Omura's whale (Balaenoptera omurai), or the dwarf fin whale, is a species of rorqual about which very little is known. Before its formal description, it was referred to as a small or "pygmy" Bryde's whale by various sources (including Ohsumi 1978, Wada and Numachi 1991, Perrin et al. 1996, Kahn 2001, LeDuc and Dizon 2002, Kato 2002, among many others).
The scientific description of this whale was made in Nature 2003 by three Japanese scientists. 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. Later abundant genetic evidence confirmed Omura's whale as a valid species and revealed it to be an early offshoot from the rorqual lineage, diverging much earlier than the Bryde's and sei whales. It is perhaps more closely related to its larger cousin, the blue whale.
In the third edition of Mammal Species of the World, the "species" is relegated to being a synonym of Balaenoptera edeni. However the authors note that this subject to a revision of the genus. The database ITIS lists this as a valid taxon, noting a caveat on the disputed systematics of this species, Balaenoptera edeni and Balaenoptera brydei.
Taxonomy[edit source | edit]
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 weren't differentiated from the others taken in the same area. As a result of allozyme analysis, their distinctive baleen and small size at physical maturity compared to Bryde's whale, and photographs obtained of the harvested whales (showing their fin whale-like coloration), Dr. Shiro Wada and Kenichi Numachi (1991) decided that these eight individuals represented members of a new species of baleen whale. However, due to the lack of a detailed osteological study and the absence of "conclusive data", the International Whaling Commission (IWC) decided to consider them only as a regionally distinct group of "small-form Bryde's whale". 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).
The identify 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 Dr. 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. In honor of the people of Tsunoshima, who helped remove the flesh from the type specimen, it was given the Japanese vernacular name of "Tsunoshima kujira" (English: "Tsunoshima whale").
Holotype and paratypes[edit source | edit]
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) in the southern Sea of Japan on 11 September 1998. It includes a complete skeleton, both complete rows of baleen plates and frozen pieces of muscle, blubber, and kidney collected by T. K. Yamada, M. Oishi, T. Kuramochi, E. Jibiki and S. Fujioka. The type locality is the Sea of Japan – which may not be representative of the species’ typical range. The paratypes include the eight specimens (five females and three males), NRIFSF1-8 (National Research Institute of Far Seas Fisheries, Fisheries Research Agency, Shizuoka), collected by Japanese research vessels in the Indo-Pacific in the late 1970s. The longest baleen plate (NRIFSF6 includes 18 more baleen plates), an earplug, and a piece of the sixth thoracic vertebrae with associated epiphysis were collected from each individual.
Description[edit source | edit]
Omura's whale is among the smallest of the rorquals – only the two species of minke whale, the common and Antarctic, which reach 10.7 m (35 ft) and 9.75 m (32 ft) in length, respectively, are smaller. Of the eight specimens taken during Japanese whaling in the Indo-Pacific, the five females ranged in length from 10.1 to 11.5 m (33.1 to 37.7 ft) while the three males ranged from 9.6 to 10 m (31.5-32.8 ft). The females ranged in age from perhaps only 9 years-old (the earplug was damaged or partially lost) for an 11.2 m (36.7 ft) individual to 29 years-old for the longest female, whereas the three males ranged from perhaps 21 years-old (another damaged or partially lost earplug) for the longest male to 38-years-old for one of the 9.6 m (31.5 ft) specimens. All were physically mature with the exception of the smallest female. Of individuals found stranded in Taiwan and Thailand between 1983 and 2004, five males ranged in length from 5.13 to 10 m (16.8 to 32.8 ft), while two females were 4.3 m (14.1 ft) and 5.95 m (19.5 ft), respectively – a specimen of unknown sex that stranded in 1983 in Phuket Province, Thailand, was 7 m (23 ft) in length.
Its appearance resembles the larger fin whale (thus the alternate common names of dwarf fin whale and little fin whale), both having the asymmetrical white, right mandible patch, a white blaze, a dark eye stripe, a white interstripe wash, and a white chevron. It also resembles the fin whale by having pectoral fins with a white anterior border and inner surface and flukes with a white ventral surface and black margins. It has a similar dorsal fin to the Bryde’s, being upright and falcate – in some individuals it may be extremely falcate. It usually has a more rounded tip than the latter species, which can appear very pointed and even ragged. Unlike Bryde's, however, they have a single prominent median ridge on the rostrum, whereas Bryde's typically have auxiliary ridges on either side. It is estimated to have 80 to 90 ventral grooves that extend past the umbilicus. The type specimen (NSMT-M32505) had 203-208 pairs of baleen plates that were "short and broad with uncurled, stiff, greyish-white fringes", while NRIFSF6 had an estimated 181-190 on the right side – fewer than any other species in its genus. Like the fin whale, NSMT-M32505 exhibited asymmetrical coloration in its baleen as well: on the right side, the front third are yellowish-white, the intermediate 100 plates are bi-colored (dark on the outer side and yellowish-white on the inner side), and the remaining plates in the back were all black, while on the left side, the majority are bi-colored with the remaining back plates being all black like the right side. The average length and width for the nine specimens was 26 cm (10.4 inches) by 21.4 cm (8.5 inches), the smallest length-to-breadth ratio for any species in its genus.
