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Information about Mobula Birostris

[Phylum: Chordata] [Class: Chondrichthyes] [Order: Myliobatiformes] [Species: M. birostris]

A dorsoventrally flattened fish (compressed), with a wingspan much wider than its length, and a long whiplike tail, characterises the biggest of all ray fishes (Batoidea) - the giant oceanic manta ray.

This section contains interesting facts about the gigantic Mobula birostris, including where they live, their diet, and how they reproduce.

Oceanic Manta Ray Habitat and Distribution

In fact, all manta rays are related to two other species of cartilaginous fishes, the shark Phylum Chordata and the skate fish (Rajidae).

The best place to find large graceful manta rays is tropical, subtropical, and some temperate waters (e.g. above 20° Celsius).

Here's the thing:

Mantas congregate close to the continents of all major oceans (except the Arctic and Southern Ocean) and near to the islands in some warm water seas.

Their migratory, somewhat fragmented lifestyle, means it's difficult for scientists to gather accurate information about the worldwide population of manta rays. But congregations of fifty or more giant mantas are commonplace in selected environments.

Nonetheless, official records show that this massive pelagic fish can live in most of the open oceans far away from the equator.

For example:

Scuba divers and snorkelers have spotted manta rays in North Carolina (USA) and near to the North Island of New Zealand. But, it seems fair to say that the largest population of mantas currently exists in Ecuador, especially the Galapagos Marine Reserve.

One thing is certain, manta rays travel huge distances with strong moving currents, especially where upwellings of nutrient-rich water occur. Typical examples include most of the Bali dive sites in Indonesia and around the atolls in the Maldives.

Pro Tip: Scientists have determined two different species of mantas, that being the giant oceanic manta ray and the smaller, less elusive, reef manta ray.

Mobula Birostris Characteristics

Over the years, scientists and zoologists have invented a few stupid fish names for new specimens. But, some of the best-known names for ocean rays (batoids) include:

Fun Fact: Most manta rays display variances of black colouring (melanism) or white (leucism). But, there have been sightings of a pink coloured manta ray at Lady Elliot Island in the Great Barrier Reef, Australia. Scientists believe the erythrism (abnormal redness) is the result of a genetic mutation.

How Big is the Giant Manta Ray?

One astonishing fact about the wingspan of the giant oceanic manta ray is that it can actually measure up to nine (9) metres wide (29 feet). In the biggest specimens, the weight of that colossal body mass can be close to 3,000 kilograms (6,600 pounds).

Pro Tip: According to the Guinness World Records, the largest manta ray wingspan ever recorded was 9.1 metres (30 feet).

In reality, the two manta species differ in body colouring, in placoid scales (dermal denticles), and in their dentition (the arrangement of their teeth). Most of them are dark on the top with a pale underbelly - often white.

Even so, there are several features that distinguish mantas from other similar sized fishes. For example, all manta rays have a broad head and flattened triangular pectoral fins. Plus, having two horn-shaped cephalic lobes on each side of its mouth is somewhat unique to the species.

Key takeaways:

The horizontal, mucus-covered body lacks any strong skeletal support for their short, whiplike tail. But, mantas do have small dorsal fins located at the base of the tail whip.

The giant oceanic manta ray (Mobula birostris) can have a disc width of nine (9) metres (up to 29 feet). Whereas, the smaller reef manta species rarely grow wider than five (5) metres (around 18 feet).

How Do Manta Rays Swim?

Despite the seasonal migration patterns, manta rays tend to spend more time around the coastlines in the summer months. Thus, cold winters provide a good time for scuba divers to spot these majestic pelagics swimming further offshore in the open oceans.

Furthermore, the best time of the day to see manta rays flapping their pectoral fins near the surface is during the daytime. This is when they will be swimming closer to the top of the water column - or breaching it.

