Scalloped hammerhead (Sphyrna lewini)
|Also known as:||bronze hammerhead shark, kidney-headed shark|
|Size||Length: 370 – 430 cm (2)|
Length at birth: 43 – 55 cm (3)
Maximum weight: 152 kg (3)
The scalloped hammerhead is classified as Endangered on the IUCN Red List (1).
This large hammerhead shark can be distinguished from other hammerhead species by the ‘scalloped’ front edge of its hammer-shaped head, having three evenly spaced indentations between the wide-set eyes. The body of the scalloped hammerhead is relatively slim and is coloured brown-grey to bronze above and white below. The first dorsal fin is large but the second is much smaller. Juvenile scalloped hammerheads have darker fins than the adults (2).
The scalloped hammerhead is found in the warm temperate and tropical waters of the Atlantic, Indian and Pacific Oceans (1). It may also occur in the western Mediterranean Sea (2) (4).
Occurring mainly over continental and insular shelves and the deeper water around them, the scalloped hammerhead also regularly enters enclosed bays and estuaries. It swims at depths of between 0 and 275 metres, and is migratory in some areas, moving poleward in summer (1).
Forming impressively large schools, female scalloped hammerheads gather in the Gulf of California during the day, around underwater mountains known as seamounts, where they perform a wide range of poorly-understood behaviours (2). These aggregations are thought to be a result of many sharks, particularly younger females, seeking refuge in a safe place near a rich food supply, although many alternative theories have been put forward (5). Young scalloped hammerheads also tend to live in large schools, whereas adults usually occur singly, in pairs, or in small groups (2). These sharks feed on fish, cephalopods, lobsters, shrimps, crabs, other sharks, and rays. They are thought to be potentially dangerous to humans although few attacks have been recorded (3). The teeth of the scalloped hammerhead are best suited to seizing prey that can be swallowed whole, rather than ripping into larger prey. The hammer-shaped head is thought to be a mechanism to spread out the ampullae of Lorenzini – sensory organs that detect electric currents, chemicals in the water, and temperature changes (5). Larger shark species may attack young scalloped hammerheads, but adults have no natural enemies. Adults visit cleaning stations where fish known as cleaner wrasse remove parasites from their skin and mouths (2).
During the 9 to 10 month gestation, the eggs of the scalloped hammerhead hatch inside the body of the female. After hatching, but before birth, they are nourished by a yolk sac placenta. The female moves to shallow waters during the summer where she will give birth to between 15 and 31 live young (3).
The scalloped hammerhead is fished in low numbers commercially and as game-fish, and is also caught as by-catch in longline fisheries. Its liver is used for vitamins, its fins for soup, its meat for human consumption and its carcasses for fishmeal (1). Pups occupying shallow coastal nursery areas are particularly exposed to fishing pressures (2).
No direct conservation action is targeted at the scalloped hammerhead.
For further information on the conservation of sharks and rays see:
To find out more about scalloped hammerhead conservation projects, see:
Mohamed bin Zayed Species Conservation Fund
This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact:
- By-catch: in the fishing industry, the part of the catch made up of non-target species.
- Cephalopoda: from the Greek for ‘head-foot’, a class of molluscs that occur only in marine habitats. All species have grasping tentacles, and either an internal or external shell. Includes nautiloids, cuttlefish, squids, octopuses, and extinct ammonites and belemnites.
- Dorsal fin: the unpaired fin found on the back of the body of fish, or the raised structure on the back of most cetaceans.
IUCN Red List (January, 2010)
Florida Museum of Natural History (April, 2005)
FishBase (April, 2005)
Shark Gallery (April, 2005)
Reef Quest Centre for Shark Research (April, 2005)