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ESR 45:1-12 (2021)  -  DOI:

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

Richard M. Gunner1,*, Rory P. Wilson1, Mark D. Holton1, Rebecca Scott2,3, Alex Arkwright1,4, Andreas Fahlman4, Marie Ulrich5, Phil Hopkins1, Carlos Duarte6, Christophe Eizaguirre7

1Swansea Lab for Animal Movement, Biosciences, College of Science, Swansea University, Swansea SA2 8PP, UK
2GEOMAR Helmholtz Centre for Ocean Research, Kiel, Düsternbrooker Weg 20, 24105 Kiel, Germany
3Natural Environmental Research Council, Polaris House, North Star Avenue, Swindon SN2 1FL, UK
4L’Oceanogràfic, Ciutat de les Arts i de les Ciències, Carrer d’Eduardo Primo Yúfera, 1B, 46013 Valencia, Spain
5Institutionen för fysik kemi och biologi (IFM), Linköping Universitet, Olaus Magnus väg, 583 30 Linköping, Sweden
6Red Sea Research Centre, King Abdullah University of Science and Technology (KAUST), Thuwal 23955, Saudi Arabia
7School of Biological and Chemical Sciences, Queen Mary University of London, London E35SA, UK
*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 many tracking methods show only horizontal displacement and 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 conventionally labelled as resting dives on the seabed because they involve no vertical displacement of the animal. Video- and acceleration-based studies have demonstrated this is not always true. Focusing on sea turtles nesting on the Cabo Verde archipelago, we describe a new metric derived from magnetometer data, absolute angular velocity, 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 5 individuals over 13 to 17 d at sea during a single inter-nesting interval (over 75 turtle d in total). We defined absolute resting within the bottom phase of type 1a dives as periods with 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 need to be accounted for in energy budgets, particularly since energy budgets may impact conservation strategies.

KEY WORDS: Animal behaviour · Angular velocity · Accelerometer · Caretta caretta · Dive type · Magnetometer

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Cite this article as: Gunner RM, Wilson RP, Holton MD, Scott R and others (2021) Activity of loggerhead turtles during the U-shaped dive: insights using angular velocity metrics. Endang Species Res 45:1-12.

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