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ESR prepress abstract   -  DOI: https://doi.org/10.3354/esr01125

Activity of loggerhead turtles during the U-shaped dive: new insights using angular velocity metrics

Richard M. Gunner*, Rory P. Wilson, Mark D. Holton, Rebecca Scott, Alex Arkwright, Andreas Fahlman, Marie Ulrich, Phil Hopkins, Carlos Duarte, Christophe Eizaguirre

*Corresponding author:

ABSTRACT: Understanding the behavioural ecology of endangered taxa can inform conservation strategies. The activity budgets of the loggerhead turtle Caretta caretta are still poorly understood because much tracking shows horizontal displacement that ignore dives and associated behaviours. However, time-depth recorders have enabled researchers to identify flat, U-shaped dives (or “Type 1a” dives) and these are often labelled as ‘resting’ dives on the seabed. Video- and acceleration-based studies have demonstrated this is not always true. Focusing on sea turtles nesting at the Cabo Verde archipelago, we describe a new metric, ‘absolute angular velocity’, derived from magnetometer data that integrates indices of angular rotation in the horizontal plane to infer activity. Using this metric, we evaluated the variation in putative resting behaviours during the bottom phase of type 1a dives for five individuals at sea between 13 and 17 days during a single inter-nesting interval (over a total of 75 turtle days). We defined ‘absolute resting’ within the bottom phase of type 1a dives when there was no discernible acceleration or angular movement. Whilst absolute resting constituted a significant proportion of each turtle’s time budget for this 1a dive type, turtles allocated 16–38% of their bottom time to ‘activity’, with many dives being episodic, comprised of intermittent bouts of rest and rotational activity. This implies that previously considered ‘resting behaviours’ are complex and needs to be accounted for in energy budgets, particularly since it may impact conservation strategies.