The Great Fiji Shark Count

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You are here: Home / Species / Shark Species / Scalloped hammerhead shark

Scalloped hammerhead shark

Sphyrna lewini

Biology

Scalloped Hammerhead Sharks (Sphyrna lewini) are probably the most commonly found species of hammerheads located in coastal regions, appearing in very shallow waters such as estuaries and inlets. Their distribution in the water reaches from the surface down to a depth of approx. 275 m. The young, however, remain mostly in shallow waters along the shore to avoid the danger of falling into the mouths of predators. At certain times of the year and places, and during certain phases of their lives, scalloped hammerheads form very large schools, sometimes counting hundreds of individuals, but they also swim the oceans alone. Some populations remain stationary, others clearly wander, migrating in the direction of the poles in summer. Some sexually-related migrations have also been observed, e.g. females who undertake migrations during particular periods of their sexual development.

Appearance

Hammerhead sharksThe scalloped hammerhead shark belongs to the large hammerhead species, and like all representatives of this family, has the typically formed “hammer” consisting of a central dent and an arched front edge (hence the name). Another typical characteristic is the free end tip of the second dorsal fin which almost reaches the tail fin. Their coloring is mainly olive, bronze or light brown with a white belly. The edges of the fins are usually darker on young animals but becomes lighter as they grow older.

Size

Mature females can reach a length of more than 4 meters, the average length is, however, less. Males reach sexual maturity at a length of about 160 cm, females when they reach approx. 210 cm. The pups measure approx. 50 cm at birth.

Feeding

This hammerhead species feeds mostly on fish such as sardines, herring and mackerels, occasionally also on invertebrates such as octopuses. Large scalloped hammerhead sharks also eat small-sized shark species such as the Atlantic sharpnose shark (Rhizoprionodon terraenovae) or the blacktip reef shark (Carcharhinus melanopterus).

Reproduction

Scalloped hammerheads bear their young alive and have an egg yolk placenta. Pregnancy lasts between 9 and 10 months. Depending on their size, the females give birth to between 15 and 30 pups. The “hammer” is made of cartilage and is very soft when the young are born so as to easen the birth process. Young scalloped hammerheads grow relatively slowly when compared to other shark species.

Distribution

Scalloped hammerhead sharks are found practically around the world in the coastal regions of tropical, subtropical and moderate climate zones.

Behavior

As already mentioned, this shark species tends to form huge schools whose function is presumed to be manifold and may, among other things, concern feeding habits and reproduction. Although many studies also consider this behavior to be a group protective function, this is somewhat questionable since the animals have practically no natural enemies after reaching full maturity. Groups of scalloped hammerheads prefer staying in regions which have pinnacles or sea mounts which reach from great depths practically to the water’s surface. Latest research also shows that these sharks can make use of the earth’s magnetic field during their migrations.

Encounters with Humans

Although these sharks have definitely been involved in accidents, they are not really considered dangerous in the sense of being aggressive. Since they often appear in estuaries where visibility is very limited and where the influence of fresh water does not allow an optimal reaction of their electrical sensors (ampullae of Lorenzini), any accidents with humans are more likely a defensive reaction when surprised or frightened.

Similar Species

When it comes to size and appearance three additional species resemble the scalloped hammerhead and are commonly found in the latter’s area of distribution. These include the great hammerhead(Sphyrna mokarran), the smooth hammerhead (Sphyrna zygaena) and the whitefin hammerhead(Sphyrna couardi). They can be differentiated by the form of their “hammers”, the first dorsal fins and by color. Identification problems with the whitefin hammerhead are only possible in the latter’s area of distribution which is limited to the Ivory Coast.

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Welcome to The Great Fiji Shark Count !

Throughout the months of April and November every year, you have the opportunity to help celebrate and record Fiji’s amazing coral reef biodiversity, show you care about our world’s delicate coral reef systems, and have fun, by taking part in the FIJI-WIDE SHARK COUNT!

Easy to do, this is suitable for visitors and locals alike, whether you like to fish, snorkel, or SCUBA dive. We hope that tourists, school children, scientists and all people with an interest in the marine environment will take to the reefs with us to search for the Sharks of Fiji!

The Great Fiji Shark Count will be held across Fiji every April and November every year.

You can do a single count, or take part as many times as you like during that month, so that you cover different reefs. All data will be gratefully accepted!

So, see your resort, watersports operator or travel agent, get your Shark identification materials and dive into the beautiful blue waters of Fiji, to be a part of history!

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