Marine Turtles of Cobourg Peninsula, Northern Territory
: Nesting Ecology and Threat Abatement

  • Jennifer Elin Petursson

Student thesis: Coursework Masters - CDU

Abstract

The neritic habitat and large geographic range of marine turtles means that many questions about fundamental aspects of their ecology and population dynamics remain unanswered. Marine turtle populations are likely to be affected simultaneously by multiple threatening processes across different life stages. Conservation management must prioritise effective, achievable, and sustainable methodologies to address these threats.

Cobourg Peninsula, in north-west Arnhemland, provides important nesting habitat for five species of marine turtles. This study documents key nesting characteristics of green turtles (Chelonia mydas), flatback turtles (Natator depressus), hawksbill turtles (Eretmochelys imbricata) and olive ridley turtles (Lepidochelys olivacea) in the Smith Point area of Garig Gunak Barlu National Park. Additionally, it assesses the effect of installing custom-made predator exclusion devices to minimise the depredation of L. olivacea nests by monitors (Varanus sp.) and dingoes (Canis lupus dingo).

Weekly track surveys and opportunistic nest excavations conducted from 2015 to 2020 provide seasonality and abundance of nesting emergences, nesting success, frequency of predator presence and nest depredation events, chamber depth, clutch size and incubation success for all species. For L. olivacea, the Smith Point area is identified as ‘habitat critical to the survival of a species’. Predator presence and nest depredation events were more frequently associated with L. olivacea and E. imbricata than C. mydas and N. depressus. Monitors and dingoes were responsible for the majority of nest depredations.

The installation of predator exclusion devices had a significant impact on the hatching success of L. olivacea nests. None of the treated nests experienced any predation, and mean hatching success of treated nests was 60.89% (± 31.53 SD, range 0 - 95.77%, n = 10). Of the control nests, 90% were completely destroyed by predators within five days of oviposition. Hatching success of the one remaining control nest was 0.303% (± 0.96 SD, range 0 – 3.03, n = 10). Hatching success amongst L. olivacea was higher in nests that had a chamber depth of less than 500mm, and where the depth to the top of the egg chamber was greater than 200mm.
Date of Award2022
Original languageEnglish
SupervisorCarla C. Eisemberg (Supervisor)

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