Balaenoptera omurai

Geographic Range

While the full extent of their range is still poorly studied, present findings indicate that Omura's whales ( Balaenoptera omurai ) live throughout the Indian Ocean and the western Pacific Ocean. Distribution within the Indian Ocean appears to be cosmopolitan, with the species having been recorded in the Persian Gulf, Japan, western Australia, Sri Lanka, the Cocos Islands, as well as the northwest coast of Madagascar. Records of their distribution in the Western Pacific Ocean are largely centered around the South China Sea and Sea of Japan, but the full extent of their presence in pelagic Western Pacific waters are undocumented.

Despite the vast majority of collected data indicating an Indo-Pacific range, two independent instances of stranded juveniles have been recorded from Mauritania and northeastern Brazil. This provides evidence that there is a potential self-sustaining population of Omura's whales within the Atlantic Ocean. There is little information regarding this potential population.

• Biogeographic Regions
• palearctic palearctic
  • native native
• oriental oriental
  • native native
• ethiopian ethiopian
  • native native
• neotropical neotropical
  • native native
• australian australian
  • native native
• indian ocean
  • native native
• atlantic ocean atlantic ocean
  • native native
• pacific ocean pacific ocean
  • native native

Habitat

Beyond inferences on habitat preference from other balaenopterid whales (especially the species’ close relative, Balaenoptera brydei ), the sole in-depth study of Balaenoptera omurai specimens in a natural habitat setting was conducted in waters off the northwestern coast of Madagascar. During the timeframe wherein the whales were observed, they were noted to primarily inhabit the shallow continental shelf waters off the Ampasindava Peninsula (range of 4 – 202 meters; mean depth of 31 meters). No specimens were recorded in shallow coastal/bay or deep-water regions, suggesting deliberate avoidance of these areas; the reason for this preference is unknown. Further data on the species’ habitat preferences, particularly for different geographical regions, remains absent.

• Habitat Regions
• saltwater or marine saltwater or marine

• Aquatic Biomes
• pelagic pelagic
• coastal coastal

Physical Description

Omura's whales are among the smallest of the balaenopterid whales, with adult length in holotype and paratype specimens ranging from 10.3 to 11.5 meters in females and 9.6 to 10 meters in males. In terms of overall physical structure, Omura's whales are similar in physical appearance to other balaenopterid whales, particularly the fin whale ( Balaenoptera physalus ) and Bryde’s whale ( Balaenoptera brydei ). It is distinguished from these species by its number of ventral grooves (80-90 in B. omurai, in contrast to the 42-54 of B. brydei ), and from all other balaenopterids by its low number of baleen plates. Baleen plates are keratinous structures on the upper jaw of mysticetes that are used to filter zooplankton from water; B. omurai possesses approximately 200 per maxilla, the lowest of any balaenopterid. The species exhibits noticeable asymmetrical coloration, possessing significant dark pigmentation of the left half of the throat in contrast to an otherwise white ventral coloration; this trait is shared with B. physalus . Asymmetrical coloration of baleen plates is also present, with the left side of the jaw lacking the presence of entirely white baleen plates at its anterior (as is the case with the right side of the jaw).

• Sexual Dimorphism
• sexes alike
• female larger

Reproduction

Multi-year photographic records of a female specimen from the Madagascan population, identified by distinctive markings, indicate that the Madagascar site may serve as both a residential region and breeding ground for that population. Beyond this, the reproductive behaviors and mating patterns of Balaenoptera omurai are presently unknown. Further research is needed to determine the species-unique reproductive activity systems of Omura's whales.

At present, only limited knowledge exists about the reproductive biology of Omura's whales. The species is believed to attain sexual maturity at approximately 9.0 meters in length in males and females; this is in contrast to the related Balaenoptera brydei , which attains sexual maturity at approximately 11.2 meters in males and 11.7 meters in females. One female specimen, aged approximately 18 years, was sexually mature and had undergone three prior ovulation events in spite of being physically immature (indicated by incomplete fusion at the 6th thoracic vertebra), indicating that sexual maturity is reached substantially prior to completion of physical growth.

