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 and Sand 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 slowreproducing 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.