Where giants roam: The importance of remote islands and seamount corridors to adult tiger sharks in the South Pacific Ocean

The movements of tiger sharks (Galeocerdo cuvier) across their global distribution are diverse and complex, and there remains a dearth of information about the cues that influence migrations of adults to and from offshore islands. We aimed to delineate broad-scale movements of a seasonally abundant tiger shark aggregation at Norfolk Island, a remote small island in the South Pacific Ocean, by identifying migratory pathways and important areas, as well as quantifying the association between space use and environmental factors. We satellite tracked 35 tiger sharks, consisting of some of the largest individuals ever monitored (median total length: 4.0 m), between February 2020 and April 2023. Tracking periods averaging 305 days (14 – 686 days) showed movements throughout large parts of the South Pacific Ocean including near New Caledonia, the Great Barrier Reef, Papua New Guinea, Chesterfield Islands, Vanuatu, Fiji, and New Zealand. The longest track was close to 17,000 km over 468 days. There was high seasonal fidelity to Norfolk Island with 88% of sharks tracked across multiple seasons returning at least once, mainly from New Caledonia. The median date of arrival and departure from Norfolk Island were in December and May, respectively. Coastal use of islands was the most important factor across monthly habitat suitability models, whereas sea surface temperature explained seasonal departures/arrivals from/to Norfolk Island. The findings of our study show diverse potential movement trajectories and cues used by tiger sharks, but importantly highlight the critical role of Norfolk Island and other nearshore areas in supporting large adult female tiger sharks.