Episode 235: Almost Gone, The Great Hammerhead Shark

We continue to cover species from the ocean during this Plastic Free July with the Great Hammerhead Shark. There are 9 species of hammerhead sharks, all are on a trajectory to extinction. Alarmingly, the largest of the family, the Great Hammerhead, is critically endangered. Due to the pressures of overfishing, shark finning, by catch, and others, the Great Hammerhead is in deep peril. These incredibly unique sharks with their hammer heads deserve our attention and they need your help.

Great Hammerhead History

Sharks are one of the oldest classifications of animals still living on our planet. They date back nearly 450 million years and have survived every mass extinction event known. In fact, sharks were swimming in the world’s oceans before there were even trees, which first made their appearance nearly 385 million years ago. This is what makes this current “Sixth” mass extinction so alarming. Many shark species, to include hammerheads, are on a steep decline to extinction.

Our modern group of sharks emerged around 195 million years ago. There are over 400 species of shark. They are separated into 8 different orders. Hammerheads belong to the order Carcharhiniformes. This also includes other shark species like tiger, blue, lemon, bull and whitetip sharks. Hammerheads first emerged about 20 million years ago and in the family of Sphyrinidae there are 9 species. The Great Hammerhead’s scientific name is Sphyrna mokarran.

Great Hammerhead Physiology

The most obvious physiological feature of the hammerhead shark is their head, also called a “cephalofoil.” It is one of the most unique physiological adaptations in the natural world. The huge advantage the hammer shaped head of this shark is it gives them a superior field of vision compared to any other shark species. In fact, Hammerhead sharks can see 360 degrees around them. This allows them to spot prey above and below them. It also gives them superior binocular vision compared to other types of sharks. Another advantage to the large cephalofoil is it increases the amount of surface area for their special electrical receptors that help them find prey. These “ampullae of Lorenzini” are a network of electroreceptors, sensory organs that detect electric fields in water. Thus, they have a greater ability to find prey.

Another aspect of the large hammerhead on these sharks is its affect on its ability to move in the water. Some thought the cephalofoil acted like a wing and would aid in lift while swimming. Yet, recent research didn’t show this to be true, but rather it does act like a wing in that when the shark moves its head up or down, it allows greater maneuverability. Thus, Hammerheads are more agile compared to other sharks.

Gaylord, M.K., Blades, E.L. & Parsons, G.R. A hydrodynamics assessment of the hammerhead shark cephalofoil. Sci Rep 10, 14495 (2020). https://doi.org/10.1038/s41598-020-71472-2

The Great Hammerhead’s main prey species are sting rays. They are thought to be immune to the venom from the stingrays barbs, as many hammerhead sharks have been found with many barbs in their mouths and even throats. The Great Hammerhead will also eat fish, crustaceans, cephalopods, others sharks, and even other Great Hammerheads.

It is through the Great Hammerhead can live up to 45 years in the wild. They have been found in depths of almost 1000 feet (300 m), but typically live in coastal shallow waters of 260 feet (80 m).

Attacks on humans by any hammerhead shark are extremely rare. There are only 16 documented reports of attacks on humans with no fatalities. Hammerheads mouths are smaller than other sharks and preying on any mammal is extremely rare, to include people.

Great Hammerhead Conservation

The Great Hammerhead is Critically Endangered! They are highly sought for their fins and are often casualties of bycatch. While we do not have population numbers, sightings of Great Hammerheads are now becoming even more rare.