The Marine Life of South Ari atoll MPA
The South Ari atoll MPA is arguably the finest place in the world to see these huge but harmless animals all year round. The species was first recorded in 1828, but since then they have been recorded and studied in every tropical region on earth, though still very few hard facts are known about them. Part of the reason for this lack of knowledge is their open ocean way of life, with sharks living away from the reaches of human scientists for months at a time. Another reason is that that they never seem to conform to a set pattern, with individual sharks that have been present in one location for years suddenly disappearing and re-appearing months later and thousands of miles away! Even the most basic information – such as how big do they grow? – is a matter of much scientific debate and dive school bar discussion.
The largest known individual, scientifically measured and recorded, was a 12.3 metre female. She weighed in at 15 tonnes, a fair bit heavier than a fully laden London Bus. Reports of individuals being 15, even 18 metres long are not uncommon, but so far these have yet to be proven. And all this size is achieved by eating a diet of marine plankton and small fish no larger than a herring. Most encounters with whale sharks happen during seasonal aggregations, where for a few weeks or months at the same time each year, large numbers of sharks gather at specific locations. They generally coincide their visits perfectly with the mass breeding events of other species, such as the famous red land crabs of Christmas Island or the snapper spawning of Gladden Spit, Belize. As soon as these breeding events finish, the sharks simply melt away into the blue until the following year. This is where South Ari atoll in the Maldives is unique. The sharks we see on the reefs of the MPA are seen year round and for periods of at least 7 years and counting. While there have been regular sightings of the sharks here feeding, it is still not understood exactly why this location is so unique as to keep the sharks in this area year round.
In order to begin untangling the mystery of the sharks in this area, a team of scientists from the UK and US undertook a tagging program of the Maldivian sharks in 2007. The tags were a mixture of satellite tracking units and data recording devices, designed to show not only where the sharks go after leaving the reef, but also to record how deeply they can dive, how much of their time is spent at the surface and what kind of temperature variances they can tolerate. The tags were put into the skin behind the dorsal fin, into an area of fatty insulating tissue up to 10cm thick so as to minimise harm to the sharks. The tags showed that the sharks may travel many hundreds of kilometres
between their visits to the MPA, with one wondering up to the coast of western India before returning. Similar studies have found more remarkable results, with one shark tagged in the Gulf of California migrating nearly 13,000 km over a period of 37 months, ending up in Tonga! From the data recording tags, some remarkable information was gained on the depth that the sharks seen in the MPA can dive to, with one individual going so deep that a pressure sensitive safety release mechanism was triggered at 1600 metres! To date, the worldwide deep diving record is 1928 metres, though this is likely to increase when considering the tiny proportion of sharks that have been tagged in this way. The tags showed that the sharks regularly visit 600m, though the reasons for this are still only speculation.
A similar mystery surrounds whale shark reproduction. What is known about this part of the whale sharks life cycle comes from a single large female harpooned off Taiwan in 1995. This female was carrying 304 embryos, the largest of which was near birth and 63cm long. The smaller individuals in the female were enclosed in egg sacs, however the pups closest to terminal period were live and free swimming, confirming that whale sharks are ovoviviparous, or live birthing.
Very recent genetic studies have shown that all of the whale sharks in the litter of 304 were fathered by the same male. This would suggest that the female shark is either capable of storing sperm for long periods of time and using it as required, or can somehow regulate the rate of foetal development. That the female only had one partner would also suggest that there may not be one location where whale sharks go to breed. It is likely that a system where so many eggs are fertilised from one encounter would develop in a species that does not regularly encounter members of the opposite sex. So when they do mate, they have to produce as many offspring as possible from the encounter. This makes it feasible that mating may take place 200m down in the middle of the Pacific Ocean!
There have also been genetic studies done on the whale sharks found here in the Maldives. The most surprising development to come from these studies is that the sharks we see in the MPA vary little genetically from those found in other whale shark haunts around the world. So as incredible as it may be when considering their geographical distribution, there is a possibility that there is just one global population of whale sharks, meaning that all sharks currently living in the MPA have the potential pass on their genes to any other whale shark anywhere in the world within just a few generations. Unfortunately however, this makes monitoring their population and protecting those individuals currently safe here in the Maldives which move to other areas where the species is not protected, very difficult.
A long term conservation effort based on photo identification of individual whale sharks, is under way to try and establish where whale sharks here in the Maldives go to both within the Maldives and internationally. The project is supported by SAMPA, as well as guests of Diva Maldives, but is headed by the Maldives Whale Shark Research Programme. This project uses photographs of the area around the whale sharks gills to identify individual sharks, which are then recorded on an international database. If these sharks are seen again, then the difference in location and time can be recorded, helping scientists understand the movement patterns of this species. If you would like to submit pictures or get further information on this programme, then please get in touch on our ‘Contact Us’ page.
