SMART Drumlines Ineffective in Catching White Sharks in the High Energy Capes Region of Western Australia: Acoustic Detections Confirm That Sharks Are Not Always Amenable to Capture

SIMPLE SUMMARY: Shark hazard mitigation measures are often introduced after human-shark interactions, which are increasing. Such measures are often contentious, and care is needed to reduce the risk to ocean users without causing negative ecosystem impacts. Here, we examined the effectiveness of Shark-Management-Alert-in-Real-Time (SMART) drumlines to catch, tag, relocate and release white sharks (Carcharodon carcharias) in the Capes region of Western Australia. The project aimed to examine the movement patterns of white sharks’ post-release to determine whether their relocation provided a reduction in risk for ocean users. The effectiveness of the program was also evaluated in terms of minimising the mortality of all animals caught. In total, 352 fish were caught over the 27-month trial period and 91% of animals were released alive in good condition. Only two white sharks (target species) were caught, both of which moved immediately offshore after capture and remained predominantly in offshore waters for the duration of tag deployment. The detection of 24 other tagged white sharks within the acoustic array during the trial period confirms that the target species were not always amenable to capture. Our results reiterate there is no simple remedy for dealing with the complexities of shark hazards and reinforce the importance of trialing mitigation measures under local conditions. ABSTRACT: The management of human-shark interactions can benefit from the implementation of effective shark hazard mitigation measures. A Shark-Management-Alert-in-Real-Time (SMART) drumline trial in the Capes region of Western Australia was instigated after several serious incidents involving surfers and white sharks (Carcharodon carcharias). The project aimed to determine whether white sharks (target species), which were relocated after capture, remained offshore using satellite and acoustic tagging. Over a 27-month period, 352 fish were caught, 55% of which comprised tiger sharks (Galeocerdo cuvier). Ninety-one percent of animals were released alive in good condition. Only two white sharks were caught; both were relocated ≥ 1 km offshore before release and moved immediately further offshore after capture, remaining predominately in offshore waters for the duration of their 54-day and 186-day tag deployments. Our results confirm that desirable animal welfare outcomes can be achieved using SMART drumlines when response times are minimised. The low target catches and the detection of 24 other tagged white sharks within the study area supported the decision to cease the trial. Our results reiterate there is no simple remedy for dealing with the complexities of shark hazards and reinforce the importance of trialing mitigation measures under local conditions.