Grey Reef Shark – Marine Life of the Similan Islands

While they are around, we don’t see them as frequently as some of our other sharks - Leopards and Black tips. this is more to do with the geology than anything else. They tend to be a bit more open and in sites we don’t dive as often or that we spend as much time in. Such as Deep off Christmas point and off Koh Tachai

They are also pretty timid when it comes to humans.

Order: Carcharhiniformes
Family: Carcharhinidae
Genus: Carcharhinus
Species: amblyrhynchos

Habitat

GREY REEF SHARK

Order: Carcharhiniformes
Family: Carcharhinidae
Genus: Carcharhinus
Species: amblyrhynchos

Habitat

Primarily distributed in shallow tropical and subtropical waters, the grey reef shark is often found near coral atolls and lagoons adjacent to reef habitats. It is often observed swimming along the outer edges of coral reefs. Its depth ranges from 0-920 feet (0-280 m). However, this species has been observed in waters down to 3,280 feet (1,000 m). Although more active during the night, grey reef sharks sometimes form schools during the day. These schools swim close to the bottom, over flat habitats. Grey reef sharks also form loose aggregations that lurk close to reef drop-offs. Lone individuals may be seen over shallow reefs either lying motionless on the bottom of the sea floor for long periods of time or swimming. Tagging studies show that sharks living near ocean reefs are nomadic and travel long distances along the reef habitat each day. Sharks residing in lagoon areas tend to return day after day to the same site.

Taxonomy

The grey reef shark was originally described as Carcharias amblyrhynchos by Bleeker in 1856. He later changed this name to the currently valid name of Carcharhinus amblyrhynchos. The genus name Carcharhinus is derived from the Greek “karcharos” meaning sharpen and “rhinos” meaning nose. Synonyms used in previous scientific literature that refer to the grey reef shark include Carcharias nesiotes Snyder 1904, Carcharhinus menisorrah Whitley 1944, Galeolamna fowleri Whitely 1944, Galeolamna turfiensis Whitely 1949, Galeolamna coongoola Whitely 1964, and Carcharhinus wheeleri Garrick 1982.
Common Names

English language common names include grey reef shark, blacktail reef shark, black-vee whaler, bronze whaler, gray reef shark, gray shark, gray whaler shark, longnose blacktail shark, shark, and whaler shark. Other common names from across the world include ‘anga (Tongan), bagea totoho (Gela), grijze rifhaai (Dutch), grys rifhaai (Afrikaans), ikan yu (Malay), jarjur (Arabic), kortneus-swartsterthaai (Afrikaans), mago (Niuean), malie-aloalo (Samoan), marracho enlutado (Portuguese), nga-man-nee (Burmese), pako mej (Marshallese), pating (Tagalog), qio dravu (Fijian), raira (Tahitian), requin à queue noire (French), requin bar (French), requin blanc (French), requin dagsit (French), requin gris (French), te alava (Tuvaluan), te bakoanimarawa (Kiribati), tiburón coralero rabinegro (Spanish), and tiburón de arrecifes (Spanish).
Geographical Distribution The grey reef shark is limited to the Pacific and Indian Oceans. In the Indo-Pacific, it is found in the waters off Madagascar and in the Mauritius-Seychelles region. In the western Pacific Ocean, this shark ranges from southern China to northern Australia and the Tuamoto Archipelago. It is one of the most common reef sharks in the Pacific Ocean, along with the blacktip reef shark (Carcharhinus melanopterus) and the whitetip reef shark (Triaenodon obesus). It is also found in the Indian Ocean, off the coast of India to South Africa, including the Red Sea. In this region it is often referred to as Carcharhinus wheeleri.

Biology

· Distinctive Features

This shark is medium to large in size, growing up to 8.4 feet (2.6 m) in length. It has a long, broadly rounded snout and large eyes. It does not have an interdorsal ridge running between the first and second dorsal fins. The origin of the first dorsal fin is over or just in front of the free rear tips of the pectoral fins. The first dorsal fin is semifalcate with a narrowly rounded or pointed tip. The second dorsal fin originates over the anal fin origin. The pectoral fins are large, narrow, and falcate in shape with narrowly rounded or pointed tips.

· Coloration

The dorsal side of the grey reef shark ranges from dark gray to bronze gray, paling to a white ventral side. The entire trailing edge of the caudal fin has a distinct wide black margin. The pectorals, second dorsal, anal, and pelvic fins have black or dusky tips while the first dorsal fin is either entirely gray or irregularly edged with white.

The blacktip reef shark can be distinguished from the grey reef shark by the black-tipped first dorsal fin
source: FAO Species Catalogue, Vol. 4 – Sharks of the World

The grey reef shark may be confused with the blacktip reef shark (C. melanopterus). The blacktip reef shark can be distinguished by the distinct black tip on the first dorsal fin as well as black tips on the remaining fins.

Grey reef shark upper and lower teeth
source: FAO Species Catalogue, Vol. 4 – Sharks of the World

· Dentition

The teeth are triangular and serrated with 13-14 teeth in each jaw half. The upper teeth are narrow and serrated, semi-erect to oblique in shape with high cusps. The crown feet have coarse serrations. The lower teeth are erect or semi-oblique with narrowly serrated cusps.

·Size, Age, and Growth

The grey reef shark may grow to a maximum size of 8.4 feet (2.6 m) in length and to weights of up to 74.3 pounds (33.7 kg). However, the average size of a grey reef shark is less than 6.6 feet (2 m) in length. The maximum reported age of this shark is about 25 years. Males mature at lengths of 4.3-4.9 feet (1.3-1.5 m) and females mature at 3.9-4.6 feet (1.2-1.4 m) in length, both corresponding to an age of approximately 7 years.

