Some Facts About Our Beloved Hammerheads

Species of Hammerhead

Great Hammerhead (Sphyrna mokarran)

Great Hammerhead

• The largest of all the Hammerhead Species 
• It's hammer is particularly wide and straight but with a distinctive notch in the centre 
• It's dorsal fine is impressively large
• They can grow up to an intimidating 610cm and can weight up to 500kg!! (although they tend to average more around 230kg)
• The will often feed on rays, they will use their hammer to pin the ray down, then bite off its wings until its immobilised
• They can be found around in the world in warm, temperate, waters. 
• It had been spotted at Pulau Siapdan!! 
• They are listed as 'Endangered' on the IUCN Red List.

Smooth Hammerhead (Sphyrna zygaena)

Smooth Hammerhead

• The Smooth Hammerhead has a tall and sickle-shaped dorsal fins and black tips on its pectoral fins 
• They can grow up to 350cm and can reach up to 400kg
• They exhibit impressive schooling behaviour as juveniles, but as adults they form much smaller groups
• They, on occasion, can be cannibalistic!
• In the summer months it migrates north in search of cooler water 
• It had 11-12month gestation period - the eggs hatch inside the females body. They are nourished by the yolk sac, once this is depleted 20-40 sharks hatch
• They are listed as 'Vulnerable' on the IUCN red list 

Scalloped Hammerhead (Sphyrna lewini)

Scalloped Hammerhead

• It is clearly distinguishable from other Hammerhead species by the scalloped shaped of it's hammer
• The juveniles have darker fins than the adults 
• It's a relatively slim shark 
• Similar to the Smooth Hammerhead in that the younger sharks will form large schools, whilst the adults live in smaller groups. 
• Larger shark species may attack the smaller Scalloped Hammerheads, but the adults have no natural threats - just humans 
• The gestation period is 9-10months. Similar to the Smooth Hammerhead, the eggs hatch inside the body and are nourished by the yolk sac. They will move to shallower waters to give birth to 15-30 pups. 
• We see them at Pulau Sipadan!!
• They are listed as 'Endangered' on the IUCN Red List

Scalloped Bonnethead (Sphyrna corona)

Scalloped Bonnethead

• As the smallest of the hammerhead shark species, it reaches a maximum length of 92 cm! 
• The head is much smaller than other hammerhead species and much more rounded. For this reason it is sometimes called a 'mallethead shark'
• Sadly, there is not much known about this species of Hammerhead.
• It is a costal shark that is believed the be threatened by various fishing practices. 
• It is listed as 'Near Threatened' on the IUCN Red List, but it is believed that it will be moved to 'Vulnerable' once more information is found. 

Winghead Shark (Eusphyra blochii)

Winghead Shark

• As the name suggests, these sharks have a very long wing-shapes hammer - the width of the head is nearly half the body length!
• They are a very slender shark 
• They are one of the smaller species of Hammerhead, reaching just 150cm
• This species occurs close to and on continental shelf waters of the Indo-West Pacific from the Arabian Gulf though south Asian, Indonesia and northern Australia
• The gestation period is 8-11 months and they produce just 6 - 11 pups each year. 
• They are listed as 'Near Threatened' on the IUCN Red List, but again, very little is known about them. 

Scoophead shark (Sphyrna media)

Scoophead Shark

• Another smaller species of Hammerhead that grows to 150cm. 
• Very little is known about their habitat and ecology
• Sadly they are listed as 'Data Deficient' on the IUCN Red List 

Bonnethead shark (Sphyrna tiburo)

Bonnethead Shark

• These sharks have a narrow, shovel like head. 
• They live in abundance in shallow estuaries on the Atlantic and Pacific coats of the United States of America
• It has one of the highest population growth rates calculated amongst sharks 
• This shark has one of the shortest gestation periods, with eggs hatching after 4 1/2 - 5 months. they produce around 9 pups in one litter. As with other species of Hammerhead, they eggs hatch inside the body and sustain themselves off the yolk sac. 
• It is listed as 'Least Concern' on the IUCN Red List  

Smalleye Hammerhead ( Sphyrna tudes)

Smalleye Hammerhead

•  As well as having small eyes, these sharks are recognised by their distinct gold colouring. The juveniles are often a brighter orange colour, which fades and they grow.  
• They are believed to be able to reproduce annually 
• It can be found between depths of 9m and 40m
• They are seen in the western Atlantic.
• Their gestation period is 10months and they give birth to 5 - 12 pups. Again, these sharks hatch inside the female and consume the yolk sac. 
• It is listed as 'Vulnerable' on the IUCN Red List 

 Carolina Hammerhead shark (Sphyrna gilberti) 

Carolina Hammerhead Shark

• This species of Hammerhead was only identified in 2013
• It is very similar to the Scalloped Hammerhead, but it has 10 less vertebrae
• It is found exclusively in salt water
• As a new species of shark, it has not yet been placed on the IUCN Red List 

Whitefin Hammerhead (Sphyrna couardi)

Whitefin Hammerhead

• There seems to be very little known about this species of Hammerhead
• It is not yet listed on the IUCN Red List
• It is listed on the Shark Data base and a few other websites online
• http://www.fishbase.org/summary/911

There are many species of Hammerhead and we are still finding out more about them. They are a shy and elusive shark and we love them!!

Why do they have such a bizarre shaped head? 

It is the curious appearance of the Hammerhead that makes it such a coveted sighting by many divers. The 'hammer' of the shark is actually called the 'cephlafoil'. There are many theories put forward as to why this peculiar shape has developed. 

It is generally thought to benefit them as it allows them to have a large surface area for a sensory organ known as the Ampullae of Lorenzini. The Ampullae of Lorenzini is found in all shark species and is used to detect electrical currents, chemicals in the water and changes in temperature. It is thought that it is used by some species of sharks to navigate long distances between the submerged oceanic sea mounts. The large surface area of the cephlafoil allows for a more sensitive and developed Ampullae of Lorenzini. 

Some believe that it is allows them a wider field of vision. A study in 2009 showed that it actually gave them incredible binocular vision, as well as the ability to see 360 degrees. By definition, binocular vision allows for a fantastic perception of depth - something that is key for hunting prey. 

There are also theories that it benefits their swimming efficiency and as previously mentioned it can be used to pinned down prey. 

No matter what it is used for or how it benefits the shark, it undoubtedly makes it one of the coolest sharks to see underwater! 

The information here was found on several sites, main ones being www.arkive.org and www.iucnredlist.org