The charismatic manta ray can be found throughout the worlds tropical and sub-tropical oceans, and are the largest species of all rays. The largest captured specimen was measured at 6.8m from wing tip to wing tip, and weighted just short of 2 tonnes. This is an extraordinary specimen nowadays however, as they are usually encountered in the MPA as being around 3 to 4m in width.
Like the whale shark, manta rays achieve this size on a diet of marine plankton – tiny organisms which are filtered out of the water column by a series of sieves called ‘rakers’ at the inside edges of the mantas gills. The ray simply swims through the water with its mouth wide open, scooping up whatever happens to be in its path. If it happens upon a particularly dense patch of plankton, the ray begins a graceful ‘loop-de-loop’ series of backflips, focussing the plankton into a smaller area in which to feed. Aiding in the channelling of water into the mouth are a pair of fins, called cephalic fins, which unfurl from the side of the mouth and act as funnels when the ray is feeding. When they are not feeding, these cephalic fins roll up and resemble horns on the head of the manta, which is the likely reason to the alternative name of ‘Devil Ray’, which was bestowed on the manta by early sailors.
While the mating habits of this species have been well documented in the wild, it was not until a 2007 success at captive breeding by a Japanese aquarium that a greater understanding of the reproductive biology aspects of the cycle was achieved. During the mating season, male manta rays form up in a chain behind a single receptive female, with the suitor who is able to remain with her as she leads them on a high speed chase being the one deemed fit to father her offspring. Mating itself involves the male manta ray biting onto one of the female’s wingtips and using this to position himself so he is able insert a clasper into her. This process may take several minutes. Once fertilised, the gestation period lasts around a year, with the offspring getting it’s nutrients from an egg yolk during this time. One or two ‘Pups’ are live born, and enter the world backwards with their wings wrapped up over their bodies. They are immediately able to swim.
At birth, mantas have very long tails, but these are often bitten shorter by predators, such as sharks, as the manta ages. Unlike other closely related species, the mantas tail lacks any defensive spines at the base, so they are wholly reliant on their size and incredible bursts of speed to elude predation. Perhaps the biggest development in Manta biology has occurred in the last few years, with the long suspected news that there are two distinct species of manta rays being confirmed. They are broadly broken down into the ‘reef’ manta, which is almost exclusively what can be seen in the MPA and the ‘oceanic’ manta, which is a larger species with several physiological and morphological differences to the near shore variants.
In the Maldives, the species is part of a mark / recapture scheme, which uses photographs of each animal encountered to try and understand if there is a settled Maldivian population and where they travel between the different seasons, as well as to try and estimate the number of individuals that may call the Maldives home. Individual manta rays can be identified from the spot patterns which cluster around the central undersides of their bodies.
If you have seen a manta ray in the Maldives and are interested in contributing to the understanding of this species in there, then visit http://www.maldivianmantas.com/index.htm where you can see how to find further information and get involved with cutting edge manta ray research.
This inhabitant of the open ocean is right at home in the wild, deep waters around the South Ari MPA. On any given trip in this area, it is a common thing to see these majestic fish leaping acrobatically in a series of high octane jumps out to sea and away from the reef. In rare instances it is possible to see the ‘sail’, which is an enormously extended dorsal fin cutting through the water as the fish hunt for their prey. Why would a sailfish jump? In this instance it is likely that they are removing parasites from their bodies, although there are other theories.
The sailfish holds the record as the fastest swimming fish in the sea, with reports of it reaching 70mph in short bursts. Every part of a sailfishes’ body is adapted to a high speed life; the powerful tail has equally sized top and bottom lobes, with water slipping down the side of the fish being directed to it by large caudal peduncles at the joint of the tail and the body. A slim body behind a large head is excellent for hydrodynamic efficiency, and small groves in the body allow all but the tail fin to be tucked in completely flat with the body when they are swimming rapidly. They need to be able to perform at high speed, as they hunt fast moving shoaling fish such as tuna and mackerels, using the long, rough bill to swat their prey.
In the Maldives, that bill is used against them by local fishermen, who have devised a unique way of capturing them. On occasions around the MPA, it is possible to see fishermen towing what looks like an old style mop head behind their dhoni. These are lures for the sailfish, supposedly replicating something like a squid. When the fish hits the lure with its bill, it becomes entangled in it, and the fisherman is able to pull it in by hand. There are no hooks involved, just the friction between a straggly cotton pile and the rough skin on the bill. Once to the boat, a powerful fish 80kg fish which may measure up to 3 metres in length could cause trouble for the fisherman or indeed the stability of some of the smaller dhonis, but the fishermen have learnt that there is a weak joint in the spine – just behind the head – which can be broken if the fish can be yanked forward by the bill. A swift lifting motion of the bill and the fish is instantly still, allowing the lucky fisherman to hall it on board with ease.
