Photo via TravelforSenses.com
I've spent a long time floating above sea grass beds, sitting in watchtowers and on viewpoints, as well as reading research papers. So perhaps the info below will help others in their quest for the dugong. I should mention from the start that I have never actually seen one! [edit, I have now
] But I think I've been unlucky and that if you put the time in you should get a sighting averaging roughly every 8-12 hours. I must have spent approx 25-30 hours looking for them, most of that on the water kayaking and snorkeling.
The best place to go by far is Trang province. Koh Libong, Koh Mook, Hat Chao Mai National Park, Sikao and Koh Sukorn area. Other parts of Thailand have dugongs e.g. Krabi, Trat, but in so few numbers that you would need to be doing an aerial survey to have any realistic chance of seeing them.
Koh Libong (sometimes called Koh Talibong) is the main hotspot but the waters are never very clear in my experience; max 5 metre vis. So Libong works better when viewing from above i.e. a viewpoint, or surface watching from a boat. There's no point snorkeling. Koh Mook is a better opportunity for snorkeling because the waters are a little clearer - typically visibility in dry season around the sea grass bed area is 8-10 metres. Mook is the place to go to try and snorkel with them and get good underwater pictures, but there are fewer dugong around Mook.
Most boat trips (from Libong or Hat Yao Pier) last about 4 hours and are reported to have a roughly 1 in 3 chance of a sighting. Most people attempt to see dugongs from these longtail boat trips. I don't really agree with them because dugongs are occasionally injured or killed by boat strikes. But on the flipside, it does provide many of the locals with a source of income and encourage them to protect the marine life. In the not so distant past they used to eat dugong, which doesn't happen anymore. I think kayaking is better but the distances involved from the kayak rental to the dugong areas can be far, except off Koh Mook where the sea grass beds are only a few hundred metres from the nearest kayak rental.
I notice that on a few review and blog sites where people have reported seeing dugongs, they have actually posted a picture of a dolphin. Dugongs don't have dorsal fins... Dolphins and turtles are common around these islands. I've seen two pods of dolphins and I see at least one turtle almost every time I snorkel/kayak. Turtles eat sea grass just like dugong. If you see something grey break the surface 20 metres away but can't really tell what it is, it's more likely to be a turtle than a dugong. However the research papers record more dugong sightings than turtles, I think that's because dugong are bigger, move more and stay in shallower water longer. The turtles are often found resting on the seabed and would not be picked up by aerial surveys unless surfacing. Also dugong are more inquisitive and (apparently) more likely to come to the kayak/boat (when the engine is off). Turtles never hang around. The dolphins around Trang break the water surface with more of a splash, but it's not like you see on documentaries where the bottlenose variety launch themselves out of the water... This green turtle was resting on the seabed until I disturbed it:
This research is from 2005/2008 but it is still useful to show you where to look and what to look for.
tinyurl.com/vfgbq4n
www.warthai.org/files/AerialSurvey_Jan%202008.pdf
Most people head to Koh Libong but you might be better kayaking from Hat Yao on the mainland (there is kayak rental there) to the 2 circled areas (taken from link above). Hat Yao Pier also has longtail boat rental. But still a long 6-7km kayak (at least an hour each way) and there are currents which might help or hinder depending on the tide. Also the wind direction and strength should be checked on a site like Windguru. Ideally you want to be kayaking with the wind, but more than a light breeze is not ideal as it creates bigger waves.
If on Libong itself there are two main viewpoints - Point Dugong which is a short walk through a cave system and up onto a craggy outcrop of rocks, and a 4-storey watchtower at the end of a fishing pier in the main village of Bata Bute. I am not sure if there is kayak rental in that village but if you could find it it would save you a lot of paddling. On the map above I've added a third circle where there seems to be frequent sightings of dugong, perhaps not because there are many more dugong there than elsewhere but because the vantage points make it easier to see them. I have done the Point Dugong walk before and the guy manning a drinks' stand there said tourists earlier in the day had seen dugong.
This is a water monitor swimming about 200m below Point Dugong, probably a little smaller in length than the average dugong. So you should be able to get some okay/good images of dugong from there with a good zoom.
A view of Koh Phettra from Point Dugong:
A view of the watchtower at the end of the pier from Point Dugong: You can see how much higher Point Dugong is.
A turtle breaking the surface: I was in a kayak I'd paddled around from Libong Sunset Beach Resort.