Scuba diving with manta ray in Bali.
What is a manta ray?
Manta rays, one of the world’s largest fish, are unique-looking and peaceful creatures.
They are commonly found in tropical and subtropical waters around the world, typically near the equator and coral reefs.
“Manta” means blanket or cloak in Spanish, describing the look of the animals’ large, flat, diamond-shaped bodies.
Giant manta vs Reef manta
Previously, it was believed that there was only one species of manta ray. However, in 2008, scientists discovered that there are actually two species: giant manta ray (manta birostris) and reef manta ray (manta alfredi).
Both species belong to the order Myliobatiformes and Mobulidae family.
They are closely related to sharks. Both have skeletons made entirely of cartilage instead of bone.
The giant manta ray is the largest species of ray. The largest known specimen was more than 7 meters across and weighed more than 2 tons. However, the average is usually around 4 and 4,5 meters and 1,350 kgs.
On the other hand, reef manta is the smaller of the two species and generally measures between 3 and 3,5 meters. Species up to 5 meters have been recorded.
Both species are pelagic
The reef manta ray habitat is less oceanic than the giant manta ray. They usually stay near the coast in shallow water, around islands, reefs, atolls, and even bays and seamounts. In English, it also calls them”resident manta ray” and “coastal manta ray”, referring to their habit of residing longer in specific areas.
By contrast, Manta birostris often roams across the ocean, solitary or in groups, but also comes to shallow reefs and regularly visits cleaning stations.
Manta ray – Fun facts
1. Swimming behavior differs across habitats
When traveling over deep water, mantas swim constantly in a straight line, reaching speeds up to 24 km / h. While further inshore, they usually bask or swim idly around.
On the other hand, when mantas visit cleaning stations on coral reefs, they adopt a near-stationary position close to the coral surface for several minutes. This behavior allows cleaner wrasses to remove parasites from the skin.
Manta rays visit cleaning stations most frequently during high tide, and many return to the same stations repeatedly.
Mantas may travel alone or in groups of up to 50. They may associate with other fish species, sea birds, and marine mammals.
2. Manta rays are continuously swimming
These fish have two sets of gills and must swim continuously to keep oxygenated water passing over their gill.
3. Manta rays can dive to great depths
Manta alfredi t0 400 meters and giant manta rays down to 2,000.
4. Manta rays sometimes breach, leaping partially or entirely out of the water
Individuals in a group may jump one after the other. These leaps come in three forms: forward leaps, where the fish lands head first; similar jumps with a tail first re-entry; or somersaults.
We don’t know exactly the reason for the breaching. Possible explanations include mating rituals, birthing, communication, or removing parasites and commensal remoras.
There are records of mantas jumping above 7 meters out of the water!
5. Each manta ray is unique
Each manta ray has a unique pattern of spots that identifies them. They are like fingerprints. Each manta is different.
Color varies, but in general, the upper part of the body is black or dark brown, while the lower part is white.
All-black color morphs exist. We call them black mantas. We can also see them very often in Bali.
Manta alfredi has a Y-shaped patch on the top of the head, while the giant oceanic manta ray patch is T-shaped, with less presence of white coloration.
In addition, the mouth of the first one is white and not black like the giant manta ray, with the lower edges of the wings being black or darker.
6. Manta ray – Morphology
Each member of the Manta genus has a large, flattened body whose center is called “disk.” The head of both species is broad, with eyes on the side of its head, behind the cephalic fins. Inside are several rows of 300 small, square teeth that are not good for chewing food, but are used by males to grab the female’s pectoral fin while mating.
It has two large and triangular pectoral fins, a small dorsal fin, and a long tail.
The tail has lost its venomous sting throughout evolution. Thanks to its large size and speed, mantas don’t need the sting to defend themselves.
Manta birostris has a caudal fin, but manta alfredi lacks it.
Another distinguishing feature is the presence of horn-shaped cephalic fins on either side of their mouths, called cephalic lobes.
When navigating, manta ray keeps these lobes rolled up, but when feeding it stretches them for these to push food-rich water into its mouth and the small particles are collected by the tissue between the gill arches.
The skin of these animals is rough to the touch because it has conical dermal denticles, similar to dental structures. The skin is covered in mucus, which protects it from infections.
