Abstract
Greater Sydney is the largest coastal city in Australia and is where bull sharks (Carcharhinus leucas) are present every summer and autumn. A decade of acoustic telemetry data was used to identify drivers of space use for bull sharks and their potential prey, according to standardised 6-h intervals using dynamic Brownian bridge movement models. Influences of environmental, physical, and biological variables on the areas of space use, location, and predator–prey co-occurrence were investigated with generalised additive mixed models. Rainfall in the catchment affected space use for all animals (i.e. teleost species and both sexes of sharks), with varying temporal responses. Male sharks responded most promptly to high rainfall moving upstream in < 1 day, followed by teleosts (2 to 7 days), and female bull sharks after 4 days. Environmental luminosity affected male shark dispersal and space use, possibly indicating use of visual cues for foraging. Physical characteristics of habitat were important factors driving spatial overlaps between predator and prey in estuarine areas. In sandy embayments < 10-m deep, males and female bull sharks overlapped with different species, whereas males and silver trevally (Pseudocaranx georgianus) co-occurred in deep holes (> 30 m). Shark size influenced overlap between sexes, with smaller females less likely to co-occur with larger males (~ 50 cm). Variability in space use suggests spatial segregation by sex and size in bull sharks, with individuals targeting similar prey, yet either in different areas or at different times, ultimately enabling them to exploit different resources when in the same habitats.
Highlights
A variety of abiotic cues underpin behavioural responses in animal movement; effectively determining their effects on habitat use is hindered by complex relationshipsCommunicated by Kevin M
Yellowtail kingfish had the greatest number of detections across the study region, yellowfin bream were detected for longer periods of time (Fig. S2b), and bull sharks were detected across a greater number of stations than any teleost species (Fig. S2c)
While many studies have identified linkages between animal movements and particular abiotic conditions, it is likely that concomitant changes in additional drivers such as predator avoidance or prey availability contribute to the patterns observed (Schlaff et al 2014)
Summary
A variety of abiotic cues underpin behavioural responses in animal movement; effectively determining their effects on habitat use is hindered by complex relationshipsCommunicated by Kevin M. For example, within estuaries, animal movements are influenced by a complex interplay of factors such as tide (Walsh et al 2013; Smoothey et al 2019) and freshwater runoff and their associated effects such as salinity levels (Childs et al 2008; Taylor et al 2014). Fine-scale diel variability (i.e. over the circadian cycle of 24 h) in movement is closely related to energy expenditure, facilitating biological processes such as foraging (Hammerschlag et al 2006; Taylor et al 2018a) and reproduction (Walsh et al 2013; Gannon et al 2015)
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