Caretta caretta

Description

The loggerhead turtle is named for its large head. It has thick jaws that crush its food of crustaceans and molluscs. Adults are brown and are often highlighted with light brown, reddish-brown and black on their carapace (shell). The plastron (bottom of shell) is yellow. Hatchlings have a dark brown carapace and light brown plastron.

Distribution and habitat

Loggerhead turtles are found in all tropical and subtropical oceans. They inhabit subtidal and intertidal coral and rocky reefs and seagrass meadows as well as deeper soft-bottomed habitats of the continental shelf.

Loggerhead turtles feed on animals such as crabs, sea urchins, and jellyfish. Two genetic stocks inhabit Australian waters, one on the east coast and the other on the west coast.

For loggerhead turtles nesting and foraging in the Great Barrier Reef World Heritage Area, research shows migration to the Gulf of Carpentaria, Arnhem Land, Torres Strait, and Papua New Guinea (Figure 1).

Figure 1 Indicative migration path of Great Barrier Reef loggerhead turtles

All migration paths are indicative only.

Breeding areas

In Queensland, breeding and nesting occurs mainly in the southern Great Barrier Reef (Capricorn/Bunker group) and adjacent mainland near Bundaberg (Figure 2). Approximately 95 per cent of all nesting marine turtles on the Bundaberg coast are loggerheads. A few hundred females now nest annually in the region.

The eastern Australian loggerhead turtle nesting beaches support the only significant stock of the species in the South Pacific Ocean.

Population decline

The population has declined since the 1970's from about 1000 breeding females. This combined with the long time before their first breeding (age around 20 years) and low reproductive rate (breeding every two to five years), means that the remaining loggerhead population is at serious risk of extinction from any increases in mortality.

An annual loss of only a few loggerhead turtles could result in the extinction of the Queensland population. As female turtles return to nest in the area where they hatched, it is highly unlikely that a population that has ‘died out’ would be recolonised by turtles from another population somewhere else in the world.

Evidence for recovery

The mandatory use of turtle excluder devices in the Queensland East Coast Otter Trawl Fishery was implemented in 2001. This has reduced the incidental capture and mortality of sub-adult and loggerhead turtles.

With this major reduction in loggerhead turtle mortality, the nesting population increased over the next few years because more sub-adult turtles were able to become breeding adults and more adult turtles were able to complete their migrations to the nesting beaches.

Fox baiting programs implemented at mainland nesting beaches along the Bundaberg coast have positively influenced the success of loggerhead turtle nesting.

Figure 2: Great Barrier Reef loggerhead turtle nesting sites

 

Loggerhead facts

Breeding season	Late October to early March, peaking in December
Years between breeding	Three to four years
Age at first female breeding	20 to 25 years
Age when first move into feeding area	About 15 years (60cm carapace length)
Nesting female length	95.9cm (range from 85 - 108cm)
Nesting female weight	99kg (range from 76 - 149kg)
Clutch size (number of eggs)	127 eggs (range from 89 - 151 eggs)
Hatchlings  emerge	December to April
Hatchling success	80 per cent
Hatchling size	4.33cm (range 4.13 - 4.49cm)
Hatchling weight	19.2g (range from 17 - 20.4g)
Predators of hatchlings	Foxes, kookaburras, crows, raptors, gulls, reef egrets, ghost crabs and fish such as trevally and sharks