Context drives movement patterns in a mobile marine predator

Abstract

Intra-specific variability in movement behaviour occurs in all major taxonomic groups. Despite its common occurrence and ecological consequences, individual variability is often overlooked. As a result, there is a persistent gap in knowledge about drivers of intra-specific variability in movement and its role in fulfilling life history requirements. We apply a context-focused approach to bull sharks (Carcharhinus leucas), a highly mobile marine predator, incorporating intra-specific variability to understand how variable movement patterns arise and how they might be altered under future change scenarios. Spatial analysis of sharks, acoustically tagged both at their distributional limit and the centre of distribution in southern Africa, was combined with spatial analysis of acoustically tagged teleost prey and remote-sensing of environmental variables. The objective was to test the hypothesis that varying resource availability and magnitude of seasonal environmental change in different locations interact to produce variable yet predictable movement behaviours across a species’ distribution. Sharks from both locations showed high seasonal overlap with predictable prey aggregations. Patterns were variable in the centre of distribution, where residency, small- and large-scale movements were all recorded. In contrast, all animals from the distributional limit performed ‘leap-frog migrations’, making long-distance migrations bypassing conspecifics in the centre of distribution. By combining multiple variables related to life history requirements for animals in different environments we identified combinations of key drivers that explain the occurrence of differing movement behaviours across different contexts and delineated the effects of environmental factors and prey dynamics on predator movement. Comparisons with other taxa show striking similarities in patterns of intra-specific variability across terrestrial and marine species, suggesting common drivers.

Seasonal occurrence and individual variability of bull sharks, Carcharhinus leucas, in a marine reserve of the southwestern Gulf of California

“…As a top predator it is hard to argument that the primary productivity could determine the occurrence patterns directly. However, some fish species like the yellowtail amberjack, Seriola lalandi , that are bull shark prey, tend to aggregate and spawn when the chlorophyll is high ( Sala et al, 2003 ; Lubitz et al, 2023 ).…”

Bull Shark (Carcharhinus leucas) Occurrence along Beaches of South-Eastern Australia: Understanding Where, When and Why

“…Individuals were also recorded revisiting coastal areas on multiple years post-release. Many animals, across a variety of taxa exhibit philopatry [ 68 ], with individuals repeatedly returning to the same stretch of coast for reproductive needs [ 66 , 69 , 70 ], foraging opportunities [ 37 , 71 , 72 , 73 ] or for reasons still largely unknown [ 26 ]. Additionally, ocean currents [ 19 ], water temperature [ 18 , 74 , 75 , 76 , 77 ], rainfall [ 38 , 39 ] and swell height [ 26 , 78 ] are well documented drivers of shark movement patterns and drivers of the behaviour shown here.…”

Both environmental conditions and intra- and interspecific interactions influence the movements of a marine predator

“…acoustic receivers) attributes as explanatory variables Robins, Snijders, et al, 2007;Snijders et al, 2006). These models account for the non-independence of the data expressed as movements between sites acting as sources or sinks (Silk & Fisher, 2017) Bull shark movements are known to be influenced by both biotic and abiotic factors (Lee et al, 2019;Lubitz et al, 2023;Niella et al, 2022;Werry et al, 2018), and anthropogenic factors (Hammerschlag et al, 2022;Werry et al, 2012), but less is known about the importance of con-and heterospecifics in movement decisions. Even if most studies on the movements of these marine predators have identified environmental factors as most influential to their movement ecology, we expect that social and competition factors may be just as important in explaining individual movements.…”