1. Reptiles of the North Marine Region 3

Название1. Reptiles of the North Marine Region 3
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Species group report card
– reptiles

Supporting the draft marine bioregional plan for the North Marine Region

prepared under the Environment Protection and Biodiversity Conservation Act 1999


© Commonwealth of Australia 2011

This work is copyright. Apart from any use as permitted under the Copyright Act 1968, no part may be reproduced by any process without prior written permission from the Commonwealth. Requests and enquiries concerning reproduction and rights should be addressed to Department of Sustainability, Environment, Water, Population and Communities, Public Affairs, GPO Box 787 Canberra ACT 2601 or email public.affairs@environment.gov.au

A gorgonian wtih polyps extended – Geoscience Australia, Hawksbill Turtle – Paradise Ink,
Crested Tern fishing – R.Freeman, Hard corals – A.Heyward and M.Rees, Morning Light –
I.Kiessling, Soft corals – A.Heyward and M.Rees, Snubfin Dolphin – D.Thiele, Shrimp, scampi
and brittlestars – A.Heyward and M.Rees, Freshwater sawfish – R.Pillans, CSIRO Marine and
Atmospheric Research, Yellowstripe Snapper – Robert Thorn and DSEWPaC


1. Reptiles of the North Marine Region 3

Flatback turtle 4

Green turtle 4

Hawksbill turtle 5

Leatherback turtle 6

Loggerhead turtle 7

Olive ridley turtle 7

Sea snakes 8

Saltwater crocodile 9

2. Vulnerabilities and pressures 11

Vulnerabilities 11

Assessment of pressures 13

3. Current protection measures 22

EPBC Act conservation plans and action plans 23

International agreements 23

References 24

Attachment 1: Reptiles occurring in the North Marine Region 34

Attachment 2: Biologically important areas (BIAs) for marine turtles
in the North Marine Region 37

Species group report card – reptiles

Supporting the draft marine bioregional plan for the North Marine Region prepared under
the Environment Protection and Biodiversity Conservation Act 1999

Report cards

The primary objective of the report cards is to provide accessible and up-to-date information on the conservation values found in Commonwealth marine regions. This information is maintained by the Department of Sustainability, Environment, Water, Population and Communities and is available online through the department’s website (www.environment.gov.au).

Reflecting the categories of conservation values, there are three types of
report cards:

  • species group report cards

  • marine environment report cards

  • heritage places report cards.

While the focus of these report cards is the Commonwealth marine environment, in some instances pressures and ecological processes occurring in state waters are referred to where there is connectivity between pressures and ecological processes in state and Commonwealth waters.

Species group report cards

Species group report cards are prepared for large taxonomic groups that include species identified as conservation values in a region; that is, species that are listed under Part 13 of the Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act) and live in the Commonwealth marine area for all or part of their lifecycle. All listed threatened, migratory and marine species and all cetaceans occurring in Commonwealth waters are protected under the EPBC Act and are identified in the relevant marine bioregional plans as conservation values.

Species group report cards focus on species for which the region is important from a conservation perspective; for example, species of which a significant proportion of the population or an important life stage occurs in the region’s waters.

For these species, the report cards:

  • outline the conservation status of the species and the current state of knowledge about its ecology in the region

  • define biologically important areas; that is, areas where aggregations of individuals of a species display biologically important behaviours

  • assess the level of concern in relation to different pressures.

1. Reptiles of the North Marine Region

The North Marine Region is an important area for several species of reptiles, including marine turtles, sea snakes and saltwater crocodiles.

Six of the seven species of marine turtle in the world are known to inhabit Australian waters, and all six of these species are known to occur in the North Marine Region. All six species of marine turtle are listed under the EPBC Act as vulnerable or endangered, migratory and marine species. Important breeding, nesting and feeding areas for marine turtles are found throughout and adjacent to the region. The region supports globally significant breeding populations of green turtle (Chelonia mydas), hawksbill turtle (Eretmochelys imbricata) and flatback turtle (Natator depressus). Large immature and adult-sized loggerhead turtles from eastern and western Australian populations are known to forage in the eastern Arafura Sea, the Gulf of Carpentaria and the Torres Strait (Limpus 2009), and have been sighted in Northern Territory coastal waters from Fog Bay to north-east Arnhem Land (Chatto 1998). There are also two significant nesting aggregations of olive ridley turtles adjacent to the region: north-west Arnhem Land (including Melville Island, Bathurst Island, Cobourg Peninsula, the McCluer Island group and Grant Island), and north-east Arnhem Land (including the Sir Edward Pellew Group, the Wessel Islands and Crocodile Islands) (Chatto 1998; Limpus & Miller 2000). Leatherback turtles have also been recorded nesting on the Cobourg Peninsula (Chatto & Baker 2008).

