Coastal dolphins

Several species of coastal dolphins occur in the GBR region. Bottlenose dolphins Tursiops spp. occur in both coastal and pelagic waters in the GBR region. The Indo-Pacific humpback dolphin, Sousa chinensis (Fig. 30.1), and the Australian snubfin dolphin, Orcaella heinsohni, occur in small populations mainly close to the coast and estuaries.

Recent morphological and genetic studies of the genus Orcaella have revealed that Australian snubfin dolphins populations (Fig. 30.2) are a separate species from the Asian O. brevirostris. The species level taxonomy of humpback dolphins is unresolved and the humpback dolphins that occur in northern Australia are likely to join the Australian snubfin dolphin as the only cetaceans endemic to Australian waters. Thus, both species have extremely high biodiversity value at a national and international level. However, comprehensive research on these species in Australia has only been undertaken in Queensland, particularly in Cleveland Bay near Townsville.

The species are best distinguished by: (1) the shape of their head: the Australian snubfin dolphin lacks the beak characteristic of bottlenose and humpback dolphins, and the humpback dolphin has a longer and more defined beak than the bottlenose dolphin; (2) the shape of the dorsal fin: high and hooked in bottlenose dolphins, low and triangular in the humpback dolphin and small and triangular in the snubfin dolphin; (3) location: snubfin and humpback dolphins are likely to be in waters less than 10 m deep and up to 6 km offshore (sightings of humpback dolphins up to some 50+ km from the coast have been recorded in the northern GBR region, probably due to the physiography of the coastlines and continental shelves in this area), bottlenose dolphins occur in more open water or close to rocky headlands, (4) colouration: snubfin dolphins vary from different tones of pale grey to brownish grey; humpback dolphins are uniformly grey, with flanks shading to off-white and spotting towards the ventral surface; in some animals the dorsal fin, rostrum and melon whiten with age, while the rest of the dorsal surface remains pale grey; bottlenose dolphins are mainly dark grey (but mature individual of the aduncus form is spotted ventrally), and (5) school size: snubfin dolphins are mainly found in schools of 5-8 individuals (schools of one to 21 individuals have been observed in the wild), humpback dolphins form smaller schools of usually 2-3 individuals (school size ranges from one to 12 individuals); Bottlenose dolphins occur in schools of various sizes ranging from single animals to several individuals (>20). Dugong

The dugong (Dugong dugon) looks rather like a cross between a rotund dolphin and a walrus. Its body, flippers and fluke resemble those of a dolphin without a dorsal fin. Its head looks somewhat like that of a wal-

MEDIUM SIZED WHALES from 5 to 10 metres long.

RELATIVELY SMALL FIN SET FAR BACK

Recurved fin usually visible when animal surfaces to breath

Dark bluish grey head and back Narrow pointed head

Recurved fin usually visible when animal surfaces to breath

LARGE FJN

White flipper patch

LARGE FJN

White flipper patch

Ba/aenoptera acutorostrata

Very streamlined shape

Length: up to 7.8 metres

Usually seen singly or in small groups

Note: The Antarctic Minke Whale also occurs uncommonly in the reef region. It lacks a white band on the flipper and has a light to dark grey shoulder

White eye

Fin up to 0.9 metres high and curved in females and young males Fin up to 1,8 metres high and erect in adult males

Grey saddle (sometimes absent)

White eye

FIN SMALL, RECURVED, SET MJD BACK

CONSPICUOUS BLACK AND WHITE MARKINGS

j^L Length: up to 10 metres

Often seen in small groups • KILLER WHALE Orcinus orca

Medium sized hooked fin set mid back

Rounded snout

Medium sized hooked fin set mid back

Rounded snout

Distinctly bent flipper

Colour usually all black Length: up to 6 metres Often seen in large groups

Fin set far forward

FIN CLOSER TO HEAD THAN TAIL

Grey saddle (sometimes absent)

Pronounced bulging forehead \

Back and flanks brownish grey

Distinctly bent flipper

Colour usually all black Length: up to 6 metres Often seen in large groups

Fin set far forward

Grey saddle (sometimes absent)

Back and flanks brownish grey

-Grey belly patch -Strongly recurved flippers

-Grey belly patch -Strongly recurved flippers

• FALSE KILLER WHALE Pseudorca crassideris

Length: up to 7,5 metres Often seen in large groups

• SHORT-FINNED PILOT WHALE

Ctobicephala macrorhynchus

Fin very small and triangular

Fin very small and triangular

Flippers very small

DOLPHINS less than 5 metres long-

with a beaked head. Wide based dorsa! fin

VERY SMALL BEAK

Flippers very small

Broad dark stripe from face to anus (may not be obvious at a distance) Length: up to 2.7 metres long Pelagic, most likely to be seen off continental shelf

