Green turtles

Green turtles (Chelonia mydas)

Green turtle

Green turtles are found worldwide in tropical and sub-tropical waters. There are seven distinct genetic stocks in Australia, including the coastal North-West Shelf stock off the Pilbara coast , the largest group found in Western Australia.

Green turtles are the most common species seen in Western Australia . Between , with up to 20,000 and - 30,000 thousand s to tens of thousands of females nesting on along their chosen beaches between October and February each year.

The numbers of green turtles that nest each season in Western Australia is, like those on the Great Barrier Reef, affected by the El Nino or Southern Oscillation of the Pacific Ocean, so numbers visiting a breeding beach can vary between a few dozens to hundreds in very poor seasons and many thousands at the best.

Resident adult green turtles can be seen along the edge of the reefs fringing the cliffy coast south of Shark Bay down to the mouth of the Murchison River, and around the reefs of the Houtman Abrolhos islands. Divers may see large juveniles around Rottnest Island reefs.

Green turtle nesting areas of the Gascoyne and Pilbara are found on the sandy mainland beaches of the Ningaloo Marine Park from around Point Cloates northward, the Muiron Islands, Serrurier Island, the western coastal parts of Barrow Island, some islands of the Montebello group, and some of the Dampier Archipelago islands.

The main nesting areas in the Kimberley are at the Lacepede Islands, with smaller regionally important nesting stocks visiting Browse Island and Scott and Ashmore Reefs areas.

The larger sized, mainly including female adult turtles are harvested for food by Aboriginal people living along the northern coast. If turtle eggs are readily accessible, they will also be collected. Expatriate Torres Strait Islanders and other Indigenous ‘salt-water' people living off-country in Western Australian communities such as the Dampier-Karratha area are also known to be hunters of green turtles.

Indonesian fishers are also known exploiters of green turtles in Australian waters.

Legal commercial turtle harvesting took place in Western Australia from as early as 1870. Between 1931 and 1936 a turtle soup factory operated at Cossack (near Karratha). It is estimated that up to 2500 large green turtles were taken annually from around the Dampier Archipelago and Montebello Islands. In the 1940s and 1950s an unregulated green turtle harvest continued to supply soup canneries in Perth and Cossack.

Between 1958 and1973, a commercial turtle fishery authorised by State fisheries legislation operated along the north-west coast. Green turtles were taken for harvest from Coral Bay to the Montebello Islands. It is estimated that at least 60,000 green turtles were caught. Commercial products were exported to mainly European markets.

Migrating adult green turtles are known to cross international boundaries. For example, breeding female green turtles tagged and released from nesting beaches in Western Australia have been captured in Indonesia. Reciprocal exchanges have also been recorded.

Flatback turtles

Flatback turtles (Natator depressus)

Flatback turtle

The flatback turtle only nests in Australia and is the second most abundant visible turtle species in Western Australia. Nesting sites are widely distributed along the mainland coast of the Pilbara and Kimberley, as well as among offshore islands northward from Exmouth Gulf, including some beaches shared with the green turtle and other species.

Two of the largest rookeries of the Pilbara are found on the mid-eastern coast of Barrow Island, and on the mainland coast on Mundabullangana Station near Cape Thouin. Smaller rookeries are centred on Cemetery Beach within the town of Port Hedland, and Bell's Beach near Wickham. Nesting occurs mainly in December and January.

In the west Kimberley, there is an extensive nesting presence on Eighty Mile Beach, with the greatest concentrations in the Mandora-Wallal section. Other known north-west Kimberley region rookeries include some King Sound islands, the Slate Islands near Camden Sound, and numerous other beaches of the Buccaneer and Bonaparte Archipelago islands. The Needles beach near Cape Domett is the best known north Kimberley site. Nesting at far northern Western Australia flatback sites occurs mainly in the dry season (winter) months , rather than during the summer months .

In the Kimberley region, flatback turtles provide the most accessible source of eggs for coastal Aboriginal communities, but adult turtles are generally not taken.

Bycatch Reduction Devices (BRDs) and Turtle Excluders (TED) have been progressively introduced in Australian prawn trawl fisheries. These have alleviated the risk of capturing flatback turtles in those fisheries.

Hawksbill turtles

Hawksbill turtles (Eretmochelys imbricata)

Hawksbill turtles occur worldwide in tropical and sub-tropical waters. There are two genetically distinct populations in Australia, one in on the west coast and one in on the east coast .

In Western Australia, hawksbills generally have smaller annual nesting populations of tens to hundreds of turtles. However, they have an extended nesting period and may nest at any time of the year.

The peak period for nesting on the Pilbara coast is between October and December. Hawksbills often share the nesting beaches mid-season with other species of turtles, but commence breeding much earlier.

