Abstract
An understanding of the role that large marine predators play in structuring trophic flow and nutrient cycling in marine ecosystems requires knowledge of their fine-scale (m-km) movement behaviours. In this study, biologging tags were used to reveal new insights into the three-dimensional fine-scale movement ecology of tiger sharks (Galeocerdo cuvier) at Ningaloo Reef, Western Australia. Tags deployed on 21 sharks in April-May 2017 for durations of 5-48 hours recorded both physical parameters such as depth and temperature, and, through the use of accelerometers, gyroscopes and compasses, in-situ measurements of animal trajectory and locomotion. Animal-borne-video enabled the validation of behavioural signatures, mapping of habitat, and recording of interactions with prey. Collectively, these data were used to examine the link between vertical (oscillations) and horizontal (tortuosity) movements, and link sensor data to prey interactions recorded by the video. This biologging approach revealed complex movements that would otherwise be invisible within the time-depth records provided by traditional tagging techniques. The rate of horizontal turning was not related to vertical oscillations, suggesting that vertical movements occur independently of searching behaviours in tiger sharks. These animals displayed tortuous movements possibly associated with prey searching for 27% of their tracks, and interactions with prey elicited varied responses including highly tortuous paths and burst movements. Accurate speed measurements and GPS anchor points will considerably enhance the value of magnetometer data in future studies by facilitating more accurate dead-reckoning and geo-referencing of area-restricted search behaviours.
Highlights
The movement patterns of large predatory marine fishes such as tiger sharks (Galeocerdo cuvier) have typically been sampled using acoustic telemetry and satellite tagging approaches (Andrews et al, 2009; Papastamatiou et al, 2009, 2015; Barnett et al, 2010; Brunnschweiler et al, 2010; Vaudo et al, 2014; Comfort and Weng, 2015; Heupel and Simpfendorfer, 2015)
We explore the extent to which multiple sensors in biologging tags reveal new insights into the fine-scale movement ecology of tiger sharks
We found evidence of foraging behavior based on path tortuosity and video recorded encounters with potential prey
Summary
The movement patterns of large predatory marine fishes such as tiger sharks (Galeocerdo cuvier) have typically been sampled using acoustic telemetry and satellite tagging approaches (Andrews et al, 2009; Papastamatiou et al, 2009, 2015; Barnett et al, 2010; Brunnschweiler et al, 2010; Vaudo et al, 2014; Comfort and Weng, 2015; Heupel and Simpfendorfer, 2015) Biologging in Tiger Sharks generate either presence/absence data sets (acoustic telemetry), or movement patterns of animals over large horizontal spatial scales (satellite tagging, 10–1,000s km) Such studies continue to transform our understanding of the ecology and biology of these animals (Chapman et al, 2015), they have two major shortcomings. Given that the behavior of large marine predators is thought to have a major role in structuring trophic flows and nutrient cycling within marine ecosystems (Heithaus et al, 2008; Lavery et al, 2010), it is imperative that we link their large-scale movement patterns with their day-to-day behaviors within the environment
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