Dwarf Minke Whale

Balaenoptera acutorostrata

Dwarf Minke WhaleClass: Mammalia
Order: Cetacea
SubOrder: Mysticeti
Family: Balaenopteridae
Genus: Balaenoptera
Species: Acutorostrata

Physical Description
The dwarf minke whale has the most complex colour pattern of any baleen whale. Some features are found only in dwarf minke whales: (1) Dark band of colour on the neck, between the end of the mouth and the flipper, which continues as a dark throat patch extending on each side well down onto the throat. These dark throat patches are seen very clearly if the whale turns to expose the underside of the body. (2) Flipper colour, which is dark at the tip but completely white at the base of the flipper. (3) Colour of the shoulder region, which is completely white where the flipper joins the body and extends as a white shoulder patch around much of the flipper. (4) A light grey, roughly triangular thorax patch, which extends up each side of the animal from just above the white shoulder patch and flipper.

Length & Weight
Minke whales grow to be about 7 – 9 metres long, weighing about 5 – 7 tonne. Females are about 0.5 metres longer than males, as with all baleen whales. The largest minke whale was about 10.5 metres long weighing 8.5 tonne. Minke whales have a snout that is distinctively triangular, narrow, and pointed (hence its nicknames “sharp-headed finner” and “little piked whale”).

Mating and Breeding
The life span of dwarf minke whales is unknown. Other minke whales live for 50 to 60 years. The life span is calculated by counting the number of layers in a waxy plug near the eardrum. The layers are thought to be deposited each year. Dwarf minke whales reach sexual maturity at about 6.5 m long when they are probably about 6 – 8 years old. Based on what is known about other minke whales, dwarf minke whales probably have one calf each year. It is about 2 m long at birth. Minke whales suckle their young with a rich milk that contains about 30% fat (human milk has about 4% fat). Calves are probably weaned after 5 – 6 months.

Feeding
The great whales, such as blue and humpback, undertake regular migrations between higher latitudes (where they feed) and lower latitudes (where calves are nursed). During their stay in subtropical and tropical waters, they feed little and apparently subsist on energy reserves laid down at high latitudes. It is not known whether migration of dwarf minke whales follows this pattern. They are known from sub Antarctic waters during December to March and whales taken there have been feeding on open ocean lantern fishes and krill. Dwarf minke whales have never been seen feeding on the northern Great Barrier Reef. With their much smaller size, dwarf minke whales cannot lay down energy reserves to the extent of their larger relatives. It is possible that while they are in the tropics, they feed opportunistically in the open ocean.

Distribution and Migration
Dwarf minke whales are found in the waters of South Africa, Australia, New Zealand, New Caledonia, Vanuatu and the east coast of South America. They have been recorded from all states of Australia (except Tasmania) but not yet from the Northern Territory. Between December and March, most sightings of the dwarf minke whales are in sub Antarctic waters (58° 60°S) to the south of Australia and New Zealand. They are occasionally found close to the ice edge (at 65°S). Between March and October, dwarf minke whales are seen in the northern Great Barrier Reef.

Natural History
Minkes tend to be solitary animals, though sometimes they are seen traveling in pairs or in small groups of 4 to 6. In the polar regions, where food is concentrated, it is common to find larger aggregations of feeding animals in an area. They appear to segregate by age and sex more than do the other baleen whales. Females remain close to shore, while males are farther out to sea. Some minkes migrate long distances, but others may move only within a restricted area. In some regions, minkes may be found year-round. Their life span is believed to be about 50 years. Killer whales are known to prey on minkes, especially in parts of the southern hemisphere.

Status
Only in recent decades have minke whales been taken by whalers to any extent; they were thought to be too small to be a worthwhile catch. But as the larger whale species became depleted, the whalers began to hunt the minke as a replacement. Since the late 1960s and 1970s, Japan, Russia (which has now ceased whaling), and (to some extent) Norway have focused their whaling efforts on minke whales. Scientists are still examining the populations of minke whales in areas where they are harvested, and have discovered that the largest numbers of minkes are found in the southern hemisphere. It is thought that minke populations have increased as they started to eat the food that was previously eaten by the now-depleted large whale species. The present population worldwide is believed to be over a millions animals.

Acknowledgements
Australian Museum; American Cetacean Society; National Geographic Society; Department of the Environment, Water, Heritage and the Arts