• FRASER'S DOLPHIN Lageriodelphis hosei

High hooked fin

High hooked fin

STUBBY BEAK

Curved "smiling" mouth line

"Flip per" type dolphin seen in ocean aria Length: up to 2.6 metres

Usually seen In small groups of up to 30 animals Often seen bow riding

• BOTTLENOSE DOLPHIN Tursiops spp.

Animals from Queensland lack a hump in front of dorsal fin. Mottled light to dark grey colour, usually darker dorsally. Slow moving coastal species usually seen in small groups close to shore Length: up to 2,4 metres * INDOPACIFIC HUMPBACK DOLPHIN Sousa chinensis

ARTWORK: Bozena Jantulik, Geoff Kelly and

Rebecca Fong, SCIENTIFIC ADVISORS: Peter Arnold, Helene Marsh, Isabel Be as ley

VERY SMALL BEAK

Broad dark stripe from face to anus (may not be obvious at a distance) Length: up to 2.7 metres long Pelagic, most likely to be seen off continental shelf

• FRASER'S DOLPHIN Lageriodelphis hosei

STUBBY BEAK

Curved "smiling" mouth line

"Flip per" type dolphin seen in ocean aria Length: up to 2.6 metres

Usually seen In small groups of up to 30 animals Often seen bow riding

• BOTTLENOSE DOLPHIN Tursiops spp.

LONG LOW DORSAL FIN

Dark grey (may have brownish tinge)

Long thin snout White Light grey

Dark or purplish grey

Dark or purplish grey

SMOOTH SLOPING FOREHEAD pinkish, white blotches Length: up to 2.7 metres

Usually seen in open ocean off the continental shelf • ROUGH TOOTHED DOLPHIN Sreno bredanensis

Dark grey to purplish upper back

Dark grey to purplish upper back

White

Grey

White

Grey

LONG LOW DORSAL FIN

Yellowish cream to tan Length: up to 2.3 metres

Distinct "crossover" colour pattern on sides. Usually seen in open ocean, often in large schools • SHORT-BEAKED COMMON DOLPHIN Delphinus delphis HIGH DORSAL FIN ■

Distintive grey shoulder blaze

Brownish black

Dark grey (may have brownish tinge)

Distintive grey shoulder blaze

Brownish black

Long thin snout White Light grey

Often seen in small groups within the Great Barrier Reef region but may be form large schools offshore Commonly bow rides Size: up to 1.7 metres

• SPINNER DOLPHIN Stenella longirostris

Black streaks from eye to anus & eye to flipper Length: up to 2,6 metres May occur In large schools

• STRIPED DOLPHIN

Stenella coeruleoalba

Note: this species list is not exhaustive

Figure 30.3

A-D, Identification guide to the marine mammals most likely to the seen in the Great Barrier Reef region. Not all animals from the region are illustrated. Table 30.1 provides a more complete list. (Figure: Bozena Jantulik, Geoff Kelly and Rebecca Fong.)

rus without the long tusks. Growing to a length of up to about 3 m, the dugong is the only extant plant-eating mammal that spends all its life in the sea. Dugongs can be difficult to distinguish from Australian snubfin dolphins in the wild, especially as both species often occur in inshore turbid waters. Dugongs surface very discreetly, often with only their nostrils showing above the water. Dugongs tend to move more slowly than dolphins and the lack of a dorsal fin is their most distinguishing characteristic for observers at sea.

Adults are grey in colour but may appear brown from the air or from a boat. Older 'scarback' individuals may have a large area of unpigmented skin on the back above the pectoral fins. The dugong's head is distinctive with the mouth opening ventrally beneath a broad, flat muzzle. The tusks of mature males and some old females erupt on either side of the head. There are two mammary glands, each opening via a single teat situated in the 'armpit' or axilla. The mammaries are somewhat reminiscent of the breasts of human females, which probably explains the legendary links between mermaids and sirenians. The tail of the dugong is triangular like that of a whale.

The dugong mainly occurs in the coastal waters of the GBR lagoon where its distribution is broadly coincident with that of its seagrass food. It is seen up to about 100 km offshore inside the reef in the northern GBR region in the summer.

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