Behavior and diet[edit source | edit]
Omura's whales in the Komodo National Park have been observed repeatedly lunge feeding, defecating, breaching, and rolling at the surface in apparent mating (the last of which allowed the identification of a male). The diet is not known. The stomach contents of six of the paratypes appear to have been examined, but they weren't differentiated from the Bryde's whales caught during the same expedition. Only euphausiids were reported.
Range[edit source | edit]
Omura's whale appears to be restricted to the shelf and deep waters of tropical and subtropical regions, with records from the eastern Indian Ocean (off Cocos Islands, Thailand, and Malaysia), Indonesia, the Philippines, China, Taiwan, the Sea of Japan, the Seto Inland Sea, the Timor Sea, Western and South Australia, and the Solomon Sea. On 14 May 2012 an Omura's whale was sighted and photographed off New Caledonia.
Sightings[edit source | edit]
In 1999 and 2000 an unidentified species of rorqual was repeatedly seen in the waters of Komodo National Park. They were small (most estimated to be only 7 to 10 m [23-33 ft] in length) with asymmetrical coloration similar to the fin whale, only had a single prominent ridge on the rostrum, and an extremely hooked dorsal fin. 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. There its DNA was analyzed and found to be a complete match with a "pygmy Bryde's" sample obtained from the Philippines — later, however, it was discovered samples from the Philippines corresponded to B. omurai and not B. edeni. On 26 September 2000, an unidentified balaenopterid was sighted off Rarotonga. It was said to move "through the water like a sei whale, the size resembled a minke whale, the head looked like a blue whale and the chevron resembled a fin whale". Later it was suggested to possibly be an Omura's whale, but it lacks the asymmetrical coloration and upright, very hooked dorsal fin typical of species.
The species appears to have been sighted off the northwest coast of Australia on three separate occasions in 2009 and 2010. On November 2, 2009 a birder sighted three individuals – which he overestimated to be 15 to 20 m (49.2 to 65.6 ft) in length – northwest of the Bonaparte Archipelago, Western Australia at 13° 34" 54' S, 122° 52" 15' E; the same day another sighting was made of an estimated 15 m (49 ft) individual north of the Lacepede Islands, Western Australia. In October 2010, in the Timor Sea west of Darwin, Australia, sightseers encountered and photographed up to 15 individuals ranging in length from an estimated 10 to 14 m (33 to 46 ft), seeing groups of three or four animals together, as well as at least two cow-calf pairs.
Hunting and other mortality[edit source | edit]
Of the eight individuals taken by Japanese scientific whaling in the 1970s, six were processed aboard the factory ship Tonan Maru No. 2 in the Solomon Sea on 24 October 1976 and two were processed aboard the factory ship Nissin Maru No. 3 near the Cocos Islands in November 1978. Of the skull specimens examined by scientists that had been collected from "Bryde's whales" taken by artisanal whalers from the Philippines in the Bohol Sea in the 1990s, only four could be reliably identified as the former species, whereas twenty-four were confirmed to actually be from Omura's whales. This has been supported by genetic studies, which found that the "small-type" Bryde's whales from the Philippines corresponded to Omura's whale. Two individuals were also recently[when?] incidentally caught in set nets in Japan.
Conservation[edit source | edit]
The Omura's whale is listed on Appendix II  of the Convention on the Conservation of Migratory Species of Wild Animals (CMS). 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.
See also[edit source | edit]
References[edit source | edit]
- "Balaenoptera omurai". Retrieved 2012-01-17.
- Jefferson, Thomas, Marc A. Webber, and Robert L. Pitman (2008). Marine Mammals of the World: A Comprehensive Guide to their Identification. London: Academic. ISBN 9780123838537. OCLC 272382231.
- Wada, S.; Oishi, M.; Yamada, T.K. (2003). "A newly discovered species of living baleen whale". Nature 426: 278–281. OCLC 110553472.
- Sasaki, T.; Nikaido, M.; Wada, S.; Yamada, T.K.; Cao, Y.; Hasegawa, M.; Okada, N. (2006). "Balaenoptera omurai is a newly discovered baleen whale that represents an ancient evolutionary lineage". Molecular Phylogenetics and Evolution 41 (1): 40–52. doi:10.1016/j.ympev.2006.03.032. PMID 16843687.
