Dive with
Manta Rays

FIND OUT MORE
ENQUIRE NOW

Diving with Manta Rays

Manta Rays are common in South Africa and Mozambique during our summer months. The Manta Rays are not shy at all - they are in fact quite inquisitive and not scared of divers. Some of the Mantas are resident and therefore easy to find, others frequent certain areas but seem to migrate as we see different individuals over a period of time.

The Manta Rays are often seen on or just under the surface - it is therefore possible to at times snorkel with Manta rays. The best diving with Manta Rays can be expected in Mozambique, with fewer Mantas occurring as divers move Southwards towards the colder waters of Gansbaai where one cannot dive with Manta Rays at all.

Kingdom: Animalia
Phylum: Chordata
Subphylum: Vertebrata
Class: Elasmobranchii
Order: Rajiformes
Family: Myliobatidae
Subfamily: Mobulinae
Genus: Manta
Species:
birostris - Atlantic Manta ray - occur in South Africa and Mozambique
hamiltoni - Pacific Manta ray - do not occur in South Africa and Mozambique
Prince Alfred's Manta ray - do not occur in South Africa and Mozambique

The latter two species of manta, known as the "lesser" devil rays, Manta hamiltoni (Pacific manta ray) and Manta alfredi (Prince Alfred's manta ray) were considered separate from Manta birostris. Recent studies of genetic samples show that they are all the same species though - Manta birostris.

Taxonomy
The name of manta is derived from the Spanish word, meaning blanket. (Manta birostris was first described by Dondorff in 1798. Synonyms include Cephalopterus vampyrus, Cephalopterus manta, Manta americana, Ceratoptera johnii, Ceratoptera alfredi, Brachioptilon hamiltoni, Raja manatia, Manta hamiltoni and Manta alfredi. Manta ray, Atlantic manta, Australian devilray, blanketfish, devil ray, devilfish, devil-ray, eagle ray, giant devil ray, giant manta, giant Atlantic manta, great devilfish, manta, manta ray, Pacific manta, prince alfreds ray, sea devil, and skeete are common names in English language. Other names include mante, diable de mer (French), duivelsrog , mantel vis, sjaal vis (Dutch), jamanta, xale (Portuguese), manta (Italian), manta atlantica (Spanish), oni-itomaki-ei (Japanese), manta, frazada, mantarraya, raya (Spanish), teufelsrochen (German), and urjamanta (Portuguese), ???????? (Greek), ??????? (Russian), ??? (Simplified Chinese), ??? (Traditional Chinese), ???(Japanese) ??????? (Arabic), ?????? (Hebrew).

Description
The Manta ray is closely related to sharks. One of the distinct features of manta rays, and of the class Chondrichthyes, is that the entire skeleton is made of cartilage. The skin of manta rays is rough and scaly, like that of most sharks.

The Manta ray is the largest member of the ray family with a maximum disc size of 9 meters (25 ft) across its pectoral fins (or "wings") and weighing up 3,000 kg (3 tons). The average Manta ray has a width of about 22 feet (6.7m) and there is only a slight difference in size between males and females - males ranging from 5.2 - 6.1 meters and females ranging from 5.5 - 6.8 meters. The average life span of Manta birostris is 18-20 years.

Adults are easily recognized by their large triangular pectoral "wings" and distinctive "horns" (also called cremoriol fins) on either side of its broad head that are rolled like spirals when swimming and flattened when eating.

Unlike other mobulids, the manta has a broad, rectangular terminal mouth located at the front of the head. There are 18 rows of teeth on the center of the lower jaw, with row number decreasing to 12-14 toward the corners of the mouth.

To breathe, the manta has two sets of five gills on the underside of the body, and holes called spiracles just behind the eyes. The manta can alternate which spiracle is used for inhaling and which for exhaling. Mantas have a smooth skin, a , and a tail that lacks a spine. The tail from cloaca to tip is as long as the cloaca to the front of head. The tail is slightly flattened and is shorter than disc width.

Manta rays are normally solitary, free swimmers who are not territorial, but sometimes swim in loose aggregations. They spend considerable time near the surface and have been observed breaching, jumping clear of the water and returning with a splash. Three types of jumps have been observed, forward jumps landing head first, forward jumps landing tail first, and somersaulting. Groups of these animals have been seen participating in this behaviour, breaching one after the other. While it is not understood why this behaviour is exhibited, some speculate it may play a role in attracting mates or is a form of play.

Coloration
Mantas are most commonly black above and white below, but some are blue on their backs. Individual mantas possess distinct dorsal and ventral coloration that is unique to each animal. Generally, it is dark brown, greyish blue, or black on top with pale edges and white underneath. Some individual mantas have pale patches and colour patterns on top as well as dark blotches underneath. These colour variations have been used to identify individuals.

Distribution & Habitat
Manta rays are found in tropical and warm temperate coastal regions of the world's oceans, generally between 35 degrees north and south latitude, including the coasts of South Africa and Mozambique. Manta birostris, unlike most other rays, are found near the surface of the ocean and to depths of 120 meters. Atlantic manta rays stay closer to shore in the warmer waters where food sources are more abundant, but occasionally can be found further from shore. Usually they migrate around the world in search of plankton-rich waters, but some are resident to particular areas.

