Download Bryde`s Whales - Auckland Council

TREASURES OF THE
HAURAKI GULF
MARINE PARK
Bryde’s whales – Tohorā: Very special, nationally significant qualities are recognised in
the designation Hauraki Gulf Marine Park.
Among these features is an unusual diversity and abundance of marine mammals.
Most frequently encountered around the Hauraki Gulf are common dolphins, sometimes
in groups of hundreds, and pods of bottlenose dolphins and killer whales. Around 20
species of whales and dolphins have been recorded in the Gulf.
Perhaps most remarkably, the Hauraki Gulf has its own population of large baleen
whales, breeding and raising calves throughout the year.
Around 50 Bryde’s whales are estimated to live year-round within the Gulf, mixing
with another 150 seasonal visitors; one of the few resident populations of this species in
the world.
The New Zealand population of Bryde’s whales is
listed as a nationally critical threatened species by the
Department of Conservation because its population
is small and predominantly found in one location (the
Hauraki Gulf).
The probability of a ship strike being lethal is close
to 80 percent when a large ship is travelling above
14 knots. Slowing down to 10 knots reduces the
chance of a fatal strike to around 20 percent. Average
large vessel speed in the Gulf is 14.2 knots. This has
prompted calls for an urgent code of conduct to slow
ship speed and/or a marine mammal sanctuary with
rules to protect the whales from vessel collisions.
Bryde’s whales are sometimes seen with their
heads out of the water, known as spy hopping. They
occasionally roll when surfacing to breathe and feed
and you can see their small, curved dorsal (top) fin,
short pectoral (side) fins and notched fluke (tail).
Australasian Gannet
Tākapu
Bryde’s whales make infrequent low frequency
moans and downsweep calls. The sounds
recorded around a workup include rapid clicks of
dolphins, the thump of diving gannets and snap
of fish and crustaceans.
When feeding the big whales dive steeply, roll
sideways, take a big gulp then float slowly upwards.
At the surface they expel water, sieving small fish and
marine animals through their baleen plates.
The 13-15m long, 14-17 tonne Bryde’s whales frequent
channels and sheltered waters around the Gulf to live,
breed and gorge on schools of bait fish and krill.
Bryde’s whales are shallow divers, spending 90% of
their time in water less than one adult body length
from the surface. They have been recorded in the
Gulf diving for up to nine minutes and to depths of
55m searching for prey.
The shallow-diving, hard-to-spot and widely dispersed
Bryde’s whale makes it very vulnerable to vessel traffic.
An average of two Bryde’s whales per year have been
killed by vessels in the Gulf since 1989, a concerning
number, given the small size of the population.
At night whales change behaviour, spending time
close the surface, either resting or skim-feeding by
swimming slowly with their mouth agape.
The Bryde’s whale has relatively little blubber and was
not a favoured species by whalers. Nineteen Bryde’s
whales were caught from a whaling station on Great
Barrier Island which operated between 1956 and 1963.
The Bryde’s whale has a bluish-gray body with white
on the underside, three distinctive ridges running
from the tip of the snout to the twin blowholes, and
about 40 to 50 very long throat grooves.
Bryde’s whales mate throughout the year and have a
gestation period of around 12 months. Calves suckle
their mother’s milk for six months to a year. They can
breed every two years.
Common Dolphin
Aihe
Some whales have distinctive fin shapes and notches
enabling researchers to recognise the same individual
repeatedly, confirming the resident status of Bryde’s
whales in the Hauraki Gulf.
Bryde’s whales can swim fast – up to 30 knots. They
are usually observed singly or in small groups of two
or three. They sink when diving, rather than arching
to show their flukes. Condensation of their breath
when surfacing is usually the first sign of presence.
PRODUCED BY
Bryde’s is pronounced ‘Brooders’, and the species
is named after Johan Bryde, a Norwegian consul to
South Africa who created the first whaling station in
Durban. Its scientific name is Balaenoptera edeni.
SPONSORED BY
IN ASSOCIATION WITH
Project director: Tim Higham, Manager, Hauraki Gulf Forum | Art: Dave Gunson | Scientific advice: Dr Rochelle Constantine, University of Auckland | Graphic Design: Kylie Hibbert | Further information: State of our Gulf: Tikapa Moana – Hauraki Gulf State of the Environment Report 2011, available at www.haurakigulfforum.org.nz