Food Habits

Reef fishes, along with smaller quantities of cephalopods (squid and octopus), and crustaceans (shrimp and lobster), provide the majority of the grey reef sharks’ prey. Reef shark prey also includes bony fish including cowfish, surgeonfish, and butterflyfish. The grey reef shark will also prey on young individuals of their own species. Most of the feeding activity occurs during the nighttime hours which is also this shark’s peak activity period.

· Reproduction

The grey reef shark is a viviparous species, which refers to reproduction when the embryos are nourished with a yolksac placenta during gestation inside the mother. The gestation period lasts approximately 12 months, followed by live birth of a litter of 1-6 pups. Each pup measures between 15.7-23.6 inches (45-60 cm) in length at time of birth.

Predators

Predators of the grey reef shark include larger sharks such as the silvertip shark (Carcharhinus albimarginatus).

Parasites

The grey reef shark is host to parasitic copepods including Nemesis robusta (gill filaments) and Alebion carchariae (snout, fins, body). These copepods were documented on specimens from waters off western Australia. Ganthiid isopod larvae have also been reported on the gills of this shark.

Importance to Humans

The grey reef shark may be taken by longline shark fisheries and are valued for their fins that are used in shark fin soup. It is also utilized for human consumption and fishmeal. However, this species often occurs out of the range of most commercial shark fisheries.

Conservation

The gray reef shark, Carcharhinus amblyrhynchos, is listed as Lower Risk (LR/nt) on the IUCN Red List of Threatened Species:

LOWER RISK (LR) – A taxon is Lower Risk when it has been evaluated, does not satisfy the criteria for any of the categories Critically Endangered, Endangered or Vulnerable. Taxa included in the Lower Risk category can be separated into three subcategories:

1. Conservation Dependent (cd). Taxa which are the focus of a continuing taxon-specific or habitat-specific conservation program targeted towards the taxon in question, the cessation of which would result in the taxon qualifying for one of the threatened categories above within a period of five years.
2. Near Threatened (nt). Taxa which do not qualify for Conservation Dependent, but which are close to qualifying for Vulnerable.
3. Least Concern (lc). Taxa which do not qualify for Conservation Dependent or Near Threatened.

The grey reef shark is vulnerable to overfishing due to its restricted habitat, small litter size, and relatively late age of maturity. These factors, along with an increase in unmanaged fishing pressure, make this shark vulnerable to threats. However, at this time there is not enough data on the grey reef shark to analyze the status of populations.

The grey reef shark is currently listed by the World Conservation Union (IUCN) as “Near Threatened”. More fisheries data is required for future assessment. The IUCN is a global union of states, governmental agencies, and non-governmental organizations in a partnership that assesses the conservation status of species.

Danger to Humans

Although it is one of the most aggressive sharks, the grey reef shark will usually only attack a person when it is threatened. Even so, it has been responsible for 7 unprovoked attacks resulting in no fatalities according to the International Shark Attack File. If cornered or threatened is some way, the grey reef shark will display threat behavior explicitly. It will raise its snout, depress the pectoral fins, and arch its back while swimming with an exaggerated sway. If the threat continues, the shark will move with lightening speed, delivering quite bites prior to retreating. Although the bites are often serious, they are rarely fatal. This species of shark is also more likely to attack while solitary rather than schooling perhaps due to an increased feeling of vulnerability.

The Coral Reefs of Thailand

Coral Reefs

In most minds, corals are virtually synonymous with the tropical reef. But, apart from the fact they know corals come in many forms and colours and that they are associated with a great variety of other marine creatures, most people have very little idea what a coral really is. Until 250 years ago, even biologists thought that these organisms were plants.

In fact, the corals belong to a large grouping (about 9000 species) of marine animals that includes not only the various corals but the sea anemones, hydroids, and jellyfish as well. It is not clear which other phyla the coelenterates themselves might be most closely related to. They have specialized tissues, but no complex organs — they have nerve cells, for example, but no concentrations of such that could be called a brain, and there is no head. Evolutionarily, then, they seem to lie somewhere between the sponges and the worms. Some evidence suggests that they have evolved either from colonial protozoans or from early creatures resembling flatworms.

Although superficially the coelenterates seem very different one from the other, the coral polyp shares with all these other animals a simple sac-like body plan, one in that the same opening is used for feeding, for elimination, and even for reproduction. And the polyp shares another distinctive feature with its relatives — the opening is surrounded by nematocysts, or stinging cells that aid it in catching its prey (zooplankton and sometimes even small fish). Any diver who has come into contact with certain jellyfish or “fire coral” (really a hydroid, rather than a true coral) can testify to the potency of at least some of these stinging cells.

Simply among the corals themselves, there is variety enough. The most commonly recognized are the “hard corals”. Over 200 species of hard coral belonging to 75 genera have so far been recorded in the Phuket area alone; 60 species have meanwhile been cataloged in the Gulf of Thailand, and there are certainly more.

Hard corals are of the phylum Coelenterata — that is to say, in the Greek, “with a hollow gut”. They are at the same time of the class Anthozoa, or “flower animals”. Finally, they are of the order Scleractinia, or “hard”. These corals, in short, are hollow-gutted flower-like animals with a hard exoskeleton into that they can retreat when threatened.

The hard corals are the main builders of reefs that in some parts of the world extend down for well over a hundred metres. In these cases the living reef itself is just a thin veneer. Similarly, while a single coral head can be some metres high and two-three meters across, the living coral colony itself is only a thin, ever-expanding skin building on the limestone skeletons of earlier generations. (Whereas the branching corals, for example those of the genus Acropora, grow much faster than their massive relatives, the massive corals [e.g. Favites, Porites] are far less vulnerable to storms and other damage; and they can continue growing for hundreds of years, with individual colonies sometimes reaching enormous sizes.)

