The great hammerhead shark, Sphyrna mokarran, is the largest hammerhead, recognized by its distinctive T-shaped head (cephalofoil). As an apex predator, it plays a significant role in maintaining marine ecosystem balance and indicates oceanic well-being.
Global Range of the Great Hammerhead
Great hammerhead sharks inhabit tropical and warm temperate waters globally. Found between 40° North and 37° South latitudes, they inhabit all major ocean basins: Atlantic, Pacific, and Indian Oceans.
In the Atlantic, their presence extends from North Carolina to Uruguay, encompassing the Gulf of Mexico and the Caribbean Sea. They are found along the coasts of Morocco to Senegal and occasionally in the Mediterranean Sea. In the Pacific Ocean, their range stretches from Southern Baja California to Peru, and across to regions like the Ryukyu Islands, Australia, New Caledonia, and French Polynesia. The Indian Ocean also serves as a home for these sharks, with sightings reported along its entire rim.
Specific Habitat Preferences
Within their global range, great hammerheads prefer specific coastal and offshore environments. They are frequently found over continental shelves and island terraces, often in shallow waters (as little as one meter deep). These include coral reefs, lagoons, and coral atoll passes.
While known for coastal presence, they also inhabit deeper oceanic waters, recorded up to 300 meters, but more commonly around 80 meters. They tolerate varying salinities, entering brackish waters like estuaries and bays, often as nursery areas. They prefer warmer waters, typically above 20°C.
Seasonal Movements and Migration
Great hammerhead sharks undertake seasonal movements and extensive migrations. These journeys are influenced by prey availability, water temperature, and breeding grounds. Some populations, like those off Florida, move northward along the Atlantic coast in summer, seeking cooler waters or following prey.
Tagging studies reveal individuals travel over 1,200 kilometers in months. Sharks tagged in Florida have been tracked migrating as far north as Virginia and back, covering approximately 3,000 kilometers. Despite long-distance travels, research indicates great hammerheads often exhibit site fidelity, returning to specific locations year after year for up to five months.
Conservation of Their Habitats
Understanding great hammerhead habitats and migratory patterns is paramount for their conservation, as populations face significant threats. The species is Critically Endangered on the IUCN Red List, with a global population decline over 80% in three generations.
A primary threat is overfishing, driven by demand for their large fins in the international shark fin trade. Great hammerheads are vulnerable to incidental capture (bycatch) in various fisheries, with mortality rates exceeding 90% once caught. Beyond fishing pressure, habitats are threatened by degradation from coastal development, pollution, and climate change. Rising ocean temperatures and altered prey distribution due to climate change directly affect their living spaces and migratory routes. Effective conservation requires protecting critical habitats, implementing stricter fisheries management, and establishing marine protected areas that safeguard residential and migratory corridors.