Confirmed northern Gascoyne region nesting locations include Ningaloo Marine Park beaches from the Coral Bay area north to the Muiron Islands. There are no records of hawksbills nesting at more southerly locations.

The most important Pilbara and Western Australian hawksbill turtle nesting sites are found in the Dampier Archipelago and among the Montebello Islands and Lowendal Islands groups. The best documented breeding populations are found on Varanus Island in the Lowendal Islands group, and at Rosemary Island in the Dampier Archipelago.

Hawksbill turtle nesting in the Kimberley region is poorly known, but apparently insubstantial. Nests have been reported from near One Arm Point in King Sound and at the Lacepede Islands. This minor presence largely reflects a lack of nesting beaches available among the majority of the numerous offshore islands. Hawksbill turtles do nest in small numbers at the Ashmore Reef N ational Nature Reserve .

As at December 2005, a total of about a round 2500 nesting female hawksbill turtles had been tagged and released for population studies.

There is a widespread belief that the hawksbill turtle can be poisonous. Australian Aboriginal people believe this, and usually harvest only the eggs at coastal sites. Some minor illegal trade in hawksbill turtle shells has been detected in recent times but there is now no evidence of organised or substantial trade within Australia. Historic external trade did occur.

Loggerhead turtles

Loggerhead turtles (Caretta caretta)

Loggerhead turtle (Photo - Kevin Crane/DEC)

Loggerhead turtles are found in tropical and subtropical waters around the world. There are two distinct Australian populations, one in on the west coast and one in on the east.

The loggerhead turtle is one of the more visible turtles on the lower west coast of Western Australia, with resident adult and large sub-adult turtles sometimes found in the Perth region. Animals from this group are the most common victims of accidents and strandings on beaches of the Perth region and Western Australia's south west. Small young-of-the year (post-hatchling) loggerheads sourced from the Gascoyne region breeding beaches are also regularly washed ashore through winter-early spring after westerly storms around the south and lower western coasts of Western Australia, particularly in years with an early onset strong Leeuwin Current flow.

Loggerhead turtle nesting areas extend from Shark Bay (including on the mainland near Steep Point) to the North-West Cape and Muiron Islands region. Occasional late summer nesting crawls have also been recorded as far north as Barrow Island, the Lowendal Islands and Dampier Archipelago.

The most concentrated nesting presence is found on the northern Dirk Hartog Island Turtle Bay-Cape Levillain coast. There is widespread low to medium intensity nesting across Ningaloo Marine Park-North West Cape beaches, and secondary concentration at the nearby Muiron Islands.

The main threat to Western Australian coastal-nesting loggerhead turtles is the risk of predation of nests and hatchlings by European red foxes which invaded the Ningaloo coast in the 1940s and early 1950s. Fox baiting programs implemented at Ningaloo coast nesting beaches have reduced nest predation rates. Continuing enhanced reproductive success resulting from the fox-baiting programs will potentially assist recovery of numbers with in the future Ningaloo coastal breeding population of this species. The Shark Bay and Pilbara islands breeding loggerheads have not suffered fox predation. There are however unresolved regional commercial trawl and longline fisheries interaction problems of the past that affected all populations. Disturbance to mainland nesting loggerheads from vehicles driving on beaches and uncontrolled tourist interactions also occurs.

Leatherback and Olive Ridley turtles

Leatherback and olive ridley turtles (Dermochelys coriacea and Lepidochelys olivacea)

Leatherback and olive ridley turtles have not been confirmed as nesting species in Western Australia.

It is possible that a few olive ridleys nest in the northern Kimberley because low intensity breeding has been reported from the Northern Territory and Gulf of Carpentaria Queensland coast. High intensity arribada breeding presence is not found in Australia. Olive ridleys are one of the smaller species of marine turtle, growing to less than one metre in length. A few olive ridley turtles have been caught in trawl or longline fisheries off the Kimberley-Pilbara coast.

Leatherbacks are very different to other marine turtles because they lack the rigid bony shell of the Cheloniid species. The five distinct ridges of the leatherbacks carapace reflect the different underlying structure. The leatherback skin also is devoid of scales, and the limbs lack the nails found in other species. The leatherback is also the largest marine turtle, with adults growing up to three metres long, and sexual maturity being achieved at body sizes near the maximum recorded for the largest of the Cheloniids. Leatherbacks are occasionally seen at sea, mostly around the mid-west and south-west of the State, where they feed on soft bodied invertebrates such as jellyfish.

They are also regularly, but not frequently, reported as a fisheries by-catch in the western rock lobster fishery. It is thought that leatherbacks that feed in Australian waters migrate to other countries to nest.