fisheries Science Center in La Jolla, California.

[1][3][30] During marine mammal surveys conducted in the Solomon Islands in 2009 and 2010, what were "most likely" Omura's whales were sighted on three occasions.

[48] In October 2015, an international team of scientists, led by Salvatore Cerchio of the New England Aquarium and Woods Hole Oceanographic Institution, released the first images and field observations of the species from a population off northwestern Madagascar.

The specimens were deposited in the collections of the Marine Research Laboratory of Silliman University in Dumaguete, Negros Oriental, Philippines, where they were examined by T. K. Yamada and co-workers (2008).

Later examination of photographs of those skulls by one of the scientists (Tadasu K. Yamada) that had formally described Omura's whale showed that two of them, one from Bangsri, Java, and another from Lamakera, Solor, belonged to B. omurai.

A 4.4 m (14 ft) male calf was also caught in small-mesh herring seine nets in the Gulf of Thailand, Songkhla Province, in May 2011, while a 7.5 m (25 ft) whale (thought to likely be an Omura's whale) was caught in fishing gear off Negombo, Sri Lanka, in August 1985.

[19] Omura's whale is listed on Appendix II of the Convention on the Conservation of Migratory Species of Wild Animals.

It is listed on Appendix II as it has an unfavourable conservation status or would benefit significantly from international co-operation organised by tailored agreements.