Scalloped Hammerhead Shark

(Sphyrna lewini)


Web site designed by Julie Watson

          

Pictures from Bioinfo Animal Pictures Archive, and Scuba Diving and Snorkeling World Wide with Carl Roessler. See bibliography.

Classification: The Scalloped Hammerhead Shark belongs to the Family Sphyrnidae, and are distinguished by their unusually wide heads. There are eight species within the Family Sphyrnidae within the Class Chondrichthyes, which includes the rays and chimaeras. The Scalloped Hammerhead is the most common of the hammerheads, followed in abundance by the Great Hammerhead (Sphyrna mokarran.)

Appearance: The hammerheads are the most distinguishable of the sharks with their wide, blunt heads in the shape of a doubleheader hammer. The Scalloped Hammerhead are light gray with white undersides. They typically grow to be 8 to 10 feet in length, and weigh 250 to 350 pounds. Their eyes are located on either side of their elongated heads, giving their brains two completely separate images. In relation to their body size, the Scalloped Hammerhead's mouth and teeth are small. The different species of hammerheads are difficult to tell apart by most people.

Range: The Scalloped Hammerhead is found in all the world's tropical waters, and most warm temperate regions. In late spring to fall they can be sighted in the Gulf of Mexico or off Florida's Atlantic coast. Scalloped Hammerheads have also been seen in the waters of the Mediterranean, Australia, and numerous islands.

Habitat: They prefer to be near shore, sometimes within estuaries or bays. They can also be found wandering offshore, yet this is rare.

Prey: The Scalloped Hammerhead is a viscous hunter, feeding on a wide variety of fish, squid, and crustaceans, and they have been known to be cannibalistic. Their most common prey by far is stingrays. one hammerhead caught was found to have 96 stingray barbs imbedded in his mouth and jaws!

Reproduction: Scalloped Hammerheads have live young, as do all the Sphyrnidae. The females come into shallow waters to breed, and the pups are born between October and January. They have litters of between four and 37 pups, which are born about two feet in length. Little else is known of the breeding patterns, as is with most species of sharks.

Behavior: Most species of hammerheads are solitary, however the Scalloped Hammerhead is found exclusively in schools. The schools range in numbers, from between fifty to over 200 individuals. The schooling pattern is believed to be useful in breeding and hunting. Hundreds of sharks will gather around offshore islands, lending to stories of their aggressiveness. Within the schools, they display intricate interactive movements, including a corkscrew rotations. The Scalloped Hammerhead usually displays non-agressive behavior, yet a few unofficial attacks have been reported, mostly on spear fishers.

Why the Head?

  Of all the sharks, the hammerhead is probably the most distinct with it's wide, rectangular head. Scientists have pondered this question, and they have come up with three possible explanations.
        1. The head may act as a hydrofoil, or wing, allowing the shark better swimming control. It adds
                lift to provide them more agility.
        2. Water is channeled through grooves on the head, providing enhanced smell.
        3. To aid in location of prey, the head is saturated with electromagnetic sensors. This theory is
                parallel with the notion that stingrays are a favorite food of the hammerhead, as the sharks then
                can detect the stingrays, which hide underneath the sand.

     Threat or Threatened?
    Although hammerheads in general are usually not aggressive, some of the larger specimens have on occasion attacked people. Their mouths are uncommonly small, and are more suited to eating fish. Hammerheads are important in both commercial and sport fishing. They are sought for their oil, meat, and skin. Due to their large schooling patterns while they feed, they are often caught in fisherman's nets.
 

Links to Try:
 Scalloped Hammerhead Biology
 Shark Attack!
 Sportsman's Paradise

Bibliography:

    1.    Beach-Net: The Common Hammerhead Shark
                http://www.beach-net.com/Sharkhammer.html
    2.    Bioinfo Animal Pictures Archive
                http://www.best5.net/animal/APAsrch3.cgi?dspNum=5&qt=hammerhead+shark
    3.    Compton's Encyclopedia Online
                http://www.comptons.com/ceo99-cgi/article?'fastweb?getdoc+viewcomptons+
                            A+18796+0++hammerhead'
    4.    Encarta Online Concise - Hammerhead Shark
                http://encarta.msn.com/find/Concise.asp?ti=01505000
    5.    From the Shore to the Deep Blue Sea with the San Diego Natural History Museum
                http://www.sdnhm.org/kids/sharks/shore-to-sea/hammerhead/html
    6.    Hammerhead Sharks
                http://www.liddiard.demon.co.uk/photoix/hammerhead/hammerhead.html
    7.    PBS: Sea Dwellers
                http://www.pbs.org/oceanrealm/seadwellers/hammerhead.html
    8.    Scuba Diving and Snorkeling World Wide with Carl Roessler
                http://www.divexprt.com/animals/hshark.html
    9.    Shark Attack
                http://bentaylor.com/hammer2.htm
    10.  Shark Species
                http://www.music.upm.edu.my/~hongling/ham.htm
    11.  Shark Trust
                http://ds.dial.pipex.com/sharktrust/scalhamm.shtml
    12.  Sportsman's Paradise
                http://www.sportsmans-paradise.com/species/hammerhead.html
    13.  Why the Hammer Head?
                http://www.knowledge.co.uk/frontiers/sf065/sf65b06.htm