Corals provide homes for many thousands of species of marine organism. A hard coral head — perhaps already festooned with such cousins as gorgonian sea fans, wire corals, and soft corals — may provide the substratum for a congregation of feather stars, crstaceans, reef fish, and organisms of many other types. Still other creatures live inside the coral. A piece of coral weighing just a few kilograms may harbor hundreds of individual worms and scores of species (one study conducted in Australia found 1441 worms of 103 species in a piece of dead coral weighing something more than three kilograms).

The symbiosis between corals and photosynthetic algae has made animal life possible in waters that might otherwise be barren. Because the coral can first of all produce its own food where carbon dioxide and sunlight are abundant, and because the coral ecosystem is self-contained and capable of recycling scarce nutrients, the reef is an oasis of biological activity. More than that it is — with the single exception of the tropical rain forest — biologically the richest habitat on Earth, supporting hundreds of thousands of species.

As successful as they have been from the time they first appeared 450,000,000 years ago, however, the hard corals still require certain conditions if they are to survive.

For instance: the hard corals require warm water to grow. Year-round temperatures of 26-29C in Thailand’s seas provide perfect conditions both for coral and for divers, who don’t need wetsuits except perhaps as protection against stings and abrasions.

And they need sunlight. Though they may sometimes be found to about 50 meters, since they normally depend for much of their nourishment on their symbiotic relationship with photosynthetic algae (as does the reef community as a whole, ultimately) they do not thrive at depths below 30 meters, where there is limited light for photosynthesis. Too much sediment in the water, then, will reduce available light and inhibit growth. Sediment in sufficient quantities furthermore directly smothers the coral polyps. (Thailand’s seas are naturally crystal clear, much of the time and in many locations; but there are areas today where tin-mining, coastal shrimp-farming, untreated waste disposal, and longshore tourism development is dumping so much silt into the sea that large areas of coral are being affected.)

Aside from the hard corals, those which most people associate with the reef, there are the soft corals, the gorgonians, and the black corals. All the hard corals — the actual reef-builders — are hexacorals, showing a six-sided radial symmetry, while octocorals (the soft corals, gorgonians, and black corals) are eight-sided. The polyps of the gorgonians (sea fans, harp corals, and wire corals), for instance, have eight tentacles rather than the six or multiples of six characteristic of hard coral polyps. The octocorals, which do not depend on symbiotic relationships with photosynthetic algae, grow well at depths that do not permit hard coral growth, that explains some of the differences you’ll encounter in underwater scenery as you swim deeper.

Sea fans and other gorgonians and among those that live down the reef faces where their hexacoral cousins have ceased to grow. Aside from the sclerites (see below) a second hard, internal flexible skeleton of “gorgonian” holds them erect across currents that carry plankton to the waiting polyps.

The antipatharian black corals, perhaps even more than the soft corals and gorgonians, resemble bushy plants. The antipatharians are not in fact black, usually. It is only the very tough skeleton which is black; the thin living tissue that covers it may be a variety of delicate colors.

Soft corals come in a vast variety of shapes and bright colors. Although they seem not to have a skeleton, their tissues contain tiny crystalline bits of limestone called sclerites that help give the colony structure. Because the soft coral polyps are usually extended and hence visible, and because these animals do not enter into association with photosynthetic algae, they are generally much more vivid than their hard coral cousins.

Finally — whether hard or soft, gorgonian, or ‘black’ — the corals of the Andaman seas are the basis of a complex and valuable marine habitat, one of the two most fascinating ecosystems on Earth. Just one value of this precious resource is that it makes a recreational wonderland for divers and snorkelers. But please remember that every one who explores Thailand’s reefs has a responsibility. In the words of one local dive shop, “Take nothing away with you; leave nothing behind but your bubbles.”

This means not even touching the corals, for the disturbance of their mucous covering may expose them to infection by bacteria and fungii. Weight yourself properly, if scuba diving, so that you don’t bump against delicate coral growth; a moment’s carelessness can destroy years of growth. Above all, do not collect souvenirs from the reef. Given the reported 75,000 snorkellers and divers who, in 1990, enjoyed just the Andaman Sea area (and without even mentioning the commercial collectors of coral and shellfish), it wouldn’t take long before souvenir hunters left little of interest for those who come later.

Coral Reef of The Andaman Region (Similan and Surin Islands)

The Andaman Sea

There are significant climatic and oceanographic differences between the Andaman Sea and the Gulf of Thailand which affect coral reefs. Coral reefs in the Andaman Sea are subject to semidiurnal tides and are exposed to predominant Southwest monsoons from May to October. Approximately 55% of Thailand’s major coral reefs occur in the Andaman Sea. Within this region, there are significant differences in coral reef species composition and morphology. Reef conditions and coral coverage tend to vary with the degree of exposure to the monsoon, distance from the mainland, current and substrata. Fringing reefs predominate. The coral reefs in the Adang-Rawi group are a classic example. There are also some coral communities where corals grow on rocky shores and vertical granite walls. There is no substantial limestone reef development. This is the case for the Similan Islands and the Mu Ko Phi Phi group. The Surin Islands group (i.e., Pachumpba and Stok Islands) are considered to be the most extensive, pristine and perhaps best developed reefs in Thailand. Other coral reefs of major ecological significance in the Andaman Sea include Ko Kradan dan Ko Ngai in Trang Province; and Ko Damhok, Damkwan, and Yong in Krabi Province. From the northern part, Surin and Similan Islands, which are now Marine National Parks, are becoming very famous spots for tourists and divers. Even though these islands can not be visited all year round due to heavy seas from the monsoon, their degradation is evident. Many shallow water reefs have been damaged from tourist activity. Growth of algae is also increasing. Conservation activities are now underway including the installation of mooring buoys and formulation of management plans for the parks.

