Post-release survival, movement, and habitat use of school shark Galeorhinus galeus in the Great Australian Bight, southern Australia

Abstract

Bycatch of marine mammals in the gillnet sector of the Southern and Eastern Scalefish and Shark Fishery in the Great Australian Bight prompted managers to assess the use of demersal automatic longlines as an alternative method to target gummy shark (Mustelus antarcticus). The school shark (Galeorhinus galeus) is a migratory species that is occasionally taken as bycatch when targeting gummy shark, and the stock is currently managed under a rebuilding strategy. We used pop-up satellite archival tags (PSAT) to investigate the survival, movements, and habitat use of mature female school shark (147–170cm total length) following capture and release from demersal automatic longlines. Satellite telemetry data indicated lively school sharks survived the capture, on-board handling, tagging and release processes. Tracked school sharks mostly moved offshore and across the continental shelf in south to south-easterly directions. Depth habitat use reflected semi-pelagic behavioural traits and a preference for lower mixed layer depths of 50–100m where water temperatures were 15–21°C. Two PSATs provided data that we interpreted as indicative of tag and/or tagged shark ingestion, and tag regurgitation by endothermic predators. This study also identified an area where neonate and large, mature female school sharks were observed together during the Austral summer. Findings of this study are crucial to informing current fisheries management, stock recovery and bycatch mitigation strategies off southern Australia.