by Matt Walker Editor, BBC Earth News

The once secret life of a huge, recently discovered species of manta ray has been unveiled.

Biologist Dr Andrea Marshall has discovered that the giant fish, which she first described as new to science last year, undertakes huge journeys.

As well as making the longest migration known across the Indian Ocean, the fish gathers in large numbers to feed and survives attacks by sharks.

The behavior is revealed in the BBC documentary series Natural World.

Growing up to 7m wide, manta rays are the largest living ray in the ocean and one of the largest of all fish.

Previously, it was thought there was just one species of manta ray, known by the scientific name Manta birostris.

But the more Dr Marshall swam with them, the more she noticed how different manta rays that frequent reefs and the open ocean are, both in their behavior and markings.

Mantas evolved from sting rays, and it was thought they had lost their sting. But Dr Marshall has found that the larger ocean-going mantas have retained a vestigial sting on their tails, proving that the two are separate species.

In July last year, she announced the discovery that there are not one but two species of manta ray at the American Elasmobranch Society’s annual conference in Montreal, Canada.

Manta Ray

The larger giant mantas retain the name Manta birostris, while the reef-going mantas have been newly named Manta alfredi, in tribute to Alfred Whitley who first scientifically described manta rays in the 1930s.

However, Dr Marshall’s studies have uniquely revealed a host of manta ray behaviors.

The rays sometimes swim across the ocean floor, skimming the reefs with their mouths, a behavior filmed by the camera crew for the first time.

Usually the fish feed on plankton, but what they feed on when skimming is unclear.

Dr Marshall studies manta rays off the coast of Tofo in southern Mozambique.

It was always thought that manta rays stayed in shallow waters.

Manta ray mating behavior

But Dr Marshall has discovered that the larger giant species of manta ray dives deeply, and migrates 700 miles (1,100km) in just 60 days to the Maldives, the longest migration known for a fish living in the Indian Ocean.

In the Maldives, researchers have also uncovered a unique gathering place of reef mantas, where hundreds of the fish gather.

Around 80% of the fish are female, with many pregnant, suggesting the area is a critical breeding site for the species.

Studies by Dr Marshall and colleague Dr Simon Pierce of the Manta Ray and Whale Shark Research Centre based at Tofo Beach in southern Mozambique have also revealed that manta rays living off Tofo bear huge scars inflicted by large sharks.

Mysterious giants

Manta rays appear capable of surviving such attacks and will queue up to have their wounds tended by cleaner fish, which nibble at the wound to remove dead tissue and prevent infection.

Dr Marshall’s studies have also revealed new aspects to the fishes’ reproduction.

Many male mantas follow a single female, mirroring her behavior in a bid to attract her as a mate.

Females, which give birth to a single pup after a 12-month gestation, rarely give birth in consecutive years, Dr Marshall has found.

That extremely slow reproduction could place the fish in danger from overfishing, both for subsistence and for export to be used in traditional Chinese medicines.

The Kuda Giri Wreck dive site in the Maldives is a treat for avid scuba divers!

The Kuda Giri dive site, located in the South Male Atoll of the Maldives, possesses a small boat wreck and a reef / pinnacle.

Kuda Giri Dive Site Information

• Location: South Male Atoll, 22km south of Male’
• Description: Wreck / Reef
• Depth: 31 meters (102 feet)
• Visibility: Approximately 10 to 25 meters (50 feet)
• Currents: Gentle
• Surface Conditions: Calm
• Water Temperature: Approximately 27 to 30°C
• Experience Level: Beginner to Intermediate
• Diving Season: All Year Round
• Access: Maldives Liveaboard

Kuda Giri Dive Site – Wreck

The Kuda Giri dive site features a small ship wreck, a fishing trawler that was scuttled (or sunk deliberately) 10 years ago. The fishing trawler was sunk to form an artifical reef, which has proved to be a success. The wreck is now covered by stony, staghorn and table corals, not to mention the colorful red, orange and yellow sponges that reside amongst the coral.

The Kuda Giri wreck sits upright on the sea floor, and can be explored from its bow (which points towards the giri, or pinnacle) at 18 meters all the way down to its stern at 30 meters.

Experienced divers can swim through the Kuda Giri wreck, discovering the plethora of sea life that now calls the captain’s cabin, cargo hold and machine room home. Divers can enter the Kuda Giri wreck through the machine room and exit at the stern, or enter at the front cargo hold and exit at the bridge.

While diving amongst the Kuda Giri wreck‘s remains, divers should look out for large schools of glass fish and bat fish that have made this sunken ship their home. Divers can also expect to see turtles, napoleon wrasse, jack fish, trigger fish, shrimp, lobsters, frog fish, blue fin trevally, fusiliers and leaf fish, among others!

Kuda Giri Dive Site – Reef / Pinnacle

After the Kuda Giri wreck, you can swim back to the reef / pinnacle, where you can enjoy a typical reef dive, as well as all the Maldivian marine life that comes along with it, including napoleon wrasse, parrot fish, oriental sweetlips and many more.

The reef tower features beautiful overhangs overflowing with colorful soft coral. Fish playfully swim amongst the coral, often making for a great photo opportunity.