Phuket once had good fringing reefs. However, now many coral reefs exist with only a small percentage of living coral cover. Tourism development seems to be the most factor causing the deterioration of coral reefs in this province.

Beautiful islands in Phuket, Pang-Nga, Krabi, Trang and Satun are now caught between the struggle of conservation and rapid tourism development. Many coral reefs are now in very bad condition. Some developers do have a conservation ethic and are trying to protect the coral reefs. However, many others still exploit their coral reefs resulting in rapid degradation

Resources – Reef Fisheries

The coral reefs in Thailand waters support a variety of activities that can be classified as tourism and recreation; fisheries-related uses; and other uses, including research and education. In the last decade, there has been a marked change in reef use patterns, as small-scale or traditional fisheries have gradually been replaced by tourism activities. Local fisherman have converted their boats into tour boats and paid more attention to shell collections for souvenir trade. This shift in coral reef use is most notable in Trad, Surathani, Pang-Nga and Trang.

Threats to coral

An estimated 1,800 km² of coral reefs grow along Thailand’s coastline in the Gulf of Thailand and the Andaman Sea. The structure and distribution of coral reefs vary significantly between the two. Because of climatic and oceanographic variations in their water bodies, threats and reef condition can also be substantially different.

Fishing has long been an important economic activity in Thailand, but widespread destructive fishing techniques and trawling have had impacts on coral reefs since the early 1960s. Destructive fishing practices on both coasts have damaged countless reefs, but these activities are believed to have declined as the tourism industry has grown. The rise in tourism and other population pressures, however, have caused sedimentation and wastewater pollution to increase, and damage from boat anchors, divers, garbage, erosion, and sewage and wastewater discharge is evident.

Significant coral bleaching episodes have also plagued Thai reefs. Coral reefs in the Andaman Sea suffered extensive coral bleaching and subsequent mortality in 1991 and 1995, and some bleaching was observed in 1998. Coral bleaching during the 1997-98 ENSO event was widespread in the Gulf of Thailand, where it had not previously been recorded; as many as 60 percent of corals may have bleached in some locations. Unfortunately, the frequency and intensity of bleaching in Thai waters appear to be increasing.

From 1995 to 1998, Thailand began a comprehensive reef survey program that included coral reef mapping and field surveying. Scientists surveyed 251 reef sites in the Gulf of Thailand and 169 sites in the Andaman Sea. Reef condition was evaluated based on a ratio of live to dead coral cover. Using this indicator, 16 percent of reefs in the Gulf of Thailand were rated as excellent, 29 percent good, 31 percent fair, and 24 percent poor. In the Andaman Sea, 5 percent of reefs were rated as excellent, 12 percent good, 34 percent fair, and 50 percent poor (The Similan Islands had the highest concentration of Excellent and Good Reefs – Phuket the lowest). Monitoring suggests that the condition of coral reefs in the Gulf of Thailand has worsened since the late 1980s, while the condition of reefs in the Andaman Sea has remained stable or improved slightly.

The RRSEA model shows that about 77 percent of Thailand’s reefs are threatened by human activities, with over 60 percent of corals in the Andaman Sea and nearly 90 percent in the Gulf of Thailand at risk. Overfishing is the most pervasive threat, affecting about one half of all reefs. Sedimentation and pollution associated with coastal development and inland activities threaten over 40 percent of the country’s reefs. Destructive fishing activities have damaged many reefs in the past and may continue to be a problem in some areas.

Guitar Sharks – Thailand Marine Life

This special fish is seen most frequently at remote sites like Richelieu Rock and Koh Tachai, but has been seen at several other sites with less frequency.

For more information on the other kinds of sharks we see at the Similan islands check our Shark Page. If you are interested in Rays – please see our Similan Island Rays page

Shark Ray

Rhina ancylostoma

Endangered!

Much of this information is from the Australian Museum, as there is little information on this rare shark….

The Shark Ray is a very distinctive, deep-bodied fish which is found widely in the Indo-Pacific.

The upper surface of this species is a blue-grey color with white spots. There is a large blue-edged, black blotch above each pectoral fin and dark bands between the eyes. Unfortunately the specimen in the images has faded and these markings are not visible. This colouration is often not as distinct in large individuals which may only have faint markings.

Some of the most obvious features of this species are the wide, blunt snout, the large thorns on the bony ridges on the head and the large spiracles (the holes in the head behind the eyes). The tail of this species is much longer than the disc. The Shark Ray belongs in the family Rhinchobatidae (the guitarfishes). Two of the characters that separate the guitarfishes from other fishes are the well developed lower caudal fin lobe and the distinct demarcation between the head and pectoral fins. Both of these characters are clearly visible in the top image.

Aust. Mus. specimen AMS I.39214-001.

The Shark Ray is a very distinctive, deep-bodied fish which is found widely in the Indo-Pacific.

The upper surface of this species is a blue-grey colour with white spots. There is a large blue-edged, black blotch above each pectoral fin and dark bands between the eyes. Unfortunately the specimen in the images has faded and these markings are not visible. This coloration is often not as distinct in large individuals which may only have faint markings.

Shark Ray – eye and spiracle.

Some of the most obvious features of this species are the wide, blunt snout, the large thorns on the bony ridges on the head and the large spiracles (the holes in the head behind the eyes). The tail of this species is much longer than the disc. The Shark Ray belongs in the family Rhinchobatidae (the guitarfishes). Two of the characters that separate the guitarfishes from other fishes are the well developed lower caudal fin lobe and the distinct demarcation between the head and pectoral fins. Both of these characters are clearly visible in the top image.

