Temporal-spatial distribution of an island-based offshore population of common bottlenose dolphins (Tursiops truncatus) in the equatorial Atlantic

A little-studied common bottlenose dolphin (Tursiops truncatus) population inhabits the offshore waters surrounding Saint Paul's Rocks, a Brazilian marine protected area in the equatorial Atlantic Ocean. Five field expeditions (May 2011-May 2013) were conducted to characterize the habitat use, population size, and site fidelity of this population. Three different survey methods were employed: line-transect surveys, land-based surveys, and photo-identification surveys. A population size of 23 individuals (19-28, CI 95%), which were present on most sampling days (>90% of surveys), was estimated. The maximum resighting interval of photo-identified animals was 9 yr and 3 mo for five distinct individuals, based on data from nonsystematic efforts that have been ongoing since 2004. The dolphins exhibited strong site fidelity, as the minimum convex polygon (MCP, 95%) method revealed that they restricted their movements to a 0.5 km(2) area across seasons and a 0.99 km(2) area across years (95% kernel). The dolphins preferred shallow waters close to the archipelago (<1.2 km from the islands), especially on the eastern and southeastern sides, where oceanographic models have revealed persistent upwelling that may result from underwater currents and where food may be more predictably available.