Imagine diving in waters off of East Coast Australia or the Maldives and a dark 29 foot angelic shadow covers you. Are you in heaven? No (well if heaven was a place on earth then it would be). The shadow over you would be one of 2 species of Manta Ray: the reef manta (Mobula alfredi) or the giant oceanic manta (Mobula birostris). You spot their cephalic fins, located at the front of their mouth, which look like devil horns, however you do not fret as they are filter feeders, and only consume plankton and krill which are filtered through their gill plates. Seeing the ray on its own would not be a concern as they are known to live alone or in small groups, only coming together to feed. So you sit on the ocean floor and observe the spectacle.
The manta ray is such a breathtaking animal. Until 2008 it was thought there was only 1 species, until it was observed there was in fact more than 1! The reef manta is found on the indo-pacific coastlines. They regularly revisit the same coral sites, transporting nutrients in their faeces to coral. The nutrients act as a fertiliser and drastically increase the growth of the coral. They are, however, much smaller than the giant oceanic rays at only 3-3.5 m long.
The giant oceanic rays can grow up to 4.5m long and are found in all the worlds major oceans, spending most of their life away from the coast lines. An interesting point to note about the oceanic rays is that the juvenile stage of their life is largely unknown. The discovery of a nursery off the coast of Texas, at the Flower Garden Banks National Marine Sanctuary was a key find for marine biologists.
Manta rays are known to have the largest brain size of any cold blooded fish. Studies have shown that they can recognise themselves in mirrors, and are able to create mental maps of their environment through smell and visual cues (showing that they have a highly developed long term memory). Even from a young age the young manta ray pups can survive immediately without parental care.
In the 50 years that manta rays live they can reproduce every couple of years and have 1 or 2 pups each litter. The gestation period is 12-13 months long.
The long gestation period coupled with threats such as over-fishing, being caught as by-catch, boat strikes, entanglement and natural predation has meant that the manta ray has been put on the IUCN red list as vulnerable. One of the most infuriating points (in my opinion), is the fact that the chinese medicine trade are the biggest buyers of manta rays because their gill plates are supposed to help treat ailments from high blood pressure to chicken pox, all which has little scientific evidence to back up the claims. The slow reproduction rates and the great longevity makes it hard for numbers to recover. Fortunately they have been protected by the convention on migratory species since 2011, and Ecuador, Mexico, Peru, the Philippines, and New Zealand all have bans in place but like many laws it is hard to enforce all the way out in the open ocean. As well as this, it has been found that the manta rays are worth $500 dead, compared to the $1 million dollars that one ray can contribute throughout its life, alive, to the tourist industry whether that is diving with them or manta spotting.
If you want more information then follow the links below!
Stay safe and just keep swimming!
Belinda VP :)