Dwarf minke whales were first recognised as a distinct form in
the mid 1980s and there is still little known about them. They
attracted attention in northern Great Barrier Reef waters
because they regularly approached close to boats and swimmers.
While many countries have
banned programs where visitors can swim with whales, a swim with
whales industry has developed in waters of the northern Great
Barrier Reef based on the voluntary approaches of dwarf minke
whales.
To ensure the encounters have a minimal impact on the whales,
research is being focused on learning more about the dwarf minke
whales and their interactions with swimmers.
A lack of knowledge about basic
aspects of the biology and behaviour of these inquisitive
visitors to the Great Barrier Reef presents many unique
challenges for marine park managers, dive industry operators and
their clients as well as researchers. The interactions between
humans and whales must be managed so that they are ecologically
sustainable.
Minke whales
Until recently, it was thought
that there was a single, variable species of minke whale
throughout the world's oceans. The 'true' minke whale
Balaenoptera acutorostrata is known only from the Northern
Hemisphere. It has a characteristic white band across the middle
of the flipper. The Antarctic minke whale B. bonaerensis is
found mostly in the Southern Hemisphere. It lacks the white band
on the flipper and has alight to dark grey shoulder.
The dwarf minke whale is known
only from the Southern Hemisphere. It has a white shoulder and
flipper base, with a dark grey tip on the flipper. Unlike the
Antarctic minke whale, it has a large dark patch extending onto
the throat. Female dwarf minkes are on average about two metres
shorter than Antarctic minkes (in baleen whales, the female is
larger than the male). The largest dwarf minke whale that was
accurately measured was 7.8 m long; adults weigh 5 6 tonnes.
Minke Recognition
Chart
Both Antarctic and dwarf minke
whales are found in Great Barrier Reef waters. However in six
years of surveys, only one Antarctic minke whale has been seen
in the northern Great Barrier Reef (compared with up to 200
dwarf minke whales per season).
Hunting
Commercial whaling targets the Northern Hemisphere minke whale
in Norwegian waters. The Antarctic and north Pacific minke
whales are the object of scientific whaling research by Japan,
with about 400 and 100 whales respectively taken from each
species each year.
Dwarf minke whales were taken
during commercial whaling in South African waters until this
ceased in 1975. Sixteen dwarf minke whales were taken in the
Japanese research whaling program but since 1993, no takes have
been reported to the International Whaling Commission. If
commercial whaling were to resume in the Southern Hemisphere it
would target Antarctic minke whales. It is possible that some
dwarf minke whales would also be taken incidentally.
Biology
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.
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.
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.
More ...
Minke
Whale Biology
Sounds
Minke whales, like all baleen whales, lack the system of air
sacs and sound generating 'phonic lips' in the forehead region
above the skull, that are found in toothed whales, such as
dolphins. In minke whales, the sounds probably come from the
larynx, although none of the baleen whales have vocal cords.
Dwarf minke whales produce sounds between 50 - 9400 Hz, which
are within human hearing range of 18 Hz 20,000 Hz.
More ...
Whale
Sounds
Migration
We know that dwarf minke whales occur broadly from Victoria to
northern Queensland between March and October, with maximum
sightings on the northern Great Barrier Reef in June and July.
More ...
Minke Whale Migration
