Do some tiger sharks prefer beaches? Insights for shark management from a broad-scale comparative tracking study

Abstract

Human coastal populations and water-based recreation are growing, increasing potential for interactions with sharks near beaches. At popular beaches in Australia's Great Barrier Reef Marine Park, potentially dangerous sharks are tagged using acoustic tags and relocated away from bathing areas by the Queensland Shark Control Program. This includes tiger sharks Galeocerdo cuvier, one of three species involved in most unprovoked shark bites globally. A broad-scale acoustic tracking network off eastern Australia was used to assess movement of relocated sharks and potential for recurrent risks to beachgoers posed by relocation. Over more than two years, movements of 51 relocated tiger sharks were compared to 82 sharks tagged at locations up to 135 km away from monitored beaches in the marine park (which extends ∼2300 km along Australia's northeast coast). Monitored beaches were visited by 43.1 % of relocated sharks, after median intervals of three months, compared to only 6.1 % of sharks tagged elsewhere in the marine park. Despite return visits by some individuals over extended periods, beach use remained limited, with low residency and mostly transient visits (<30 min) peaking at night, limiting risks to humans. Network analysis revealed relatively localised movements (median network diameter: 123 km), particularly in north Queensland where seasonal migrants from temperate areas were less common inshore. Our results indicate beaches are low-use areas within the home ranges of some sharks. These findings highlight challenges to coexistence with potentially dangerous sharks at beaches but support the efficacy of non-lethal relocation of tiger sharks for immediate reduction of risk.