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

Samantha Andrzejaczek,Adrian C Gleiss,Charitha Pattiaratchi,Mark G Meekan,Taylor K Chapple,Karissa O Lear

doi:10.1098/rsos.200789

Abstract

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 oscillatory diving by tiger sharks 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 h. Using overall dynamic body acceleration 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 smallest possible angle and ascending at an angle of 5–14°, meaning that vertical oscillations conserved energy compared to swimming at a level depth. The 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.

Highlights

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 oscillatory diving by tiger sharks conform to these patterns, we used a biologging approach to model their cost of transport
Using overall dynamic body acceleration 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

Summary

Introduction

Galeocerdo cuvier, are a keystone, top-order predator that are assumed to engage in cost-efficient movement and foraging patterns. Tagging studies have revealed that the fine-scale movements of tiger sharks are characterized by patterns of oscillatory ascents and descents (dives) throughout the water column [2,11], a behaviour that is shared by many species of large epipelagic fishes [12]. For tiger sharks, these dives have been recorded in a number of habitats, ranging from very shallow (less than 4 m) seagrass beds in Shark Bay [2], to deeper (greater than 100 m), offshore waters in Hawaii and Brazil [11,13,14]. We predict that the diving energetics and kinematics of these animals will be dependent on the depth of the habitat being occupied, with deeper waters featuring steeper dive angles when searching for prey to allow for faster transit times between the surface and seabed

Methods

Results

Discussion

Conclusion