Comparative Space Use of Sympatric Sharks at a Remote Island in the South Pacific Ocean

Seamounts and offshore islands support unique assemblages of sharks. The aim of this study was to contribute to the limited knowledge of how co-existing shark species partition spatial resources at these remote bathymetric features, particularly those influenced by a mix of temperate and tropical oceanographic conditions, as well as human activities. The space use of 34 dusky (Carcharhinus obscurus), 32 Galapagos (C. galapagensis), 47 tiger (Galeocerdo cuvier), and 20 sandbar (C. plumbeus) sharks was monitored with acoustic telemetry between 2021 and 2024 in coastal waters around Norfolk Island, Australia, a remote island in the southwestern Pacific Ocean. Seasonal patterns of residency and fine-scale site fidelity were compared across species during this multi-year study. Tiger sharks, consisting primarily of mature females, were seasonally present at Norfolk Island with peak residency during the Austral summer (November to April). A similar pattern existed for juvenile sandbar sharks, although departures from the island were not as common. Both species rarely overlapped in space with each other or resident (year-round) juvenile dusky and Galapagos sharks, which were often detected in shallow waters at boating/fishing piers where incidental feeding readily occurs. Tiger sharks also showed a strong affinity to a specific area on the west side of the island where organic waste (livestock) disposal into the ocean has been ongoing for several decades. Nearshore areas of Norfolk Island support mature and immature sharks in unique ways, and human activities may further influence the space use of these species. The consistent use of specific areas around Norfolk Island across species highlights the importance of offshore islands as hotspot areas fulfilling basic biological needs at both local and oceanic scales.