Field Guide to Manta Rays
One of the world's most striking and intrirguing marine species, manta rays are both highly sociable and intelligent. Katie Lee-Brooks, head of operations at the Manta Trust, introduces this icon of the oceans
Manta rays are one of our oceans’ most iconic and charismatic species, with many divers listing them high on their dive career bucket list. They boast the biggest brains of all fish species and their curious and often seemingly friendly nature makes them a captivating creature to watch and interact with.
Born into a life of perpetual motion they must keep swimming to survive. Driven forwards by powerful beats of their wing-like pectoral fins they search the ocean currents for concentrated patches of the tiny planktonic food upon which they feed. Moving and migrating in this way with the ebb and flow of tides and currents, there one moment and gone the next, adds to the intrigue that surrounds these animals and their lives.
Despite the fact that these manta rays are of huge fascination to divers, it is only in the last 10 years that dedicated research into the mysterious lives of these creatures has begun in earnest. What we have learnt so far is just the tip of the iceberg; therefore on-going studies are vital if we are to truly protect these vulnerable species. Already many regional populations have been severely depleted and are incredibly fragile as a result of fishing pressures which have driven these populations to the edge of their biological capacity to survive.
Manta rays are members of a small, but highly specialised family of rays called Mobulidae. This family consists of two genus Mobula (9 species) and Manta (2 species). The defining feature of mobulid rays is that they are filter feeders with specially modified feeding apparatus, gill plates, which they use in order to strain their planktonic prey from the water column.
The two species of manta ray, the Giant Oceanic Manta (Manta birostris) and the Resident Reef Manta (Manta alfredi) were recently re-classified (2009) having been previously considered to be a single species. However, several important differences exist between the two species which have vital implications for their ongoing management and conservation.
Manta rays are found throughout the tropics and subtropics of the world and while their ranges overlap, distribution is one of the key factors that separate the two species.
Reef mantas, as the name might suggest, usually occur and are encountered in the shallow waters along the coastal reefs of continents and around remote oceanic islands and archipelagos. They are resident to a specific home range, migrating around this area as they follow changes in the seasonal abundances of their planktonic food source, or the urge to reproduce.
Giant mantas appear to be much more transitory in nature, wandering large distances across open oceans. The oceanic mantas are most frequently sighted along productive coastlines with regular upwellings, at oceanic island groups and offshore pinnacles or seamounts although often not with the same regularity as their reef manta counterparts, with years and even decades passing between sightings of the same individuals. Oceanic mantas also venture into the slightly cooler waters of the higher latitudes. Their elusive and migratory nature means that we know much less about these giants.
Both species of manta rays share several similar features which make them distinctly a manta ray! Their large bodies are diamond-like in shape with a large terminal mouth along the front. Either side of this huge mouth are a pair of cephalic fins (head fins). These cephalic fins play a vital role in manta ray feeding, however mantas can roll up these fins, making them look like horn like protrusions, hence the common name devil rays, which has long been used to refer to mantas.
In both species, most commonly manta rays have a black dorsal (topside) surface with a white ventral (underside), this is known as a chevron morph manta. Both their dorsal and ventral surfaces are shaded and marked. The markings on the ventral surface are particularly important to researchers as they are unique to each manta and have proved to be stable over time. By documenting the mantas we encounter with a photograph and comparing these between different locations and over time we can begin to build up individual life histories of each animal in our database and gaining a wider understanding of the populations we study. In some locations a small proportion of the population exhibit a black morph. In this colour morph mantas are completely black dorsally and almost totally black ventrally.
Several physical traits differentiate the manta species. The first of these is their size; fully grown reef mantas usually average 3-3.5m in width, however, giant oceanic mantas can reach much larger sizes, occasionally in excess of 7m, making them the largest ray in our oceans. Differences in dorsal shading also allow for distinction between the two. Giant mantas exhibit a well defined T-shape to their white dorsal markings with the areas of black and white quite distinct from each other. Reef mantas conversely have a Y-shaped shoulder stripe and often with the white areas fading into the black. Location of the ventral markings are another way to tell the difference between the species with researchers in fact using different areas of marking as the primary ID areas for each species.
Despite being one of the largest creatures in our oceans, manta rays feed almost exclusively on some of the tiniest animals in the marine world – plankton! Plankton are a vast and diverse group of organisms who drift with the oceans currents. Plankton can be divided in two key groups, the plant, or phytoplankton and the animal, or zooplankton. Zooplankton consists of tiny animals, worms, shrimps, crustaceans and even larvae and eggs. It’s this rich protein source that mantas target.
Mantas are highly evolved to target this prey roaming the oceans in search of abundant areas of food. Upon finding it they transform their bodies into filter feeding machines, unfurling their cephalic fins to help funnel water into their large mouths, ingesting countless litres of water which flows into their mouth and out over the five pairs of gill slits that line their throats. Any plankton flowing over these gills that is larger than a grain of sand is sieved out of the water and trapped by feathered gill plates.
