Bull sharks (Carcharhinus leucas) are highly adaptable apex predators that depend on riverine and estuarine environments as critical nursery habitats. However, the combined roles of kinship and movement in shaping population structure remain poorly resolved off the Australian east coast. In this study, we integrated single nucleotide polymorphism (SNP) data with acoustic telemetry to examine fine-scale genetic structuring, relatedness, and spatial connectivity across three river systems on the Sunshine Coast, southeast Queensland (SEQ), Australia.
Genetic analyses revealed significant differentiation among rivers, indicating that each nursery operates as a discrete natal ground. Close kin relationships (full- and half-siblings) were detected exclusively within individual river systems, while relatedness between rivers was limited to distant (cousin-level) relationships. These patterns are consistent with strong female philopatry coupled with male-mediated gene flow.
Acoustic tracking revealed that sub-adult females from differing rivers overlap in their broader coastal habitat use across SEQ, including intermittent visitation to neighbouring rivers and regular return to the lower estuaries of their natal systems. These dynamics underscore the vulnerability of local populations to the loss of reproductively important females before they recruit to the breeding population–emphasising the need to consider both genetic structure and ecological connectivity when implementing local shark control management arrangements for these apex predators.