Eretmochelys imbricata
Description
Adult hawksbill turtles have extensively variegated patters of brown and black on their carapace (shell). The plastron (bottom of shell) is cream with occasional black spots. A distinguishing feature of the hawksbill turtle is their beak-like mouth and narrow head. The carapace has overlapping scutes made of material much like fingernails. Hatchlings are dark brown.
Distribution and habitat
Hawksbill turtles occur in all oceans usually in tidal and sub-tidal coral and rocky reefs in tropical and subtropical areas. In Australia, hawksbills feed in rocky areas and on coral reefs. Their main feeding area is on the east coast, including the Great Barrier Reef.
Sponges make up a major part of the hawksbill's diet, although they also feed on seagrasses, algae, sea cucumbers, soft corals and shellfish. The pointed jaws are well adapted to prising food from crevices in and around coral.
Research on hawksbill turtles that nest or forage in the Great Barrier Reef Marine Park shows migration to Indonesia, Papua New Guinea, the Solomon Islands, and Vanuatu (Figure 1).
Breeding areas
Hawksbill turtles are found all over the world. The entire far northern section of the Great Barrier Reef Marine Park and the Torres Strait region is internationally significant for hawksbill turtle nesting as numbers have declined in many parts of the world.
There are three main breeding areas in Australia - northern Great Barrier Reef (several thousand nesting females), north-eastern Arnhem Land (about 2000 nesting females), and Western Australia (several thousand nesting females).
Hawksbill turtles tend to nest in low numbers and in the Great Barrier Reef Region. Nesting areas mainly occur north of Princess Charlotte Bay and in the Torres Strait (Figure 2).
The only Great Barrier Reef nesting population for which there is sufficient information is at Milman Island, where data indicates since 1990 numbers of nesting females have been declining at about three per cent each year.
Figure 1 Indicative migration path of Great Barrier Reef flatback and hawksbill turtles
Dashed lines (- - -) represent movements of hawksbill turtles.
Solid lines (-) represent movements of flatback turtles.
All migration paths are indicative only.
Hawksbill turtle facts
| Breeding season | Year-round, concentrated from November to February, peaking in January |
| Years between breeding | Two to five years |
| Age at first female breeding | 30 - 35 years |
| Age when move into feeding area |
Four to seven years (30cm carapace length) |
| Nesting female length | 81.6cm (range from 63.5 - 91cm) |
| Nesting female weight |
50.4kg (range from 32 - 72kg) |
| Clutch size (number of eggs) |
122 eggs (range from 18 - 210 eggs) |
| Hatchlings emergence | Year-round concentrated from February to April |
| Hatchling success | 79 per cent |
| Hatchling size | 3.98cm (range 3.2 - 4.36cm) |
| Hatchling weight |
13.8g (range from 8 - 17.5g) |
| Predators of hatchlings |
Gulls, reef egrets, ghost crabs, crocodiles, fish, sharks, crabs and dingoes |
Figure 2: Great Barrier Reef hawksbill turtle nesting sites