Shark Ray – thorny ridges.

The Shark Ray is not dangerous to humans. It uses its flattened pavement-like teeth to feed on crabs and shellfish.

On the Similan Islands we find these most frequently at Richelieu Rock. In addition sightings have occurred at Koh Tachai, Shark Fin Reef and Boulder city.

Animals that hold their breath while diving….

Nature has shaped through evolution they way animals behave. This means that some animals have adapted to feed in places where the rest of the animal kingdom living around them cannot go. This naturally then eliminates a large part of the competition from the food chain.

The Similan Islands have whales, dolphins, turtles, birds and many other non-aquatic species that dive under water

So how are they able hold their breath for so many minutes without losing consciousness or dying? First, let’s revise some other physiological principles in order to understand more clearly what is happening.

The need to breath is felt when the carbon dioxide (CO2) level rises above a certain threshold. The CO2 will dissolve in the blood causing its pH to decrease, which is making the blood slightly more acidic. The sensors in the medulla oblongata (the base of the brain) will then “tell” the animal that it is time to breath again.Oxygen (O2) and CO2 are carried around the body by the blood in two different ways. One is simply the fact that both O2 and CO2 can dissolve in the blood. This will account for a small fraction of the whole transportation process. The other method uses the haemoglobin, a protein present inside red blood cells. Both O2 and CO2 molecules have the ability to attach themselves to the haemoglobin, but the carbon dioxide has a much greater affinity to do this. Therefore, whilst haemoglobin can carry up to four molecules of O2 it carries a much larger amount of carbon dioxide, normally about 23 percent is transported in the blood. However. The main point is that in most animals the O2 reserve is solely in the lungs and the blood. Once this reserve is depleted, the animals will need to breathe again to exhale CO2 and inhale new O2.

Breath holding diving animals have the advantage of an additional mechanism which, relies on another very similar protein called myoglobin. This protein is located inside muscle cells. In humans it makes up for only a very small percentage of the muscle mass. This percentage changes drastically in the animals with the need to hold their breath and it goes up to 45% of the muscle mass in sperm whales, animals that can hold their breath for up to two hours.

How does it work? Simply the blood will carry O2 to the tissues and the extra oxygen that is not used “immediately” will be stored in the myoglobin more or less in the same way as in the haemoglobin. Once the animal is under water and can no longer breath, the O2 stock of the blood will become depleted, the myoglobin will then release its O2 in to the blood that will carry it around where it is needed. At the same time the myoglobin will “catch” the excess CO2 in the blood restoring to a level that does not trigger the need to breath. When eventually the animal returns to the surface to breath air, the myoglobin releases all of its stored CO2 and replaces it with fresh O2. The amount of myoglobin present in the animal muscles will determine the maximum time the animal can spend underwater.

The more the animal wants to stay under water, the longer the period it has to stay at the surface for the gas exchanges to take place. A dolphin needs to breathe a few times (about two to four minutes) to stay submerged 20 to 30 minutes. A sperm whale will breathe 4 or 5 times per minute for up to 15 minutes at the surface to stay two hours under water. Sea birds normally dive for 3 to 10 minutes according to the species they belong to and need to breathe for about 2 to 3 minutes before diving.

Anglerfish – AKA “Frogfish” – Incredible Similans!

From One of our staff…

Two hundred plus dives in the Similan National Park had brought me my first whale shark and a subsequent two more. Mantas! Again after never seeing one I have since become an expert observer of the beautiful water gliders as they cut through the ‘air’ swimming effortlessly through currents and circling divers, sightings of which, like the whale shark, produces a new genre of ‘adrenalin junkie’ divers who dive simply for the ‘hit’ of seeing the big stuff. Working on our Similan Liveaboard blessed me with these opportunities. That is of course until time and multiple dives pulls you over to what has become to be termed the ‘dark side’…

Several weeks ago at Koh Tachai Plateau a fellow guide gave me an insight into a new addiction; an addiction of finding what spends its life, and the lives of its species before it, trying not to be found. The guide swam over to me excitedly pointing at his compact camera and waving his arms frantically. Meanwhile, a manta soared over our heads. I replied with a confused look and a raised arm towards the performer. If he had a great shot of the manta I would rather appreciate it later back on the boat, but at the moment I was enjoying the live show. My friend spared it a glance but clearly felt his camera deserved all of our undivided attention. I felt reluctant to draw my eyes away from the giant pelagic dancer, but humored him. He rapidly pressed the giant buttons on his digital camera until he found his prize. Through the excitement, the sea water and the thick plastic housing I saw a red blob. ‘Great. I’ll return to my manta thanks.’ That was his first frog fish. I’d yet to see one, but all was to change on my last liveaboard…

East of Eden, 17 meters, just before a renowned sandy patch which I must have swam over countless times. A patch of rubbley indistinct coral. A tiny piece of rubbley indistinct coral. A miniature rubbly piece of fish, commonly known as a ‘clown frog fish’, white adorned with orange spots and extremely cute. It was reminiscent of a garden gnome, well hidden but clearly the rightful proprietor of its little coral patch. The clown frog fish was fixed onto the side of a piece of coral, utterly at one with its surroundings. So still that it was looked glued to its perch. I was mesmerized. I wanted to move closer. Meanwhile, my customers took a quick snap and moved on. After the dive they professed that they didn’t understand what all the fuss was about. Why become so excited over a tiny indistinct fish when the reef is swarming with the most beautiful and exotic fish just screaming out to be noticed and admired?

Strangely enough, although I had been a virgin frog fish viewer, the experience was repeated the very next day. Perhaps this was because my eyes had received its first lesson in obscure marine life identification. Or perhaps it was just luck. However, my second ever encounter was equally as intriguing.

