The Hammerhad Shark Family – Sphyrnidae

There are currently three members of the Hammerhead Shark or Sphyrnidae Family, and all three are  from both the Atlantic Ocean and the Pacific Ocean are presented in this website:

FROM THE ATLANTIC AND PACIFIC (3):

The Sphyrnidae Family includes the Bonnethead, the Hammerhead and the Scoophead Sharks and has eight global members all found in one genus, Sphyrna, of which six species are found in Mexican waters, three in the Pacific Ocean and three in both the Atlantic and Pacific Ocean.. They are global travelers found in all tropical seas along coastlines and continental shelves.

The Hammerhead Shark is characterized by a strongly flattened front head with side extensions in the shape of an axe, mallet, or spade with eyes on the outer edges. Their distinctively-shaped head is known as a cephalofoil and is used for sensory reception, maneuvering, and prey manipulation. Their eyes, mounted on the extreme edges of the cephalofoil, afford these sharks with 360-degree vision in the vertical plane and allow them to see above and below at all times. They have elongated rounded bodies that are moderately slender, cylindrical or somewhat compressed. They are normally light gray with a greenish tint that transitions to white ventrally. They have a set of massive teeth with their front and rear teeth being blade-like with 1 point; their lower teeth are straight and their upper teeth are oblique and deeply notched on the rear side. Their teeth are distinctive and commonly found as fossils dating to the Miocene Epoch, 20,000,000 years ago. They have 5 gill slits with the last 1 located over the front of their pectoral fins. Their heads also have electrosensory pores that allow them to locate electric signals emitted by potential prey. They have strongly asymmetrical crescent-shaped caudal fins with a notched base and a well-defined ventral lobe. They have 2 dorsal fins, the first being high, pointed, with a short base, and located behind the pelvic fins, and the second being much smaller and similar to the anal fin.

There are 8 species of Hammerhead Sharks known globally, of which 6 frequent Mexican waters. They range in length from 90 cm (3 feet 0 inches) to 6.0 meters (19 feet 8 inches) and 3.0 kg (6 lbs 10 oz) to 580 kg (1,279 lbs) in weight. They typically swim in large schools of as many as 100 individuals during the day and become solitary hunters at night. They consume a large range of prey including crustaceans, fish, octopus, and squid. Stingrays are one of their favorites. They normally patrol the bottom stalking prey and then utilize their head to pin down prey. Some Hammerheads are cannibalistic consuming other hammerheads including their own young. Hammerheads reproduce once a year with reproduction being viviparous with internal fertilization. Litter sizes are 12 to 15 pups, which are born as miniature adults. Juveniles are left to fend for themselves and tend to form schools and travel together; they are known to inhabit shallow shoreline waters to avoid predation.

Attacks on humans are attributed to only 3 of the 8 known hammerheads – the Great, the Scalloped, and the Smooth. Globally these attacks occur at a level of about 50 per year with fatalities exceedingly rare. They are generally very timid around divers and will depart the area.

From a conservation perspective these sharks are in serious trouble. Due to human demand for their fins, predominantly in southeast Asia, they have been significantly overfished. Historically fishermen cut off their fins (finning) and discarded the balance of the fish. Globally seven Sphyrna and one Eusphyra are currently being monitored from a conservation perspective. The Great Hammerhead, Sphyrna mokarran and the Scalloped Hammerhead, Sphyrna lewini are considered to be Endangered; the Golden Hammerhead, Sphyrna tudes and the Smooth Hammerhead, Sphyrna zygaena are considered  to be Vulnerable; the Scalloped Bonnethead, Sphyrna corona and the Winghead Shark, Eusphyra blochii are considered to be Near Threatened; the Bonnethead, Sphyrna tiburo is considered to be of Least Concern; and the Carolina Hammerhead, Sphyrna gilberti, the Scoophead, Sphyrna media, and the Whitefin Hammerhead, Sphyna couardi are presently being assessed. Globally catch rates of Hammerheads are in significant decline. As recently as 10 years ago I was personally catching large Scalloped and Smooth Hammerheads on a fairly regular basis. Due to their overabundance of sharp teeth, they require strong wire leader to boat. The last time I caught one was at least 5 years ago. Both the Mexican and United States Governments have very recently placed a ban on the retention of all sharks by fishermen and this ban is actually being enforced and respected by local fishermen. As such they are no longer a targeted species.

The Hammerhead Sharks are important as food fish globally. They are also used to produce various sub-products, most significantly Vitamin A, which is obtained from their livers. Their fins are in high demand for use in Shark-Fin Soup predominantly in Asian markets and command high prices. In certain areas the Great Hammerhead and Scalloped Hammerhead are popular subjects for ecotouristic diving. Bonnetheads and Smooth Hammerheads can be found in many public aquariums, especially along the East and Gulf Coasts of the United States.