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Connecting hammerhead shark populations from the Eastern Tropical Pacific

Blogpost by Mariana Elizondo Sancho, Álvaro Ugalde grant awardee

Sphyrna lewiniis one of the nine species of hammerhead sharks, and it lives across the tropics worldwide. This species is categorized as Endangered, since its populations have declined more than 50% in the last 10 years, according to the IUCN. This shark is threatened by fisheries, both as bycatch and as directed fishing, since their fins are highly valued in the international fin market. 

Hammerhead shark school in the open waters from Cocos Island in the Pacific of Costa Rica. Photo: David Garcia

This shark has an interesting behavior in which females come to coastal waters called nursery areas to deliver their pups. Juveniles remain in these areas for their first years, so coastal marshes and wetlands are an important habitat for their nurturing. In Costa Rica, these areas are threatened both by habitat degradation and by fisheries. One of the most important nursery areas is the Golfo Dulce in the southern pacific of Costa Rica. 

After this first stage of life, adults move to open waters and islands, where constant migration is observed. Once in open waters and near the Cocos Island, this shark is specifically targeted for its fins. Protecting this highly mobile animal that can migrate long distances is a hard task since its populations are not in a specific geographic place during their whole lifetime. 

Also in the Eastern Tropical Pacific, population structure is not well known. Is it one population or are there several? Do females prefer specific nursing grounds to deliver their pups? Understanding population structure and movements of hammerhead sharks is vital to establish regional management and policies.

DNA extraction of hammerhead shark tissue. Photo: Mariana Elizondo

I have been researching the connectivity and genetic population structure of S. lewiniin various coastal nursing areas in Guatemala, Costa Rica and Panamá. The results of this research will be important to provide biological information for management plans that will aim to protect specific important geographical areas for this species’ persistence.


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