Sharks Les requins Contrary to other fishes, sharks, rays, skates and ghost sharks have a cartilaginous skeleton. As these species evolved, following a phase of bony development, nature went back to using cartilage which makes their bodies both lighter in weight and supple. Their evolution lasted 400 million years, and very quickly, morphological and physiological adaptations gave these predators a real edge. Over this time period, all sorts of shapes were tried out, and the best of them selected. Thus, Carcharocles megalodon, which was “too gigantic” at 15 m and weighing about 25 t, disappeared three million years ago. Sharks have a range of distribution covering every sea, every biotope and every possible prey. There are over 300 species of sharks and many books have been devoted to them. Intensive fisheries, which are now rampant in every ocean of the globe, are threatening many species of shark with overfishing, or even extinction, for those which are the most sought-after or the most vulnerable. Indeed, sharks’ reproduction strategy relies on having offspring which are well adapted to marine life, right from birth, but in very small numbers compared with those of bony fishes. Thus, the natural rate of renewal of these populations cannot compensate for the excessive fishing pressure. Furthermore, some barbaric fishing practices, like that called “finning”, which consists in cutting off the sharks’ fins before throwing them back in the water still alive, thus dooming them to a terrible and certain death, still exist today in many too many fisheries. It is therefore important to realise that these exceptional creatures, which in the great majority of cases are simply trying to feed and not to deliberately harm humans, are in great danger and must absolutely be protected. That is why in this guidebook we have chosen to present the species which divers in the Indian Ocean and Red Sea are mostly likely to see. ■ Sharks ◗◗ Family Rhincodontidae Whale shark Requin baleine Rhincodon typus This is the largest of all fish, usually measuring a dozen metres in length, though the biggest specimen caught was nearly 20 m long. Blue-grey in colour, with white patches on the head and fins arranged on the body in series of large spots separated by thin white bars. Its body has four longitudinal keels. This is a pelagic shark found all over the planet’s inter-tropical belt and reaching into some temperate zones. Entirely harmless for humans, its square snout has a capacious terminal mouth which enables it to filter zooplankton*, crustaceans and small pelagic fish. The female can carry up to 300 embryos at various stages of maturity. At birth they are 70 cm long and little is known about how they grow. This shark is rare, especially considering its size at adulthood. However, they fall victim to ships and fishermen’s nets, killer whales and large carnivorous sharks. They often travel accompanied by live sharksuckers, cobias and jacks. In the Indian Ocean, whale sharks migrate and, depending on the season, may be sighted in large numbers in north-western Australian waters, at Djibouti, in the Mozambique Channel, the Seychelles, the Maldives, etc. They sometimes gather in groups of several individuals to more efficiently hunt shoals of small fish. Size Zone Depth Habitat 12 m 0-980 m Deep-sea and coastal pelagic environments 30 Fishes of the Indian Ocean and the Red Sea Sharks ◗◗ Family Hexanchidae Sevengill cowshark Requin platnez Notorynchus cepedianus This large shark can be recognised by the absence of the first dorsal fin, a massive head with huge jaws and its seven gill slits. Its back is greyish or brown, scattered with black spots and white dots. The belly is a creamy grey colour. It lives in kelp forests where it is safe from great white sharks and where it can find fish to feed on. It attacks sea lions (sometimes in coordinated teams). Peacefully zigzagging through the giant Laminaria, it comes close to divers, then turns away and swims off, indifferent to them. Remains, bones and skin from mammals can be seen on the seabed, but there have been only very few unprovoked attacks by them (5 or 6 known attacks, some of them in public aquariums). The Pyramid Rock site in False Bay, on the eastern coast of the Cape of Good Hope, is the easiest place to dive in order to admire them, all year round. Size Zone Depth Habitat 3 m + 1-140 m Benthic ◗◗ Family Stegostomatidae Zebra shark Requin léopard Stegostoma fasciatum Its slender body has four longitudinal keels running from its short snout to its very long tail, which extends outwards along the axis of the body. It is yellow-grey in colour, scattered with black spots. Being oviparous*, the female leaves