Of the 35 species of sea snake (including sea kraits) known to inhabit Australian waters, 19 species are known to occur in the North Marine Region; a further nine species may occur in the region. All sea snakes are listed under section 248 of the EPBC Act as protected marine species.

The saltwater (or estuarine) crocodile (Crocodylus porosus) has a tropical distribution that extends across the northern coastline of Australia, where it can be found in coastal waters, estuaries, freshwater lakes, inland swamps and marshes, as well as far out to sea (Webb et al. 1987). High densities of saltwater crocodiles are found adjacent to the North Marine Region in the river systems of Kakadu and the Mary River, and throughout the Gulf of Carpentaria. The saltwater crocodile is listed under section 248 of the EPBC Act as a protected migratory and marine species.

Of the listed reptiles known to occur and observed to infrequently occur in the North Marine Region, this report card focuses on the saltwater crocodile, and the six species of marine turtle and the 19 species of sea snake known to occur in the region. These species were selected following consideration of their conservation status; distribution and population structure in the region; life history characteristics; and the potential for the populations in the region to be genetically distinct from populations elsewhere.

Flatback turtle

Flatback turtles are endemic to the northern Australian – southern New Guinea continental shelf, with all breeding occurring on Australian beaches (Limpus et al. 1988). There is a low level of genetic variation within the flatback turtle population (compared to other marine turtle species), and limited gene flow between rookeries has been reported (Dutton et al. 2002). At least four separate stocks are recognised in the continuum of flatback turtle nesting from Exmouth Gulf in Western Australia to south-east Queensland (Dutton et al. 2002; Limpus 2009): the eastern Queensland stock; the Gulf of Carpentaria stock; the western Northern Territory stock and the Western Australia stock (Dutton et al. 2002; Limpus et al. 1993).

Flatback turtles differ from other species of marine turtle in that post-hatchlings do not go through an oceanic dispersal but are believed to follow a surface-water-dwelling life over the continental shelf and remain within pelagic habitats (Limpus et al. 1994a; Walker 1994). A substantial number of medium and high density nesting sites of flatback turtles exist along the Northern Territory coastline (Chatto 1998), north-eastern Gulf of Carpentaria and western Torres Strait.

Flatback turtles forage over soft-bottom habitats across the northern Australian continental shelf and as far north as New Guinea and Indonesia (Limpus 2009). They prefer inshore waters and bays where their feeding ground is the shallow, soft-bottomed seabed, away from reefs (DSEWPaC 2011a). Post-hatchling diet consists mainly of macroplankton, gastropods, siphonophores, pelecypods and cuttlefish. Immature adult and adult flatback turtles eat mainly sea cucumbers, sea-pens, cuttlefish and jellyfish (Limpus 2009).

Green turtle

The North Marine Region supports at least two genetic breeding stocks of green turtle, the Gulf of Carpentaria breeding unit and the north Great Barrier Reef breeding unit (Limpus & Chatto 2004; Limpus 2009). The Gulf of Carpentaria supports two main green turtle rookeries: one in the Wellesley Group (Bountiful Island, and Pisonia and Rocky islands), and one in the eastern Arnhem Land, Groote Eylandt and Sir Edward Pellew Islands area. Low density green turtle nesting also occurs in northern and western Arnhem Land and adjacent islands (Chatto 1998; Hope & Smit 1998; Limpus & Preece 1992). In the Gulf of Carpentaria, nesting occurs year round with a mid-winter peak (Limpus 1995).

It appears that all foraging areas linked to the Northern Territory breeding assemblage lie within the Gulf of Carpentaria (Limpus 2009). For example, research undertaken by the Dhimurru Land Management Aboriginal Corporation in Nhulunbuy, in which turtles were fitted with satellite tracking devices, indicates that most (and possibly all) of the green turtles that nest in north-east Arnhem Land remain in the gulf to feed (Kennett et al. 1998).

Post-hatchling and juvenile green turtles with shell sizes up to 30 centimetres in length are pelagic, drifting on the surface of the water, and are usually associated with driftlines and floating sargassum rafts. When their shells are around 30–40 centimetres in length they move to shallow benthic foraging habitats such as coral and rocky reefs, seagrass beds and algal mats, where they feed primarily on seagrass and algae. Adult green turtles will occasionally eat other items including mangroves (Forbes 1994; Limpus & Limpus 2000; Pendoley & Fitzpatrick 1999), fish-egg cases (Forbes 1994), jellyfish (Limpus et al. 1994b) and sponges (Whiting 2000). Young turtles tend to be more carnivorous than adults (Brand-Gardner et al. 1999; Cogger 2000; Whiting 2000). During their pelagic phase, young green turtles also eat plankton (Cogger 2000).