Manta behaviour is often characterised by the migrations they make in search of their planktonic prey. While the lives of reef mantas seem to follow a seasonal rhythm as they frequent the sites within their small home ranges that yield the greatest nutritional rewards, the lives of the giant mantas are far less simple to document and seem to follow a much less regular pattern of behaviour.
The oceanic mantas, as their name suggests, are more at home in the deep sea than their close relatives. Considered to be ocean voyagers, it is thought they follow the highway of ocean currents, travelling great distances across the open seas in search of seasonal planktonic blooms. Satellite tracking data recovered from tagged oceanic mantas shows that they are capable of moving large distances in relatively short periods of time.
Both species of manta interact with a variety of other marine species, their giant bodies provide host to remoras (or suckerfish), juvenile fish species can ride the pressure wave in front of the manta’s head gaining shelter and a range of parasites attach themselves to the mantas surface. Mantas use cleaning stations to rid themselves of these parasites and form symbiotic relationships with a number of fish species who clean these giants in return for a tasty meal of parasites!
Much of what we know and understand of manta reproduction has been learnt from populations of reef mantas with only a single documented mating in oceanic mantas.
Courtship rituals can be fascinating to watch sometimes continuing for days or even weeks. Eager male mantas usually make their way to cleaning stations where females are known to spend several hours daily and upon finding a female who is ready and willing to mate they pursue her. These pursuits known as mating trains have been documented to have consisted of up to 25 males following a single female. The female is in charge, leading the males on a twisting turning journey, even leaping from the water. It is believed this is a test of the strength, stamina and persistence of her potential suitors and as the males are whittled down she finally selects just one to mate with.
Mating its self takes place near the water’s surface. Mantas mate belly to belly, the male taking the female’s left wing tip in his mouth and using it to allow him to manoeuvre under her. Copulation lasts just a few minutes with the pair, negatively buoyant, falling through the water column.
Mantas are ovoviviparous, that means that after internal fertilisation has taken place the egg develops inside the mother until it is ready to hatch. Gestation periods are likely to be around a year in length and in most pregnancies mantas will give birth to a single pup. Manta pups are roughly 1.5-2m when they are pupped and are miniature replicas of their parents, completely equipped to survive alone in the open ocean.
Long pregnancies resulting in the birth of a single pup alongside other life history traits including longevity, late maturity and slow growth make manta rays extremely vulnerable to any form of consumptive exploitation.
Like most wild animals manta rays face threats from natural predators, far more dangerous to mantas however are humans. In recent years manta rays have faced increasing threats from both targeted and by-catch fisheries due to a growing trade in their highly valued gill plates.The international trade in manta and mobula gill plates is being driven by the demand in the Chinese Medicine trade and appears to be a relatively new phenomenon. Those selling or promoting the use of this product claim the plates can treat a range of health issues, however, reviews of available literature, along with interviews of well respected practitioners have revealed that there is no evidence to support any of these claims, with some practitioners even admitting that gill plates are not effective and that many other alternatives are available.
Both species of manta are listed as “Vulnerable” on the IUCN Red List of Threatened Species and much work is currently being undertaken to ensure their ongoing persistence. In November 2012 giant mantas were listed on the Convention of Migratory Species (CMS) and in March 2013 the genus Manta was listed on Appendix II of the Convention on Trade in Endangered Species of Wild Fauna and Flora (CITES) which seeks to ensure that any trade in these species is closely controlled in order to avoid detrimental effects on populations. This legislation will come into force in September 2014.
Viewing mantas in the water is an experience unlike any other wildlife encounter. However, care must be taken during interactions since the two times and places that provide the greatest likelihood of manta interactions are during feeding and on cleaning stations, both vital activities for the mantas.
Work carried out by The Manta Trust into human manta interactions has resulted in a number of key guidelines for low impact, successful and prolonged encounters with manta rays. At feeding aggregations mantas are predominantly seen at the water’s surface so snorkelling is highly recommended to enjoy this at its best. In addition keeping a minimum distance of 3m between yourself and any mantas (unless they approach you) refraining from chasing, following or intentionally creating an obstruction, and trying to avoid splashing on the surface or approaching mantas from behind are all highly advised. At cleaning stations the best interactions are achieved on SCUBA, but it’s recommended to maintain a distance of 5m from the cleaning mantas and to try to avoid diving under or near them. Ask your operator if they follow an approved Code of Conduct for interactions too.
Responsible and sustainable tourism with mantas could hold the key to the long term conservation of mantas. A recent paper conservatively valued the direct economic impacts of manta ray watching tourism at US$140 million annually. This far outweighs the estimated US$5 million trade in manta ray gill plates each year.
About The Manta Trust
The Manta Trust registered as a UK charity in January 2012 with the ultimate goal of sustaining the long term persistence of all mobulid species within healthy ocean ecosystems using robust scientific research, education and awareness. The charity brings together numerous field projects from around the globe along with a diversity of experts in biology, social science, education, photography, filmmaking and advocacy to work towards this common goal.
