Inter-island movements of scalloped hammerhead sharks (Sphyrna lewini) and seasonal connectivity in a marine protected area of the eastern tropical Pacific

Marine top predators are common at offshore bathymetric features such as islands, atolls, and seamounts, where most pelagic reef fish reside, while certain sharks perform inter-island movements between these formations. Scalloped hammerhead sharks are known to school in great numbers at small islands and seamounts in the eastern tropical Pacific (ETP) and are very susceptible to fisheries while moving into the open sea. It is, therefore, essential to understand hammerhead inter-island movements and environmental effects to provide baseline information for their conservation and management within and beyond an insular marine protected area. Movements of scalloped hammerheads were analyzed in the Galapagos Marine Reserve (GMR) and ETP, and environmental factors were linked to their movements. Hammerheads were tagged (N = 134) with V16 coded pingers (July 2006 to July 2010) in the northern Galapagos and detected at listening stations around four islands in the GMR and two isolated islands in the ETP, 700 and 1,200 km away. Hammerheads formed daytime schools at specific locations, but dispersed at night. Overall, more daytime than nighttime detections were recorded at all receivers in the northern Galapagos Islands, and more detections in the up-current sides of these islands. Hammerheads remained more days at the northern islands during part of the warm season (December–February) compared to the cool; however, fewer individuals were present in March–June. Movement modes were diel island excursions (24-h cycles) in the northern Galapagos and inter-island in the GMR and ETP at different scales: (1) short back-and-forth (