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Examining annual catch trends and gear selectivity of bull sharks (Carcharhinus leucas): Implications for Queensland's coastal management

Riley Banaghan , Alexis Levengood, Bonnie Holmes

Abstract

Context. In coastal waters of eastern Australia, the bull shark (Carcharhinus leucas) is one of the most frequently caught shark species within the Queensland Shark Control Program (QSCP). Aims. An analysis of 27 years of QSCP catch data (1996 – 2022) involving 2352 bull sharks from nine locations spanning 1700 kilometres captured in gillnets or on drumlines identified changes in catch composition and gear selectivity. Methods. Linear regression tested trends in length and catchability, while selectivity and bias were evaluated through mean and distribution comparison tests. Key results. Drumlines caught more sharks (80.1%), indicating stronger selectivity for C. leucas of all size classes. A decline in standardised catch per unit effort (CPUE) was noted in tropical regions for each gear type, yet increases of bull sharks caught within subtropical gillnets (p < 0.001). The sex ratio was female biased on drumlines (1.85:1) and in gillnets (1.53:1). Conclusions. Our findings corroborate previous research highlighting the significance of considering regional variations in CPUE, sex ratios and size compositions of sharks caught in shark control programs. Implications. Catch rates provide insights into shark population trends, particularly where gear configurations have remained relatively consistent. Downward trends may indicate unsustainable harvest, or external influences.