For more information, to submit your manta sighting to our global database, or to learning more about our educational expeditions please visit our website http://www.mantatrust.org/
Where to see mantas
There are dozens of places around the world where mantas can be viewed by divers and snorkellers alike. Here are our top recommendations:The Republic of Maldives
The Maldives is renowned as one of the best places in the world to see mantas and both species frequent the waters of this island nation. Most commonly encountered are the reef mantas and to date almost 3,000 different individual mantas have been identified; by far the largest known population of manta rays anywhere in the world. Mantas can be sighted year round in the Maldives although they are known to follow the shifting of the seasons (monsoons) migrating around and between the atolls in search of food. One of the most famous sites for mantas in the country is Hanifaru Bay, now a Marine Protected Areas and a core zone in the recently designated UNESCO World Biosphere Reserve which encompasses the whole of Baa Atoll. Aggregations of over 200 individual mantas feeding together in this small bay have been seen at this unique site. Hundreds of cleaning stations also exist throughout the Maldives archipelago offering further opportunities for manta ray encounters.
When to go: The peak season for manta in Baa Atoll is July-November, with the full moon and new moon periods giving rise to the greatest aggregations. Most resorts and dive liveaboards have a good awareness of the peak season for manta ray sightings and can advise accordingly.The Revillagigedos Islands, Mexico
The Revillagigedo Archipelago is perhaps the most reliable place in the world to find oceanic manta rays, the larger of the two manta species. A chain of volcanic islands and seamounts, the Revillagigedos serve as a stopping-over point for a variety of large pelagic species, including sharks, whales, and of course manta rays. Dramatic, rocky seascapes adjacent to deep abyssal waters attract pelagic species, which reef fish rid of parasites at cleaning stations.
Divers can expect close, personal encounters with huge, curious manta rays, (even the occasional black morph manta) as well as exhilarating dives with other large marine species. Mantas have been described as perhaps the most intelligent species of fish in the ocean, in large part due to their curiosity and highly developed regions of the brain associated with complex social interactions. Nowhere is this more apparent than at the Revillagigedo Islands, where mantas have been known to follow divers for an entire dive, swooping overhead and even circling the boat during surface intervals. A dive at the islands is not soon to be forgotten!When to go: Mantas can be found at the Revillagigedo Islands throughout the year, but due to weather concerns most liveaboard boats operate from October to June. Hit the islands in January/February for bonus humpback whale sightings.
Yap & Palau
The small remote Pacific island of Yap had been featured in diver magazines going back three decades as one of the top destinations in the world to encounter reef mantas. With water and air temperatures around 27 degrees Celsius, this destination is truly a tropical paradise. With three notorious manta-cleaning stations divers can expect close encounters with mantas and with a residential manta population of over 100 individuals, a surprise interaction at all dives sites is possible.
The Republic of Palau is a small island nation in the western Pacific located close to Yap. Palau’s diving is world renowned with rich and varied marine life, large schools of fish, spawning aggregations, reef sharks and of course manta rays! Over 200 reef mantas have been and of these just over 5% are the distinctive black morph. There are two key sites for seeing manta rays, German Channel and Devilfish City and cleaning and feeding events can be enjoyed by dive or by snorkel. Research into this population has begun in the last few years and sites for seeing these animals feeding and cleaning are being discovered all the time.
When to go: In Yap manta encounters occur year-round but intensify from December to April. Divers who travel to Yap the first week in March will not only have the incredible experience diving with mantas during mating season but help the Yapese celebrates their culture, tradition, food, family, and community at Yap Day’s. The best time to see mantas in Palau is between November and May especially in the days before the full or new moon. Feeding events of up to 70 mantas have been encountered in the spring months at these key times!Raja Ampat, Bali & Komodo, Indonesia
Boasting over 17,508 islands and the planet’s highest marine biodiversity, Indonesia is definitely the jewel in the Coral Triangle crown. The country holds a large collection of manta hotspots and recently created marine sanctuaries.
Raja Ampat is made up of over 1,500 tiny emerald islands surrounded by turquoise waters. In the north the infamous Manta Sandy is home to a large resident population of both the Chevron and Black variation of manta alfredi, and on a regular occasion heavily pregnant females. Magic Mountain in the south of Misool is a spectacular site which is one of the only places in the world where both Oceanic and Reef Mantas can be witnessed at the same time.
Visit the island of Bali and the clear waters of Nusa Penida to witness reef mantas zooming around a breath-taking volcanic environment. Always keep your eye into the blue for the possibility of seeing the world famous Mola Mola! Visit the prehistoric Komodo National Park, and the zooming currents of Karang Makassar to have a close encounter with both black and chevron reef mantas.
When to go: Mantas can be seen in Indonesia on a year round basis. If considering Raja Ampat the South Misool Region of Raja Ampat is best avoided from June to late August; choose December to March for spotting mantas in the North region. All are reachable by Live-aboard or staying at one of the intimate resorts. Head to Bali any time of year to witness these magnificent creatures! Komodo Manta Season is also year round but avoid the months of January and February due to monsoon rains and high winds.