Intra-specific variation in movement and habitat connectivity of a mobile predator revealed by acoustic telemetry and network analyses

Abstract

Few studies have considered linkages of mobile predators across large spatial scales despite their significant and often critical role in maintaining ecosystem function and health. The bull shark (Carcharhinus leucas) is a large, widespread coastal predator capable of undertaking long-range movement, but there is still limited understanding of intra-regional differences in movement and habitat connectivity across latitudes within the same coastline. This study used acoustic telemetry data and network analyses to investigate long-range movements, residency patterns and seasonal habitat linkages of sub-adult and adult C. leucas along the east coast of Australia. Our results revealed that C. leucas tagged in Sydney Harbour were mainly present within this temperate estuary in summer and autumn; the rest of the year individuals were detected in tropical and subtropical habitats from southern and central Queensland. In contrast, the detection probability of C. leucas tagged in the Townsville Reefs (central Great Barrier Reef) peaked in spring, with a portion of the tagged population migrating south during the summer months. Differences in residency time between tagging locations were also detected, as all C. leucas tagged in Sydney Harbour were absent between June and November, but 35% of the tropical-reef tagged population remained resident year-round. Network analyses complemented these findings by revealing different seasonal habitat use between regions, thus highlighting complex seasonal-habitat linkages of C. leucas along the coast. Our findings support the hypothesis that the timing, duration, and drivers involved in the long-range movements and connectivity of sub-adult and adult C. leucas vary between latitudinal regions, most likely driven by the interaction between seasonal temperature changes, foraging and reproduction.

Using stable-isotope analysis and acoustic telemetry data to infer broad-scale migration patterns of Port Jackson sharks (

“…There is a growing body of evidence that elasmobranchs of the same sex and age class exhibit intraspecific variation in residency, movement and habitat use within a season or on an annual cycle (Vaudo et al 2014;Bass et al 2021a;Espinoza et al 2021). Intraspecific variation in migration behaviour in other taxa, in particular overwintering or nonbreeding locations of birds (Saino et al 2004;Leyrer et al 2013;Goodenough et al 2017;Steenweg et al 2017), can influence the fitness and reproductive success of individuals, with consequences for their survival and resilience.…”

Factors Affecting Shark Detection from Drone Patrols in Southeast Queensland, Eastern Australia

“…This result is similar to, albeit slightly higher than, findings from the NSW drone trial, where only 1.9% of flights recorded bull, white and/or whaler sharks [ 11 ]. Importantly, there were only nine sightings of bull or white sharks during the current trial, with only four beach evacuations, highlighting that occurrence of these shark species close to beaches are rare, even though they migrate through the study region [ 26 , 27 , 28 ]. No tiger sharks were sighted during the trial, despite them occurring in this area [ 26 , 29 ] and being caught on drumlines at North Stradbroke Island Ocean Beach during the drone trial period (Queensland Shark Control Program, unpublished data).…”

Ontogenetic changes in the tooth morphology of bull sharks (Carcharhinus leucas)

“…The bull shark Carcharhinus leucas Valenciennes, Müller & Henle 1839 is a versatile bite-feeding predator capable of inhabiting both freshwater and marine environments in tropical and temperate regions worldwide and exploiting diverse resources (Espinoza et al, 2021;French et al, 2017;Heupel et al, 2015;Lee et al, 2019;Livernois et al, 2021;Niella et al, 2017Smoothey et al, 2016Smoothey et al, , 2019Thorburn & Rowland, 2008;Werry et al, 2011). Juvenile C. leucas use estuaries as nursery areas Matich & Heithaus, 2015) and while adults are considered apex predators, juveniles are not.…”

“…e ., up to 4 years) in rivers and estuaries before transitioning to the marine environment (Pillans et al ., 2005 ; Thorburn & Rowland, 2008 ). This size‐based segregation in space use consists of larger animals using open marine environments to follow resources (Espinoza et al ., 2021 ) and habitats with less competition, while the smallest individuals make use of environments with lower associated risk (Heupel et al ., 2015 ; Heupel & Simpfendorfer, 2008 ).…”