FACT FILE
The Blue Whale
FAMILY: Balaenopteridae GENUS/SPECIES/SUBSPECIES: Balaenoptera musculus brevicauda
Blue whales are giant ocean wanderers of both Hemispheres, although 96% of all blue whales killed by whalers were in the Southern Hemisphere. They are adapted for rapid, long-range movements between feeding areas that may be hundreds of kilometres apart, or feeding and breeding areas thousands of kilometres apart.
ABOVE: Pygmy Blue Whale (Balaenoptera musculus brevicauda) cruising off Bonney coastline, Victoria (Photo BWS)
They are the largest animal ever to live on earth!
The maximum length recorded for a female Antarctic blue whale (the sub-species of blue whale that feeds in Antarctic waters), was 33.5m which is as long as a Boeing 737. The maximum adult weight recorded is 190 tonnes, equivalent to approx. 38 African elephants! The pygmy blue whale, the sub-species commonly seen in Victorian waters, reaches 24m in length and approximately 150 tonnes.
Blue whales may live for 100 years or more. Newborn blues weigh between 2.5 and 4 tonnes and increase in size by 30 times in their first year of life. They belong to the rorqual (groove-throated) group of baleen whales (which also includes Minke, Bryde’s, Omura’s, Humpback, Sei and Fin Whales).
Blue whales feed by gulping large quantities of krill. Recent estimates suggest that a blue whale weighing around 80 tons needs about 10-15 tonnes of food a day, which equates to millions of krill (in our region, Nyctiphanes australis). They are capable of diving up to 500m in depth when feeding, but usually feed in depths between 40-200m in the Bonney Upwelling. They are ‘gulp feeders’ which can engulf their own volume of seawater and krill into their extendable throat, straining out the krill through the fringe of jet black baleen plates hanging from their upper jaws.
As specialist krill feeders, worldwide blue whales are usually found in upwelling or frontal zones with high productivity, such as the Great Southern Australian Coastal Upwelling System (GSACUS). Even in these productive areas, krill are patchy in their distribution. Blue whales search vast areas in search of krill ‘hot spots’ , and upon finding them, they will remain to feed until this resource is exhausted. It is likely that they remember areas where they have had previous feeding success, and are sensitive to subtle temperature changes which indicate fronts and upwellings.
We now think that if blue whales find a food resource that is far greater than the needs of an individual or small group, they will use their low-frequency calls to ‘call in’ their companions. Researchers call this ‘reciprocal altruism’, where favours will be returned.
Blue whales make the loudest sound of any animal (as low as 9Hz), with their low-frequency calls being detected more than 1000km away under ideal conditions.
Distinguishing Features
Colour: Silver-grey to grey-black with mottled pigment patterns used to identify individuals. Appears pale blue or aqua when submerged.
Blow pattern: Blow is powerful, tall and straight, in calm conditions may exceed 20m and be heard 3 to 5km away.
Mating season: June – August
Calving season: June – August
No. of Calves: 1
Calving interval: 2 – 3 years
For more information about blue whales, see the Commonwealth Government’s blue whale species profile.
ABOVE LEFT: Blowhole splashguard protects blowholes from water (Photo BWS). ABOVE RIGHT: Blue whale with distended throat pleats following a feeding lunge (Photo BWS)
ABOVE: Blue whale with distended throat pleats following a feeding event (photo BWS)
Blue whales are very large, slender and streamlined. The single prominent rostral ridge on top of the head leads back to a prominent blowhole with a splashguard – seen in photo below left.
Their small dorsal fin, set well back on the body, enhances the impression of a very long back. Their grey skin is mottled with individually unique pigment patterns, but they appear aqua-blue when seen underwater. On their underside, longitudinal pleats allow the throat to expand massively as they engulf huge mouthfuls of krill – seen in photo below right.
Distribution and Habitat
Antarctic Blue Whales Baleanoptera musculus intermedia breed and calve in warm water (north of latitude 20° S) during the southern hemisphere winter. They then migrate to cold Antarctic waters (60 – 77° S) during the southern hemisphere summer to feed on krill.
Pygmy Blue Whales B.m. brevicauda occur only in the southern hemisphere. In summer they are generally found north of latitude 55°S, and during winter migrate north to Indonesian waters. They enter Victorian and South Australian waters during November-May to feed on krill in the nutrient-rich waters of the GSACUS. Historical whaling and sightings data show that pygmy blue whales spread out to feed through an immense area of the Southern Ocean, including the productive Sub-Tropical Convergence not far to the south of Australia and extending across the southern Indian Ocean.
Conservation Status
The devastating historical impacts of whaling, coupled with contemporary threats such as climate variability and change, ocean acidification, noise interference from marine industry and shipping, habitat modification, vessel disturbance through collisions and whale watching, and over-harvesting of prey species (krill) have led to the same conservation status for blue whales in both the Northern and Southern Hemispheres:
ENDANGERED!
The Antarctic blue whale subspecies remains severely depleted from historic whaling and its numbers are recovering slowly. For the pygmy blue whale there is uncertainty in the numbers pre-exploitation, and their current numbers are not known. At least 363,648 blue whales were killed by whalers in the Southern Hemisphere during the 20th century (96%), while only 15,537 were killed in the Northern Hemisphere (4%).
References
WW2010 University of Illinois, Department of Atmospheric Sciences. Upwelling: the transport of deeper water to shallow levels.
1998, Geerts, B., Ocean upwelling and phytoplankton. The SeaWiFs Project.
Middleton, J.F., C. Arthur, P. Van Ruth, T.M. Ward, J. McLean, M. Maltrud, P.Gill, A. Levings and S. Middleton. 2007. El Niño effects and upwelling off South Australia. Journal of Physical Oceanography 37(10): 2458-2477.
Gill, P.C., R. Pirzl, M.G. Morrice and K. Lawton. 2015. Cetacean diversity of the continental shelf and slope off southern Australia. Journal of Wildlife Management 79(4):672–681; DOI: 10.1002/jwmg.867
Rocha, R.C., P.J. Clapham & Y.V. Ivashchenko. 2014. Emptying the oceans: a summary of Industrial whaling catches in the 20th century. Marine Fisheries Review 76(4): 37-48. http://doi:dx.doi.org/10.7755/MFR.76.4.3
Wikipedia
https://en.wikipedia.org/wiki/Great_South_Australian_Coastal_Upwelling_System