Sharks
The earliest known sharks date from more than 420 million years ago and there are now over 440 species of shark known, ranging in size from the small Dwarf Lantern shark, a deep sea species of only 17 centimetres in length, to the Whale shark which reaches approximately 12 metres!
Sharks are cartilaginous fish, which means their skeletons are made from cartilage and connective tissue and no bones, which makes them very flexible for swimming.
Sharks are found in all seas and are common down to depths of 2,000 metres (6,600 feet). They generally do not live in freshwater, with a few exceptions, such as the Bull shark.
Sharks breathe through five to seven gill slits and have several sets of replaceable teeth. They might even lose up to 30,000 in their lifetime!
Sharks have a covering of dermal denticles that protects their skin from damage and parasites, and enables them to move faster through the water.
Well-known species such as the Great White shark, Tiger shark, Blue shark, Mako shark, and the Hammerhead are apex predators, at the top of the underwater food chain. Their extraordinary skills as predators fascinate and frighten humans, even as their survival is under serious threat from fishing and other human activities.
Bowmouth Guitar Shark
Known as a Ray shark, the Bowmouth Guitar shark is highly distinctive with a wide thick body, a blunt snout and a large shark-like dorsal and tail fins. There are multiple thorny ridges over its head and back, and it has dorsal color pattern of many white spots over a bluish gray to brown background, with a pair of prominent markings over the pectoral fins.
Bowmouth Guitar sharks prefers sandy or muddy flats and areas adjacent to reefs, where they hunts for crustaceans, molluscs, and bony fishes. They are widely distributed in the tropical Indian and Pacific Oceans.
They are typically encountered on or near the bottom of the sea bed, though on occasion they may be seen swimming well above it. They generally are more active swimmers at night.
The Bowmouth Guitar Shark has sharp thorns on the bony ridges of its head which are used to defend itself by head butting. The mouth is shaped like a clamshell and has around 100 rows of teeth.
The International Union for Conservation of Nature (IUCN) has assessed this species as Vulnerable; its sizable pectoral fins are greatly valued as food and it is widely caught by artisanal and commercial fisheries.
Sand Tiger Shark
Sand Tiger sharks – or Carcharias Taurus - look ferocious, and they are! They are voracious predators, feeding mostly at night and close to the ocean floor. They can grow to be over three metres long.
But don’t worry. Their diet consists of just small fish, crustaceans and squid. They are found in warm or temperate waters throughout the world’s ocean, with the exception of the Eastern Pacific. Sand Tiger Sharks get their name from the dark strips on their grey backs, which are pronounced in young sharks but disappear in large adults.
When they are born Sand Tiger Sharks are already one metre long, but they breed very slowly. Because of its low reproduction rate, the species is listed as vulnerable and is protected by many different countries against commercial fishing.
The Sand Tiger shark has one curious habit: they are the only shark we know of that comes up to the surface of the water and take gulps of air, which they hold in their stomachs. This clever trick enables them to achieve neutral buoyancy and float motionless in the water, waiting for prey.
Blacktip Reef Shark
The blacktip reef shark is a species of requiem shark, along with Tiger sharks, Blue sharks and Bull sharks. They are easily identified by the prominent black tips on its fins, especially on the first dorsal fin and the caudal fin.
Found on the tropical coral reefs of the Indian and Pacific Oceans, Blacktip Reef sharks prefer shallow, inshore waters, although they are sometimes found in brackish waters (a mixture of salt and fresh water found where rivers meet the ocean), though they cannot tolerate low salinity levels to the same degree as the Bull shark.
This shark is viviparous, meaning they give birth to live young like people do. Some sharks, such as the Zebra shark and Dogfish, are oviparous which means that they lay eggs. Others such as the Nurse shark andSand Tiger sharks, are ovo-viviparous which means that their eggs hatch inside their body and then they give birth to live young. They give birth to 2-5 young at a time.
This shark is sometimes used for its meat, fins and liver oil but is not considered to be a commercially significant species.
The International Union for Conservation of Nature (IUCN) rates the Blacktip Reef shark as Near Threatened – overfishing has led to its decline as it is a slow-reproducing species (like all sharks).
Young or small Blacktip Reef sharks often fall prey to larger fish such as Groupers, Grey Reef sharks, Tiger sharks or even bigger Blacktip Reef sharks.