Limpus et al., 2002:

"There are consistent differences in the timing of the nesting seasons, in size of nesting females, number of eggs per clutch and size of eggs between the EA nesting population and the adjacent nesting population concentrated in eastern Gulf of Carpentaria (Limpus et al., 1993). These data are consistent with the EA nesting population being reproductively isolated from the northern Australian population(s). Population genetics research now supports this conclusion (Moritz et al., 1998). This EA population forages and breeds within a single nation and lives almost totally within a World Heritage Area and within the world’s largest multiple use marine park (Great Barrier Reef Marine Park). Approximately 70% of the total annual nesting for this stock occurs within National Parks or equivalent.

Data spanning 32 years of tagging studies provide insights into the population trends and conservation status of this EA stock: tagging census studies at the minor rookery of Mon Repos and adjacent beaches on the Woongarra Coast since 1968 (Fig. 3), nightly census studies (average number of females ashore per night at peak nesting season) at Wild Duck Island, which is the second largest east coast nesting population, since 1981 (Fig. 4) and track count census data from the intermediate sized nesting population at Curtis Island since 1970 (Fig. 5). These demonstrate no obvious trend in the size of the annual nesting population at these rookeries over three decades, which is presumed to span about one generation. On average, females recruiting to breed for their first breeding season are significantly smaller than turtles with a past breeding history (remigrants) (Parmenter and Limpus, 1995). A constant mean size of turtles at three rookeries across three decades (Fig. 6) is indicative of a long term, approximately constant ratio of first time breeders to remigrants in these populations.

With long term mark recapture studies using secure tagging methods, the rate of recruitment of first time breeders into the adult population (adult recruitment rate) can be estimated by measuring the proportion of untagged females entering the annual nesting population. This adult recruitment rate, measured using the total nesting populations at widely scattered EA rookeries (Wild Duck Island, Woongarra Coast), are similar, in the range of 10-20% and approximately stable over several years (Fig. 7). A similar adult recruitment rate has been estimated at Peak Island, the largest EA rookery (Parmenter and Limpus, 1995). Adult recruitment rates in the range of 10-20% are what we expect for an approximately stable marine turtle population.

The comparison of the limited abundance data from early this century and present reduced breeding numbers at some sites are suggestive of a substantial population decline having occurred within the EA genetic stock of flatback turtles within the last century. However, the results of rigorous tagging studies at multiples sites (annual census; stable adult size; low, stable adult recruitment rate) over the last three decades of this century are indicative of currently stable populations for this EA stock. No comparable data sets exist for assessment of the status of the flatback turtle stocks of northern Australia. With its distribution effectively contained within the Great Barrier Reef World Heritage Area and the Great Barrier Reef Marine Park and with ~70% of annual nesting occurring within National Parks, the EA N. depressus stock has the potential for being the most secure population of marine turtles globally. This is supported by the current population stability of this stock."

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Citation and/or URL

Limpus, C.J., Parmenter, J. & Limpus, D.J. 2002, The status of the flatback turtle, Natator depressus, in eastern Australia. In: Proceedings of the twentieth annual symposium on sea turtle biology and conservation, eds A. Mosier, A. Foley & B. Brost, NOAA Technical Memorandum NMFS-SEFSC 477, Miami, USA,  140-142.

Spatial Coverage

Eastern Queensland

Temporal Coverage

1968 - 2000

Update Frequency

Not applicable

Other Information

None