7. Their tissues regenerate incredibly quickly
When attacked, they usually suffer severe injuries and big cuts. Luckily for them, their tissues regenerate incredibly quickly. An injury can heal quickly, and tissue can be regenerated almost entirely weeks later. Cleaner wrasse also helps to speed up this process, removing all the dead tissue.
8. Manta ray has the biggest brain of all fish
They have one of the highest brain-to-body mass ratios and the largest brain size of all fish.
Their brains have a net of veins and arteries called retia mirabilia, which may keep them warm during long, deep dives into colder waters.
9. An individual manta eats about 13% of its body weight each week
Both species are filter feeders. Manta rays consume large quantities of zooplankton in the form of shrimp, krill, and planktonic crabs.
When foraging, it slowly swims around its prey, herding it into a tight “ball”. Then, it speeds through the bunched organisms with a wide-open mouth. If a ball is particularly dense, a manta may somersault through it.
They usually feed in shallow water, where plankton is floating. As many as 50 individuals may gather at a single plankton-rich feeding site.
When food is near the seafloor, they have to swim close to the bottom, placing their body a few centimeters above it, which often causes minor injuries due to eventual contact with abrasive sand.
10. Mating occurs at different times of the year in different parts of the manta’s range. It usually starts with the full moon
Females can be slightly larger than males. The male hits sexual maturity if the width between his “wings” is about 4 to 4,5 meters, and the females can already reproduce when they are 8 to 10 years old.
The courtship process begins with several males swimming behind the female for 20-30 minutes at a constant speed. The male makes several attempts to get closer to the female. When the female slows down, the male bites her pectoral fin. After, the male turns to the female. He inserts his sperm into the female’s cloaca, and they stay together for about 60 – 90 seconds. Afterward, the male continues swimming next to the female, grabbing her fin for a few more minutes, followed by the rest of the males.
11. Manta rays are ovoviviparous
The fertilized eggs develop inside the female’s oviduct, and the embryos absorb the yolk.
After hatching, the pups remain in the oviduct and receive additional nutrition from milky secretions. With no umbilical cord nor placenta, the unborn puppy relies on buccal pumping to obtain oxygen.
Pregnancy lasts about 12 to 13 months, and manta rays give birth to a single pup or two wrapped in their pectoral fins.
Babies look like a smaller version of adult manta rays. When born, they can immediately survive without parental care.
Manta rays give birth every two to five years.
12. Manta rays live for at least 50 years
13. Threats
Thanks to their enormous size, manta rays have few predators. They can be victims of attacks by killer whales and large sharks such as tiger sharks, hammerheads, or bull sharks.
The greatest threat to manta rays is overfishing.
Mantas are appreciated in the market for their meat, liver oil, and skin. But also especially for their gill plates. It has recently been in high demand in traditional Chinese medicine.
Another threat to manta rays is fishing nets.
Because mantas have to keep swimming constantly, they may die due to suffocation when they get entangled in a fishing net or line. Also, mantas cannot swim backward. When entangled, they often attempt to free themselves by somersaulting. As a consequence, they tangle themselves further.
Some mantas are also injured by collisions with boats. Other threats or factors that can affect the number of mantas are climate change, tourism, contamination by oil spills, and the ingestion of microplastics.
Both sub-species of manta ray are classified as vulnerable by the International Union for Natural Conservation. Since 2011, manta rays have been protected in international waters by the Convention on Migratory Species.
Where can we dive with Manta ray in Bali?
In Bali, we can see both species of manta rays at the cleaning and feeding stations in the Indian Ocean south of Nusa Penida and occasionally on the reefs of Bali.
You can dive with manta rays in Bali all year round! How cool is that?
We can see reef mantas, oceanic mantas, and even black manta rays in Bali.
Interaction with manta rays. Be a responsible diver
In Bali guidelines have being designed to provide a satisfactory and safe diving experience while insuring the lowest sustainable impact on the sunfish and manta ray population of the island. The aim of developing the Code of Conduct for Sunfish and Manta Ray interactions is to ensure Sunfish and Manta Ray are able to settle onto cleaning stations without being disturbed. Once settle, the Sunfish and Manta Ray can remain on station for longer periods, offering better quality interactions for divers.
👉 Get the latest news about marine life in Bali on our blog
Would you like to dive with us?