iDAP’s Blog

The whitetip reef shark, Triaenodon obesus, is a requiem shark of the family Carcharhinidae, the only member of the genus Triaenodon. The whitetip reef shark is one of the most common sharks found in shallow tropical and warm temperate water around coral reefs in the Indian and Pacific oceans. It occurs at depths down to 330m. They are commonly seen harmless while snorkeling. As its name suggests, the tips of the shark’s first dorsal fin and upper caudal fin are white. The upper body is grey / brownish. This bottom dwelling shark is nocturnal and is often seen resting on the bottom during the day, sometimes in small groups. It is not aggressive and will generally swim away if disturbed, although it may bite if harassed. At night it hunts among crevices in the reef.

Sightings: This is the most common shark seen here in Puerto Galera. Almost always it can be seen at Shark Caves dive site either in the large main cave or one of the two smaller caves. Years ago they used to be seen resting on the sandy slope out behind the canyons. A juvenile whitetip was once spotted hiding under a mushroom coral at the hole in the wall. Years ago it was also possible to see them sheltering in a small cave in coral gardens as well. On one night dive in West Escarceo one was spotted swimming down the reef from very shallow.

Quick Facts:

Sharks of Puerto Galera / Verde Island Passage

Kingdom: Animalia (animals)

Phylum: Chordata (chordates)

Subphylum: Vertebrata (vertebrates)

Infraphylum: Gnathostomata (jawed vertebrates)

Class: Chlondrichthyes (cartilaginous fish)

Subclass: Elasmobranchii (sharks, rays and skates)

Superorder: Selachimorpha (sharks)

Order: Ground Sharks

Family: Requiem Sharks

Ø Whitetip Reef Shark, Triaenodon Obesus

Ø Blacktip Reef Shark, Carcharhinus Melanopterus

Ø Grey Reef Shark, Carcharhinus Amblyrhynchos

Ø Tiger Shark, Galeocerdo Cuvier

Family: Cat Sharks

Ø Coral Catshark, Atelomycterus Marmoratus

Order: Mackerel Sharks

Family: Thresher Sharks

Ø Common Thresher Shark, Alopias Vulpinus

Order: Carpet Sharks

Family: Whale Sharks

Ø Whale Shark, Rhincodon Typus

Family: Nurse Sharks

Ø Tawny Nurse Shark, Nebrius Ferrugineus

Family: Carpet or Nurse Sharks

Ø Tasseled Wobbegong, Orectolobus Dasypogon

Sharks

Sharks (super order Selachimorpha in the subclass Elasmobranchii in the class Chondrichthyes.) are a type of fish with a full cartilaginous skeleton and a streamlined body. They respire with the use of five to seven gill slits. A modified slit called a spiracle is located just behind the eye; the spiracle assists the water intake during respiration and even plays a major role in bottom dwelling sharks, but is also reduced or missing in active pelagic sharks. Sharks have a covering of dermal denticles that protect their skin from damage and parasites and improve fluid dynamics; they also have replaceable teeth. Sharks range in size from the small pygmy shark, Euprotomicrus bispinatus, a deep sea species of only 22 centimeters (9 in) in length, to the whale shark, Rhincodon typus, the largest fish, which grows to a length of approximately 12 meters (39 ft) and which, like baleen whales, feeds only on plankton, squid, and small fish through filter feeding. The bull shark, Carcharhinus leucas, is the best known of several species to swim in both salt and fresh water and in deltas.

Evidence for the existence of sharks extends back over 450 – 420 million years, into the Ordovician period – before land vertebrates existed and before many plants had colonized the continents. All that has been recovered from the first sharks are some scales. The oldest shark teeth are from 400 million years ago. The first sharks looked very different from modern sharks. The majority of the modern sharks can be traced back to around 100 million years ago.