Hawksbill turtle

Australia’s hawksbill turtle population is considered to comprise two distinct genetic stocks, one in the north-east of Australia and the other in Western Australia (Limpus 2009). Due to significant differences in the timing of the breeding season across the north-eastern stock, it is considered as two subpopulations for the purposes of management on the basis that interbreeding is highly unlikely (Limpus 2009). These are two of the largest remaining nesting populations of hawksbill turtle in the world (Limpus & Miller 2000). Australian stocks of hawksbill turtles are genetically different from those that breed in neighbouring countries such as Solomon Islands and Malaysia (Moritz et al. 2002). The breeding stock that nests adjacent to the North Marine Region at Arnhem Land is associated with the rookeries of the Torres Strait and the northern Great Barrier Reef (Limpus 2009). Other rookeries near the North Marine Region include Torres Strait and the mainland coast of western Cape York Peninsula north of Cotterell River, and four main sites in Arnhem Land (outer islands of the English Company Islands area; and north-east, north-west and south-east areas of Groote Eylandt). Groote Eylandt is the most significant area for hawksbill turtle nesting in the Northern Territory. Hawksbill turtles breed throughout the year but the peak nesting period in north-eastern Arnhem Land is in winter and early spring (approximately July to October) (Gow 1981; Limpus & Preece 1992; Limpus et al. 2000).

Hawksbill turtle post-hatchlings are believed to follow an oceanic, surface-water-dwelling, pelagic life, although the distribution and biology of this age class is poorly understood in Australian waters (Limpus 2009). Young turtles (with shell sizes around 35 centimetres in length) settle in feeding areas on the continental shelf, foraging in rocky and coral reefs, primarily feeding on sponges and algae (Whiting 2000). They have also been found, less frequently, in seagrass habitats of coastal waters, as well as the deeper habitats of trawl fisheries (Poiner & Harris 1996; Robins et al. 2002). Recovery of flipper tags suggests that hawksbill turtles are highly migratory, as animals tagged in the northern Great Barrier Reef have been recaptured in foraging areas in the southern Gulf of Carpentaria, south-eastern Indonesia and southern Papua New Guinea (Limpus 2009). The species is highly migratory, moving up to 2400 kilometres between foraging areas and nesting beaches (DSEWPaC 2011b). Hawksbill turtles are omnivorous, eating a variety of animals and plants including sponges, hydroids, cephalopods (octopus and squid), gastropods (marine snails), cnidarians (jellyfish), seagrass and algae (Carr & Stancyk 1975; Whiting 2000). During their pelagic phase (while drifting on ocean currents), young hawksbill turtles eat plankton (Meylan 1984). Marine turtles exhibit strong fidelity to foraging areas and nesting beaches.

Leatherback turtle

No major breeding sites of leatherback turtles have been recorded in Australia (Limpus 2009); however, scattered nesting occurs adjacent to the North Marine Region along the coast of Arnhem Land. For example, low numbers of nesting females have been recorded at Cobourg Peninsula in north-west Arnhem Land (Chatto & Baker 2008), with breeding occurring mostly during December and January. Leatherback turtles were sighted on the Queensland coast of the Gulf of Carpentaria in 1997, along with nesting tracks observed that were possibly made by leatherbacks. Leatherback turtles are occasionally observed on the continental shelf in the Gulf of Carpentaria and near Cobourg Peninsula. It is thought that most leatherback turtles found in Australian waters have migrated from nesting areas elsewhere to feed in the tropical waters of northern Australia (Limpus 1995).

Leatherback turtles are the largest of all marine turtles, weighing up to 500 kilograms and with shells averaging 1.6 metres in length (Limpus et al. 1994a). Their large body size, high metabolism, thick fatty tissue layer and ability to regulate blood flows allows them to use cold water foraging areas (DEWR 2007). This species is primarily pelagic in both the juvenile and adult phases of its life history. Small juveniles seem to ‘disappear’ for several years but may concentrate around upwellings where food sources are abundant. Large juveniles and adult turtles are found in both pelagic and coastal waters from tropical to cold temperate areas. Foraging occurs throughout the water column, from close to the surface to depths of more than 1200 metres (Gulko & Eckert 2004). Leatherback turtles are carnivorous and feed extensively on colonial tunicates, jellyfish and other soft-bodied invertebrates (Bone 1998; Limpus 1984; Limpus & McLachlan 1979). Leatherback turtles are able to dive comparatively deeply due to a flexible carapace (top shell) and plastron (bottom shell) that are made of cartilage embedded with miniature bones and that resist cracking under pressure, as well as the ability to retain large amounts of oxygen in their blood and muscles (Gulko & Eckert 2004).

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