Shark depredation and behavioural interactions with fishing gear in a recreational fishery in Western Australia

Shark depredation, whereby a shark consumes an animal caught by fishing gear, can cause higher mortality for target species, injury to sharks and the loss of catch and fishing gear. A critical first step towards potential mitigation is understanding this behaviour and the shark species involved, because the identity of depredating shark species is unknown in many fisheries, and behavioural dynamics of shark interactions with fishing gear are not well understood. We used line-mounted video cameras in a recreational fishery in the Ningaloo region of Western Australia to: (1) identify shark species responsible for depredation, (2) investigate behavioural interactions with fishing gear, (3) identify the prevalence of retained fishing gear in sharks and (4) quantify the influence of environmental variables and fishing methods on shark abundance during demersal fishing at 92 locations. The study was led by UWA (Jon Mitchell - then PhD student) and performed in the Ningaloo region of Western Australia. We mounted high-definition video cameras on fishing lines to monitor shark depredation events and interactions with fishing gear. We recorded location, number of lines in the water, whether fishing vessels were fishing at anchor vs. drifting, fishing depth, gear and bait type The influence of fishing methods and environmental variables on the abundance of sharks at each location was investigated. All data were collected on an ipad using the software application 'Collector for ArcGIS'. Video was analysed using EventMeasure.