Great Hammerhead Sharks, Sphyrna mokarran, are apex predators found in warm coastal waters throughout the world. They are solitary marine animals that migrate long distances of more than 1,200km (756 miles) at a time.
They are the largest of the Hammerhead species, reaching an average length of 13ft and 500 lbs.
Habitat/Distribution
Great Hammerhead Sharks are found in a vast range of territories. They are usually found in coastal-pelagic and semi-oceanic waters with water temperatures 20°C (68°F) or higher. They are seen both close to shore (along continental shelves, passes/lagoon of coral reefs, island terraces) and open waters.
Image courtesy of calicojackcharters
They are commonly found near coral reefs. at shallow depths but have also been reported at depths of up to 300 meters (984ft).
Reproduction
Great Hammerhead Sharks give birth to live young (are viviparous), giving birth to an average litter of 13-42 pups, with some reports of litter sizes up to 55. These sharks grow faster than some other species of the same size, sexually maturing between 5 and 9 years of age. Their gestation period lasts around 11 months, and they usually reproduce once every 2 years, giving birth in the late spring and summer.
Image courtesy of P.Salinas-De-Leon
Did you know? The distinctive shape of hammerheads changes slightly as they grow. Newborn sharks have a much rounder shape, that flattens out as they get older.
These sharks copulate via internal fertilization, and have been seen synchronize swimming, and spiraling slowly around each other prior to mating. They are among the only species that seen copulating at the surface; most mate at or near the seafloor.
The average Great Hammerhead Shark’s lifespan is 30-40 years in the wild, with some reports of 44+ years.
Description
The largest species of hammerhead shark, the Great Hammerhead grows to an average length of 13ft and weight of 500lbs but there have been records of Great Hammerhead Sharks growing up to 20ft long and weighing up to 991lbs.
Great Hammerhead Sharks have a more prominently rectangular shaped head than other hammerheads. It is nearly straight with a slight indentation in the middle. They also have a very tall first dorsal fin, unproportional compared to other shark species.
Colors range from gray, deep olive green, to brownish green, with a whitish grey underbelly.
This species is sexually dimorphic, with the female generally growing larger than the male.
They have long triangular teeth with serrated edges used to tear apart prey.
Image courtesy of sharkresearchinstitute
Diet
Hammerhead sharks use their specialized hammer-shaped head to help them hunt for prey. The shape of their head is thought to have evolved to help maximize sensory input from organs like the Ampullae of Lorenzini. They use this sensory organ to detect chemical, physical, and thermal changes in prey as well as electrical fields.
They feed on a large range of prey including stingrays, cephalopods, crustaceans, bony fish and other sharks. They use the sensory organs in their head to detect prey buried in the sand and have been observed using the side of their head to pin down one of their favorite meals, stingrays.
Image courtesy of Steve Hincyznski
They primarily feed at dusk and have a preference for stingrays, other rays, and skates.
Threats
Great Hammerhead Shark populations have declined drastically due to overfishing. They are caught as bycatch and targeted specifically for their fins. Often caught in longlines, bottom trawls, gillnets, purse seine, and hook-and-like fisheries, more than 90% of Great Hammerhead Sharks die once captured. This means even with recreational fishing, where this species is especially valued, even when released they have a high mortality rate.
Once caught, they are commonly sold for meat, oil, shark fin soup, leather, and fishmeal.
They have been registered as Critically Endangered due to their rapidly declining numbers.
Image courtesy of IUCN Red List