Leatherback Turtle Dermochelys coriacea - endangered species listing

NSW Scientific Committee - final determination

The Scientific Committee, established by the Threatened Species Conservation Act, has made a Final Determination to list the Leatherback Turtle Dermochelys coriacea (Vandelli, 1761) as an ENDANGERED SPECIES in Part 1 of Schedule 1 of the Act, and as a consequence, to omit reference to the Leathery Turtle Dermochelys coriacea (Vandelli, 1761) from Part 1 of Schedule 2 (Vulnerable species) of the Act. Listing of Endangered species is provided for by Part 2 of the Act.

 

The Scientific Committee has found that:

 

1. The Leatherback Turtle or Leathery Turtle Dermochelys coriacea (Vandelli, 1761) is the largest of the marine turtles, ranging from 1.50-1.74 m (curved carapace length for females), and weighing around 200-300 kg (Hamann et al. 2006; Wells 2007). The species is readily identified from the distinct longitudinal ridges present on the carapace (five ridges excluding the carapace margin). The carapace is covered with a leathery ‘skin’ that is usually coloured very dark brown to black, although pale creamy to yellow spotting or blotching can also be present in varying degrees (Wells 2007). Adult males and females are similar in appearance, although males have a longer tail (Limpus 2009). Hatchlings are black, both dorsally and ventrally and show the five longitudinal ridges that characterise adults (Limpus 2009).

 

2. The Leatherback Turtle has a worldwide distribution in tropical and temperate oceans with a number of widely separated and therefore distinct breeding stocks (Limpus 2009). The geographic range of the species is considered the largest of all living marine reptiles (Benson et al. 2007).

 

3. Leatherback Turtles from a range of size and age classes can be found foraging in Australian waters year-round (Hamann et al. 2006) and are seen in small numbers in the coastal waters of NSW, which are considered part of a migratory corridor for the species (Cogger 2001; Wells 2007; C. Limpus pers. comm. 2011). A total of 58 sightings of Leatherback Turtles have been recorded in NSW, extending as far south as Jervis Bay (NSW Atlas records accessed Jan 2011). It has been suggested that NSW waters may also contain important feeding grounds for the species and that significantly more animals may visit the state to forage than are reported (Cogger 2001).

 

4. The main nesting beaches for the Leatherback Turtle are located in tropical and subtropical areas outside of Australia (e.g. Java, Papua New Guinea, Solomon Islands, Vanuatu) (Wells 2007). There is no evidence that Australia has ever supported a large nesting population of Leatherback Turtles (Limpus 2006), with only 33 nesting attempts recorded in Australia up to 1991 (Tarvey 1993). NSW is considered a peripheral area for nesting Leatherback Turtles (C. Limpus pers. comm. 2011) and nesting has only been recorded on two occasions; once near Ballina and once at Lennox Head. This represents the southern-most limits of successful breeding so far recorded for the species in Australia (Tarvey 1993; NSW Atlas records accessed Jan 2011). Records from the NSW Atlas also indicate one failed nesting attempt from Seven Mile Beach, south of Forster. No breeding for the Leatherback Turtle has been recorded in NSW, or indeed eastern Australia, since 1996 (Hamann et al. 2006; C. Limpus pers. comm. 2011).

 

5. It has not yet been determined whether animals found in Australia represent outliers from genetic stock in Papua New Guinea, Solomon Islands and West Papua (Limpus 2009), although it is thought that the majority of Leatherback Turtles within Australian waters are likely to be foraging migrants (TSSC 2008a).

 

6. As a pelagic species, the Leatherback Turtle occurs in both coastal waters and the open ocean and in Australia is most commonly seen in warmer, subtropical waters (Wells 2007). The species has been seen in the mouths of rivers and in sheltered bays, but foraging can occur throughout the water column, up to water depths of 200 m (Wells 2007). As with other marine turtles, the Leatherback Turtle has very specific requirements in relation to nesting beaches. Nesting beaches usually have deep water approaches (Wells 2007) and for hatching to be successful, nesting substrate must be between 25°C – 33°C, be well ventilated, have high humidity and not be subjected to flooding (TSSC 2008a).

