ORCID

Abstract

BackgroundMeasuring coastal-pelagic prey fields at scales relevant to the movements of marine predators is challenging due to the dynamic and ephemeral nature of these environments. Whale sharks (Rhincodon typus) are thought to aggregate in nearshore tropical waters due to seasonally enhanced foraging opportunities. This implies that the three-dimensional movements of these animals may be associated with bio-physical properties that enhance prey availability. To date, few studies have tested this hypothesis.MethodsHere, we conducted ship-based acoustic surveys, net tows and water column profiling (salinity, temperature, chlorophyll fluorescence) to determine the volumetric density, distribution and community composition of mesozooplankton (predominantly euphausiids and copepods) and oceanographic properties of the water column in the vicinity of whale sharks that were tracked simultaneously using satellite-linked tags at Ningaloo Reef, Western Australia. Generalised linear mixed effect models were used to explore relationships between the 3-dimensional movement behaviours of tracked sharks and surrounding prey fields at a spatial scale of ~ 1 km.ResultsWe identified prey density as a significant driver of horizontal space use, with sharks occupying areas along the reef edge where densities were highest. These areas were characterised by complex bathymetry such as reef gutters and pinnacles. Temperature and salinity profiles revealed a well-mixed water column above the height of the bathymetry (top 40 m of the water column). Regions of stronger stratification were associated with reef gutters and pinnacles that concentrated prey near the seabed, and entrained productivity at local scales (~ 1 km). We found no quantitative relationship between the depth use of sharks and vertical distributions of horizontally averaged prey density. Whale sharks repeatedly dove to depths where spatially averaged prey concentration was highest but did not extend the time spent at these depth layers.ConclusionsOur work reveals previously unrecognized complexity in interactions between whale sharks and their zooplankton prey.

Publication Date

2024-01-31

Publication Title

Movement Ecology

Volume

12

Issue

10

Acceptance Date

2024-01-16

Deposit Date

2024-07-11

Funding

This collaborative work was led by researchers from the University of Western Australia Oceans Institute, Oceans graduate school and the Australian Institute of Marine Science (AIMS) with assistance from researchers based at the James Cook University, the University of Tasmania, St Andrews University, Scotland, Australian National University (ANU) and The Marine Biological Association of the United Kingdom. The authors and their respective organisations acknowledge the Yinggarda, Baiyungu and Thalanyji peoples who are the Traditional Owners of Sea Country of Nyinggulu (Ningaloo) reef and its surrounding waters on which this work was undertaken. The authors recognise these peoples ongoing spiritual and physical connection to Country and pay our respects to their Aboriginal Elders past and present. We would like to thank Vijay Udyawer for his help and guidance with the 3DKUD calculations and plotting. We would also like to thank the RV Solander crew for field support, Miles Parsons, Simon Spagnol and Roland Proud for the technical assistance with echosounder installation and operation; Laurance Dugal for analysis of samples, and volunteers Emily Lester and Sammy Andrzejaczek for capturing ID photos, Lauren Peel and Danielle Su for their contribution to the ship-based work. B.D was supported by the Australian Government Research Training Program (RTP) Scholarship at UWA. A.M.M.S. was supported by a 2020 Fellowship in Marine Conservation by the Pew Charitable Trusts, and an ARC DP DP210103091. This collaborative work was led by researchers from the University of Western Australia Oceans Institute, Oceans graduate school and the Australian Institute of Marine Science (AIMS) with assistance from researchers based at the James Cook University, the University of Tasmania, St Andrews University, Scotland, Australian National University (ANU) and The Marine Biological Association of the United Kingdom. The authors and their respective organisations acknowledge the Yinggarda, Baiyungu and Thalanyji peoples who are the Traditional Owners of Sea Country of Nyinggulu (Ningaloo) reef and its surrounding waters on which this work was undertaken. The authors recognise these peoples ongoing spiritual and physical connection to Country and pay our respects to their Aboriginal Elders past and present. We would like to thank Vijay Udyawer for his help and guidance with the 3DKUD calculations and plotting. We would also like to thank the RV Solander crew for field support, Miles Parsons, Simon Spagnol and Roland Proud for the technical assistance with echosounder installation and operation; Laurance Dugal for analysis of samples, and volunteers Emily Lester and Sammy Andrzejaczek for capturing ID photos, Lauren Peel and Danielle Su for their contribution to the ship-based work. B.D was supported by the Australian Government Research Training Program (RTP) Scholarship at UWA. A.M.M.S. was supported by a 2020 Fellowship in Marine Conservation by the Pew Charitable Trusts, and an ARC DP DP210103091. This research was supported by funding from Santos Ltd and The Australian Institute of Marine Science (AIMS).

Keywords

3D utilisation distribution, Bio-physical drivers, Foraging ecology, Habitat use, Marine megafauna, Oceanography, Predator–prey, Zooplankton

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