At Koh Tachai Plateau at 27 meters there stands a barrel sponge. Sitting directly on the top, wedged in between the circular rim is a large, red, about the same size as a football, an utterly ugly, utterly delightful frog fish. Instantly I was mesmerized. Tiny little eyes glazed over in what looked to be a deep state of meditation, mouth slightly agape in a way that actually made it look to be taking slow and controlled inhalations. The creature really did belong to another world – the underwater one – and upon closer examination it was possible to see its inbuilt fishing line extending from its first dorsal spine and hanging above the gaping mouth. Invisibly observing. Invisible. It was eerily still. It was incredible.

Ultimately what these two encounters have taught me is that there are alternatives to the adrenaline hits of having a whale shark charge through your dive group or a manta circle you. In fact part of the beauty of the ugly frog fish is the dedication it takes to spot, which can result in such a sense of satisfaction, causing dive instructors to dance around at 20 meters in front of a digital image.

Similan Diving

Similan Marine Life – Cuttlefish – weird and cool

Space ships. I don’t think I have ever dived anywhere else where I have seen so many space ships – and not just during night dives but during the day as well. For me these highly evolved, highly intelligent, elephantine mollusks have always appeared extraterrestrial. The way in which they hover, speed backwards and perform a stunning display of electric flashes so utterly hypnotic that leaves you wondering what level of evolution they have achieved.

The Bon Soon Wreck, East of Eden, Richelieu Rock and of course the ‘Three Lovers’ (shown above) at Koh Bon; always together and always vying for one another’s attention. Reaching out one of their eight arms here and another one there, meanwhile emitting an auroral glow around their floating bodies. A marine biologist once warned me never to shine my flash light in the eyes of a passing space ship due to the real risk of permanently blinding it, and yet their pulsating electric ripples are best observed in the dark (although this does carry the risk of losing ones customers who always have a tendency to disappear during complete darkness).

Their vision is one of the most highly developed in the animal kingdom, and they perceive contrast rather than color, so their light display has a secondary purpose of allowing them to communicate with other spaceships. Why they have W-shaped pupils has yet to be explained, although it has been proposed that this is to allow them to see backward and forward at the same time. Perhaps their extraordinarily large brains may hold the key. However, they are clearly aware that any potential enemies are still an evolutionary stage or two behind as they possess and impressive array of chameleon skills allowing them to reflect the coloring of their environment as they travel over different shades of coral, rocks and sand, which leaves the reptilian master of disguise lagging behind; not only is this an effective disguise from predators and prey, but with the ability to change color in less than a second, it is the speediest transformer in the entire animal kingdom

Closer observation will actually reveal finely tuned buoyancy. Unlike their Octopi cousins, who scramble over the coral, they can regulate their depth by changing the liquid-to-gas ratio in their chambered cuttle-bone.

Italians like to eat space ships. Last month I dived with an Italian chef and as I made the ‘cuttlefish’ hand signal he replied with the ‘spaghetti’ symbol – consisting of a twist of the wrist and a greedy glint in the eye. After learning that some marine biologists believe that they learn by observation, I felt a protective urge to shield these culinary inclinations from the three spaceships in view. Indeed I have spent many a happy dive hovering face to face, with a hand positioned on my forehead slowly raising a finger. The spaceship humors my mimicking and has been known to raise an opposite arm. Hurrah! Communication with life from the blue planet!

Similan Diving

Similan Islands – Marine life resource

Divers Enjoy the Diverstiy of the Similan Island Marine Life

In Thailand The premier dive sites are located on and around the Similan Islands.  These uninhabited tropical islands are home to some of the most dynamic and vibrant underwater ecosystems in the world.

Rocky boulder sites dropping off into the blue on the Western side

Sloping Reefs cover the Eastern side of the Similans.

Then the Pinnacles of Elephant Head Rock, Koh Tachai, Sharkfin Reef, Koh Bon and of course the most famous site in Thailnad (and one of the best inthe world) Richelieu Rock also bring a wide diversity to the dive sites.

It also means a huge amount of marine life! With so many different ecosystems it’s hard to keep track of all the different species of marine life that we encounter. Whether it’s the passing Manta ray or the sharks…what are they?

Fortunately there is now  good resource for Similan Marine Life.

While this is still in it’s initial phases, the page is certainly off to a good start – featuring plenty of things that are commonly senn as well as many things that are acommonly overlooked! here are articles about Cuttlefish, Wenteltraps and even Frogfish. As a resource – this will help any diver on their plans to visit and for those who have been fortunate enough to visit already – this is the place to help identify those strange things you saw on underwater The site will be updated frequently so we will be revisiting frequently and looking at all the new and amazing creatures.

Similan Marine Life

With some fish, critters and coral out there – it is hard to sometimes realize that the stories and details about each species can be truly amazing. There are several stories and lots of information about the Marine life around the Similan Islands. I had a good laugh about some of the analogies made!

There are some articles about Bumphead parrotfish, nudibranchs and turtles. These are all things tat people commonly see and are curious to learn more about.

However the articles on the Wenteltraps and Cuttlefish were really fun to read. Not just scientific dribble that you see in a lot of these postings.

from the cuttlefish article:
“Space ships. I don’t think I have ever dived anywhere else where I have seen so many space ships (cuttlefish – and not just during night dives but during the day as well. For me these highly evolved, highly intelligent, elephantine mollusks have always appeared extraterrestrial. The way in which they hover, speed backwards and perform a stunning display of electric flashes so utterly hypnotic that leaves you wondering what level of evolution they have achieved.”

