Tantalising Thailand Liveaboard: Diving the Similan & Surin Islands Aboard Thailand Aggressor

Richard Aspinall joins a Thailand liveaboard to explore the Similan and Surin Islands in the Northern Andaman Sea. Aboard the Thailand Aggressor he finds an abundance of marine life, from fish shoals to macro critters

Thailand Liveaboard Diving: The Pinnacle

It is heart-warming to know that in this age of industrial-scale fishing and declining ocean health, places like Richelieu Rock still exist. This isolated pinnacle of granite is home to such a concentration of life that it can be hard to see the rock for the fish!

From the smallest glassfish, in shoals hundreds if not thousands strong, to the jacks, trevally and lionfish, cruising and hunting between the tumble of house-sized boulders, this is a hotspot for life of every conceivable hue and habit. Shoals of blue-lined snapper, anthias, yellow-tailed blue damsels, fairy wrasse in the coral heads and shoals of neon fusiliers overhead and more besides, all gloriously compete for your attention, as they swirl around and between the rocks. It is easy to understand why Richelieu is one of the top dives on the planet – I certainly added it to my own ‘best ever’ list. Richelieu was the undoubted highlight of seven days of diving aboard the Thailand Aggressor, but getting there was enormous fun too.

After flying into Phuket, I stayed in a hotel on the coast, near Khao Lak, to acclimatise and sleep after the long journey from Scotland, before transferring to the Thailand Aggressor. Refitted throughout in late-2024, she’s an older vessel (built in 1977), with a solid steel, no-nonsense approach to marine engineering. My cabin and facilities were new and comfortable and as I assembled my kit and camera, I met some of the other 15 guests and we chatted over what we expected from the week. I was hoping for interesting fish encounters, with several species on my shooting list. Top was a ghost pipefish, along with a few other little oddities, and as many of the local clownfish species as possible.

Similan Dive Highlights: Reefs, Granite Formations and Macro Finds

The Similans’ name derives from the Yawi for ‘nine islands’, and while each has a ‘proper’ name, they are mostly referred to by number by the dive crews. Our itinerary took us west from the Thailand coast and then north to the Surins, weaving our way through the tree-clad Similans, each a collection of immense rounded blocks of pink granite piled by some giant mythical hand. Two other islands, Koh Bon and Koh Tachai, have been added to the National Park, making 11 in total.

That first evening, after a full safety briefing, we enjoyed the first of many superb Thai meals, before we left our berth at Tap Lemu Pier. We’d wake at 6am for a check dive at Anita’s Reef and then south a little to Shark Fin Reef close to Island 3. Islands 1 to 3 are set aside as a turtle sanctuary.

Shark Fin Reef (it resembles a shark’s fin at low tide) was an easy introduction to the locality. The jumble of mammoth rocks offers a mix of swim-throughs and channels, with changes in current depending on tide. Limited to 100ft or thereabouts by our nitrox blend, we generally started dives around 70-80ft before shallowing up into the 30ft45ft range before safety stops and DSMB deployment for a tender pick-up. Many of the dives followed this pattern.

Typically, there are a lot of filter feeders like sea whips, sea fabs, sea plumes and soft corals thriving on the rich plankton. The rocks were also home to sprays of black sun coral and carpets of anemones and their resident clownfish. The orange skunk clownfish, with its single dorsal stripe and the common were everywhere.

I switched out my wide-angle lens and port in favor of macro for a few dives, including one of the only two night dives on offer – the National Park authorities limits night diving to protect sensitive corals. They also impose a six-month ban on diving during the monsoon season and maintain an impressive network of fixed moorings.

A macro dive is always fascinating, and after shooting some of the seemingly unlimited color variations of Christmas tree worms, I found small gobies amid the sea fans and whip corals. Happily, my buddy had her own camera, and we worked well as a team of two patient people. I managed to ‘tick off’ another clownfish species – the large and quite ebullient Clark’s. The adults are a rich chocolate to black, with bold stripes. They seem to favor the pizza-like Stichodactyla haddoni anemones.

The next day, I was back to wide-angle, and encountered my first-ever sea snake, the venomous, but generally safe to be around, banded sea krait. Based on this sole encounter, I think sea snakes are possibly the hardest animal to photograph I’ve ever come across. They never stop moving, and getting the whole animal in focus was tricky to say the least.

The Island 7 and 8 area, especially the ‘West of Eden’ site, offered some of the best hard corals of the trip. There was a mild current, but it was easy to fin between the rocks. By the side of a vertical wall, a guide waved me over and pointed at a large patch of Siphonogorgia, with its red branches and white polyps. ‘Could it be?’ I thought, and yes, blending in, nearly perfectly, was an ornate ghost pipefish. The guide and I looked at each other, then to my dome port, and he realised I was shooting wide. It is easy to tell when someone is laughing (albeit sympathetically) underwater! Fortunately, we abandoned the main group on the next dive to get shots of a creature I’ve wanted for years. My luck continued with several nudibranchs also putting in an appearance.

