Today it’s time for something a little different. In light of all the sightings we have been having recently I have decided to look at one of the office favourites, the stunning Scalloped Hammerhead shark! Most of you will know a few things about these amazing sharks but hopefully I can tell you something new.
The Scalloped Hammerhead, also known as the Bronze, Kidney-Headed or Southern Hammerhead, is the most commonly seen member of the Sphyrnidae family. This family holds just 10 species including the Hammerheads, Bonnetheads, Scoopheads and Wingheads. They all show a distinctive “hammer” shaped head, albeit with slight species variations, which make them instantly recognisable.
What’s in a name?
The Scalloped Hammerhead gets its name from the indentations in the front of its head. The name Sphyrna comes from the same Greek word meaning hammer and although I cannot find anything to explain lewini, I suspect it is something to do with the Leeuwin Current. As a bonus fact for you, the name for the flattened hammer-shaped head is a cephalofoil but we’ll talk more about them later.
Habitat and distribution.
Scalloped Hammerheads are the most common hammerhead and can be found in warm temperate to tropical oceans, from coastal areas to islands and seamounts far offshore. They are most commonly found in the ‘Hammerhead Triangle’ between Cocos, Galapagos and Malpelo as well as the Red Sea. While they can be seen in other locations such as Australia, Indonesia and Philippines but they are not so regular. The sharks tend to spend the day closer to shore before heading into deeper water offshore at night to hunt. These sharks can be seen from the surface down to at least 275m with male sharks being observed swimming deeper than female sharks, although they are most often seen around the 25m mark. Usually Scalloped Hammerheads are found alone or in small groups, however they can be seen in huge shoals around seamounts and pinnacles.
Looks that kill.
Hammerheads of all kinds are amazing to look at underwater and Scalloped Hammers are no exception. Their body shape is very similar to many other requiem sharks, albeit with slightly larger dorsal, pectoral and pelvic fins. The caudal fin (tail) has a larger top lobe than bottom lobe, again similar to the requiem sharks. This design fits a perfect balance between turning ability, cruising effort and straight line speed.
The Scalloped Hammerhead displays a colouration called countershading. It is a dark brown to a grey bronze on top and is pale white underneath. This is so they can hide from potential prey from both above and below, the grey camouflaging against the seabed from the top and the white camouflaging against the white sky from below.
Right, let’s talk about their heads! While looking rather goofy, the cephalofoil structure is both highly advanced and perfectly designed. Both the eyes and nostrils of the shark are on the tips of the hammer and while this limits their forward vision, they swim sweeping their heads left and right. This gives them a much larger field of vision than other sharks, as their view overlaps. The front edge of the cephalofoil has deep indentations and this is what gives this species its name. These a very clear to see underwater as well so you can easily get a positive ID. Like all other sharks, Scalloped Hammerheads also possess the ampullae of Lorenzini, a network of electroreception pores under the snout that help detect prey. The Scalloped Hammerhead has these all along the underside of its hammer giving it a much larger area to detect prey with. Much like a huge metal detector, it’s larger sweeping area means anything hiding in the sand won’t stay hidden for long! One more thought about this head shape is that it acts as another set of stabilising fins to help with turning and swimming up and down quickly without losing its stability, like the nose fins on a fighter jet.
As mentioned earlier, Scalloped Hammerheads are usually solitary but can be seen in huge shoals when it’s time to breed. Gathering around seamounts and islands, such as Cocos or the Galapagos islands, the shoals can number in the hundreds. It has been observed that these shoals are single sex, with females swimming shallower than males. Scalloped Hammerheads show slight sexual dimorphism (each gender looking different) with male sharks having a pair of elongated pelvic fins called claspers. These are used to transfer sperm to the females and they have two so they can use one depending which side of the female they attach to while breeding. Scalloped Hammerheads are viviparous, which means they are born live and have a placenta like link to their mother while growing. They have a gestation of around 9-10 months, usually delivering in the summer and a litter is around 12 to 38 individuals. Breeding is dictated by size rather than age, with males reaching maturity smaller than females. Female Scalloped Hammerheads mature at a larger size than other sharks, around 240cm, as their uteri need to be large enough to deliver the large heads of the offspring. Female sharks also need to be large to cope with the breeding process, as the males need to bite on to attach themselves! This is rather rough and can leave the females with cuts and scars but this is perfectly normal, in fact female sharks have a reduced level of nerve endings in the skin for this reason.
Life on the reef.
Scalloped Hammerheads can be seen at all times of day in warm temperate coastal waters. They are a fairly skittish animal despite their size and tend to leave divers alone. Their diet consists mostly of oily fish such as sardines, herrings and mackerel and cephalopods such as squids and octopus. They also eat stingrays and other animals hiding under the sand. Larger individuals have also been seen predating smaller species of sharks such as blacktip reef sharks. They have not been seen eating each other, no matter how hungry they are! They grow to an average size of 2.5 to 3m with a maximum size of 4.2m. Average weights are 80 to 100kg and maximums are around 150kgs. The life expectancy for the Scalloped Hammerhead is around 20 to 30 years.
They are currently listed as endangered on the IUCN Red List. This is because they are heavily overfished, mostly for the shark fin soup trade. These sharks have large fins compared to their body size, making them priority targets for fishermen.
Nothing can prepare you for your first Hammerhead sighting! Whether they are in a shoal, up close or far off in the viz, Hammerheads always set my pulse racing. They can move quite quickly when they want to so keep your eyes peeled and your head on a swivel. When encountering them on a reef, give them space. Don’t crowd them and just let them do their thing. If you are encountering them on a wall or in the blue water it is imperative that you keep an eye on your buoyancy, depth and gas consumption as they can often be found at depth, swimming up and down the water column quickly. The last thing you need is to get bent chasing a photo. As I have said they are a very skittish animal so a calm, careful approach will give the best results. Keep yourself calm and just enjoy the totally surreal experience!
The bottom line.
We travelled on the Hurricane to the southern Red Sea, getting some awesome shots of these beautiful animals on the Daedalus reefs. Divers currently on the Simply the Best trips have been filling our inbox with pictures of Hammerheads, driving us all green with envy! We also saw them in the Galapagos and Cocos islands but for the ease of getting there, you can’t beat the Red Sea. Why not jump on our new Shark Quest trip to find out for yourself! Seeing hammerheads in an awesome experience and you will never get tired of photographing them. Every dive with a Hammerhead on it will be one of the best you will ever do!