Monday, October 3, 2011

Fiji Times: The Kings of the Reef

SHARKS are an ancient life form. 400 Million years ago, before man was on the Earth, before the Dinosaurs walked the planet, there were primitive sharks. The body and biology of the shark is so perfectly adapted to its lifestyle that it has hardly changed in the past 65 million years,

This amazing fish has no bones, a skeleton made of cartilage, and teeth that never stop replacing themselves as old ones fall out. They can live to be at least 25 years old, but for many species exact maximum ages are not known,

Most sharks do not breed until they are between 5 and 15 years old, and usually only once every year or less often. Most of the sharks found in Fiji give birth to between 2 and 10 live babies at a time. Because of this late breeding age and small number of babies born, sharks are very vulnerable to overfishing, being slow to replace their numbers once killed.

Reproductive ages of different shark species

Some sharks give birth to live young (Viviparous), some lay leathery eggs (Oviparous), and some reproduce in a mixture of the two methods, where eggs form but are kept inside the mother's body until they hatch and are born (Ovoviviparous).

Food Pyramid

Carnivores eat fish. Herbivores eat seaweeds. Corallivores eat corals

Sharks are the top of the Food Pyramid. As "Apex predators" they eat second level predators and thereby control the entire natural ecosystem. Without sharks to hunt second level predators, the ecosystem becomes imbalanced, and eventually coral reefs die, and fish stocks disappear.

At least 35 species of shark are found in Fiji's coastal and near coastal waters. The most common ones are quite easy to tell apart.

Photo: Angelo Villagomez
Whitetip Reef Shark, Triaenodon obsesus
(Qio Tukivula/ Qio Dina):

Rounded nose, white tip on dorsal fin (back fin) and tail fin. Small; largest around 2 metres long. Found on or near shallow coral reefs.

In daytime rests on sandy slopes and caves, sitting motionless. At night feed on crabs, lobster, octopus and fish sleeping in holes in the reef.

Gives birth to 1-5 live babies. Stay within a few kilometres of their home range

Photo: Rodolphe Holler, Tahiti Private Expeditions
Blacktip Reef Shark, Carcharhinus melanopterus
(Qio Tukiloa/ Qio Mokomoko)

Sharp nose, black tip on dorsal fin (back fin), pectoral fins (side fins) tail and smaller fins. Small; largest around 1.6 metres long. Found on or near shallow coral reefs, young sharks often on reef flats near beaches

Feed on shrimp, octopus and small fish. Are sometimes eaten by large groupers and other sharks.

Gives birth to 2 to 4 live babies.

Photo: Rodolphe Holler, Tahiti Private Expeditions
Grey Reef Shark, Carcharhinus amblyrhynchos
(Qio Saqa/ Qio Rewasaqa)

Sharp nose, plain grey dorsal fin (back fin) and pectoral fins (side fins), black edge to tail and smaller fins. Medium size; largest around 2.5 metres long.

Found in deeper reef passages and walls, females often in small schools.

Feed on crabs, lobsters, octopus and small fish.

Gives birth to 1 to 6 live babies, which stay in nursery grounds for some months.

Photo: Veronique Arnoldi
Tawny Nurse Shark, Nebrius ferrugineus
(Qio Dramila)

Round nose, two plain grey dorsal fins (back fin) and pectoral fins (side fins),very long top lobe on grey tail fin. Large; largest around 3.2 metres long.

In daytime found resting motionless in shallow reef passages and caves, sometimes in groups. At night feed on corals, crabs, lobster, sea urchins, octopus and small fish sleeping in holes in the reef.

Gives birth to 4 or more live babies

Photo: Rodolphe Holler, Tahiti Private Expeditions
Sickle-fin Lemon Shark, Negaprion acutidens
(Qio Damu)

Round nose, two plain grey dorsal fins (back fins), grey pectoral fins (side fins) and tail fin. Large; largest around 3.2 metres long

Found in bays and estuaries, often in cloudy water, swimming slowly.

Feeds on bottom feeding fish such as porcupine fish and stingrays.

Give birth to 1 to 13 live babies.

Photo: Guy Stevens
Silvertip Shark, Carcharhinus albimarginatus
(Qio Dina):

Sharp nose, white tips to dorsal fin (back fin), pectoral fins (side fins), tail and smaller fins. Large; largest around 3 metres long

Found in deep water inshore and offshore, often seen in deeper reef passages.

Feeds on midwater and bottom fish, tuna, wahoo, eagle rays, octopus.

Give birth to 1 to 11 live babies.

Photo: Angelo Villagomez
Bull Shark, Carcharhinus leucas
(Qio Tovuto)

Sharp nose, plain grey dorsal fin (back fin), pectoral fins (side fins), tail and smaller fins, thick bodied.

Large; largest around 3.4 metres long.

Found on deeper reefs, shallow estuaries, river mouths in cloudy water.

Feeds on many species including other sharks, dolphins, rays, reef and midwater fish such as walu, tuna, snappers, jacks and tuna, seabirds.

Gives birth to 1 to 13 live babies, often many kilometres up river.

The only shark to be found in completely fresh water.

Photo: Rodolphe Holler, Tahiti Private Expeditions
Tiger Shark, Galeocerdo cuvier
(Qio Taika/ Qio Oria)

Sharp nose, plain grey dorsal fin (back fin), pectoral fins (side fins), tail and smaller fins, thick bodied. Younger sharks show dark grey bars on sides.

Very large; largest around 6 metres long, unconfirmed sightings up to 9 metres.

Found in deeper ocean and steep reef areas.

Spends days in deeper water.

Feeds at night in shallower water on many species, Has been seen to consume other sharks, dolphins, seals, turtles, sea snakes, rays, fish, seabirds, dead and live land animals, and even non-edible items such as metal, wood, and plastic.

Give birth to 10 to 80+ live babies.

Published in the Fiji Times on Monday, October 3, 2011. Written by Helen Sykes, Manager of the Coral Reef Alliance and Pew Environment Group shark campaign in Fiji.

The photos in this story were all donated by people like you.  Shark Defenders depends on the generostiy and support of underwater photographers donating royalty-free photos for our use in online and print media.  If you have the rights to high quality photos of sharks, please consider donating them for our use.

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