 

7. Nesting in the Leatherback Turtle in eastern Australia occurs from December to February (Hamann et al. 2006; Wells 2007). Between 60 and 100 white eggs are usually laid at a time. Females nest between two and five times per season, with each nesting attempt separated by 9-11 days (Wells 2007). The timing of reproductive migrations to Australia is unknown but could be every two to three years, and the species is thought to display a high level of fidelity to particular nesting beaches (Limpus 2009). Hatching occurs after 56-65 days. In Australia, incubation success for the species is generally poor (Limpus 2009). Upon hatching, juveniles swim out to sea. Predation by crabs and birds during the crossing from nest to sea, although not quantified, may be very high (Limpus 2009). Little is known about the species’ habits and development at sea, although individuals are thought to maintain a solitary, pelagic lifestyle. The main prey items for the Leatherback Turtle are coelenterates (e.g. jellyfish, bluebottle), however squid, planktonic tunicates and ascidians can also be eaten (Wells 2007). In NSW, Leatherback Turtles have been known to aggregate at the mouths of estuaries to feed on swarms of jellyfish (Cogger 2001).

 

8. Age at maturity for the Leatherback turtle is 13-14 years (Sarti Martinez 2000). Leatherback turtles are long-lived, possibly up to 100 years (Wells 2007), and are estimated to spend at least 20 years as breeding adults (Reina et al. 2002). Generation length is estimated to be 22 years (Sarti Martinez 2000).

 

9. The species is known to make long migrations from feeding areas to breeding sites. Recent tracking studies have recorded what is thought to be the longest migration of any Leatherback Turtle, from breeding grounds in New Guinea to foraging sites in the shelf waters off Oregon USA; a distance of over 20,000 km (Benson et al. 2007).

 

10. Population estimates for the species are invariably based on the number of breeding females encountered at nesting beaches. The current global estimate is 36,500 adult females (Dutton 2007). Potentially, 10 subpopulations of Leatherback Turtles are recognised globally (based on major nesting sites) and while not confirmed, individuals seen in Australian waters are likely to be migrants from one of two closely related Pacific populations (an eastern and western population) (Hanamm et al. 2006). Leatherback Turtles off the east coast of Australia, and therefore off NSW, are likely to derive from the western Pacific population (Hamann et al. 2006). The estimated number of adult female Leatherback Turtles in this population is 2,800 (TSSC 2008b). Available evidence suggests that animals found throughout the western Pacific, including breeding sites in Java, Papua New Guinea, Solomon Islands and Vanuatu, form a single genetic stock (Hamann et al. 2006).

 

11. The migratory nature of the Leatherback Turtle makes it susceptible to threats across its vast migration routes. In Australia, the main threats include entanglement in float lines used in lobster and crab fisheries, boat strike, accidental death in shark control programs and ingestion of marine debris (Hamann et al. 2006). A very low level of mortality is reported in association with trawl fisheries (Limpus 2009) and around 10 to 40 Leatherback Turtles are thought to die through longline fishery operations in Australian waters each year (TSSC 2008a). ‘Entanglement in or ingestion of anthropogenic debris in marine and estuarine environments’ is listed as a Key Threatening Processes under the NSW Threatened Species Conservation Act 1995.

 

12. On land, threats include predation or nest destruction by foxes, dogs, goannas and pigs (Hamann et al. 2006) and disorientation of hatchlings in response to artificial lighting (Limpus 2009). The sex ratio of Leatherback Turtle populations may be adversely affected by climate change, as rising temperatures at their current nesting beaches may produce more female than male hatchlings (Binckley et al. 1998). Changes in substrate temperature and the frequency of storm events may also negatively affect hatching success at some sites (Hamann et al. 2006). However, as no nesting has been recorded in eastern Australia since 1996 (C. Limpus pers. comm. 2011), and given the intermittent history of nesting in NSW, these land-based threats should all be regarded as potential threats to Leatherback Turtles in NSW.

