Mapping the Inter-Island Shark Highways

Hammerhead sharks are highly migratory animals, executing long journeys in search of feeding, reproduction, and socialization sites. They are not distributed randomly in the open ocean, but rather tend to congregate in certain ‘‘hotspots’’. It has long been known that hammerhead sharks congregate at several islands of the Eastern Tropical Pacific, such as Cocos Island (Costa Rica), Malpelo Island (Colombia), and the Galapagos Islands (Ecuador). Through shark tagging experiments, scientists are learning more about the relationships between these shark populations and how to develop efficient regional management strategies for these animals.

Migramar researchers attach a satellite tracking transmitter to the dorsal fin of a silkey shark

Hammerhead shark movement studies began in Cocos Island National Park, Costa Rica in 2004. The consortium of NGOs taking part in this research is know as Migramar. The group got its start by tagging hammerhead sharks with acoustic telemetry, and is now moving on to tag and study several pelagic shark species with satellite receivers.

Preliminary data shows that hammerhead sharks migrate between the Islands of the eastern tropical Pacific in direct routes. One shark tagged in Galapagos Islands traveled 693 km to Cocos Island in 14 days. Movements are yet to be confirmed between the islands and the mainland.

Tagged sharks are tracked as the migrate between islands in the eastern tropical Pacific

Knowledge of the migratory trends of these animals will assist in the establishment of regional management plans. If a marine reserve is established, where should the boundaries be? Should it be permanent or temporary? Would the expansion of current marine reserves benefit sharks? Good science is needed to answer these questions, and that’s what Migramar is all about.

Visit Migramar’s website ( for a list of its partners and projects.


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