Depth dependent dive kinematics suggest cost-efficient foraging strategies by tiger sharks

Tiger sharks Galeocerdo cuvier are a keystone, top-order
predator that are assumed to engage in cost-efficient movement and
foraging patterns. To investigate the extent to which patterns of
oscillatory diving by these animals conform to these patterns, we used
a biologging approach to model their cost of transport.
High-resolution biologging tags with tri-axial sensors were deployed
on 21 tiger sharks at Ningaloo Reef for durations of 5-48 hours. Using
overall dynamic body acceleration (ODBA) as a proxy for energy
expenditure, we modelled the cost of transport of oscillatory
movements of varying geometries in both horizontal and vertical planes
for tiger sharks. The cost of horizontal transport was minimized by
descending at the lowest possible angle and ascending at an angle of
5-14°, meaning that vertical oscillations conserved energy compared to
swimming at a level depth. Reduction of vertical travel costs occurred
at steeper angles. The absolute dive angles of tiger sharks increased
between inshore and offshore zones, presumably to reduce the cost of
transport while continuously hunting for prey in both benthic and
surface habitats. Oscillatory movements of tiger sharks conform to
strategies of cost-efficient foraging, and shallow inshore habitats
appear to be an important habitat for both hunting prey and conserving
energy while travelling.
Methods
Tiger sharks (n=22) were captured and tagged at Ningaloo Reef, Western Australia in April and May 2017 following the methods described in Andrzejaczek et al.

In brief, tiger sharks were captured using baited drumlines and secured alongside a 5.8 m vessel with the leader and tailrope. Either a CATS (Customized Animal Tracking Solutions, Australia) Diary Tag (dimensions and weight with clamp: 15 x 4 x 6 cm and 300 g) or CATS Cam Tag (23 x 4 x 7 cm and 500 g)  were then clamped to the dorsal fins for periods of 7-48 hours (see table S1). All tags were equipped with tri-axial accelerometers, magnetometers and gyroscopes, and sensors for depth, temperature and light. All sensors recorded continuously at 20 Hz. In addition, 14 of the 22 deployments recorded video at pre-programmed hours of the day for a maximum of six hours per deployment. The tags detached from the clamp in the days following tagging, and were recovered using a handheld VHF receiver operated from a vessel.

Datasets are in the raw format downloaded from the tags. Deployment notes can be found in the supplementary information of the manuscript.