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Description |
Geographic Range [top]
Range Description:
The range of Omura’s Whale is poorly known because very few specimens have been confirmed to date. The type specimen was a stranded individual collected near Oyama in the southern Sea of Japan in 1998 (Wada et al. 2003). Confirmed specimens and suspected sightings recorded to date are listed by Cerchio et al. (2017b) and summarized here.
The only genetically confirmed population of living Omuras Whales to date occurs off northwestern Madagascar (Cerchio et al. 2015), on the shallow continental shelf, mainly in the 10-25 m depth range. Sightings of 44 groups including four mother-calf pairs, and a re-sighting of an individual the following year, suggest a resident breeding population. Feeding was also observed. Photographs of living whales taken off New Caledonia appear to show Omuras Whales. There have also been suspected live sightings off eastern Australia.
Stranded, caught, and museum specimens have been confirmed genetically or morphologically from Japan, China (including Hong Kong and Taiwan), throughout southeast Asia (Thailand, Vietnam, Malaysia, Philippines and Indonesia), Solomon Islands, South Australia, Western Australia, Cocos Islands, Sri Lanka (de Vos 2017), the Persian Gulf (Ranjbar et al. 2016), and the Red Sea (Egypt). In the Atlantic, there has been one confirmed stranding in northeastern Brazil (Cypriano-Souza et al. 2017) and one in Mauritania (Jung et al. 2016). The latter appeared to be a neonate, which suggests a breeding population rather than a vagrant.
Eight specimens taken under scientific permit in the 1970s, identified at the time as Bryde’s Whales, were subsequently re-identified genetically from archived tissue samples as Omura’s Whales (Wada et al. 2003, Sasaki et al. 2006). Six of the Omuras Whale specimens were taken in deep water in the Solomon Sea in 1976, and reported as unusually small Bryde’s Whales (Ohsumi 1978). Two specimens were taken in deep water near the Cocos (Keeling) Islands in 1978, and reported as ordinary Bryde’s Whales, which were also taken in the same area (Ohsumi 1980).
Omura’s Whales may have been caught elsewhere without being recognized. Bannister (1964) reported eight “Brydes” Whales taken off Western Australia during 1958-63 that “do not match the published descriptions of specimens from other parts of the world” and their small size (11.2-11.7 m for mature animals) would be consistent with either Omura’s Whales or a smaller form of Brydes Whale.
The recent recording of acoustic calls of this species (Cerchio et al. 2017a) may help in the future to confirm its presence in areas where visual confusion with other balaenopterids would be likely. Acoustic signatures similar to those recorded from Omuras Whales off Madagascar have been detected off Diego Garcia and northwestern Australia.
Omuras Whales are at least partially sympatric with Brydes Whales, and occur both in deep water and in inshore areas. All records to date have been between 35°N and 35°S. It is unclear whether Omuras Whale is mainly a coastal species or a substantial oceanic population exists.
Countries occurrence:
Native:
Australia; Brazil; China; Cocos (Keeling) Islands; Egypt; Indonesia; Iran, Islamic Republic of; Japan; Madagascar; Malaysia; Mauritania; New Caledonia; Philippines; Solomon Islands; Sri Lanka; Thailand; Viet Nam
FAO Marine Fishing Areas:
Native:
Indian Ocean – eastern; Pacific – northwest; Pacific – western central
Additional data:
Range Map: Click here to open the map viewer and explore range.
Population [top]
Population:
The only population estimate that may relate to Omura’s Whales is an estimate of 1,800 from sightings data for the Solomon Islands “Bryde’s Whale” stock (Ohsumi 1980). However, given the small sample size, the use of methods that are no longer accepted, and the likelihood that some of the animals seen were either B. edeni edeni or B. e. brydei, no reliance can be placed on this figure. The global population size is unknown.
Based on genetic identifications (LeDuc and Dizon 2002), it can be inferred that Omura’s Whales have been taken by artisanal whalers in the Philippines (Dolar et al. 1994, Perrin et al. 1996), but more analysis is needed to determine what proportion of the “Bryde’s Whales” taken there were in fact Omura’s Whales. Because the range of the species is poorly known and the species has only recently been described, it may have been subject to catching by commercial whaling operations in the past, especially in southwestern Japan, but to an unknown extent.
Current Population Trend: Unknown
Additional data:
? Continuing decline of mature individuals: Unknown
? Extreme fluctuations: Unknown ? Population severely fragmented: Unknown
Habitat and Ecology [top]
Habitat and Ecology:
The diet, habitat, and ecology of Omura’s Whales are not well known. The stomach contents of five of seven Omura’s Whales taken in the Coral Sea (Solomon Sea) in 1976 under a scientific permit by Japan contained only euphausiids, Euphausia diomedae (Kawamura 1977, 1980). The stomach of a 7 m long female from the Seto Inland Sea contained both crustacean and fish remains (Cericho and Yamada 2017). Omura’s Whales off northwestern Madagascar were observed lunge feeding in the upper water column (Cerchio et al. 2015). Omura’s Whales occur in both deep and shallow water, and are at least partly sympatric with Bryde’s Whales.
Systems: Marine
Continuing decline in area, extent and/or quality of habitat: Unknown
Movement patterns: Unknown
Use and Trade [top]
Use and Trade:
Omuras Whales were harvested by artisanal whalers in the Philippines and possibly also in Indonesia. Omura’s Whales may also have been taken by commercial whalers in the past off southwestern Japan, Republic of Korea, China, and the Philippines (but identified as Brydes Whales).
Threats [top]
Major Threat(s):
Omuras Whale is no longer hunted, but small catches by artisanal whalers could still be occurring in Indonesia (Lamakera, Solor). Given its occurrence in shallow waters, it may be subject to entanglement or bycatch and vessel strikes. Three Omuras Whales have been recorded caught in set nets in Japan (Cerchio and Yamada 2017). Because the species has only recently been described and its range is poorly known, it is not yet possible to assess the level of threats.
Conservation Actions [top]
Conservation Actions: No specific conservation measures have been taken, but Omuras Whales have been incidental beneficiaries of the area restrictions on pelagic (offshore) whaling that were originally designed to protect the low-latitude winter breeding grounds of other baleen whale species (Tønnessen and Johnsen 1982). The species is on Appendix I of the Convention on International Trade in Endangered Species.
Citation: Cooke, J.G. & Brownell Jr., R.L. 2018. Balaenoptera omurai. The IUCN Red List of Threatened Species 2018: e.T136623A50386113. http://dx.doi.org/10.2305/IUCN.UK.2018-2.RLTS.T136623A50386113.en. Downloaded on 07 January 2019.
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