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Foraging habitat locations of flatback (Natator depressus) and olive ridley turtles (Lepidochelys olivacea) in northern Australia

Justin Smith, Colin Limpus, Takahiro Shimada, Laurie Booth, Eve Hinchliffe , Mariana Fuentes, Frank Loban, Shane Preston, Mark Hamann

Abstract

Context. Understanding the spatial ecology of endangered species is important for their management. With flatback turtles (Natator depressus) vulnerable and the olive ridley turtle (Lepidochelys olivacea) endangered under Australia’s EPBC Act 1999, it is important to understand their movement activity to assess exposure to threats better and appropriately manage population demographics. Aims. Describe, quantify, and compare the foraging patterns of flatback turtles from the Arafura Sea genetic stock and olive ridley turtles from the eastern Gulf of Carpentaria (GoC) genetic stock. Methods. Satellite telemetry was used to track post-nesting flatbacks (n = 16) and olive ridleys (n = 8) to identify foraging activity behaviour and locations between 2013-2017. Key results. Overall, core foraging home ranges showed considerable variability from strong site fidelity to extensive spatial movement (flatbacks: 1 – 1065 km2, olive ridley: 2 – 113 km2). Foraging areas for both species were identified to cross over state and international boundaries (Torres Strait, eastern GoC, western GoC, Kakadu coast, Joseph Bonaparte Gulf and the Arafura Sea within Australia and Indonesia) with nine individuals foraging in Indonesian waters and five foraging in both Indonesian and Australian waters. Conclusions. Flatback and olive ridley turtles in northern Australia have a large, widespread spatial distribution with varying use levels across the space. Foraging hot spots identified in this study can improve and guide the designation of biologically important areas. Inter and intra-specific overlaps between foraging grounds were consistent with previous research, strengthening the understanding of foraging hot spots for flatbacks and olive ridleys in Indonesia and the Joseph Bonaparte Gulf. Implications. This study thus emphasises the importance of area-based management to benefit highly mobile species from multiple populations and taxa, potentially from all life cycle phases.

WR24054  Accepted 04 November 2024

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