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Mu Koh Similan National Park

For Similans Diving

Mu Koh Similan National Park was established in 1982 and is located along the western coastline of the Andaman Sea in the Indian Ocean, about 100km northwest of Phuket. The park area covers 140 km², 16 km² of which is land, composed of 9 granite islands created by upwellings of hot magma during the Tertiary-Cretaceous Period some 65 million years ago, then smoothed by glacial ice and the wave action of the sea.

The Similan Islands - photo courtesy of the Tourist Authority of Thailand

Similan is really the Malaysian word for nine, as there are 9 islands in the Similan group. The islands are named Koh Huyong, Koh Payang, Koh Payan, Koh Miang, Koh Ha, Koh Payu, Koh Pusa, Koh Similan and Koh Bangru but are often simply referred to by a number 1 through to 9. A popular game on the Thailand dive boats is to argue over which island represents which number. In 1998 the park boundary was expanded to cover Koh Tachai and Koh Bon, 2 islands to the north of the Similan group. There also 2 exposed rock pinnacles called Hin San Chalam (Shark Fin Rock) and Hin Koh Ha.

The Similans are islands of high and steep granite mountains with beaches and rock formations. The shoreline features inconsistently curved rocks worn away by direct wave action. The islands are covered in tropical jungle and the beaches have no mud, giving them some of Thailand's finest white sand beaches. The highest point, on Koh Similan is 244 metres above mean sea level. The seas around the islands are surrounded by coral reefs.

The distinctive granite boulder formations on the surface continue underwater on the west coast of the islands creating the dramatic underwater seascapes that divers love. However, what makes the area unique, at least from a divers point of view, is that around on the east coast of the islands there is a different environment. Here are white powder-sand beaches that slope down from the water's surface to about 40 metres, and feature coral gardens all the way down. The distance from the mainland and the lack of any real inhabitants on the islands keeps the water crystal clear.

Around the Similan Islands

Koh Similan is the largest island (5 km²). There is an unused lighthouse, built by Royal Thai Navy on the island, which visitors may climb to with park ranger permission. The climb is not an easy one but the views are superb. Koh Pusa is the smallest island, only really an exposed rock. It is commonly referred to as Hin Hua Chang (Elephant Head Rock).

The Thai National Park Authority maintains 2 park ranger stations, 1 on Koh Similan (island number 8) which has basic bungalow accommodation for rent and also some tented accommodation. There is a short walking trail here and another shorter one on Koh Miang (island number 4). There is also a Royal residence of a Thai Princess on island number 4, which is heavily guarded by the Royal Thai Navy whenever she feels like dropping in for a visit. Koh Tachai also has a camping area with restroom facilities.

Flora and Fauna

Marine Life

Jewelled moray eel in the Similans, Thailand - photo coutesy of Marcel Widmer - www.seasidepix.com

Beneath the Andaman Sea surface at Mu Koh Similan National Park lies a complex ecosystem. The major residents of the reef are corals and the closely related sea anemones; of the phylum Cnidaria, class Anthozoa, which contains all radially symmetrical invertebrate animals. Corals and sea anemones exist as individual polyps living in either solitary or mostly colonial forms. The polyps of hard corals construct communal limestone homes which are built up into a multitude of shapes and sizes eventually giving rise to a coral reef.

Several factors support a good environment for the reef, i.e. temperature, salinity, light, wave and tide, sedimentation and nutrients. These all create a healthy coral reef. In the Andaman Sea, coral reefs are classified as deep water and medium water. Deep water coral reefs can grow down to 30 metres, and the Similan dive sites have these reefs in abundance because of the clarity of water which allows sunlight to penetrate deeper. Medium water coral reefs grow between 8-15 metres beneath the surface. The deep water hard corals found in the Similan Islands are of mostly staghorn coral types (Acropora echinata) and the smaller cauliflower shaped types (Seriatopora histrix).



The park is not only of interest to divers, it's also popular with bird watchers. Most bird watchers who make the trip to Koh Similan do so to see the Nicobar pigeons which are seldom seen elsewhere. They are often seen foraging around the campsite on Koh Miang (island number 4). Other highlights are the close up views and large numbers of pied imperial pigeons, and regular sightings of white-bellied sea eagles. Another commonly seen species is the collared kingfisher. A survey conducted in 1992 revealed that 39 species of birds can be found on the 9 islands. Resident species include the Brahminy kite and the white-breasted waterhen, while migratory species include the pintail snipe and grey wagtail. Temporary migratory species include the barn swallow, cattle egret, watercock and the roseate tern.


Natural fresh water reserves are few, and as a result, large mammal species cannot survive. However, surveys have revealed that 27 species of small mammals exist within the park, including 16 species of bats including the black-bearded tomb bat, the lesser false vampire bat, the intermediate horseshoe bat, the lesser bent-winged bat, and the hairless bat. 3 species of squirrels can be found including the grey-cheeked flying squirrel. 4 species of rats - the yellow Rajah rat, the rice-field rat, roof rat and noisy rat can be seen scurrying around as well.

