| Summary: | Remote oceanic islands harbour unique biodiversity, especially of species that rely on pelagic resources around their breeding islands. Identifying marine areas used by such species is important to reduce or limit threats that may put these species at risk. The Tristan da Cunha group of islands in the South Atlantic Ocean hosts several endemic and globally threatened seabirds and pinnipeds; how they use the waters surrounding the islands must be considered when planning industrial activities in the entire Exclusive Economic Zone (EEZ). We identified hotspots of activity by collating animal tracking data from nine breeding seabirds and one marine mammal to inform marine management in the Tristan da Cunha EEZ.To detect statistically significant areas of concentrated activity, we calculated the time-spent-in-area that tracked individuals (breeding adults) of 10 focal species (mainly breeding adults of nine seabirds and adult female Subantarctic fur seals Arctocephalus tropicalis) invested in a grid of regular 10 × 10 km cells within the EEZ, for each of four seasons to account for temporal variability in space use. Applying a spatial aggregation statistic over these grids by each species we detected areas that are used more than expected by chance. Most of the activity hotspots were either within 100 km of the islands or were associated with seamounts being spatially constant across several seasons. Moreover, some species spend a large proportion of their time-at-sea inside the EEZ during certain breeding stages, rendering the sites we identified critical for their fitness. Our approach provides a simple and effective tool to highlight important areas for pelagic biodiversity that will benefit Tristan da Cunha’s conservation planning and marine management strategies.
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