Analysis of calves observed in the company of their mothers in coastal Madagascan waters indicates an irregular, likely protracted calving season lasting multiple months. Neonatal specimens measuring under three meters in length as well as well-developed sub-yearling specimens have been observed in August at the Madagascar population, with other reports from the same locale recording multiple post-neonatal young (approximately three meters in length and with highly curved dorsal fins, but lacking neonatal skin folds) in November.

• Key Reproductive Features
• viviparous viviparous

As in other mysticete whales, Balaenoptera omurai seems to exhibit strong maternal offspring care habits. All living, immature specimens thus far observed have been accompanied by their mothers; the age at which offspring are weaned and become independent, and other aspects of parent/calf interaction or care, remain unknown and requires further research to determine.

• Parental Investment
• female parental care female parental care
• pre-weaning/fledging
  • provisioning
    • female
  • protecting
    • female
• pre-independence
  • protecting
    • female

Lifespan/Longevity

No data has been recorded measuring the longevity of Omura's whales. The oldest specimen currently recorded, as measured by the number of growth rings in the specimen's ear plug (generally accumulated at a rate of one per year) measured approximately 38 years of age; the upper limits of the species' lifespan, as well as the average longevity of the species, remain as of yet unknown.

Behavior

Omura's whales specimens have been observed to often group into small, loose aggregations of up to six individuals. No sightings have reported more than two Omura's whales within obvious optical distance of one another; several hundred meters of open water generally separate any members of a given group. This may indicate group organization based on infrasound communication rather than sight. Entirely solitary individuals have also been observed in a sizable proportion of sighting events. Group hierarchy patterns are currently unknown for the species, though they may be similar to those of related balaenopterid whales.

• Key Behaviors
• natatorial natatorial
• nomadic nomadic
• migratory migratory
• sedentary sedentary
• solitary solitary
• social social

Home Range

No figures exist for territoriality or range size in Balaenoptera omurai . Long-term observation of populations of Omura's whales in Madagascan waters indicates that the species may form permanent sedentary habitation sites in shallow waters. Further such potential sites and the extent of such territories, however, have yet to be assessed or fully discerned. (Cerchio, et al., 2015)

Communication and Perception

Sensory perception in mysticetes, including Omura's whales, takes place primarily by way of their advanced auditory systems, as well as taste-based chemoreception via the vomeronasal organ, used often to locate other whales by way of pheremonal communication. Baleen whales have well-functioning sideways-placed eyes, though they are small, and generally unable to see well in low-light conditions far below the photic zone. Taste and smell are underdeveloped and relatively vestigial in baleen whales.

Like other mysticete whales, Omura's whales appear to communicate extensively by way of advanced vocalizations. Calls made by the species range in frequency from approximately 10-52 Hz, being generally similar in format and often featuring a "doublet" of strong pulses towards the end of a single call; these calls are generally rhythmic and repetitive, and have been observed to continue without pause for several hours. Auditory analysis of multiple calls indicates communication patterns between multiple different individuals forming a chorus of their calls.

• Communication Channels
• acoustic acoustic
• chemical chemical

• Other Communication Modes
• choruses choruses
• pheromones pheromones

• Perception Channels
• visual visual
• acoustic acoustic
• vibrations vibrations

Food Habits

Like other mysticete whales, Omura's whales are filter-feeders. The technique employed by baleen whales revolves around the intake of large masses of water orally, then the filtering of zooplankton and organic particles from said water by pushing the water (via the tongue) through a series of filamentous, keratinous baleen plates lining the sides of the whale's upper jaw. As with other rorquals, Omura's whales are lunge feeders, using selective bursts of speed with its jaws agape to intake large volumes of prey-rich water with a single lunge. The species appears to feed exclusively on zooplankton within tropical regions, completely avoiding schools of small fish when present, though sampling of the waters targeted by the whales has not shown the presence of copepods or other common prey crustaceans; the preferred prey makeup of Balaenoptera omurai is thus currently unknown, as is whether said prey preference is consistent or variable with different localities.

• Primary Diet
• carnivore carnivore
  • eats non-insect arthropods
• planktivore planktivore

• Animal Foods
• aquatic crustaceans
• other marine invertebrates
• zooplankton zooplankton

• Foraging Behavior
• filter-feeding filter-feeding

Predation

No known record of predation upon specimens of Balaenoptera omurai has been observed at present.

