Dwarf Minke Whale Biology

BEHAVIOUR

Dwarf minke whales are highly manoeuvrable, acrobatic whales which in many ways behave more like dolphins than other baleen whales.

Surfacing behaviour

Surfacing is usually inconspicuous. The snout appears first, at an angle, then the whale levels off in a slow, continuous roll which exposes the dorsal fin and finally the tail stock. The whale may appear to simply sink beneath the water, or the tail stock may be more strongly arched into a high roll.

Unlike larger whales, dwarf minke whales rarely have a visible spout or blow. When seen, it is usually an indistinct cloud rising to about a metre above the head and it dissipates almost immediately. Occasionally the whale will exhale before it reaches the surface and some water may be blown into the air.

Dwarf minke whales usually surface only once around the boat, although they occasionally take a second quick breath. Dive times can be quite variable, from about half a minute to nearly twelve minutes.

Variations in surfacing behaviour include the 'prolonged surface swim' where most of the back, from snout to fin, remains out of water as the whale swims along. The whale may take several breaths while maintaining its position at the surface.

Animals may rise vertically from the water, exposing the snout but not the eye (headrise) or much of the head, with the eye (spy-hop). In our experience, headrise is more common, but both behaviours may allow the whale to see features above the water.

Most spectacular are breaches, where the whale comes out of the water, sometimes completely. Most breaches are partial, often with the animal falling back in the water belly up. Most breaches we have seen were in the distance and it was impossible to tell if there was more than one animal. In the few breaches close to the boat where other whales were visible, it seemed to be one animal breaching. In other whales, breaching has been suggested as a way of making noise and alerting other whales to the presence of the breaching individual. This needs to be tested for minke whales.

Although most approaches of dwarf minke whales are to anchored or drifting vessels, they may for short periods keep pace with vessel travelling at up to 12 knots. We have had a whale repeatedly swim circles around the boat while it was maintaining course towards a reef at 8.5 knots.

Underwater behaviours

Underwater behaviours are diverse. One spectacular behaviour is bubble-blasting, when a cloud of bubbles is released explosively. We are examining the conditions under which this occurs; it is certainly not only directed at either swimmers or the vessel. A similar, but less frequently recorded, behaviour is the bubble trail, in which the whale releases a stream of bubbles as it continues swimming past a swimmer or vessel. More subtle behaviours include rolls with presentation of the belly or the back, prolonged swims on the side, gaping of the jaw (showing the baleen plates), apparent 'give way' behaviour between whales. We are trying to establish the significance of such actions.

Jaw gapes can extend to the most spectacular of all underwater behaviour, in which the lower jaw drops and the throat is greatly inflated by inflowing water, as when feeding. This is followed by a rapid contraction of the throat. In at least some cases, this appears to be a display directed at a swimmer but it occurs in other situations in which neither feeding nor display seems to be involved.

Disturbance

Three behaviours may be associated with disturbance. These are when the whale veers away from a swimmer, speeds-up by increasing the sweep of its tail stock (these behaviours may occur together) or when the whale dives away from snorkellers at the surface. All these behaviours have been recorded when snorkellers or scuba divers swam directly at a whale. Repeated instances of such behaviour would suggest that the whale(s) are disturbed.