As the days passed and the diving continued to be excellent, we settled into the happy routines of liveaboard life. The ‘eat, sleep, dive’ mantra may be on far too many T-shirts, but it’s a cliché for a reason. The food continued to be superb, with occasional Japanese cuisine on offer.

A real midpoint treat was visiting Island 8 (Koh Similan). This is the largest of the Similan archipelago and hosts tourist boats daily. It has a gorgeous white sand beach and a café with curious-looking Nicobar pigeons scuttling around. Most visitors take the short trail to the Sail Rock viewpoint, another monstrous granite lump, which seems to perch precariously over the trees and blue seas below. The geology above the surface, mirrors that below.

The last day of diving in the Similans would see us on the western side of Island 9 at Christmas Point, named by Cousteau after he explored it on Christmas Day. Again, boulders, tens if not hundreds of tons in weight, were piled high and it was clearly a site where currents delivered a rich soup of planktonic life.

The character of the underwater world would change significantly as we left the Similans and headed northwards once more to Koh Bon, which offers sites with more hard corals in comparison to the previous dives. Large plate corals, staghorns and encrusting corals, the latter peppered with Christmas tree worms, were resplendent in the midday sun. Butterflyfish and angelfish seemed more common and as I shot lionfish amid shoals of glassfish, our one and only manta passed overhead. A silhouette only, but a welcome sight. That night we moved north once more for two very different dives in the morning. The first at Tachai Pinnacle reminded us that currents can be very strong. We descended down a mooring line streaming off it like human flags. It was exhilarating, but not an easy dive, though I did manage a few more clownfish – the anemones must have exceptional holdfasts.

Surin Islands and Tachai: Currents, Coral and Big Encounters

A few hours later conditions at Tachai Reef, a fringing reef in lee of the island, could not have been more different. Acres of pristine coral and sheltered waters bathed in tropical sunshine were a rich compensation for the hard work earlier. It might have been coincidence, but I found four moray species. including the aptly named white eye.

Our second shore-based adventure took us to the largest of the Surins, Koh Surin, to visit a village belonging to the Moken people, known for their great prowess in diving and gathering food from the reefs and their previously nomadic nature. The Moken are a welcoming and brightly dressed people who sell handicrafts to visiting tourists, so take along some Thai baht for souvenirs. The final full day of diving, as I mentioned at the start, was without exception the finest of the itinerary – Richelieu Rock. The rock gets its name from an Admiral in the Royal Thai Navy – it appears to be a myth that it was named by Cousteau for the historic Cardinal Richelieu and his colorful robes, though the story persists online.

Richelieu Rock: Thailand’s Ultimate Underwater Spectacle

Only visible from the surface at low tide, this isolated pinnacle is a biodiversity hotspot of utmost biological importance to the region as well as the local diving economy, with several liveaboards and dayboats using the surrounding moorings at any one time. Despite diver pressure, the marine life was thriving, perhaps due to the recovery time six months of closure offers?

Every inch of this rock is cloaked in life; the more-exposed areas are carpeted in bright pink soft corals and vivid yellow sun coral polyps, and more-sheltered areas support giant sea fans and patches of anemones with scores of clownfish. All are a supporting act to the tens of thousands of fish, some in large species-only aggregations, others mixed packs of larger hunters. Photography was surprisingly hard. No sooner had you lined up a shot of hunting trevally than a shoal of snapper swept past, or one of the many multi-colored clouds of wrasse or damsels would get in the way. I would say this was the greatest concentration of life I have ever seen.

The rock is bathed in plankton-rich currents, which sustain so many species that capture morsels from the nutritious ‘broth’. We had moderate currents only, though I’m told they can be strong and descending a mooring line and tucking into the lee of a rock can be necessary.

Limited currents also meant, on this occasion, good visibility, and I was able to capture some of the splendour around me on the four dives offered, despite the fish getting in the way!

After two dives of wide-angle shooting, I swapped to macro. I’d spotted my fourth and final clownfish species, but wanted to explore the filter-feeders, the sea fans, feather stars and sea whips, for interesting critters. It was easy work, with almost too many sought-after subjects – I even gave up on a shy small yellow boxfish for a featherstar clingfish. It was a good trade, and I was very happy with my nerdy self.

I never found the boxfish again, but I was rewarded with a few wart slugs, including the pink and black Pustulose wart slug (one of the worst names in biology, surely?). I also saw several crown-of-thorns stars, in fact I’d seen one or two on every dive of the trip, though I don’t know how frequent they are in the region. I couldn’t resist a few more common clownfish shots as well.

The very tip of the rock offers an interesting ‘landscape’. Carpets of turf algae and other plant life have taken hold. It’s an unusual safety stop, as you watch grazers like lined surgeonfish pick away at the ‘lawns’ of green. The tender crew will understandably ask you to fin away into less-obstructed waters for pick up.

Richelieu Rock was without any shadow of a doubt the Andaman experience turned up to 11 (or maybe 12!). I certainly had hundreds of images on my memory card to whittle down as we turned and headed south that evening. This was truly one of the best liveaboard destinations I’ve experienced. Next time I might well extend my stay in Thailand and enjoy land-based fun a little more, but I promise, a trip on the Thailand Aggressor is well worth it.

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