Hammerhead Shark – Sphyrna zygaena
The hammerhead is easily recognized by the unique shape of the head. The eyes are located at the ends of two thin flat lateral extensions called a cephalofoil and look from above or below to be the shape of a hammer. The nostrils are found on the leading edge of the head close to each eye. The back has a notable hump shape. The first dorsal fin sits high and upright in the typical menacing manner of a pelagic shark. The upper lobe of the tail is as long as one-third of the body length. The colour is brownish-grey and is lighter underneath. All hammerhead sharks are viviparous (give birth to live young).
Hammerheads are known man-eaters. The first fatal shark attack recorded in American waters was by a hammerhead off Long Island, New York, in 1815.
According to Arthur W. Parrott in Big Game Fishes and Sharks of New Zealand, published in 1958, writes that a Dr Mitchell records that one of three hammerheads taken at Riverhead, in 1805, contained many detached parts of a man, together with his clothes, in its stomach. Parrott doesn’t state which species of hammerhead shark they were. Big hammerheads have also been reported to attack boats.
Worldwide there are nine known species of hammerhead shark
Great Hammerhead. The largest is the great hammerhead – S. mokarran, known as the great hammerhead which can reach 20 feet (6m) in length. The front of its head is almost straight with a notch in the centre. The teeth are serrated. It is a widespread tropical species of shark. It has long been the target of wasteful shark finning practices. The great hammerhead is on the ICUN Red List of Threatened Species. That large hammerheads feed on stingrays is well known. A great hammerhead was once found to have 96 stingray barbs imbedded in its jaw, mouth and head.
You can see in the video below from the Smithsonian Channel the method used by the hammerheads to find stingrays that are completely buried beneath the sandy seabed. The shark appears to be quartering the seafloor using the electrical receptors in its hammer-shaped head. Eventually, as the hammerhead draws ever closer to its hidden prey, the stingray loses its nerve and makes a run for it. It is quickly hunted down and attacked by the shark. They don’t say on the video which species of hammerhead it is. The front edge is fairly straight and with a notch in the centre. My guess is that it is a great hammerhead.
Smooth Hammerhead – S. zygaena, is known to reach a length of 16 feet (5m). This is the species found in New Zealand waters – though generally, these are smaller juveniles around a metre in length. It is the most widely distributed of the hammerhead sharks. The front edge of the head is rounded with the lateral extensions more swept back. The notch in the centre of the leading edge is absent. The teeth are serrated but the serrations are irregular and not very deep.
Scalloped Hammerhead – S. lewini. Also known as bronze hammerhead, kidney-headed shark, and southern hammerhead. Grows to a length of 10 feet (3m). The leading edge of the head is rounded and notched. The teeth lack serrations. In parts of the Atlantic Ocean, populations of the scalloped hammerhead have declined by 95 percent over the last 30 years largely as a result of the disgusting practice of finning whereby the fins are cut of, to be sold, and the live shark thrown back into the sea to die. Very good comparison of hammerhead shark heads photograph and other info on this page at the Florida Museum of Natural History.
Whitefin Hammerhead – S.couardi. This a large West-African species similar to the scalloped hammerhead.
Winghead shark – S. blochii. The head can extend as far as 50 percent of its body length and is swept well back. Reach about 6 feet (1.9m) in length. Found in the shallow coastal waters of the central and western Indo-Pacific. Winghead shark on Wikipedia.
Bonnethead Shark – S. tiburo. It has the smallest cephalofoil of all the hammerhead sharks. The head is shaped more like that of a shovel than a hammer.
Scoophead Shark – S. media. A smaller and lesser-known of the hammerhead sharks. Reaches 1.5m in length. Found in the tropical waters of the western Atlantic Ocean and in the eastern Pacific Ocean.
Scalloped bonnethead shark – S. corono. The smallest species of the hammerheads. Maximum length 92cm. Found in the East Pacific Ocean coastal waters from the Central Gulf of California to Peru.
Smalleye Hammerhead – S. tudes. Also known as the golden hammerhead, or curry shark. Found in the Southwest Atlantic, the Mediterranean Sea and Eastern Pacific. Maximum length 1.34m. It is one of the most abundant species along the east coast of South America. There are very good photographs and information about the smalleye hammerhead on this page at the Florida Museum of Natural History.
Hammerhead Sharks around New Zealand
As mentioned above only one of these species is found in New Zealand waters, the smooth hammerhead shark – Sphyrna zygaena. They are much more common around the North Island, especially during summer. The smooth hammerhead shark is a tropical to subtropical species preferring warmer water. In summer they travel at least as far south as Cook Strait.
The New Zealand hammerhead shark catch record on rod and line is held by A. Paul Jnr who caught a 211.83kg (466lb 15oz) specimen in the Bay of Islands on 18 December 1977. Most of the hammerheads found in New Zealand waters are smaller juveniles about 1m in length.
Like all the hammerhead sharks the smooth or common hammerhead is viviparous and gives birth to litters of 20–40 pups.
Hammerhead sharks will take trolled lures, and will readily take oily baits drifted in a berley trail. According to Captain Frank Mundus and Bill Wisner in their famous book Sportfishing for Sharks, “hammerheads of all species are fish eaters. They devour skates and are especially fond of stingrays in warmer seas. They will also eat other sharks, including their own kind. Mundus and Wisner believe the best all-around bait is a strip of bonito or other tuna.
According to Peter Goadby in Saltwater Gamefishing Offshore and Onshore hammerheads are a lighter shark for their length than great whites and tiger sharks. If their bodies were thinker they would rival the big two of the shark family. According to Goadby big ones are hard to subdue. They make fast surface and mid-water runs diving and circling the boat. Big ones are also difficult to hold on the leader.
Above: Rare footage shows an attack on a hammerhead shark by a tiger shark off the coast of Louisiana. A sport fisherman had gotten the hammerhead on the line only minutes before the other, much larger shark approached the fishing boat and seized its prey. Sport angler Ryan Willsea and his brother Aaron captured the footage using a selfie stick to submerge an action cam.
Above video: A hammerhead shark locates a stingray hiding beneath the ocean floor. Unnerved, the Stingray makes a dash for freedom – but is it too late?