Abstract
The expanding use of biologging tags in studies of shark movement provides an opportunity to compare fine-scale movement behaviours among species. In May 2017, we deployed high-resolution biologging tags on four mature female sandbar sharks Carcharhinus plumbeus at Ningaloo Reef for durations ranging between 13 and 25.5 hours. Pressure and tri-axial motion sensors within these tags enabled the calculation of dive geometry, swimming kinematics and path tortuosity at fine spatial scales (m-km) and concurrent validation of these behaviours from video recordings. Sandbar sharks oscillated through the water column at shallow dive angles, with gliding behaviour observed in the descent phase for all sharks. Continual V-shaped oscillatory movements were occasionally interspersed by U-shaped dives that predominately occurred around dusk. The bottom phase of these U-shaped dives likely occurred on the seabed, with dead-reckoning revealing a highly tortuous, circling track. By combining these fine-scale behavioural observations with existing ecological knowledge of sandbar habitat and diet, we argue that this circling behaviour is likely to be a strategy for hunting benthic prey. Comparing dive geometry and energetics with those of other sharks reveals common patterns in energetically efficient oscillatory swimming.
Highlights
An understanding of the movement ecology of marine megafauna requires investigation of patterns at a range of spatial and temporal scales across an individual’s lifetime (Nathan et al, 2008)
Recent biologging studies on whale sharks (Rhincodon typus) and oceanic whitetip sharks (Carcharhinus longimanus) have shown that the foraging, energetics and movement patterns of sharks are likely linked through behaviors that minimize energy outputs, while maximizing
Data Collection In Western Australia, mature sandbar sharks are predominately found in north and north-west tropical waters (McAuley et al, 2007; Braccini and Taylor, 2016), and some degree of site fidelity have been revealed around Ningaloo Reef (Figure 1A) (Braccini et al, 2017)
Summary
An understanding of the movement ecology of marine megafauna requires investigation of patterns at a range of spatial and temporal scales across an individual’s lifetime (Nathan et al, 2008). We used biologging tags to investigate the fine-scale movement behaviors of adult sandbar sharks (Carcharhinus plumbeus) for the first time This species is globally distributed in tropical and warm temperate coastal waters, and is commercially important throughout its range (McAuley et al, 2007; Ebert et al, 2013). Because of its commercial importance, there exists a robust understanding of the broad-scale (10–1,000 km) distribution, movements and diet of the species (Stevens and McLoughlin, 1991; McElroy et al, 2006; Ellis and Musick, 2007; Grubbs et al, 2007; McAuley et al, 2007; Barnes et al, 2016; Braccini and Taylor, 2016; Braccini et al, 2017). Patterns consistent across species support the contention that this type of foraging is a key determinant of the vertical movements of sharks and other megafauna in marine environments
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