Smell: Sharks have keen olfactory senses, located in the short duct (which is not fused, unlike bony fish) between the anterior and posterior nasal openings, with some species able to detect as little as one part per million of blood in seawater. Sight: Shark eyes are similar to the eyes of other vertebrates, including similar lenses, corneas and retinas, though their eyesight is well adapted to the marine environment with the help of a tissue called tapetum lucidum. Hearing: Sharks also have a sharp sense of hearing and can hear prey many miles away. A small opening on each side of their heads (not to be confused with the spiracle) leads directly into the inner ear through a thin channel. Electroreception: The Ampullae of Lorenzini are the electroreceptor organs of the shark, and they vary in number from a couple of hundred to thousands in an individual. Sharks use the Ampullae of Lorenzini to detect the electromagnetic fields that all living things produce. This helps sharks find its prey (mostly the hammer head). The shark has the greatest electricity sensitivity known in all animals. The oceanic currents moving in the magnetic field of the Earth also generate electric fields that can be used by the sharks for orientation and navigation. The Lateral Line: This system is found in most fish, including sharks. It is used to detect motion or vibrations in the water. The shark uses this to detect the movements of other organisms, especially wounded fish. The shark can sense frequencies in the range of 25 to 50 Hz.

Despite the common myth that sharks are instinct-driven “eating machines”, recent studies have indicated that many species possess powerful problem-solving skills, social complexity and curiosity. The brain-mass-to-body-mass ratios of sharks are similar to those of mammals and other higher vertebrate species. It is unclear how sharks sleep. Some sharks can lie on the bottom while actively pumping water over their gills, but their eyes remain open and actively follow divers. It is also possible that a shark can sleep in a manner similar to dolphins. In this situation, one half of the brain sleeps at a time, thereby allowing the shark to be half conscious while sleeping.

Major declines in shark stocks have been recorded in recent years – some species have been depleted by over 90% over the past 20-30 years with a population decline of 70% not being unusual. Many other threats to sharks include habitat alteration, damage and loss from coastal developments, pollution and the impact of fisheries on the seabed and prey species. An estimate states that, every year, 26 to 73 million (median value is at 38 million) sharks are killed by people in commercial and recreational fishing. Sharks are common seafood in many places around the world, including Japan and Australia. In the Australian State of Victoria shark is the most commonly used fish in fish and chips, in which fillets are battered and deep-fried or crumbed and grilled and served alongside chips. In India small sharks or baby sharks (called sora in Tamil) are caught by fishermen routinely and are sold in the local markets. Sharks are often killed for shark fin soup: the finning process involves the removal of the fin with a hot metal blade. Fishermen will capture live sharks, fin them, and release the finless animal back into the water. The immobile shark soon dies from suffocation or predators. Despite claims that this practice is rare, it has become a major trade within black markets all over the world with shark fins going at about US$220/lb. Millions of sharks a year are being illegally poached for their fins and not many governments are enforcing the laws of protecting these apex predators. The dish is considered a status symbol in Asian countries and is considered healthy and full of nutrients, even to go as for to say they prevent cancer and other ailments (not proven). Hong Kong is the world’s shark fin trading centre, accounting for 50-80% of fins traded worldwide. Currently the EU supplies 27% of all fins imported into Hong Kong. In Europe Spain is the major supplier of one third of shark fins for Hong Kong. The meat of dogfishes, smoothhounds, catsharks, makos, porbeagle and also skates and rays are in high demand by European consumers. Shark teeth are prized by collectors for their beauty, and because they are surviving relics of ancient sharks that are now extinct.

Project AWARE

Protect the Sharks

Why do sharks need our protection? Many shark species are endangered and could soon become extinct without our help. According to the United Nation’s Food and Agriculture Organization (FAO), approximately 100 million sharks are killed each year. Due to their slow growth, late sexual maturity and low number of offspring, they are susceptible to almost any fishing pressure.

Few countries have shark management plans in place. And, the demand for shark products like shark meat, fins and cartilage further contributes to their decline.

Why should you help? Sharks play a vital role in the underwater ecosystem as part of nature’s complex system of checks and balances. Known as apex predators, they are at the top of the food chain, keeping other aquatic species populations healthy and balanced.

You can read more here on what Project AWARE is doing to help protect the sharks: www.projectaware.org/uk/english/pts.asp and here: www.sharkalliance.org