Biology
Distribution
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. On the Great Barrier
Reef, dwarf minke whales have been recorded from
north of Lizard Island to the Swains Reefs. This
may reflect the distribution of vessels more
than the actual distribution of the whales.
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,
with about 80°la of sightings in June and July.
Whether this reflects the actual abundance of
the whales or only that part of the population
that is more likely to interact with vessels is
unknown.
Age 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°/Q fat (human
milk has about 4°lo fat). Calves are probably
weaned after 5 6 months; the shortest period
reported for any cetacean.
Small calves of dwarf minkes are recorded in
Australian waters from May to July. Usually,
only one or two cow and calf pairs are seen per
season in northern Great Barrier Reef waters.
This suggests either that these waters are not a
major nursing area or that cows with calves do
not regularly approach vessels there.
Gender in many toothed whales, the male is much
larger than the female or has a different body
or fin shape. Male and female dwarf minke whales
are not so easily separated. Their gender can be
determined by the shape and position of the
genital slit. in males, the slit is further
forward and obviously separated from the anus.
In females, the genital slit is close to the
anus and there are mammary slits on either side
of it.
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.
Speed and diving
Dwarf minkes are highly manoevrable and can jump
from the water like a dolphin. They can swim in
bursts at 12 knots but cannot maintain this
speed. They have been seen repeatedly circling a
vessel that was cruising at 8.5 knots.
Like all mammals, minke whales have to breathe.'
Their paired nostrils (blowholes) are on the top
of the head. Dwarf minke whales usually surface
only once with a smooth arching of the back,
then dive for periods from 0.5 12 minutes.
Toothed whales such as the bottlenose whale
Hyperoodon ampullatus and sperm whale Physeter
macrocephalus can reach depths of >. 1.5 2 km.
Most baleen whales are relatively shallow
divers, remaining in the upper 100 200 m of
water. Dwarf minke whales have been seen
swimming at 20 40 m depth and one dwarf minke
whale was recovered from a net set in 140. m of
water off the South American coast (although it
is not certain that the whale was trapped at
that depth).
