The hammerhead shark (Sphyrna lewini) is in danger of extinction throughout its worldwide distribution, primarily due to overfishing (Baum et al., 2007). Several studies have reported population reductions of up to a 90% (e.g., Baum & Myers, 2004; Ferretti et al., 2008) in areas within the marine protected areas of the Eastern Tropical Pacific (ETP). On Cocos Island, ~700 km from the Galapagos Marine Reserve (GMR), this species’ abundance has declined by 50% since the 1990s (White et al., 2015). Similarly, in Malpelo Island, ~1000 km from the GMR, hammerhead sharks have declined by 45% since the beginning of the 2000s (Soler et al., 2013).

The gregarious behavior and singular body form of this species have transformed it into one of the most important marine tourist attractions in the GMR (Danulat et al., 2003). It is one of the dominant reasons that Galapagos is listed as one of the best dive destinations in the world (Scuba-Diving, 2000; 2008; 2012). This species is distributed throughout the Archipelago, but can be observed in higher numbers at Wolf and Darwin Islands, especially during the cold season (Hearn et al., 2014). Despite the economic importance of this species for both tourism and commerce in Galapagos (Peñaherrera et al., 2013), little is known about its population status and its use of the GMR (Hearn et al., 2014). This document supports the recently adopted zoning system by summarizing published information and expanding that knowledge with new details about the population status of hammerhead sharks.