The more unusual but fairly common residents include the bush tailed porcupine, common palm civet, flying lemur and the bottlenose dolphins. 22 species of reptiles and amphibians can be found in the park including the banded krait, reticulated python, white-lipped pit viper, common pit viper, blue garden lizard, hawksbill turtle, green turtle, Bengal monitor lizard, common water monitor lizard, ornate froglet, common Asiatic frog, marsh frog, and the common bush frog. A reminder that you are never far from water is the hairy-leg mountain land crab. This crab is found in large numbers all over the islands.


The Similan forests can be divided into 3 main types:

Beach Forest - open forest with scattered plants at an approximate height of not over 15 metres such as Terminalia catappa, Barringtonia asiatica and Callophyllum inophyllum. Small perennials and large shrubs not exceeding 10 metres in height found are Xylocarpus gaugeticus, Herltiera littoralis and Hibiscus tiliaceus. Smaller shrub found are Capparis micracautha, Breynia vitris-idaea, Fischer and Pandanus odoratissimus. Grounds covering plants common in the area are beans, Vigna sp., Spilanthes sp., Ischaemum barbatum, Lophatherum gracile, Hoya parasittrica and Asplenium nidus.

Scrub Forest - habitat for shrubs which can develop on grounds with soil depth of not exceeding 30 cm. A few cacti can be found while more common shrubs found are Cercus spp., Dracaena spp., Memecylon caeruleum and Cleistanhus polyphyllus.

Primary Forest - habitation for perennials at a height of 20 metres or above such as Dipterocarpus costatus, Dipterocarpus boudii, Shores spp. Lower perennials at 15-20 metres in height are palaquium obovatum, Eugenia denaiflora, Wrightia sp.; 10-15 metres in height are Hydnocarpus ilicifolius, Semecarpus curtisii, Diospyros wallichii. Bambusa sp., Calamus longisetus and Palm. Amydrium medium and Bauhinia glauca are also found with other creepers and parasites such as betel pepper, bauhinia and orchid.

Above the water line surrounding each island lies beach forest, which gradually becomes tropical forest further inland.

The most unique vegetation found in the Similans are sapodilla and Nguang Chang Talay, while edible plants are Manilkara sp., Toumefotia argentia, Bouea oppositifolio, Lepisanthes rubiginosa, Diospyros wallichii, Neang and Copparis micracantha. Important tree species include Manilkara sp. Cordia subcordia, and Tournefotia argentia.


Nudibranch - photo courtesy of Sheldon Hey

Summer begins in mid February and ends in May. Rainy season starts from mid May and lasts until October, with north-westerly winds blowing, and the national park is officially closed from16 May - 15 November. Average annual temperature is 27 degrees C with average of humidity approximately 83% all year round. Average annual rainfall is measured at 3,560 mm with an evaporation rate of 1,708 mm per year.


The collecting of corals or shells is forbidden in the park and there is a 'hands off the coral' policy. These policies are only instigated by the dive industry itself, which is mainly self-regulated and does a better job of educating divers and keeping them off the reef, than in many other areas of Asia.

Environmental protection is less than perfect in Thailand, and it's a relatively new concept here. However, the level of protection is ahead of many other South East Asian countries. There are government education programmes regarding destructive fishing techniques such as dynamiting. Dynamite fishing is virtually unheard of in these waters now although drag net fishing is still an issue. There is a turtle hatchery programme on Similan Island No. 1 which is closed to visitors, and a number of other dive sites are made off-limits to divers each season to promote unhindered coral growth. One of the Similan parks best features is that all dive sites have several mooring buoys, laid by the Thai Royal Navy, so there is never any reason for boats to drop anchor on the reef. These are all positives at a time when diver numbers visiting the park are increasing each year.

Remoteness has kept the Koh Similan Islands unspoilt for many years. The distance from the mainland and from Phuket Island had limited visitors to those willing to travel overnight by boat. But faster and large-engine vessels are allowing more and more day-trippers to visit the park. Fortunately rough seas during the May - October monsoon season make the islands too dangerous to reach most of the time, and officially the park is closed to divers during those months. Is the park closed to fishing boats during those months too? Good question.

Another often asked question is 'How were the Similan Islands affected by the Tsunami of December 2004?' Approximately 100 research officers from the Department of Marine and Coastal Resources and many other organisations, including several southern universities, institutes and the National Parks Wildlife and Plant Department, with the cooperation of more than 120 volunteer divers, participated in an assessment of the impact of tsunami on marine resources in January 2005. Their results concluded that the degree of damage to the corals depended on geography of the islands, location and morphology of the coral reefs, as well as water depth, which promoted or protected reefs in certain areas from the effects of the tsunami. In general it is agreed that the coral reefs escaped very lightly in most areas, much more lightly than was originally feared.

A short term management plan suggested that restricted status areas be designated for heavily impacted areas such as southwest of island number 7 and the northern part of island number 8. Other initiatives included repositioning upturned corals, under the supervision of a marine biologist, and reef debris collection. Longer term management plans include the implementation of a coral reef monitoring programme, assessing the marine parks tourist carrying capacity (quota restrictions are often talked about, but remain unimplemented) and public conservation awareness. A more detailed assessment of the Tsunami's impact can be read here: Environmental Impact Assessment.

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