Mergui Archipelago Diving

Shark Cave

Shark Cave is 2 km north of Great Swinton Island and is made up of 3 small islets, the centre islet being the largest at 100 metres wide. In sharp contrast to the bare rocks that identify this site at the surface, Shark Cave will surprise you with its abundance of marine life.

Another of the top Mergui Archipelago diving sites, Shark Cave is known for its resident docile nurse sharks. The ragged cave entrance is on the north west corner of the islet, and is 5-16 metres deep. Often found guarding the entance are several long-fin trevally and silver sweetlips. They come to hunt for the masses of juvenile barracudas, cave sweepers and silversides. The tunnel is 20 metres long and the ceiling is covered in beautiful marigold cup corals, and the floors with yellow Stylotella Aurantium sponges. Watch out for the strong surge as you make your way through, but you may just find some large rock lobsters.

Grey reef sharks can sometimes be met cruising through the tunnel. These sharks have been known to show aggression to divers so the best policy is to stick close to one side of the tunnel to give them space to get past. Groups of white tip reef sharks can also make a surprising appearance. A 1 metre square hole marks the entrance to the lower cavern where nurse sharks can be seen. It is accessible 1 diver at a time and real care is needed with buoyancy control. A torch is recommended in the tunnel area to see into the deeper crevices.

The reef on the north east side of the islet (to 25 metres) is rugged with black and white featherstars, and green tube corals and cup corals. Black and white banded sea snakes and black-blotched fantail rays hunt over the reef. Look closely for yellow ornate or harlequin ghost pipefish and tigertail seahorses. Bent stick pipefish can also be seen out on the sandy bottom. At night there are decorated sponge crabs, going about their daily chores. These rather drab-looking creatures are masters of disguise. Turn their back on you, and you could well think that you are staring at a lump of sponge. In the shallow areas magnificent anemones add colour, as do Clark's and tomato anemone fish and the western clownfish.

The southwest wall bottoms at 30 metres and has many fine crevices crammed full of life. Take a careful look and you'll see Durban dancing shrimps and red and white banded boxer shrimps on the ledges, mantis shrimps, sea slugs, cowries and an amazing amount of moray eels - snowflake, white-eyed and fimbriated. If you're really lucky, you could see the feeding habits of cuttlefish. They hunt in pairs; one acts as a look-out, as the other frantically searches in the crevices with its tentacles to pull out any food it can find. The Mergui Archipelago is an excellent place to see cuttlefish.

The small rocky outcrop to the north is called Square Rock. This insignificant chalk white rock drops vertically down to about 15 metres before jumbled rocks spread out wider, reaching the sandy bottom at 26 metres. This site is dived in a circular fashion if currents will permit, and there is a smaller sister pinnacle just to the south. Currents can be fierce here with strong up and down currents. Square Rock's walls have green and orange Antipathes black corals, and white Anthothelidae sea fans. Check out the bases of these to try and spot the minute banded pipefish. In the cracks are hidden nocturnal grey bamboo sharks, a small species about half a metre in length. Under rocks at the bottom of the walls whitetip reef sharks and small nurse sharks can be found. This reef is full of scorpionfish, some small and well camouflaged, and some huge specimens almost half a metre long.

The southern outcrop, often just called The Pinnacle, is slightly deeper at 30 metres, and hosts olive green Theonella Cylindrica sponges and anemones with their attendant anemone crabs and saddleback anemonefish. Like the rest of the site too, there are innumerous scorpionfish here. At the safety stop, you're likely to see porcupinefish and occassional schools of rainbow runners, darting past. Currents can also be strong here.

This Mergui scuba diving site is also known as the Three Islets, the Three Stooges, In-Through-The-Out-Door and Colona Rocks.

Shark Cave Reef Basics: Sharks, caves, fantastic sea life
Depth: 5 - 30m
Visibility: 10 - 30m
Currents: Can be strong
Surface conditions: Can be rough
Water temperature: 25 - 28°C
Experience level: Advanced
Number of dive sites: 3
Diving season: October to May
Distance: ~75 km north northwest of Kawthaung (4 hours)
Access: Mergui liveaboard diving from Phuket, Khao Lak and Ranong in Thailand

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