two to four eggs in a brown egg case anchored to the bottom by filaments. The juveniles are black with zebra-like white stripes, and are rarely seen because they live at depths around 50 m. Zebra sharks drowse on coral or sandy bottoms, between five and thirty metres deep. They go hunting at night, exploring the seabed to discover their prey of fish, crustaceans and molluscs. Size Zone Depth Habitat 2 m 0-60 m Coral reef area, estuaries, outer reef slopes Description of groups 31 Sharks ◗◗ Family Orectolobidae Ornate wobbegong Requin tapis paste Orectolobus ornatus This is a rather flat-bodied and massive shark, whose dorsal fins are set very far back. The snout is hidden by a dozen fleshy buds or lobes of varying sizes, complementing its camouflage of dark brown with lighter patches and black spots. The female is ovoviviparous*, giving birth to a dozen baby sharks that are twenty centimetres in length. They are ambush predators, hunting fish, crustaceans and cephalopods. When attacked or threatened, they are potentially dangerous. Size Zone Depth Habitat 3 m 5-30 m Benthic ◗◗ Family Ginglymostomatidae Tawny nurse shark Requin nourrice fauve Nebrius ferrugineus This large nurse shark has two dorsal fins with straight posterior edges, set well to the rear of its back. Its colouration is plain, between sandy grey and brown. Inactive by day, in a fault or a cave (often facing the current), it is found in lagoons, in passes and outside of reefs. At night, it forages on the seabed using its nasal barbels, sucking up its prey with the sand. It is present in the Indian Ocean and in the Red Sea. Size Zone Depth Habitat 3 m 1-70 m Mixed coral areas, outer reef slopes 32 Fishes of the Indian Ocean and the Red Sea Sharks ◗◗ Family Heterodontidae Port Jackson shark Requin de Port Jackson Heterodontus portusjacksoni It has a massive head and slender body. The two dorsal fins are each armed with a short, strong spine which protects it from attacks like those by wobbegongs. It is beige or grey, with darker bands running over its flanks. This benthic and coastal species is capable of long migrations. The females lay eggs in capsules in coastal zones and the young grow in calm areas near shore. It is present along Australian coasts, except in the north. Size Zone Depth Habitat 1.50 m 0-275 m Rocky areas, caves ◗◗ Family Parascylliidae Necklace carpetshark Requin carpette à collier Parascyllium variolatum This is a small, slender shark with a short snout sporting nasal barbels. From grey to mottled brown, it can be recognised by a wide black collar spotted with white. There are black spots on its fins. They are frequently found near the coasts of Western Australia. They hide in crevices and under seaweed, coming out at night to hunt on the seabed. Size Zone Depth Habitat 90 cm Australia 0-180 m Rocky or sandy areas, seagrass beds or mixed bottoms Description of groups 33 Sharks ◗◗ Family Lamnidae Sand tiger shark Requin taureau Carcharias taurus This shark is stocky, with a short snout. Its two dorsal fins are practically identical in size. The colouration is dusky brown with a few dark spots on the flanks. Its powerful jaws are equipped with very sharp and conspicuous protruding teeth, giving it a ferocious appearance. It is a benthic shark which lives in coastal areas. Its range of distribution broadly covers tropical and temperate waters in most of the world’s oceans and seas, with the exception of the East Pacific. They often live and migrate in a group. The ovoviviparous female only gives birth to one or two pups at at time, since a drastic selection process of intrauterine cannibalism takes place, where eggs or siblings are eaten in the womb. Its maximum size is around 3.20 m. Size Zone Depth Habitat Various habitats in tropical and temperate coastal 2 m 0-220 m zones Great white shark Grand requin blanc Carcharodon carcharias It is big and massive, but with a streamlined, fusiform shape. The snout is conical and the tail symmetrical. It is slate grey to dusky brown on its back and the upper part of the flanks and white on the underside. The eye is black and its powerful jaws are armed with flat, wedge-shaped serrated teeth. The great white is present in temperate waters and is common in Australia and South Africa, especially around sea lion colonies. It was filmed in Mauritius in 2004, caught in Madagascar and can appear all over this zone of the south-western Indian Ocean. It has the ability to attack large prey, like marine mammals, sea turtles, tuna and squid. It is also capable of looking above the surface and leaping out of the water to catch sea birds. They prowl around schools or pods of dolphins in the hope of finding a weaker individual.