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06
OCT
2017

5 Things you didn’t know about manta rays

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1. How to determine the sex of a manta ray?

Female manta rays have 2 pelvic fins that conform to the contour of their body whilst male, in addition to those 2 pelvic fins, have 2 claspers. Claspers start out as small fins that grow beyond the pelvic fins and become hard and calcified as the male reaches sexual maturity. This is why juvenile male mantas can be tricky to identify and are many times mistaken for females.

Female manta rays tend to be larger and often more ‘friendly’ than males. If you encounter a large manta around a cleaning station, it is most likely a female. Female mantas spend much more time than males in cleaning stations getting cleaned by the small fish. The males, knowing this, hang around the cleaning stations waiting for the females to show up.  So next time you are at a cleaning station, pay attention to the sex of the manta ray to know if it’s here to be cleaned or to pick up a female! 😉

2. How to identify a manta?

The spots and blotches on their belly are the mantas’ version of  fingerprints and allow manta researchers to identify individual manta rays just by photographing their ventral surfaces.

3. Clever ones!

Manta (and mobula) rays have the largest brain of all fish – their brains are disproportionately large when compared to their body size.

To keep these large brains warm, mantashave an amazing counter-current heat exchange system going on within their veins and arteries, allowing them to become effectively warm-blooded, or at least keep their temperature more stable than most fish.

Mantas have been recorded to make very deep dives where sea temperatures decrease rapidly. This system of blood vessels is therefore likely to be important in helping to keep the manta’s brain functioning effectively even in these colder temperatures.

They display intelligent behaviour, such as coordinated and cooperative feeding. Moreover, the mantas’ high degree of social interactions and curiosity towards us, divers, would suggest there is a lot more going on behind those captivating eyes than is currently presumed.

4. Before 2009, we thought there was only 1 type of manta ray

Mantas belong to the Elasmobranchii, which include sharks, skates and rays, and are part of the Mobulidae family of Devil rays. Their subfamily of Myliobatidae includes two species of Manta and 9 species of Mobula devil rays.

It wasn’t up to 2009 that Dr. Marshall discovered there were actually 2 species of manta rays. The more Dr. Marshall swam with the manta birostris, the more she noticed the differences between manta rays that frequent reefs and the open ocean are, both in their behaviour and markings. The giant oceanic mantas retained the name Manta Birostris, while the reef mantas were newly named Manta Alfredi, in tribute to Alfred Whitley, who first scientifically described manta rays in the 1930s.

The two species are distinguishable by external coloration on their dorsal and ventral body surfaces. Dorsal (topside) patterning on Manta Birostis forms a ‘T’ pattern and there is a distinctive black/white division; whilst Manta Alfredi dorsal patterns form a ‘Y’ pattern fading into the black colouration on their backs. Their ventral surface is also different. Manta Birostis has almost no spots except for a small central cluster which is usually present near the tail on the manta’s belly, whilst on  Manta Alfredi those unique spots can be found all over the ventral surface.

Manta Alfredi is a more tropical, coastal, residential, smaller (around  5 m width) and schooling species compared to M. Birostris, and is found around coral and rocky reefs, tropical island groups and atolls.

Manta Birostris is a more cold-water tolerant, pelagic, migratory, larger (around 7 m width) and solitary species, which is commonly sighted at offshore pinnacles, seamounts and oceanic islands.Mantas evolved from sting rays. Manta Birostis is the only one that has retained a vestigial sting on their tails.

5. The Marquesas Islands are one of the few places in the world to find both species

In most regions globally where manta rays have been recorded, usually only one species occurs with regularity. However, the Marquesas boast significant populations of both species, which appear to be utilizing different habitats. You can specially encounter both of them at Nuku Hiva. Dive the Marquesas by live aboard with the French Polynesia Master.