April 2015 Shark of the Month: Great Hammerhead
Name: Great Hammerhead Shark Scientific Name: Sphyrna mokarran
Key Features: The Great Hammerhead Shark is light-grey in color and has an unmistakable hammer-shaped head, called a cephalophoil, which is used to improve maneuverability, increase sensory capacity (utilizing Ampullae of Lorenzini), and provide a wider range of vision. There are 9 “hammerhead” species in the genus Sphyrna, so how do you pick out a Great Hammerhead? The Great Hammerhead is the largest of the hammerheads, and mature sharks can range between 6-20 ft in length! They also have a very distinctive first dorsal fin that is very high and curved, and is easily seen while the shark is patrolling shallow water for prey.
Where it’s found: Great Hammerhead sharks can be found worldwide in tropically warm waters, and favor a diverse range of habitats. They can be found in shallow, coastal waters, hanging around continental shelves or way offshore in semi-oceanic areas. Great Hammerheads are not a schooling shark though, so you will most likely spot singular individuals instead of large groups, unlike the schooling Smooth Hammerhead or Scallop Hammerheads.
Diet: Great Hammerhead sharks feed on stingrays, boney fish and smaller invertebrates, and they utilize their broad cephalophoils to help them locate prey buried in the sand, much like how treasure hunters use metal detectors on the beach. Since their heads are covered with electroreceptors (Ampullae of Lorenzini), they can easily pick up weak electrical currents given off by live prey hidden under the sand. This is their primary way of searching for prey; as a result Great Hammerheads are commonly seen “patrolling” shallow, sandy areas with their bodies only inches off the ocean floor. Conservation Status: IUCN Red List- Endangered, CITES Appendix II. Threats: Due to their large fins, all Hammerhead shark species are specifically targeted by poachers as part of the shark fin trade. The Great Hammerhead shark is prized for it’s exceptionally large first dorsal fin and faces a steady decline in population numbers due to target fishing and bycatch. Recent market prices show that an average Great Hammerhead fin has a market value of $45- 100/lb. In 2013, the Scalloped, Smooth, and Great Hammerhead were all added to CITES Appendix II, which allows for increased worldwide protection and requires permits with the exportation of any fins.