To enter the world of the manta ray must be one of the closest things we can experience to witnessing extra-terrestrial lifeforms. Swimming below a Manta as the sunlight is snatched away by their ginormous bodies, watching a chain of giants emerge from the darkness of the big blue or hovering eye to eye with an individual as they get cleaned of parasites. Whichever way you first meet a manta ray, you will never forget it. Unfortunately, due to intense fishing pressures our worlds manta populations are under threat.
Manta rays are large rays belonging to the genus Manta. The larger species, M. birostris, can reach around 7m in width while the smaller, M. alfredi reaches around 5.5m. The word manta is Spanish for ‘blanket’ and it is easy to see why if you have a 7m wide ray swimming over you. The first rays appeared in the world’s oceans approximately 150 million years ago as elasmobranchs (cartilaginous fish) started to diversify. With the largest brain of all fish, their intelligence and curiosity make encounters with these animals a truly awesome experience.
These ocean giants can weigh as much as 5,000 pounds yet they reach this size on a diet of microscopic zooplankton. Just like the whale shark, mantas are filter feeders. Gliding through the water with their mouth open they swallow around 60 pounds of plankton a day. Despite being considered solitary creatures manta are often seen forming feeding aggregations. Perhaps the most spectacular form of feeding that can be observed with manta is when they start to chain feed. Lining up head to tail, the rays form a line of as many as several dozen individuals moving through the water column together along a horizontal plane. To see this is truly a sight to behold.
Furthermore, manta can also be seen in large numbers at ‘cleaning stations’. Manta visit these stations so that parasites and dead skin can be removed from their bodies. They rely on various types of small fish to clear their skin. Individual manta can be seen hovering in strong currents as fish feast on the giants unwanted hitchhikers. Unlike most fish mantas give birth to live pups, popping out one or two little manta pups every other year, conveniently rolled up like little burritos. Gestation lasts over one year meaning the mother must invest a lot of its energy into the pups development.
Moving on, manta ray have been iconic species to humans for thousands of years. The mochicas of ancient Peru who lived along the coast represented manta rays in their art and manta figures are present in various ceramic objects. Meanwhile Australian Aborigines were accustomed to capturing manta for consumption or for the manufacture of various materials. Modern day manta have circumglobal ranges in tropical and sub-tropical waters. They can be found in many different countries from Japan, Mozambique, Australia, Hawaii and many more coastal regions in this area.
Although widespread across the world’s oceans, their numbers are in rapid decline. The rate of population reduction appears to be high in several regions, up to as much as 80% over the last three generations (approx. 75 years), and globally a decline of 30% is strongly suspected. Unfortunetly we just don’t have accurate data on these mysterious creatures and a lot of the population data comes from the trade in manta products leaving us to estimate wild population sizes.
Following on, both species of manta are currently listed as vulnerably by the International Union for Conservation of Nature. Humans are putting enormous pressure on manta ray populations. Threats include pollution, entanglement in fishing nets and direct harvesting for their gill rakers. The pressure induced by humans is not helped by the manta life history attributes, their slow reproductive rate exacerbates any exploitation.
The greatest threat to manta rays is over-fishing. Mantas were once captured by fisheries in California and Australia for their liver oil and skin, however this practice has been stopped due to the species population decline. Unfortunately for many humans the more endangered an animal becomes, the greater their desire to possess or consume it becomes. Diminishing stocks drive a lucrative trade (often illegal) for those willing to risk their livelihood for the sale in manta products.
Much like many other animals products that are being illegally traded, the purpose is for traditional Chinese medicine. Gill plates, or branchial filaments, are the thin cartilage filaments that enable manta to filter zooplankton out of the water. Retailers claim that just as the rays use gill plates to filter plankton, they can aid in the detoxification and purification of the consumer by filtering disease and toxins from the body. The frustrating thing is that this trade is not ancient at all, the first reference in the traditional Chinese medicine texts that mention manta gill plates date back only to 1976. It is not for traditional purposes, it is falsification of a product to drive consumerism.
Furthermore, to fill the growing demand in Asia for gill rakers, targeted fisheries have developed in Philippines, Indonesia, Mozambique, Madagascar, India, Pakistan, Sri Lanka, Brazil and Tanzania. Thousands of manta are killed every year purely for their gill rakers. Another major threat to the manta is that of entanglement and subsequent suffocation in fishing nets. Because mantas must swim constantly to flush oxygen-rich water over their gills, they are extremely vulnerable to the fishing industries miles of nets that our put into our oceans. Bycatch and direct harvesting are causing manta populations to decline worldwide.
On the other hand, conservationists are doing all they can to turn the tide in the fight to save the manta. As of 2011, the manta ray became protected under the Convention on Migratory Species of Wild Animals. This means that the manta can be protected in regulated waters. In 2013 CITES included manta rays in their Appendix II; heavily restricting any trade in manta products. Unfortunetly, this kind of protection is hard to enforce. Manta can move out of protected areas where illegal fishing boats can pick off manta to sell on the black market.
Perhaps a more effective conservation strategy is that of education. We must show local people that the manta is worth far more alive than dead. It has been suggested that over the course of a lifetime, each manta generates as much as $1 million in revenue for the tourism economy. Globally it has been estimated that direct revenue generated from manta ray tourism is US$73 million annually. However, just 10 countries account for 93% of that money. Conservationists should work on showing local communities how they too can profit by keeping their manta alive.
Anybody can help in the conservation of manta rays. Firstly we must make their products undesirable. Never buy any animal product that you know has not been sustainably obtained. Tourists can also help add to the scientific knowledge we have of the manta by updating their manta photos onto the mantatrust database. Each individual manta has a unique spot pattern on its underside. By documenting which individuals are out there, we can get a better idea of population trends. Using this technique in the Maldives alone, researches have built a photo-id database containing over 50,000 sighting of more than 4,500 individual mantas.
These giant rays are still very mysterious to the scientific community. We have very basic data of their life history such as their age at maturity, lifespan and other traits. Areas of key habitat use, migration corridors and population estimates are all underdeveloped. More research is needed to fully understand this creature. Unfortunately, we are in a race against manta extinction. We must tackle the illegal trade in manta products and show local people that they can make more money with tourism rather than killing the mantas and selling them to Asia. Although populations are rapidly declining, there is still hope for the manta ray. To loose such a magnificent giant from our oceans for the sake of profits would be disastrous. Making people understand the beauty of this creature is what we must do in order to conserve it and keep it in our oceans.