#ThreatenedSpecies of the Week: Balaenoptera musculus (Blue Whale)

The Blue Whale is listed as Endangered under the Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act) and as Specially Protected Fauna under the Wildlife Conservation Act 1950.

The main threats to the blue whale include whaling, climate variability and change, noise interference and vessel disturbance.

Blue whale © Mike Johnson / Australian Antarctic Division.

The blue whale (Balaenoptera musculus) has four subspecies, two of which occur within Australian waters , these include: Antarctic blue whale (B. m. intermedia) or ‘true’ blue whale and pygmy blue whale (B. m. brevicauda). Blue whale sightings in Australian waters are widespread, and it is likely that the whales occur around the continent at various times of the year. However, much of the Australian continental shelf and coastal waters have no particular significance to the whales and are used only for migration and opportunistic feeding. The only known areas of significance to the blue whale are feeding areas around the southern continental shelf, notably the Perth Canyon, in Western Australia, and the Bonney Upwelling and adjacent upwelling areas of South Australia and Victoria

Both the Antarctic blue whale and pygmy blue whale have common phenotypic traits such as grey skin with mottled patterns, which enables identification of individuals. When submerged, the blue whale appears to be a luminous pale blue or aqua. They have a pronounced ‘splashguard’ in front of their blowholes, with a single pronounced longitudinal ridge leading forward on the rostrum. Their blow is tall and powerful (approximately 10 m). They have a long, smooth back with a small, variably-shaped dorsal fin set towards the tail.

Differences between the pygmy blue whale and the Antarctic blue whale include:

  • Morphology: the Antarctic blue whale is the largest of the two subspecies growing to maximum lengths of over 30 m; in comparison, the pygmy blue whale is recorded growing to 24.1 m.
  • Vocalisations/acoustic calls: both subspecies produce distinctive acoustic calls that can be used to identify each species as well as provide insight into geographic and seasonal distributions.
  • Genetics: both subspecies are genetically distinct, however diagnostic genetic markers are not available. The Antarctic and pygmy blue whale have been known to hybridise.
  • Austral summer distribution: the pygmy blue whale is typically found in more northern areas (north of 54° S) at lower latitudes, throughout the Indian Ocean, whereas the Antarctic blue whale is usually found further south of Australia (60° S), circumpolar wide

Blue whale habitat is variable between the two subspecies found in Australian waters. The Antarctic blue whale tends to remain at higher latitudes and migrate to lower latitudes for feeding, breeding and calving during the Australian summer, whilst some remain within the Antarctic waters year-round. In comparison, the pygmy blue whale habitat is more diverse, expanding throughout the Indian Ocean, with individuals moving between Australia and the warmer waters of Indonesia

Pygmy blue whale distribution around Australia (Department of the Environment 2015)
Pygmy blue whale distribution around Australia (Department of the Environment 2015)

Longevity is thought to be at least 80-90 years or longer. Rates of natural mortality are unknown but the blue whale is subject to predation by the killer whale (Orcinus orca) and possibly by a range of shark species, as well as smaller parasites, infection and disease.

 The mating system of the blue whale is unknown, although like other baleen whales they may mate with multiple partners. Age of sexual maturity for females is around 10 years. Age of first reproduction is estimated at 11 years for both subspecies.

Information Source: Government of Australia, Department of Environment and Department of Parks and Wildlife Western Australia


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