Classifying the diving behaviour of flatback turtles (Natator depressus) from multi-sensor tags

Renae N Lambourne

Flatback turtles (Natator depressus) are the only marine turtle endemic to Australia, occurring exclusively in turbid shelf waters and unlike other species of marine turtle, flatback turtles are considerably understudied. Understanding the diving behaviour and ecology of flatback turtles is important because they are the only species of marine turtle without a pelagic oceanic stage, and their limited geographic range means they are more susceptible to anthropogenic threats. In particular, understanding the diving behaviour during the inter-nesting interval is important as known inter-nesting areas often overlap with pressures from industry and coastal development. Flatback turtles (n=5) were equipped with Daily Diary (DD) multi-sensor tags that recorded data from movement sensors including an accelerometer, magnetometer and gyroscope as well as recording pressure (as a measure of depth), global positioning system (GPS) surface locations, speed and temperature at a temporal frequency of 50 Hz. High resolution data collected using multi-sensor tags were used to classify the diving behaviour of flatback turtles using unsupervised k-means clustering into k= 5 clusters, irrespective of dive depth. Here, the results from clustering and dead-reckoning identified that flatback turtles perform a combination of active and inactive dives in the initial days of the internesting interval, putatively performing a range of behaviours from resting to foraging, travelling and exploration. Notably, recreating the underwater movement paths of dives performed by flatback turtles using dead-reckoning revealed a single dive profile can have different functions associated. These results demonstrate that classifying the data collected using multi-sensor tags provide the opportunity to objectively quantify the diving behaviour of inter-nesting flatback turtles, and the activity budgets associated throughout the internesting interval.

Classifying the diving behaviour of flatback turtles (Natator depressus) from multi-sensor tags

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