It’s that time of year Diving in Sharm El Sheikh when the winds start to drop, the sea is often calmer in the afternoon and the water temperature is getting warmer. It’s also that time of year when the larger life starts appearing; already some species have been spotted.
So as a dive guide we also start having the requests to go to the back of Jackson reef in the Strait of Tiran to dive the blue waters and hope to have that amazing exciting encounter with one of the most beautiful creatures in the sea – the Hammerhead Shark.
But what do you know about the Hammerhead Shark?
Its scientific name is Cephalofil for its hammerhead shaped head. This shape allows the shark to have superior depth perception and binocular vision helping them to navigate and find food, although they have eyes that allow 360 vision they have a blind spot directly in front of them, you can often find small fish hiding right in front of their nose! Due to the size of their heads scientists believe that they have many more electroreceptor’s than other sharks which makes them superior to other sharks when it comes to navigation and detecting prey.
These electroreceptor’s pick up very small electrical pulses that all living things emit. They can sense the beating heart of a human from several miles away, so they know you are there a long time before you see them!
Hammerheads are bottom hunters and their main prey is sting rays which camouflage themselves under sand on the seabed, so the hammerheads distinct shape of head works like a metal detector scanning the sea floor for living creatures to eat. The shape of their head allows them to make sudden sharp turns and gives them more balance and their bodies seem to be designed to twist and bend.
Sharks have another cool secret weapon to help them hunt for prey – their skin. Shark skin is covered in a structure called Dermal Denticles these are tiny flat V-shaped scales that are more like teeth than fish scales. These denticles decrease drag and turbulence, allowing the shark to swim faster and more quietly. Hammerheads dermal denticles have evolved to be smaller and thinner and have ridges on the crowns which help send scented water to its nostrils (nares) which in turn helps them smell their prey.
Hammerheads like to hang out in shallow waters, but just like us humans their skin can tan although they have no risk of skin cancer from chilling in the sun, scientists are studying this phenomenon in the hope it will help us to prevent and treat melanoma in humans.
They don’t spend all their time sunning themselves though, recent studies have shown that Hammerheads free dive by “holding their breath”. It seems that they do this to stay warm when diving to great depths between 200-1000 metres. The body temperature of a fish is regulated by its surrounding temperature, but large predatory animals such as sharks need to maintain a certain temperature to fully function if they are to hunt for prey. Sharks and fish do not have lungs to filter oxygen from the water, instead they have gills, when water passes over the gills blood vessels on the gills absorb the oxygen from the water, if a shark gets too cold, it can’t keep itself moving to allow this water to pass over its gills and enable it to breathe. So studies have shown that at scalloped hammerheads will do vertical dives and maintain warmer body temperatures by closing their gill slits and stopping the cooler water flowing into their gills and cooling the body. They were seen to dive repeatedly to depths of 800 metres and would leisurely dive to around 100 metres then sprint down to the deeper cooler depths, with temperature changes of 26 to 5 degrees but maintained warm muscle and heart temperatures. These studies are ongoing as it’s not exactly known what the sharks are doing at these deep depths.
Scalloped Hammerheads are often seen in large schools, the belief is that these schools are predominately females and congregate together for protection against males, when a female is alone she is bombarded with males but when swimming in a shiver (the collective name for a group of sharks) the females can select which males they will have around them.
Female hammerheads can store male sperm for a long period of time, but a study showed that some females in captivity gave birth without having any males nearby for over 3 years; scientists agreed this would be most unlikely that the shark could store the sperm for that amount of time. A paternal DNA test was performed and it shown that it was a “virgin birth” and the shark pups had no father. Although studies are ongoing it is now believed that females don’t actually need the males, as the females can create offspring by fertilising their own eggs.
The female hammerhead with remain pregnant for 8- 10 months and will give birth to live babies called pups she will have 20-50 pups, but from the moment they arrive they are on their own with no parental care given. Although many hammerheads are at risk of extinction and humans are the number one threat to them they will live between 25-35 years but they are beginning to live longer lives, the reason for this is currently unknown.
So all in all what an amazing animal the Hammerhead shark is, we are so privileged to see these wonderful creatures in the waters here in Sharm el Sheikh. For those of you that have been on the dive on the back of Jackson Reef in Tiran you know it’s not a guaranteed sighting but as they can hear and sense us from a long way away it’s their choice as to whether they will show themselves to us and it’s exciting and breath taking when they do.