Preferred sites and connectivity

Our ultrasonic tagging shows that all shark species studied so far display some degree of site fidelity. These sites tend to be very specific, so that ultrasonic receivers deployed only a few hundred meters apart can often show very different patterns of presence-absence. Hammerheads and Galapagos sharks both seem to prefer these sites during daytime hours, displaying only sporadic presence at night. There also seems to be a high degree of connectivity between sites, but within each Marine Protected Area. In the Galapagos islands for example, we found that after 12 monthds, 16 from 18 tagged hammerheads displayed movements between a site in Wolf island and another site at Darwin island, some 30 miles distant. Several individuals moved back and forth between islands throughout the year.

April and May seem to be months where less hammerheads are recorded in Galapagos, but where the greatest numbers are recorded in Cocos islands. Are the Galapagos hammerheads migrating to Cocos. Preliminary evidence suggests that they travel there directly, spending as little time as possible in the open ocean. But do males behave in the same fashion? Diving behavior of hammerheads tagged in both Galapagos and Malpelo suggest that these sharks spend most of their time in the first 50 meters of the water column, but that are capable of carrying out relatively short dives to depths of several hundred meters.