Diet
Manta rays are filter feeders and primarily planktivores. They use the unfurled cephalic (head) fins on the head (which look like horns when they are not feeding) to funnel plankton-rich water into the mouth where pinkish-brown sponge-like tissue located between the successive gill bars that support the gills filter out the plankton. Mantas generally eat plankton and small fish, but anything that fits in their mouths could end up being swallowed.

Many have opportunistic remoras attached to their undersides, consuming scraps that result from feeding. Mantas have been observed swimming in slow vertical loops within rich feeding areas. They aggregate in areas that offer large concentrations of zooplankton, with up to 50 individuals within an area. Oceanic islands and submarine ridges provide precious few sites containing nutrient-rich waters and an abundance of zooplankton, in the otherwise nutrient poor tropical regions.

Reproduction
Manta birostris are sexually mature at 5 years of age when the males reach a disc width of at least 13 feet (4 meters) while females mature at a disc width of 16.5 feet (5 meters). The mating season of sexually mature manta rays occurs from early December to late April. Mating takes place in tropical waters (26-29 degrees Celsius), and around rocky reef areas from 10-20 meters in depth.

Manta rays gather in large numbers during this season, where several males will court a single female. The males swim closely behind the tail of the female at faster than usual speeds (9-12km/h). This courtship will last for about 20-30 minutes at which point the female decreases her swimming speed and a male will grasp one side of the female's pectoral fin by biting it.

He arranges his body under that of the females. The male will then insert his clasper in the cloaca of the female and insert his sperm, this usually lasting around 90- 120 seconds. The male will then swim away rapidly and the next male will repeat this same process. However, after the second male the female usually swims away leaving behind the other courting males.

Mantas reproduces via aplacental viviparity - when animals hatch from eggs, but the eggs hatch and the babies develop inside the female's body. There is no placenta to nourish the pups. The gestation period of Manta birostris is 13 months, after which females give birth to 1 or 2 live young pups which are about 1.2 m wide and roughly weigh 45 kg. Pups are born wrapped up like tubes by their pectoral fins, but soon after become free swimmers and fend for them selves. Young mantas grow very rapidly with pups virtually doubling the body width from birth through the first year of life.

Predators
Manta rays have no particular anti-predator specializations other than their tough skin, but due to their size they do not have many natural predators. Large sharks have been known to attack manta rays.

Parasites
Specific parasites associated with M. birostris are unknown. Mantas leap out of the water to heights of 2 meters, then smacking against the surface. By doing this, mantas may remove irritating parasites and dead skin on their large bodies. Also, Manta birostris have been seen at "cleaning stations" with wrasse fish swimming about them picking off parasites and dead skin. Another symbiotic interaction that mantas have is with remora fish, which attach to the giant mantas and hitch rides with them while feeding on the mantas parasites and on plankton.

Importance to Humans
In the past, Manta birostris was commercially hunted from small boats in tropical America and off the coasts of California and Australia for its liver oil and for its skin which is used as an abrasive. Today it is rarely hunted, although meat from the manta ray is considered a delicacy in the Philippines.

The biggest impact that the manta ray currently has comes from tourism, with dive industries being created for tourists who want to swim along side these gentle giants. Inquisitive mantas will approach and even solicit attention from divers, apparently enjoying the stimulation provided by human contact and the bubbles from scuba exhaust. In these areas, where divers often touch and interact with mantas, the rays can develop skin lesions in response to the removal of the protective mucous layer.

Danger to Humans
The Atlantic manta ray was once thought to be aggressive and harmful to humans as sailors created myths about them. The common myth was that mantas could capsize ones boat by leaping out of the water and crashing down upon it. Another common misconception is that mantas drown swimmers by wrapping around them. They are called "devil" ray because of the cephalic fins at the front of their heads, which resemble the horns of a devil. Also fishing boats reported that Atlantic manta rays would circle about their boats for long periods of time. These mantas were probably just displaying their corralling behaviour during feeding. According to Yapese myth, the Mantas might wrap their wings around a person and squeeze him to death. This is not true, but a blow from a wing of a full grown manta carries a very powerful punch. Manta Rays pose no danger to humans.

Conservation Status
Population sizes of Manta birostris are unknown. Because of their slow reproductive rate, they are very vulnerable to over fishing. M. birostris is categorized as "Data Deficient" with the World Conservation Union (IUCN). However, this species is listed as "Vulnerable" in the Gulf of California, off the west coast of Mexico, and in the South China and Sulu Seas. The IUCN is a global union of states, governmental agencies, and non-governmental organizations in a partnership that assesses the conservation status of species. Currently, there is a lack of scientific data to properly assess the species' conservation status. However, in locations where there are fisheries, the manta suffers decline in population because of their slow reproductive rate.

CITES - No special status.

Sources & further research
www.sharks.com
www.enchantedlearning.com
www.austmus.gov.au
www.flmnh.ufl.edu
www.boattalk.com
www.conservationinstitute.org
www.omne-vivum.com
www.funet.fi
www.marinebio.org/species

Further Research