At night-time, they will swim down to much greater depths. In fact, some species dive to depths approaching two thousand metres (6,000 feet). Either way, mantas (M. birostris) need to generate constant forward propulsion to stay alive.

Interesting Fact: The brain-to-body mass ratio of manta rays is one of the highest of all fish species. Plus, the complexity of veins and arteries in their brains (known as retia mirabilia) uses concurrent blood flow to help them keep warm.

What Do Oceanic Mantas Eat?

The manta ray uses sight to track down its food source. It can also use water as it flows over olfactory receptors (pits inside the snout) to detect its favourite prey - microscopic organic animals.

They display two distinct and different feeding styles. They are typical filter feeders that consume copious amounts of zooplankton (the animal component of the plankton).

But, these macro predators are also big enough to attack, and swallow, medium-sized fish in the mesopelagic zone (deep water). As part of their regular diet, manta rays also eat:

It is not uncommon to see mantas use several different behavioural patterns when they feed. For example, some individuals will employ the 'piggy-back' method. Whereas, others will swim horizontally in a circle to create a mini 'cyclone' as they use the 'chain-feeding' method.

Pro Tip: Often, manta rays will splay their cephalic fins wide apart to forage on the ocean floor. But, filter feeding can clog up the gills, forcing them to cough up a dark red faecal matter - usually above sergeant major fish and wrasses waiting patiently at a cleaning station.

Giant Manta Ray Reproduction Cycle

Sexual maturity for female mantas occurs when they have grown to five metres wide (around eight years old). As a result, they tend to give birth one time every two or three years.

The geographic range, and the time of year, will determine when manta rays start to mate. Even so, the individuals tend to perform their courtship ritual in shallow water.

Scientists believe a full moon may be the trigger needed for the manta mating sequence to begin. A male follows a female, both swimming in tandem around 10 kilometres per hour.

This is the important part:

It can take more than twenty minutes for the male to grasp the female's pectoral fin with his mouth. After securing a tight grip, the male will rotate upside-down so that both ventral sides are close and pressed together.

Following the insertion, the male keeps hold of the female with his teeth as they continue swimming together. Even so, it's common for a few dozen males to follow the mating couple until they finally part company.

How Do Manta Ray Pups Hatch?

As with most ovoviviparous sea creatures, fertilisation of the eggs takes place inside the oviduct. So, an egg case encloses each fertilised egg while the embryo absorbs the yolk as it starts to develop.

Manta pups remain inside the oviduct after hatching. They will be receiving extra nutrition from a milky secretion produced by the female.

There is no umbilical cord or placenta. Hence, unborn pups will be totally reliant on a process of buccal pumping to get the oxygen that they need. The typical brood size for manta rays is usually one (1) but never more than two.

Interesting Fact: Marine biologists believe the gestation period for manta rays to be around twelve (12) months. The pup will look like a miniature adult when the female expels it from the oviduct. From this point in time, there will be no further parental care.

Threats and Predators

Despite being one of the most highly intelligent of all sea creatures, the threats to the survival of manta rays are plentiful. Some of the most serious activities that are threatening the worldwide existence of the genus Mobula, include:

In addition, large sharks, killer whales (orcas), and even oceanic dolphins (Pseudorca crassidens) will eat manta rays.

Mantas also tend to harbour parasitic copepods (marine dinoflagellates) which can lead to severe internal infection.

Even though mantas can remove the parasites themselves through forced defecation, they usually leave the task to remora fish. But, the remoras can cause damage to the gills and skin of the host. Plus, having a large suckfish attached to its body also increases its normal swimming load.

Important: Even though the average lifespan of manta rays is fifty (50) years, the IUCN Red List of Threatened Species recorded the giant oceanic manta ray as being Endangered (EN) in 2019.

Related Information and Help Guides

Note: The short video [3:29 seconds] presented by 'The Departures Channel' contains some breathtaking footage of graceful giant manta rays gliding in the pristine waters of Raja Ampat, Indonesia.

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