Paul A Butcher ^1,2,3* Matt Broadhurst ^1,4 Victor Marten Peddemors ⁵ Aidan J Mcgarty ⁶ Brian Cullis ⁷

• ¹ NSW Department of Primary Industries, National Marine Science Centre, Coffs Harbour, Australia
• ² National Marine Science Centre, School of Environment, Science and Engineering, Southern Cross University, Coffs Harbour, Australia
• ³ School of Life and Environmental Sciences, Deakin University, Geelong, Australia
• ⁴ School of the Environment, The University of Queensland, Brisbane, Australia
• ⁵ NSW Department of Primary Industries, Sydney Institute of Marine Science, Sydney, Australia
• ⁶ School of Mathematics and Applied Statistics, University of Wollongong, Woolongong, Australia
• ⁷ School of Mathematics and Applied Statistics, University of Wollongong, Wollongong, Australia

For 87 years, gillnets have been deployed off up to 51 beaches in New South Wales, Australia, to reduce shark bites by three target species: white (Carcharodon carcharias), bull (Carcharhinus leucas), and tiger (Galeocerdo cuvier) sharks. Recently, concerns over excessive mortalities of target and non-target species led to trialling baited drumlines with electronic catch sensors, called 'shark management alert in real time' (SMART). The SMART drumlines are more selective than gillnets and because catches are removed within 30 minutes, nearly all survive. There is now an environmental incentive for replacing gillnets with actively fished SMART drumlines, but important questions remain unanswered, including the number of SMART drumlines required at a beach and their risk of not being deployed due to adverse weather, which doesn't affect gillnets. To address the first question, we analysed 22,025 diurnal SMART drumline deployments across 1637 days. Among 494 sharks caught, 71% were targeted species (298 whites, 43 tigers, and 9 bulls). No multiple daily catches were recorded for bull or tiger sharks, but there were 46 instances where up to five white sharks were hooked off the same beach on the same day, with twenty occurrences within five km and 60 min of initial capture. Proximal captures remained independent of the number of deployed SMART drumlines or the region. Consequently, we recommend at least two or three SMART drumlines beach -1 to ensure a baited hook remains in the water while others are checked. To answer the second question, we obtained the weather conditions during 30 years of gillnetted target shark catches (290 white sharks and 93 tiger sharks) and correlated these to known operational limitations of SMART drumlines. Adverse weather would have restricted deploying SMART drumlines to 67-83% of the period gillnets were deployed, and up to ~75% of those occasions when white and tiger sharks were gillnetted. While we acknowledge there would be fewer water users during adverse sea conditions, if SMART drumlines replace gillnets, their greater catching efficiency, selectivity, and survival of released animals need to be rationalised against fewer temporally comparable deployments.