 

13. Globally, the number of adult female Leatherback Turtles has declined from an estimated 115,000 in 1982 (Pritchard 1982) to 36,500 in more recent years (Dutton 2007), representing a 68% decline over a 25 year period, or just over one generation. It is likely the species was already in decline before the 1982 population estimate was made, however no pre-decline data are available (C. Limpus pers. comm. 2011). While it is considered likely the rate of decline has accelerated in recent years (C. Limpus pers. comm. 2011), there is no information on annual rates of decline between 1982 and 2007, making it difficult to accurately extrapolate decline over three generations. However, it is clear that the species has undergone a large reduction in population size and given the existence of on-going threats across the species’ range, continued decline of a similar or greater magnitude is expected in the future (Limpus 2009).

 

14. The western Pacific breeding stock of Leatherback Turtles, which is thought to support animals seen in eastern Australia, is regarded as one of the smallest in the world (Spotila 1996), with the species considered effectively extinct at some nesting locations (Hamann et al. 2006). For example, the major rookery in Malaysia has dropped from 10,155 clutches in 1956 to 37 clutches in 1995 (Sarti Martinez 2000). High rates of mortality are suspected at the remaining breeding sites in the western Pacific (Hamann et al. 2006), largely due to on-going human harvest of eggs and adults, pig predation, and fisheries by-catch (TSSC 2008a; C. Limpus pers. comm. 2011).

 

15. The rate of entanglement of Leatherback Turtles on drum lines set as part of the Queensland Shark Control Program is often used as an index of the species’ at-sea abundance in eastern Australia. Comprehensive datasets of the rates of Leatherback Turtle by-catch at one site (Point Lookout, south Queensland) between 1984 and 2010 indicate a decline of the species in southern Queensland, with no captures recorded since 2004 (C. Limpus pers. comm. 2011). This decline reflects trends at western Pacific nesting beaches (Limpus 2006).

 

16. Leatherback Turtles seen in NSW are likely to be a sub-set of populations in the western Pacific that are currently experiencing significant decline. The number of animals in NSW is assumed to be declining given the decline in Australia (Limpus 2009). As the breeding biology of the species pre-disposes it to slow natural rates of recovery and given the extralimital threats to Leatherback Turtles across their migratory range, the survival prospects for any Australian population of the species over the long-term is considered dire (Limpus 2009).

 

17. The Leatherback Turtle is protected in all Australian States and Territories (except the ACT) and is a listed Endangered, Marine and Migratory species under the Commonwealth Environment, Protection and Biodiversity Conservation Act 1999.

 

18. Dermochelys coriacea (Vandelli 1761) is not eligible to be listed as a Critically Endangered species.

 

19. The Leatherback Turtle Dermochelys coriacea (Vandelli 1761) is eligible to be listed as an Endangered species as, in the opinion of the Scientific Committee, it is facing a very high risk of extinction in New South Wales in the immediate future as determined in accordance with the following criteria as prescribed by the Threatened Species Conservation Regulation 2010:

 

Clause 6 Reduction in population size of species

 

The species has undergone, is observed, estimated, inferred or reasonably suspected to have undergone or is likely to undergo within a time frame appropriate to the life cycle and habitat characteristics of the taxon:

(b) a large reduction in population size,

based on either of the key indicators:

(a) an index of abundance appropriate to the taxon, or

(b) the geographic distribution, habitat quality or diversity, or genetic diversity of the species.

 

Dr Richard Major

Chairperson

Scientific Committee

 

Proposed Gazettal date: 09/12/11

Exhibition period: 09/12/11 – 03/02/12

 

References:

 

Benson SR, Dutton PH, Hitipeuw C, Samber B, Bakarbessy J, Parker D (2007) Post-nesting Migrations of Leatherback Turtles (Dermochelys coriacea) from Jamursba-Medi, Bird’s Head Peninsula, Indonesia. Chelonian Conservation and Biology 6, 150–154.

