Predicting core areas of flatback turtle hatchlings and potential exposure to threats

Abstract

The lack of data on distribution of juvenile marine species can limit conservation efforts. As hatchlings, marine turtles are too small to track using satellite telemetry, so their at-sea distribution remains unknown. This knowledge gap is critical, as hatchlings already experience high mortality in coastal zones. In addition, further risks to their survival may occur beyond these areas, linked to threats associated with in-water artificial infrastructure and/or attraction to artificial lights and thus increased mortality from higher risk of predation or exhaustion from disorientation. To fill this gap, we used particle tracking forced by an ocean circulation model to predict the dispersal of flatback turtle Natator depressus hatchlings from 12 nesting sites off the coast of Western Australia. We used the model outputs to calculate the distribution of these ‘virtual hatchlings’ and infer the core area of hatchling use over 3 dispersal phases (1-4, 10-15 and 25-30 d). We then calculated the overlap between core areas and 2 anthropogenic threats (in-water artificial infrastructure and light pollution). Core areas were predominately located on the continental shelf during all dispersal phases, supporting the hypothesis that flatback turtles remain in neritic areas. Most (70-80%) of the core area during early dispersal (Days 1-4 and 10-15) contained at least one threat. However, less than half of the area used between Day 25 and 30 was exposed to threats. In the absence of empirical data on hatchling distribution, our results have predicted the core areas used by early life stage flatback turtles to assist in conservation management of these threatened species.