Decide not to bring your camera on a dive and the odds go way up that the WS, Manta or other big fish will swim right up to you and look you in the eye.
Welcome to ScubaBoard, the world's largest scuba diving community. Registration is not required to read the forums, but we encourage you to join. Joining has its benefits and enables you to participate in the discussions.
Benefits of registering include
ssra30:May to June is a little late for the Similan and it may be closed as you already know.
Beside the Similan/Richeliue, there are some possibility of seeing whale sharks in south andaman sea (Phi Phi, Hin Maung, Hin Daeng) or Koh Tao.
However, I think whaleshark sighting in Thailand is a bit more sporadic nowaday.
For Koh Tao, the best time to see whaleshark is April and August and occasional sighting in between. Last year, there were 3 whalesharks around Koh Tao in April and there were daily sighting for almost 2 weeks straight during the 2nd half of April.
Some friends also saw whale sharks around Phi Phi at about the same time.
I am not sure what is your chance of seeing whale shark in May/June. I think either Koh Tao or south Andaman sea is worth a shot. I would recommend South Andaman as you will get better diving there even if you don't see a whale shark.