 

Binckley CA, Spotila JR, Wilson KS, Paladino FV (1998) Sex determination and sex ratios of Pacific Leatherback Turtles, Dermochelys coriacea. Copeia 1998, 291-300.

 

Cogger, HG. (2001) ‘The Status of Marine Reptiles in New South Wales.’ Unpublished report prepared for the New South Wales National Parks and Wildlife Service.

 

Department of the Environment, Water, Heritage and the Arts (DEWHA) (2010) Dermochelys coriacea in Species Profile and Threats Database, Department of the Environment, Water, Heritage and the Arts, Canberra. Available from: http://www.environment.gov.au/sprat. Accessed July 2010.

 

Dutton PH, Hitipeuw C, Zein M, Benson SR, Petro G, Pita J, Rei V, Ambio L, Bakarbessy J (2007) Status and genetic structure of nesting populations of leatherback turtles (Dermochelys coriacea) in the Western Pacific. Chelonian Conservation and Biology 6, 47–53.

 

Hamann M, Limpus C, Hughes G, Mortimer J, Pilcher N (2006) ‘Assessment of the conservation status of the leatherback turtle in the Indian Ocean and South East Asia.’ (IOSEA Marine Turtle MoU Secretariat, Bangkok)

 

Limpus C (2006) Status of leatherback turtles in Australia. In: ‘Assessment of the conservation status of the leatherback turtle in the Indian Ocean and South East Asia’. (Eds. M Hamann, C Limpus, G Hughes, J Mortimer and N Pilcher) pp. 15-21. (IOSEA Marine Turtle MoU Secretariat: Bangkok)

 

Limpus C (2009) ‘A biological review of Australian marine turtle species. 6. Leatherback turtle, Dermochelys coriacea (Vandelli).’ Queensland Environmental Protection Agency 2009.

 

Pritchard PCH (1982) Nesting of the Leatherback Turtle, Dermochelys coriacea in Pacific Mexico, with a New Estimate of the World Population Status. Copeia, 1982, 741-747.

 

Reina RD, Mayor PE, Spotila JR, Piedra R, Paladino FV (2002) Nesting ecology of the Leatherback Turtle, Dermochelys coriacea, at Parque Nacional Marino Las Baulas, Costa Rica: 1988–1989 to 1999–2000. Copeia 2002, 653–664.

 

Sarti Martinez AL (2000) Dermochelys coriacea. In: IUCN 2010. IUCN Red List of Threatened Species. Version 2010.2. <www.iucnredlist.org>. Accessed July 2010.

 

Spotila JR, Dunham AE, Leslie AJ, Steyermark AC, Plotkin PT, Paladino FV (1996) Worldwide population decline of Dermochelys coriacea: Are Leatherback Turtles going extinct? Chelonian Conservation and Biology. 2, 209-222.

 

Tarvey L (1993) First nesting records for the leatherback turtle Dermochelys coriacea in northern New South Wales, Australia, and field management of nest sites. In ‘Herpetology in Australia: A Diverse Discipline’. (Eds D Lunney and D Ayers) pp. 233–237. (Royal Zoological Society of New South Wales: Chipping Norton)

 

Threatened Species Scientific Committee (TSSC)(2008a). Commonwealth Listing Advice on Dermochelys coriacea. [Online]. Department of the Environment, Water, Heritage and the Arts. Available from: http://www.environment.gov.au/biodiversity/threatened/species/pubs/1768-listing-advice.pdf. Accessed July 2010.

 

Threatened Species Scientific Committee (TSSC) (2008b) Commonwealth Conservation Advice on Dermochelys coriacea. [Online]. Department of the Environment, Water, Heritage and the Arts. Available from: http://www.environment.gov.au/biodiversity/threatened/species/pubs/1768-conservation-advice.pdf. Accessed July 2010.

 

Wells RW (2007) Some taxonomic and nomenclatural considerations on the class reptilia in Australia. An Introduction to the Sea Turtles of Australia. Australian Biodiversity Record 2007, 1-90.

Page last updated: 09 December 2011