Lionfish Spotted at Kuda Giri Dive Site, Maldives

Maldives Fish are amongst the most beautiful marine life in the Maldives!

Paracanthurus hepatus (Regal Tang) is a colorful reef fish in the family Acanthuridae. A fish in marine aquaria, it is the only member of the genus Paracanthurus. A number of common names are attributed to the species, including palette surgeonfish, blue tang, royal blue tang, hippo tang, flag tail surgeonfish and blue surgeonfish.

Paracanthurus hepatus has a royal blue body, yellow tail, and black ‘palette’ design. The lower body is yellow in the west-central Indian Ocean. It grows to 31 cm (12.25 in.). The species’ range is broad, but it is nowhere common. It can be found throughout the Indo-Pacific. It is seen in reefs of East Africa, Japan, Samoa, New Caledonia, and the Great Barrier Reef.

The blue tang is not evaluated by the World Conservation Union (IUCN), but is of low vulnerability.

As a juvenile, its diet consists primarily of plankton. Adults are omnivore and feed on plankton, but will also graze on algae. Spawning occurs during late afternoon and evening hours. This event is indicated by a change in color from a uniform dark blue to a pale blue.

The blue tang is of minor commercial fisheries importance; however, it is a bait fish. The flesh has a strong odor and is not highly prized. This fish may cause ciguatera poisoning if consumed by humans. However, blue tangs are collected commercially for the aquarium trade. Handling the tang risks the chances of being badly cut by the caudal spine. These spines, on both sides of the caudal peduncle, are extended from the body when the fish becomes excited. The quick, thrashing sideways motion of the tail can produce deep wounds that result in swelling and discoloration, posing a risk of infection. It is believed that some species of Acanthurus have venom glands while others do not. The spines are used only as a method of protection against aggressors.

Scientific classification

Kingdom: Animalia

Phylum: Chordata

Class: Actinopterygii

Order: Perciformes

Family: Acanthuridae

Genus: Paracanthurus

Species: P. hepatus

Binomial name: Paracanthurus hepatus

Regal Tang at Rakeedhoo Corner

Where to find Paracanthurus hepatus (Regal Tang) in Maldives.

Regal Tang is not that common in Maldivian reef and appears to be localized in only few areas. Occurs on current-prone reef crests to about 20 meters depth. Indian Ocean population differs slightly in colour from Pacific fish when adult, in having white instead of blue along the loawer boady. The two forms are probably sub specifics. Juveniles form small groups and quickly dive for cover in small Acropora coral thickets.

Let’s start from north Male’ atoll Banana Reef: On the top reef on the eastern side are small acropora table corals. The ones here are juvenile and they are very timid every time a diver or snorkeler approaches they swim inside the coral and hide. But if you wait at a safe distance they will eventually come out.

Moving to Felidhu Atoll, Rakeedhoo Corner : If you start the dive with an outgoing current most probably the ending would be at the outer reef, where you will find hug coral blocks at the top of reef. The reef top is about 5 to 6 meters and this is a perfect place to spend your last minutes of the dive. The regal tangs here are a bit larger than what I have seen in north male’ atoll but the behavior remains the same. Getting a picture of these tangs is not an easy task.

Southern Ari atoll, Rangali Madivaru: During the past years I have spotted them on the southern side of Rangali madivaru reef under very similar conditions like hiding inside the small table corals. On the southern side the coral growth is not much, its mainly sand. The best way to perform would be after you dive for mantas swim inside the atoll if the current allows it.

After a fantastic dive to 5 Rocks this morning, Black Pearl began to search for whale shark.

The dive to 5 Rock was nice and easy, while the current remained mild throughout the dive and all the divers got to enjoy and observe the beauty of this unique formation of reef.

Although the visibility remained poor (7 meters), the fish life was more than acceptable. Few white tips reef sharks and napoleon were the high light.

The search began after the breakfast on the dive dhoni , starting from Dhigurah Beyru till Maamingili and past Sun Island.

The one we spotted didn’t last very long but at least all the divers could snorkel for about 5 minutes.

The 2nd dive was to Sun Island Outer Reef and on this dive were few turtles and white tip reef sharks.

Third and last dive for the day was to Dhigurah Thila: This spectacular old time favorite is located at the southern Ari atoll a kilometer north of Dhigurah Island. The eastern side of the Thila is exposed to ocean currents and drops quickly down from 8 meters to the ocean plateau at 45 meters. The reef wall is about 400 meters long, the whole length interspersed with caves and overhangs. Midway along the Thila on the eastern side is a fracture in the reef, starting at 15 meters and descending to 40 meters.

Depth range: 8 – 30 meters.

Marine life: The fracture is crowded with marine life of all types and sizes. Check out the coral outcrops along the wall of the Thila. In the southwest monsoon make it a point of watching out for the whale sharks that are commonly seen here.

A beautifully colored and designed moray eel swims around the reefs at Bodufinolhu Thila trying to shy away from the camera. Too bad the scuba diver is a fish paparazzi expert.

A barracuda seen scouring the reef for some dinner. It almost looks like the same fish from the old sword in the stone cartoon.