The best time to visit the Similan Islands National Marine Park is from mid October to early May. It is during this time that the seas are calm, the visibility is at its very best, and the large Marine Life (like Whale Sharks and Manta Rays) are making their annual migrations to feed on yearly plankton blooms. The water temperature around the Similans varies between 27 and 29 degrees Celsius, so most divers prefer a 3 mm wetsuit. Depending on environmental factors the water clarity ranges from 10 to 40 meters. Adventures to the nine islands of this amazing archipelago can either be done by Similan Liveaboard or day trip diving from Khao Lak. The Similan Islands National Park closes from May to October when western Thailand is experiencing the southeastern monsoons.

-Similan Diving

Similan Marine Life – Frog fish

From One of our staff…

Two hundred plus dives in the Similan National Park had brought me my first whale shark and a subsequent two more. Mantas! Again after never seeing one I have since become an expert observer of the beautiful water gliders as they cut through the ‘air’ swimming effortlessly through currents and circling divers, sightings of which, like the whale shark, produces a new genre of ‘adrenalin junkie’ divers who dive simply for the ‘hit’ of seeing the big stuff. Working on our Similan Liveaboard blessed me with these opportunities. That is of course until time and multiple dives pulls you over to what has become to be termed the ‘dark side’…

Several weeks ago at Koh Tachai Plateau a fellow guide gave me an insight into a new addiction; an addiction of finding what spends its life, and the lives of its species before it, trying not to be found. The guide swam over to me excitedly pointing at his compact camera and waving his arms frantically. Meanwhile, a manta soared over our heads. I replied with a confused look and a raised arm towards the performer. If he had a great shot of the manta I would rather appreciate it later back on the boat, but at the moment I was enjoying the live show. My friend spared it a glance but clearly felt his camera deserved all of our undivided attention. I felt reluctant to draw my eyes away from the giant pelagic dancer, but humored him. He rapidly pressed the giant buttons on his digital camera until he found his prize. Through the excitement, the sea water and the thick plastic housing I saw a red blob. ‘Great. I’ll return to my manta thanks.’ That was his first frog fish. I’d yet to see one, but all was to change on my last liveaboard…

East of Eden, 17 meters, just before a renowned sandy patch which I must have swam over countless times. A patch of rubbley indistinct coral. A tiny piece of rubbley indistinct coral. A miniature rubbly piece of fish, commonly known as a ‘clown frog fish’, white adorned with orange spots and extremely cute. It was reminiscent of a garden gnome, well hidden but clearly the rightful proprietor of its little coral patch. The clown frog fish was fixed onto the side of a piece of coral, utterly at one with its surroundings. So still that it was looked glued to its perch. I was mesmerized. I wanted to move closer. Meanwhile, my customers took a quick snap and moved on. After the dive they professed that they didn’t understand what all the fuss was about. Why become so excited over a tiny indistinct fish when the reef is swarming with the most beautiful and exotic fish just screaming out to be noticed and admired?

Strangely enough, although I had been a virgin frog fish viewer, the experience was repeated the very next day. Perhaps this was because my eyes had received its first lesson in obscure marine life identification. Or perhaps it was just luck. However, my second ever encounter was equally as intriguing.

At Koh Tachai Plateau at 27 meters there stands a barrel sponge. Sitting directly on the top, wedged in between the circular rim is a large, red, about the same size as a football, an utterly ugly, utterly delightful frog fish. Instantly I was mesmerized. Tiny little eyes glazed over in what looked to be a deep state of meditation, mouth slightly agape in a way that actually made it look to be taking slow and controlled inhalations. The creature really did belong to another world – the underwater one – and upon closer examination it was possible to see its inbuilt fishing line extending from its first dorsal spine and hanging above the gaping mouth. Invisibly observing. Invisible. It was eerily still. It was incredible.

Ultimately what these two encounters have taught me is that there are alternatives to the adrenaline hits of having a whale shark charge through your dive group or a manta circle you. In fact part of the beauty of the ugly frog fish is the dedication it takes to spot, which can result in such a sense of satisfaction, causing dive instructors to dance around at 20 meters in front of a digital image.

Similan Diving

Similan Islands -Nurse Sharks

As taken from the files these Similan Diving Experts

The Nurse Shark is rare, but is found among the boulders of the Similan Islands. If you would like to learn more about Sharks in the Similan Islands please check out our Shark Page. If you have any questions about how to dive with sharks – check here

Nebrius ferrugineus

The Tawny Nurse Shark’s common name is derived from its ability to suck up prey using a powerful sucking motion with its throat, just like a baby being nursed. This talent is used to vacuum out octopus, fish and crabs from the reef or it can be reversed to fire a jet of water at any captor.

A large, tropical inshore shark of the continental and insular shelves of the Indo-Pacific,often in the intertidal in water scarcely able to cover it and from the surf line down to a few meters depth, commonly at 5 to 30 m and ranging down to at least 70 m on coral reefs. It occurs on or near the bottom in lagoons, in channels, or along the outer edges of coral and rocky reefs, in areas with seagrass and sand on reefs, sandy areas near reefs and off sandy beaches. It prefers sheltered areas in crevices and caves on reefs but often occurs in more exposed areas in depressions or crevices. Young prefer crevices in shallow lagoons but adults are more wide-ranging.

The tawny nurse shark is primarily nocturnal, resting in the daytime in shelters but prowling slowly about around reefs at night, although some individuals may be active in the day. In Madagascar it is described as day and night-active, and in captivity they get quite active and vigorous when food is presented to them during the day. They are social, gregarious sharks when at rest and form resting aggregations of two to a half-dozen or more in shelters, and are often seen piled inertly across or on top of one another. When resting, they are extremely sluggish. This shark has a limited home range, and individuals often return to the same area every day after foraging.

