Australia's last great whale haven.pdf - Ningaloo Atlas

November 2011 Cetaceans of the NW Marine Region
11
Common bottlenose dolphins occur in the NW Marine
Region in both their inshore and offshore forms 90 .
Records exist of pelagic populations, nearshore
groups and residents of areas around oceanic islands.
Their diet varies between inshore and offshore forms
(fish or squid respectively) and with geographic
location, and common bottlenose dolphins can
associate with pilot whales, white-sided dolphins,
spotted dolphins, rough-toothed dolphins, Risso’s
dolphins, false killer whales and humpback whales.
In the NW Marine Region, important habitats
for resident populations are Shark Bay and the
Montebello and Barrow Islands.
Pelagic dolphins such as Fraser’s dolphins, Risso’s
dolphins and rough-toothed dolphins are generally
found in deep oceanic waters in association with
upwelling, over geomorphic features such as
seamounts and canyons or in places where islands
or reefs abut deep water where productivity is
enhanced 59, 137 . High site fidelity has been found in
Risso’s dolphins 12 and rough-toothed dolphins 13
and the latter species has been sighted regularly
around the Abrolhos Islands, the Rowley Shoals
and Scott Reef (Jenner, C. pers. comm. 2011). In
the NW Marine Region mixed-species schools of
Fraser’s dolphin, sperm whales, pilot whales, false
killer whales, common bottlenose dolphins and
spinner dolphins have been recorded 146 in the shelf
edge waters of the Browse Basin. These species
generally feed on a wide range of fish, squid and
crustaceans from throughout the water column,
and can dive to depths of 600 metres or more
46, 59, 149, 168 . Risso’s dolphins have been recorded off
the Kimberley coast in groups with sperm whales,
short-finned pilot whales, bottlenose dolphins,
common dolphins, striped dolphins, spotted
dolphins, false killer whales and pygmy killer whales
146, 147, 171 , and have been seen in the Rowley Shoals in
large numbers. Rough-toothed dolphins have been
recorded in the region in association with common
bottlenose dolphins.
Three pelagic dolphins of the genus Stenella are
found in the NW Marine Region, including the
spotted, spinner and striped dolphin, but little is
known of their exact distribution 121, 176 . They have
been recorded at the shelf edge and shelf slope in
the Browse Basin in large, mixed-species feeding
schools with other cetaceans and in association with
tuna and seabirds 89, 146 . Small, potentially resident
groups have been observed resting in nearshore
areas of the Kimberley coast on the lee side of bays
and islands. Spinner dolphins were observed in high
densities off James Price Point during recent surveys,
forming schools of up to 100 individuals at least
5km from the shore 146 . The striped dolphin is known
to be abundant around Barrow Island. These species
exhibit highly dynamic behaviour and can dive to
depths of 200–300 metres to feed on small squid,
shrimp and fish. Spinner dolphins were caught in
large numbers by the Taiwanese gillnet fishery when
it operated in the northern waters of the region 82 .
Regular visitors and potential residents
A number of species are expected to use the
waters of the NW Marine Region as part of annual
migration routes, potentially also resting or
feeding in particular locations. Pygmy blue whales,
for instance, are known to migrate between
southern feeding grounds (the Perth Canyon and
the Bonney Upwelling) and presumed breeding
and calving grounds in Indonesian waters 25, 74 .
Apart from the Bonney Upwelling and the Perth
Canyon, oceanographic conditions favourable
to pygmy blue whales exist along the southern
coasts of Java, Sumbawa and Halmahere Island,
Indonesia 25 . Recent research has found little
genetic differentiation between the Perth Canyon
and Bonney Upwelling feeding aggregations,
suggesting that both populations may use the same
breeding areas 7 . A blue whale migration corridor
is thought to exist between Scott Reef and Browse
Island 148 and blue whales have been tracked
travelling west of Scott Reef during their northern
migration 74 . Furthermore, North West Cape is used
as a migratory waypoint, and upwellings near
seamounts and canyons in the Browse Basin are
likely feeding areas during migration to Indonesia 25,
121 . Pygmy blue whales have a thin layer of blubber
compared with other migrating baleen whales,
indicating that feeding during migration is necessary,
and important feeding areas are likely to occur in the
NW Marine Region 61 .