Limpus, 2008:

"The C. caretta population that breeds in south Queensland (represented by Mon Repos specimens) is genetically different from the population that breeds in southern Japan (Bowen et al. 1994). This is consistent with similar findings for other major populations in the Atlantic basin (Bowen et al. 1993). Therefore the C. caretta populations of the north and south Pacific Oceans need to be managed as independent stocks. The Queensland population also has fixed genetic differences from both the South African and Oman populations of the western and northern Indian Ocean that represent about a million years of genetic isolation (Bowen, 2003). Preliminary genetic analyses of the C. caretta populations of eastern and western Australia indicate that they constitute separate stocks (Dutton et al. 2002). Apart from a small nesting population of a few hundred C. caretta annually in southern New Caledonia and Vanuatu, there is no predictable nesting by the species elsewhere in the South Pacific Ocean basin (Limpus and Limpus, 2003a). This breeding population has yet to be genetically assessed.

The size of the annual breeding population (females only) has been monitored at numerous rookeries for the eastern Australian stock for varying periods since 1968 (Limpus and Limpus, 2003a). Those data provide the primary measure of the stability of the C. caretta population(s) in the South Pacific Ocean basin:

• The total nesting population for Queensland was estimated at approximately 3500 females for the 1976 and 1977 breeding seasons (Limpus, 1985; Limpus and Reimer, 1994).
• The annual nesting population was estimated at less than 500 females in the 1999–2000 breeding season (Limpus and Limpus, 2003a).
• At all sites monitored since the mid 1970s there has been a marked decline in the number of females breeding annually, with an estimated 50–80% decline in the number of breeding females at various rookeries up to 1990 (Limpus and Reimer, 1994) and a decline of approximately 86% by 1999 (Limpus and Limpus, 2003a) (Figure 6).

The adult female displays a high degree of fidelity to her chosen nesting beach, with most females returning to the same small beach for their successive clutches within a nesting season and in successive nesting seasons (Bustard, 1972; Limpus, 1985; Limpus et al. 1984, 1994). The genetic studies provide convincing evidence that the breeding female is returning to the region of her birth (Bowen et al. 1993, 1994; Bowen, 2003). It remains to be demonstrated whether this fidelity is the result of imprinting to the natal beach during the egg or hatchling phase or whether the hatchling is first imprinted to the region of her birth and is later imprinted to her rookery(s) as an adult during her first breeding season.

Large immature turtles recruit from the oceanic pelagic environment to residency in inshore waters of eastern Australia at a CCL of 78.6 cm (southern GBR to Moreton Bay feeding areas, Table 9). This size at recruitment from the oceanic pelagic environment is independent of the coastal habitat to which they recruit (Table 9) (Limpus and Limpus, 2003b). These immature turtles are slow growing and are resident for an average of 13 years (SD = 3.7, range = 9–23, n= 15) before they commence breeding (Limpus, 1994; Limpus and Limpus, 2003b). A growth/aging experiment is in progress in which 129,921 hatchling C. caretta were "tagged" and released at Mon Repos and Heron Island during January 1974 to February 1980 (Limpus, 1985). The first recaptures of these turtles have now occurred in inshore coastal waters (Limpus et al. 1994: tag number T58404, captured 20 April 1992, Moreton Banks: immature female, carapace length = 75.6 cm; age = 15.2 yr; marked as a hatchling at Mon Repos in Jan/Feb 1977). The first adults that had been marked as hatchlings at the Mon Repos rookery have returned for their first breeding at 29 years of age in the 2003–2004 breeding season (C. Limpus, unpublished data). C. caretta in the southwestern Pacific Ocean are slow growing, taking about three decades to grow from hatchlings to breeding adults.

Population modelling research is progressively improving for the eastern Australian stock (Crouse et al. 1987; Somers, 1994; Heppell   et al. 1996; Chaloupka and Limpus, 1997; Chaloupka, 2003). It is now apparent that because of the protracted delay in maturity and the long intervals between breeding seasons, C. caretta populations will be at risk from even modest increases in mortality at any stage in their life history that have an extended impact. Chaloupka (2003) demonstrated that the greatest potential threats to the eastern Australian C. caretta stock are uncontrolled fox predation of eggs on the mainland rookeries; trawl bycatch mortality of the large immature and adult turtles in the coastal foraging areas of eastern and northern Australia and oceanic long-line bycatch mortality of the pelagic posthatchling.

In addition to the above, there is also the combined impacts of an array of other mortalities from anthropogenic activities that cause the death of C. caretta, including harvest by coastal communities in the South West Pacific region, boat strike, entanglement in fishing line and ropes, entanglement in crab-pot float lines, ingestion of synthetic debris and shark control bycatch in eastern Australia, that collectively may cause the loss of 60 or more adult and near adult turtles annually. Even if the population losses from trawling, fox predation and long-line fishery bycatch could be completely eliminated right now, these combined mortalities from other sources have the potential to compromise or delay the recovery of this severely depleted stock. If the cumulative impact of the remaining mortalities from anthropogenic sources on the total population continues, strong concern must be held for the capacity of the depleted and endangered eastern Australian stock to recovery to a secure population level."

 

 

 

 

 

 

 

 

 

 

 

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Citation and/or URL

Limpus, C.J. 2008, A biological review of Australian marine turtle species. 1. Loggerhead turtle, Caretta caretta (Linnaeus), Environmental Protection Agency, Brisbane.  

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Spatial Coverage

Primarily Queensland and Western Australia

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Temporal Coverage

For Queensland ~ 1960s to mid-2000s

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Update Frequency

Not applicable 

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Other Information

None