Residency, site affinity and coastal movements of the southern African endemic spotted gully shark Triakis megalopterus

Abstract

Rising global concern regarding the conservation and management of shark species makes it essential to identify key ecological species to guide conservation efforts, especially species with more restricted distributions such as endemic species. The southern African endemic spotted gully shark Triakis megalopterus is currently listed as Least Concern on the IUCN Red List of Threatened Species. Though not commercially exploited, increased catches of this species by recreational fishers and high misidentification with other species of Triakidae in commercial fisheries are bringing uncertainty regarding the future of the population. Although T. megalopterus is known for localised behaviour, the extent of its site fidelity and fine-scale movements remain largely unknown. Using passive acoustic telemetry, this study assessed the species’ residency, site fidelity and movement patterns along the Western Cape coast of South Africa. Overall, the data revealed low detections, suggesting that individuals are using coastal areas not currently covered by receivers. Tagged T. megalopterus exhibited seasonal detection patterns within their zone of tagging, with increased detections during winter months. A high number of the detections occurred after the estimated parturition period; thus, the existing receiver array might not cover potential nursery areas for the species. The results also show that some individuals do undertake long-distance movements to other zones of the coastline, possibly driven by the need to locate reliable food sources. Finally, the species did not significantly use marine protected areas (MPAs), highlighting the importance of better receiver coverage and the need to expand existing MPAs.