Reproduction ovoviviparous (aplacental viviparous) with cannibal vivipary or uterine cannibalism in the form of oophagy Inside the eggs, they eat each other!!!). This shark has been described as an oviparous or post-oviparous shark that retains the egg-cases until they hatch and the young are born, but recent evidence indicates that this is incorrect. Pregnant females collected from Okinawa have had one or two foetuses per uterus, 297 to 595 mm (the latter near term), with the yolk sac reabsorbed and a greatly expanded stomach filled with yolky material in foetuses 338 and 595 mm long, and also had cased eggs in the uterus. Apparently this species practices oophagy on relatively large, cased nutritive eggs (unlike many lamnoids which have very small nutritive eggs), and is the first orectoloboid known to have uterine cannibalism. It is not known whether foetuses of this species eat other foetuses (adelphophagy) as with the sand tiger (Carcharias taurus). The presence of two foetuses 338 and 297mmin the same uterus, with the smaller one slender and the larger bloated with yolk, suggests that competition between siblings for the relatively big eggs is likely and could even eliminate the less successful sibling. Adelphophagy is less likely although early stages need to be examined to eliminate it. Number of young per litter uncertain; at least four young per uterus has been suggested from cased eggs, but the size and enormous girth of the near-term Okinawan foetus and the two smaller foetuses in a litter suggests that litters are smaller, possibly one or two per uterus or even one per female, and that numbers of cased eggs in the uteri cannot be used to extrapolate litter sizes in this species. In captivity adult females lay cased eggs on the bottom, but these do not develop, and could be nutritive and unfertilized. Such free eggs may have been the basis of the suggestion that this species is oviparous. The tawny nurse shark breeds in July and August off Madagascar. Food of this shark includes corals, crabs, lobsters and other crustaceans, Octopus, squid and probably other cephalopods, sea urchins, and reef fish including surgeonfish (Acanthuridae), queenfish (Carangidae) and rabbitfish (Siganidae), and occasionally sea snakes. While foraging the tawny shark moves along the bottom and explores depressions, holes and crevices in reefs. When it detects prey it places its small mouth very close to the victim, and uses its large pharynx as a powerful suction pump to rapidly suck in reef organisms that may be out of reach of its teeth. A few large individuals dissected had quantities of small, active reef fishes in their stomachs, presumably sucked in by the sharks as the prey fishes lay inert in shelters or on the bottom at night. Individuals caught by fishermen may reverse this sucking action, and blast streams of water out of their mouths and into the faces of their captors; they are said to make a grunting sound between blasts. It is not known if spitting water is deliberate and defensive or if the sharks are actually aiming the water at the anglers. They also tend to spin when hooked on a line, making them difficult to handle and subdue.

The body form of the tawny nurse shark (littoral morphotype) is more fusiform and streamlined than other nurse sharks, with narrow-based, falcate, plesodic pectorals, pointed dorsal and anal fins with the anal-fin apex raked posterior to the free rear tip, a short ventral caudal-fin lobe, lateral eyes and gills, a narrow head, flat wedge-shaped snout, and compressed, semi-blade-like, imbricate teeth in discrete series. The tawny nurse shark superficially resembles certain other large, partly or mostly sympatric, active reef sharks including the sand tiger shark (Carcharias taurus), sicklefin lemon shark (Negaprion acutidens), and reef whitetip shark (Triaenodon obesus). Whether it is behaviourally divergent from other nurse sharks awaits a detailed comparative study of nurse shark behaviour. Its status as a game fish in Australia, unlike the nurse shark in the western Atlantic, suggests that it may be a more active swimmer when not resting on the bottom.

Size

Size: Maximum about 314 to 320 cm, though most individuals are smaller; size at birth has been reported as about 40 cm (Fourmanoir and Laboute, 1976) but subsequent data from a pregnant female captured off Okinawa suggest that it may reach 60 cm or more at birth (Teshima et al. 1995), while a 79 cm female from Navotas market in Manila, Philippines had a somewhat bloated stomach full of yolk, suggesting that it was newborn or a term foetus; males are mature at about 250 cm and reach at least 301 cm; adult females are 230 to at least 290 cm.

Interest to fisheries…

Common or formerly common in areas where it occurs, and caught inshore by fishermen in Pakistan, India, Thailand, and Philippines, and probably widely captured elsewhere.
It is utilized fresh and dried-salted for human food, its liver is rendered for oil and vitamins, its fins are used in the oriental sharkfin trade, and offal is processed into fishmeal. Its thick, armour-like hide is potentially valuable for leather.Off Queensland, Australia, it has been fished as a big-game shark, and large individuals are prized as powerful fighters by sports anglers. Apart from anglers who target this fish, it is apparently primarily caught only as an untargeted bycatch of fisheries in inshore waters in nets, on line gear, and in fish traps.

Conservation Status : The conservation status of this shark is uncertain and urgently needs investigation despite its wide range. In some areas, including the Gulf of Thailand where it was commonly caught in the 1960s, it may have been depleted due to increasing fisheries activity and habitat degradation. Also, reef habitats have been extensively damaged or destroyed by dynamiting and poisoning in parts of its range, including Indonesia and Philippines, which probably have had an adverse effect on this species both directly and through decimation or elimination of its prey. Its docility and inshore habitat makes it particularly susceptible to a wide variety of fishing gear, to harassment and injuries by divers, and to reef destruction and pollution.

Threat to humans: This has been described as a much more docile species than its close relative, Ginglymostoma cirratum, and apparently tolerates close proximity of divers and usually allows humans to touch and play with it without biting. However, there are a few records of these sharks biting their tormentors, and clamping tightly onto them. Because of its size, strength, powerful jaws and small but sharp cutting teeth, the tawny shark should be treated with the respect due it.