Perhaps one of the most striking features of the sailfish when seen up close is its ability to change colour. The fish is thought to use its large sail to corral shoals of fish, and also to confuse them with bursts of vibrant colours. It may also be a way of communicating to other sailfish their intention to strike at a shoal, a useful thing to know when a sharp, 3 foot long bill is just about to be unleashed. These flashes of blue and yellow are most commonly seen by humans when the fish is on the end of a fishing line, as they are revered game fish. Sailfish may be one of the most sustainable pelagic food fish in the oceans. They grow very rapidly and reproduce prodigiously. A juvenile sailfish may reach nearly 1.5 metres in its first year of life, and may be ready to breed within just 2 years. Life span is thought to be short however, estimated at around 6 years maximum. Where they go during that time is uncertain however, so some resorts such as Diva Maldives which borders the South Ari MPA are currently involved with an international tagging programme for this species. Fish caught during game fishing excursions are fitted with a small tag which holds a contact number. The date, time and location of the tag is recorded and sent to a worldwide data collection point. If the fish is caught again, the tag requests that the person who caught it calls in the date and location of capture. By comparing the two sets of information, it is possible to track the movements of the fish, which may open new leads on migration routes and aid in any future conservation efforts for this species.
To add to its embarrassment of riches, the South Ari atoll MPA is also home to a regularly seen pod of approximately 10 bottlenose dolphins. These stocky, powerful animals can reach up to 4 metres in length and weigh anything up to 600 kg. Of all the marine mammals, they are perhaps the best known. Championed as a friendly and intelligent companion in the 60’s television show ‘Flipper’, they are also the most widely used species of dolphin in oceanariums. Their intelligence and adaptability makes them easy to train, while the curved beak creates the illusion of a permanent smile.
In the wild, this intelligence and adaptability allows them to create hunting techniques which most suit their environment. Typically living in groups of around 10-30 individuals, they have been recorded creating and passing on innovative new hunting skills which include ‘hydroplaning’ into water too shallow to swim in, creating ‘nets’ of bubbles or sand around shoals of fish which force the fish to jump into the air where they can be more easily caught, and the newly discovered act of ‘conching’ – whereby the dolphins chase a fish into a large conch shell, then take the whole shell bodily to the surface to drain out the water and the accompanying fish into their mouths.
All dolphin species are well known for their echo-location abilities, and the bottlenose dolphin, with its large bulbous forehead or ‘melon’, has a particularly wide repertoire of clicks and whistles with which to communicate and to find prey.
Female bottlenose dolphins reach sexual maturity at around 5-13 years, while the males develop later at between 9-14 years. Once mated, the female gestates for nearly 12 months, before birthing the typically single calf. The calves take 18-20 months to suckle, but will stay with their mother for much longer to get the grasp of the wide and complex skill sets that she has to pass on. As a result, it may be up to 6 years after a calf is born before the female will mate again. In the wild, lifespan is estimated to be a maximum of 30 years, while in captivity 40 years is possible.
The spinner dolphin is one of the great marine acrobats. They get their name ‘spinner’, imaginatively enough from the fact that they can spin laterally during a jump – they are the only species of dolphins which are able to do this. They can also perform a repertoire of other manoeuvres including front and back flips. But why do they do this? Theories vary from them simply an expression of them having fun, to the jumps being territorial displays between males or that on landing they rid themselves of parasites which may have attached to the skin. The latest thought is that as humans, we are watching the display from the wrong medium – they are performing to other dolphins underwater, so what they do out of the water is not important. The idea is that performing a particular spin means that on landing, they create a particular splash pattern which is a form of communication to the other dolphins watching the surface. So a front flip may mean the landing splash goes forward, whist a spin to the left splashes a pattern to the left. A lot more work would need to be done to decipher the meanings of this form of communication before it can be considered as a realistic reason. Regardless of why they do this, seeing a group of spinner dolphins in an acrobatic mood is one of the great sites of the South Ari MPA.
Spinners are a much smaller dolphin than the bottlenose, growing to a maximum of 2 metres, but usually around 1.5m. They are also a light weight species, with an average of just 75kg. They are easy to differentiate from the bottlenose by their two tone body colour, being much darker on top.
Spinner dolphins are predominantly nocturnal, feeding on small fish and squid from the early evening. They generally live and feed within small family units of around 15 members, within which very strong family bonds are formed. When out in the open-ocean however, they often come together with numerous other pods and form group several hundred strong. Occasionally, these large groups can come together with others of similar size, with the result being ‘super pods’ consisting of thousands of individuals.
The females of this species reach sexual maturity at around 4-7 years, with the males at roughly 7-10 years. After a gestation period of just over 10 months, juveniles are born and then stay with their mother for up to 2 years. They can expect to live for up to 20 years in the wild.
