Dwarf Minke Whale Biology

ANATOMY

Minke whales are beautifully streamlined, with a sharply pointed snout and long tapering tail. The body is encased in an insulating layer (the blubber) which can also act as a food reserve and a source of water.

Head

The upper jaw is flattened, with a central ridge that runs from the tip of the snout to the blowholes; this ridge often reflects sunlight and glistens.

Blowholes

The nose is on the top of the head. There are two nostrils which are tightly closed when the whale is underwater and appear as two slits forming a forward pointing V. When the whale surfaces, it breathes out explosively. In large whales, moisture in the breath condenses to form a distinct 'spout' or 'blow', which in the distance can look like a column of water. The nostrils in whales have generally been called the 'blowholes'.

Eyes

These are relatively small and set just behind the mouth, facing sideways. Thus they probably work independently, picking up views to the left and right of the animal. There may be limited overlap of vision forward and below the animal. In addition, dwarf minke whales can swivel both eyes upwards, probably providing binocular vision above them.

Ears

These appear as tiny pits behind the eyes. The earbones, which receive sound, are buried deep within the body at the base of the skull. It is thought that baleen whales are capable of receiving low frequency (compared to our own hearing) sounds. Such low frequency sounds can travel vast distances underwater and may allow communication between distant groups of whales. They are not useful for fine scale echolocation, such as occurs in dolphins, but might allow the whales to pick up large objects (e.g. reefs).

Flippers

The flippers or side fins correspond to our hands, and contain the same bones. Flippers are used to manoeuvre. They are extended just before the whale surfaces and may act like the dive planes of submarines. As a whale rolls or spins, one flipper is extended, while the other remains close to the body.

Dorsal fin

The back or dorsal fin of the dwarf minke whale is about the same size as a bottlenose dolphin's fin but it is set further back on the body. Sometimes, when the whale is in the distance, the position of the fin is the best way to tell a dwarf minke whale from a large dolphin.

Tail flukes

The tail flukes are horizontal and the tail is swept up and down to propel the whale. The streamlined shape of the tail flukes provide the maximum forward thrust while minimising drag. The angle of the tail flukes can be varied as the tail beats up and down to provide thrust during both the downsweep and upsweep of the tail.

Throat and belly grooves

There are 55 to 75 grooves which run along the throat on to the belly to a point half way between the tip of the flippers and the dorsal fin. These grooves allow great expansion of the throat which enables whales such as the minke to engulf a very large volume of water and food (see Feeding). When the minkes are swimming normally, the throat muscles are contracted and the head shape is streamlined. The grooves are obvious only if the whale turns to expose its belly.

Genital slits

It is very difficult to tell male from female unless the whale rolls and gives a clear view of its belly. In the female, the genital slit is in front of but almost continuous with the anus and the mammary glands appear as slits on either side of the genital slit. In the male, the genital slit is in front of and distinctly separated from the anus. In both sexes, the umbilicus ('belly button') is a distinct groove in the midline just behind the belly grooves.

SIZE

Dwarf minke whales are distinctly smaller than the Antarctic minke whale. The largest dwarf minke whale measured was 7.8 m long while the Antarctic minke whale reaches at least 10.7m length. The size difference is less between dwarf minke whales and the northern hemisphere minke whales which may reach 10m but are usually 6-9m in length.

As with other baleen whales, the female dwarf minke whale is probably larger than the male. The longest female measured was 7.8m long while the longest male was 7.1m long.