Bali – Manta ray

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Scuba diving with Manta ray in Bali.

What is a manta ray?

Manta ray is one of the largest fish in the world. It is majestic, calm, peaceful and a unique-looking fish. They live in tropical and subtropical waters across the globe, typically close to the equator and around 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

Until 2008 it was thought there was just only one species of manta ray. But that year scientists discovered that there are actually two different 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. Also, both belong to the Elasmobranchii subclass and are characterised by having a skeleton made of cartilage instead of bone.

Giant manta ray is the largest species of ray. Actually, the largest known specimen was more than 7 meters across, and weighted more than 2 tons. Although the average is usually around 4 and 4,5 meters and 1,350 kgs.

In 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 is also call 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.

In Bali we can see both species of manta ray at the cleaning and feeding stations in South of Nusa Penida, in the Indian Ocean and occasionally in the reefs of Bali.

Bali manta ray – Fun facts

Behaviour

Swimming behaviour in mantas differs across habitats. When travelling over deep water, they swim at a constant rate in a straight line, reaching speeds up to 24 km/h, while further inshore they usually bask or swim idly around.

Mantas visit cleaning stations on coral reefs to get rid of external parasites. The ray adopts a near- stationary position close to the coral surface for several minutes while the cleaner wrasse remove parasites from the skin.

Such visits most frequently occur when the tide is high. Many individual manta rays return to the same stations over and over.

Mantas may travel alone or in groups of up to 50. They may associate with other fish species as well as sea birds and marine mammals.

Manta rays are continuously swimming

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These fish have two sets of gills and must swim continuously to keep oxygenated water passing over their gill.

Manta rays can dive to great depths. In fact manta alfredi t0 400 meters and giant manta ray down to 2,000.

They can jump out of the water!

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.

There are records of mantas jumping higher than 7 meters out of the water!

We don’t know exactly the reason for breaching. Possible explanations include mating rituals, birthing, communication, or the removal of parasites and commensal remoras.

Each manta is unique

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Each manta ray has a unique pattern of spots that identifies them. They are like fingerprints, each manta is different.

Colour 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 see then also seen 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 ones is white and not black like the giant manta ray’s that has the lower edges of the wings black colour or darker.

Bali 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. In fact, the tail has lost its venomous sting throughout evolution. Manta birostris has a caudal fin, but manta alfredi lacks it.

Another distinguishing feature is the presence of a horn-shaped cephalic fins located 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.

When attacked, usually they suffer serious injuries and big cuts. Lucky them, their tissues regenerate incredibly quickly. An injury can heal at high speed and tissue can be regenerated almost completely weeks later. Cleaner wrasse also helps to speed up this process, removing all the dead tissue.

Manta 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 made of veins and arteries called retia mirabilia which may serve to keep them warm during long deep dives into colder waters.

Diet

Both species are filter feeders. Manta rays consume large quantities of zooplankton in the form of shrimp, krill and planktonic crab.

In fact, an individual manta eats about 13% of its body weight each week.

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 riched feeding site.

When food is near the seafloor, they have to swim close to bottom, placing their body a few centimetres above it, which often causes minor injuries due to eventual contact with abrasive sand.

Reproduction

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Females can be slightly larger than males. The male hits sexually maturity if the width between his “wings” is about 4 to 4,5 meters, and the female can already reproduce when they are 8 to 10 years old.

Mating takes place at different times of the year in different parts of the manta’s range. It normally starts with the full moon.

The courtship process begins with several males swimming one after the other behind the female for about 20 – 30 minutes. The female maintains a constant speed of 10km/h. The male makes several attempts to get closer to the female. When the female slows down, then, 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. After, the male continues swimming next to the female, grabbing on her fin for a few more minutes, followed by the rest of the males.

Manta rays are ovoviviparous

Manta rays are ovoviviparous. The fertilised 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 smaller version of adult manta rays when born and can immediately survive without parental care.

Manta rays give birth every two to five years.

How long does manta ray live?

Manta rays live for at least 50 years.

Diving at Manta Point with manta rays. Nusa Penida, Bali

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 the tiger sharks, hammer heads 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. Actually, it has been in high demand recently in traditional Chinese medicine.

Another threat for manta rays are fishing nets.

Because mantas have to keep swimming constantly, when they get entangled in a fishing net or line, they may die due to suffocation. Also, mantas cannot swim backwards. When entangled, they often attempt to free themselves by somersaulting. As a consecuense, they tangling themselves further.

Some mantas are also injured by collision with boats. Other threats or factors that can affect the number of mantas are climate change, tourism, contamination by oil spills and also the ingestion of micro- plastics.

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?

There are two main manta ray cleaning station in Bali. Both are located in South Nusa Penida. And the best, we can dive with manta rays in Bali all year around!

To top, in Bali we can dive with reef mantas, oceanic mantas and even black mantas.

Bali manta ray. Be a responsible diver

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Visit our blog to learn more about marine life in Bali

Would you like to dive with us? Send us an email to southerndreamsdiving@gmail.com