Generally, the season for Manta Ray here in the Similans are from mid-October to mid-May. The time we see them varies each year. Sometimes we see them in November or every other month during the diving season. But mostly, we see them the more often during early December to end of April. When they arrive they often stick around for many days or weeks at a time, then they might disappear for a couple days or weeks, and come back.
Scientist have trouble understanding when and where they are migrating or spending their time when not seeing in the shallows. They spend a lot of time as well at great depths.
During the manta ray season in Thailand, high are the chances to see them, but remember than you only spend a minutes dive in a 24h day, so you need to be their at the right time, the ocean is big and we never know what we will see during our dive. Your best chance to see them is by doing a manta ray liveaboard trip (4-5 days is a good length, the longer the better, the more time you spend underwater increase your chances).
The Manta ray season is at the same time of the Thailand whale shark season.
Why does Thailand have a manta ray season and where to see them?
The seasonal migration of manta rays are due mainly to feeding habits, between January to May the hot weather and oceanic current brings a rich plankton current from he depth to the surface. Manta rays feed on these micro-organism, scooping the water around.
That’s why they come during a specify season. Scuba diving wise, the best place to see them are cleaning station or dive sites with strong currents. The 2 best dive sites at the Similan islands to spot manta rays are Koh Bon’s manta cleaning station and Koh Tachai pinnacle.
Mantas are big animal and their skins need special care to get rid of parasite and stay healthy. They also have a few predators such as sharks, orcas. When they do get bitten or wounded by fishing nets, their wound can heal pretty fast but still need to be cleaned. This is when Mantas come to cleaning stations. Both species of Mantas, also other reef fish and pelagic species do go to cleaning stations. Cleaning station is a patch of reef where there are specific cleaner fish that will come up to pick parasites from the skin or inside the mouth of individual Mantas or sharks or other reef fish. However, cleaning doesn’t only occur when Mantas have wounds. They just come to the cleaning station as a part of life behavior.
Here in the Similans National Park, you can often spot Manta Rays at Koh Bon island, which is one of the main cleaning and feeding stations in Thailand. From what we have encountered so far at Koh Bon, there are about twenty resident Manta Rays that are identified by divers.
Other feeding stations that Manta Rays often visit are Koh Tachai (part of the Similans National Park), Hin Deang and Hin Muang (about 65 km south of Koh Phi Phi). Because these dive sites are big pinnacles with sometimes strong current that brings in planktons, so Manta Rays often visit these sites for feeding.
Manta Rays are one of most majestic and biggest pelagic fish in the ocean. They are completely different species than the ray family such as stingrays, guitar rays, electric rays or skates etc. Those rays are benthic dwellers, which mean they live on the sea floor and eat crustaceans and other organisms that live in the sand. However, the Manta Rays have a more pelagic life style which means they are always swimming and never spend time on the bottom of the ocean. They feed on some of the smallest organisms in the ocean like zooplanktons and copepods. Manta Rays can only breathe by swimming so they have to spend their entire life constantly moving around.
There are so far two species of Manta Rays, which are “Reef Manta Rays” and “Oceanic Manta Rays”. Both species can be found all around the world in places like Mozambique, the Maldives, the Red Sea, Mexico, Indonesia, southern Japan, northern Australia, or here in the Andaman Sea (mostly in the Similans National Marine Park, Hin Deang, Hin Muang) in southern Thailand. Despite the fact that these Manta Rays live in the same area, one of the reasons that they are described as two different species is because they live in very different habitats. Reef Manta Rays live on coral reefs, whereas Oceanic Manta Rays live in pelagic open water habitats. The other difference between these two species is the white shoulder patches on their back. The white shoulder patches of a Reef Manta Ray form a more v-shaped, whereas the ones on Oceanic Manta Rays form a more defined “T” on their back.
Other feature that can be used to differentiate them is by their size. Most Reef Manta Rays can be around 3 meters wide with the maximum length of 4-5 meters. However, the Oceanic Manta Rays can be up to 7 meters in length. Here in the Similans National Park in Thailand, particularly in dive sites like Koh Bon or Koh Tachai, we mostly see Oceanic Manta Rays.
As Manta Rays have very big body size and also have very large brains. To help describe the intelligence of Manta Rays, scientists use “Brain to Body Mass Ratio”, this is a metric that is guessed to be a rough estimate of the intelligence of an animal. Manta Rays have the largest brain to body mass ratio of any fish in the ocean. This is a good indicator that they are very intelligent animal. Even though Manta Rays are cold blooded animal, they have brain warming mechanisms, which are called Counter Current Heat Exchange Systems. This allows certain areas of their brain to be warmed, which allows for more activity.
Manta Rays are not only big in size; they are also very long lived. There are lots of evidence that shows both species of Manta Rays can live up to or more than 50 years. So how can you identify the same Manta Ray many years apart? The way that scientists identify each Manta Ray is by looking at the spot pattern on its belly. Every Manta Ray has a unique spot pattern and that pattern doesn’t change throughout its life. By identifying and monitoring each individual Manta, scientists are able to look at things like population sizes in certain areas and track how the Mantas move around different sites by looking at photographs sent in by divers.
Scientists can also look at things like birth rates and pregnancy rates of the Mantas. Based on monitoring pregnancies and looking at each individual Manta gets pregnant, scientists are able to find that female Manta Rays can give birth every 2-5 years with a gestation period of 12-13 months. In a whole life time of a female Manta Ray, she can give birth to 10-15 baby mantas.
Koh Bon Manta Ray Scuba Diving is one of the most unforgettable moment in your life, don t miss the chance to see them, every Tuesday, Wednesday and Sunday at Koh Bon Island.