At-vessel mortality of tawny nurse sharks (Nebrius ferrugineus) caught in the Queensland Shark Control Program

Abstract

Context The Queensland Shark Control Program (QSCP) targets potentially dangerous sharks, using a combination of large-mesh nets and baited drumlines at beaches in Queensland, Australia. The tawny nurse shark (Nebrius ferrugineus) is caught incidentally by the QSCP, and shark control programs have been identified as a moderate threat to the species in Australia. Aims Assessing at-vessel mortality (AVM) is an important first step in determining the actual impact of the QSCP on the N. ferrugineus population. Methods Data collected by QSCP contractors were used to determine factors affecting AVM of N. ferrugineus and data were analysed using generalised linear mixed modelling. Key results Mean AVM was 5.95% and 30.1% for those animals caught on drumlines and in nets, respectively. At-vessel mortality was found to increase with total length for net-caught N. ferrugineus. Sea surface temperature and sex had no effect on AVM. Conclusions Animals caught on drumlines are more likely to survive capture, compared to those caught in nets. Implications The reduction in the number of nets deployed, and the introduction of alternative methods, such as catch alert (or SMART) drumlines and drone surveillance of beaches, has likely reduced the impact of the QSCP on the N. ferrugineus population.