The spinner dolphin is internationally listed as ‘endangered’, with the main threat to the species coming from by catch of the fisheries industry. They are particularly affected by the purse seine fisheries, as the strong family bonds usually mean that if one is caught, the whole pod are caught as they will be in the same area together. Happily however, within the Maldives they are the most common of the cetaceans.
The Hawksbill turtle derives its name from the beak at the end of its narrow head. It is the most commonly encountered turtle within the MPA and indeed within the Maldives.
It can be easily distinguished from other turtles by that prominent bill, the carapace (shell), which is usually covered in algae and other marine growth (green turtles, the other turtle occasionally seen in this area has a shiny, clean shell by comparison) has serrations around the base, and it’s small size. It is one of the smaller sea turtles, with an average carapace length of around 75cm, usually weighing at just 40-60kg.
The hawksbill’s narrow head and bill allow it to access food in the difficult to reach cracks and crevices of coral reefs. Its favoured diet is sponges, though it will also take anemones, squid and sea squirts. It has, on rare occasions been seen eating fish too. One particularly well known turtle at a popular North Ari atoll dive site uses the light from diver’s torches to hunt for trigger fish at night. The triggerfish wedge themselves into cracks in the coral during the night, but this turtle has learnt to follow along a diver’s
torch beam until it finds one, and then pull them out by the tail. If the triggerfish is hard to reach, it may even remove bits of coral rubble from around the entrance to the crevice in order to get at the unfortunate fish.
The Maldives is fortunate to play home to nesting Hawksbill turtles, with the females pulling themselves onto the beaches up to 4 times in a nesting season. After nesting, it is thought to be another 3 years before she will nest again. Once a nest has been dug, the female hawksbill may deposit up to 160 eggs, before covering them and leaving them to their fate. After around 60 days, the juveniles hatch and dash to the water. Only a few from each nest will make it to an age where they can breed themselves.
While many young turtles are taken by natural predators, mankind also takes a heavy toll on these animals. Fortunately they are protected in the Maldives, but elsewhere they are taken in large numbers for their shells, which are the source of ‘tortoise shell’ jewellery. As a result of this, accidental by catch in fishing nets and the removal of their eggs from the nest for human consumption, the hawksbill turtle is now listed as ‘Critically Endangered’. The Maldives is one of its few remaining strong holds.
White-tip Reef Shark
The white-tip reef shark is the most commonly encountered shark in the Maldives, and on dives within the MPA it is often seen along the edges of the deep water drop offs this area is well known for.
Most encounters with specimens of this species are sharks around 1.5 metres in length, although they may reach up to 2.1m. However, they rarely look as big as they are. This is because it has a very slim body in proportion to its length. White-tips hunt for fish at night amidst the cracks and crevices of the coral reef, which is where its svelte figure is advantageous. Like all other species of sharks, the white-tip cannot swim backwards, so if it gets itself into a narrow crack in the reef when chasing a fish, it has to wriggle and worm itself out again – an act which may not be possible with a bulky body. White-tips often come together on one reef to hunt, where several individuals may be observed pursuing a single fish, giving the impression of a ‘feeding frenzy’.
Unlike true pelagic sharks which can never stop swimming if they are to breathe, White-tips are often seen resting on the sea bed during the day. They will generally pick an area where there is a strong current which they can face into, which makes it easier for them to pass water over their gills. If there is no current, they have to physically ‘gasp’, sucking water into their mouths by opening it rapidly, before forcing it out over the gill by quickly closing it. Thisability to breathe without having to swim not only saves energy in adults, it is useful for juvenile sharks too, as they are able to avoid the dangerous open waters during the day by hiding in caves or under coral bommies. Divers looking under coral heads in some places along the South Ari MPA, may be lucky enough to see several juvenile sharks huddled together in safety.
The juveniles are born at around 55cm in length, as part of a litter of between 1-6 pups after an 11 months gestation. They are viviparous, meaning they give birth to live young which have been sustained during gestation by a placental cord. White-tips usually perform sexual reproduction, with the male biting onto a females fin to allow himself to position his clasper within her. However, in one captive female white-tip, asexual reproduction was recorded, with the female self-fertilising in the absence of a male. This kind of reproduction has been recorded in other shark species also and constitutes an incredible survival skill.
As is the case with most species of shark, the white-tip poses no threats to humans if they are left unmolested, despite having 42 rows of teeth. Indeed, getting close to a white-tip requires patience and slow, calm movements to avoid frightening them away.
Internationally, white tips are listed as ‘Near Threatened’ due to the weight of fishing on this species to satisfy the shark fin soup market. The Maldives government has done an exceptional job of declaring protection for this species – indeed all kinds of sharks – in their waters, though in most other areas of Asia they are heavily targeted. Fortunately, other nations are now waking up to the importance of sharks, including the white-tip to the reef environment and as an attraction to tourists.