Ecosystem Roles

As a megafaunal planktonivore, Omura's whales occupy a high position within the trophic profile of their habitat. In terms of nutrient cycling, Omura's whales and other baleen whales distribute organic material obtained from their zooplankton prey throughout oceanic waters to allow for the growth of phytoplankton and the continuation of the plankton cycle. Baleen whales also serve as hosts for a large variety of endoparasitic and ectoparasitic invertebrates, including nematodes, tapeworms, amphipod whale lice, and sessile parasitic copepods.

Economic Importance for Humans: Positive

Baleen whales such as Balaenoptera omurai are among the most iconic extant megafauna on Earth, and are thus a potent source of attraction for the nascent industry of ecotourism. Whale-watching is a common and well-known example of recreational ecotourism, and serves both as a means to increase public awareness of whales and marine ecosystems and often to help fund their conservation.

• Positive Impacts
• ecotourism ecotourism

Economic Importance for Humans: Negative

There are no known adverse effects of Balaenoptera omurai on humans.

Conservation Status

In light of the extreme lack of quantifiable and qualitative data available regarding population dynamics, range, ecological dynamics, and other important aspects of its lifestyle and safety as a species, Omura's whales are currently listed as Data Deficient by the IUCN Red List. The species is also listed alongside most other species and populations of cetaceans on CITES Appendix I.

Other Comments

Balaenoptera omurai is closely related to the Bryde's whale species complex, consisting of the Balaenoptera brydei , Balaenoptera edeni , and Balaenoptera borealis lineages. The evolutionary and genetic history of these species remains in a state of flux, with B. omurai having only been identified as distinct in 2003; because of this prior misclassification, a large amount of data stands to exist that was originally collected and recorded as scientific data for B. brydei . (Sasaki, et al., 2006)

Additional Links

Encyclopedia of Life

Contributors

Casey Shaw (author), Colorado State University, Kate Gloeckner (editor), Colorado State University, Genevieve Barnett (editor), Colorado State University.

References

Cerchio, S., B. Andrianantenaina, A. Lindsay, M. Rekdahl, N. Andrianarivelo, T. Rasoloarijao. 2015. Omura’s whales ( Balaenoptera omurai ) off northwest Madagascar: ecology, behaviour and conservation needs. Royal Society Open Science , 2: 10. Accessed February 12, 2019 at https://royalsocietypublishing.org/doi/10.1098/rsos.150301 .

Cooke, J., R. Brownell. 2018. "Balaenoptera omurai" (On-line). IUCN Red List. Accessed December 21, 2019 at https://www.iucnredlist.org/species/136623/144790120 .

Cypriano‐Souza, A., A. Meirelles, V. Carvalho, S. Bonatto. 2016. Rare or cryptic? The first report of an Omura's whale (Balaenoptera omurai) in the South Atlantic Ocean. Marine Mammal Science , 33: 80-95.

Ranjbar, S., M. Dakhteh, K. Waerebeek. 2016. Omura's whale (Balaenoptera omurai ) stranding on Qeshm Island, Iran: further evidence for a wide (sub)tropical distribution, including the Persian Gulf. Journal of Marine Biology & Oceanography , 5: 3.

Sasaki, T., M. Nikaido, S. Wada, T. Yamada, Y. Cao, M. Hasegawa, O. Norihiro. 2006. Balaenoptera omurai is a newly discovered baleen whale that represents an ancient evolutionary lineage. Molecular Phylogenetics and Evolution , 41: 40-52.

Vos, A. 2017. First record of Omura’s whale, Balaenoptera omurai, in Sri Lankan waters. Marine Biodiversity Records , 10: 18.

Wada, S., M. Oishi, T. Yamada. 2003. A newly discovered species of living baleen whale. Nature , 426: 278-281. Accessed February 12, 2019 at https://www.nature.com/articles/nature02103 .

2017. "Appendices" (On-line). CITES. Accessed February 24, 2019 at https://www.cites.org/eng/app/appendices.php .