- Balaenoptera edeni Wilson, D. E.; Reeder, D. M., eds. (2005). Mammal Species of the World (3rd ed.). Johns Hopkins University Press. ISBN 978-0-8018-8221-0. OCLC 62265494.
- "Balaenoptera omura Wada, Oishi, and Yamada, 2003". Integrated Taxonomic Information System.
- Ohsumi, S. 1978. "Provisional report on Bryde's whales caught under special permit in the Southern Hemisphere". Reports of the International Whaling Commission 28: 281-288.
- Hashimoto, Yuko and Michael D. O'Neill. Japanese Scientists Identify New Species of Whale (Applied Biosystems, BioBeat Online Magazine, 7 July 2004).
- Yoshida, H. and Kato, H. 1999. "Phylogenetic relationships of Bryde's whales in the western North Pacific and adjacent waters inferred from mitochondrial DNA sequences". Marine Mammal Science 15 (4): 1269-1286.
- Horwood, Joseph. (1990). Biology and exploitation of the minke whale. CRC Press. ISBN 0-8493-6069-2, ISBN 978-0-8493-6069-5
- Yamada, T. K., L.-S. Chou, S. Chantrapornsyl, K. Adulyanukosol, S. K. Chakravarti, M. Oishi, S. Wada, C.-J. Yao, T. Kakuda, Y. Tajima, K. Arai, A. Umetani & N. Kurihara, 2006. "Middle sized balaenopterid whale specimens (Cetacea: Balaenopteridae) preserved at several institutions in Taiwan, Thailand, and India". Memoirs of the National Science Museum, Tokyo, 44: 1–10.
- Kahn, B. 2001. "Komodo National Park Cetacean Surveys: April 2001 and 1999-2001 survey synopsis". Presented working paper CMS/SEAMAMSII/24. United Nations Environment Programme – Convention on the Conservation of Migratory Species of Wild Animals (UNEP/CMS) Second International Conference on the Marine Mammals of Southeast Asia. July 22-23, 2002. Demaguette, Philippines. 39pp.
- Ponnampalam, L. S. "Opportunistic observations on the distribution of cetaceans in the Malaysian South China, Sulu and Sulawesi Seas and an updated checklist of marine mammals in Malaysia". The Raffles Bulletin of Zoology (February 2012), 60 (1): 221-231.
- Yang, G., Liu, H., Zhou K., Y. J. Guo-Qing (2002). "Identification of a Balaenoptera edeni specimen by using mitochondrial DNA sequences". Chinese Journal of Zoology, 4, 009.
- Wang, H. G., Fan, Z. Y., Shen, H., & Peng, Y. J. (2006). "Description of a new record species of whales from Chinese coastal waters". Fisheries Science, 25(2), 85-87.
- Bannister, J. L. 2008. Great Whales. Collingwood, Vic: CSIRO Pub.
- Balaenoptera omurai, M21245, South Australian Museum Mammalogy Collection, Atlas of Living Australia
- "Extraordinarily Rare Whale Sighting – Omura’s Whale (Balaenoptera omurai)". Marine Education and Research Society. November 2012. Retrieved May 2013.
- Unidentified whale sighted 26 September, 2000, off the coast of Rarotonga, Cook Islands
- Papasula[dead link]
- "Omura's Whale (Photos from 2009)". Rohan Clarke. Retrieved May 2013.
- "Is this a new 'Great Whale'?". Simon Mustoe. 2010. Retrieved May 2013.
- Ohsumi, S. 1980. "Population study of the Bryde's whale in the Southern Hemisphere under scientific permit in the three seasons, 1976/77 - 1978/79". Reports of the International Whaling Commission 30: 319-331.
- Yamada, T. K., T. Kakuda & Y. Tajima, 2008. "Middle sized balaenopterid whale specimens in the Philippines and Indonesia". Memoirs of the National Science Museum, Tokyo, 45: 75–83.
- Yamada, T. K. 2008. Omura's whale (Balaenoptera omurai), pp. 799–801. In Perrin, W.F.P., B. Würsig, and J. G. M. Thewissen, eds., Encyclopedia of Marine Mammals, 2nd ed. Academic Press, San Diego, 1315 pp.
- "Appendix II" of the Convention on the Conservation of Migratory Species of Wild Animals (CMS). As amended by the Conference of the Parties in 1985, 1988, 1991, 1994, 1997, 1999, 2002, 2005 and 2008. Effective: 5th March 2009.
- Official webpage of the Memorandum of Understanding for the Conservation of Cetaceans and Their Habitats in the Pacific Islands Region