IMAGE: The top image shows the new species of migratory manta ray and the bottom image shows the resident species of manta ray

Manta rays (Manta birostris) are giant cartilaginous filter feeders of the order Rajiformes, which includes skates and many other species of rays. They are the largest of all ray species and are often associated with pelagic or coral reef waters (oceanodromous or residents of reefs). Giant manta rays are distributed worldwide and remain a scientific mystery. Certainly, there are more species to be discovered, and many believe that more species exist.

A marine study in Mozambique by Andrea Marshall aims to gather more information on giant manta rays. She is a PhD marine biologist sponsored by the Save Our Seas Foundation (SOSF). Recently, Andrea’s work has revealed a new species of manta ray through genetic and morphological studies.

The SOSF study has also observed reproductive behavior. Giant manta rays have a very low, minimum population doubling time, so the large marine animals are vulnerable to overfishing since they “are now known to give birth to a single large offspring about 1.4m in size after a year of gestation and, once reaching maturity at about 4m across, typically produce a pup every other year.” Modern fishing pressure may influence how large these rays can grow, since recent research on whale sharks shows that because “humans have over-exploited the whale shark — the world’s largest living fish — to such a degree that the ocean giants are actually shrinking in size.”  Giant manta rays are often bycatch in the industrial tuna fisheries as well. From the Telegraph.co.uk, United Kingdom:

The manta now confirmed as a distinct species is the larger of the two and shys away from divers rather than seeking interaction.

Little is known about its lifestyle or migration patterns and Marshall has only ever witnessed it arriving at sea-mounts or at particularly productive areas along a coastline to feed on plankton before disappearing back into the deep ocean.

Although both species are harmless the larger, migratory manta has retained the presence of a non-functioning sting in its tail.

Other differences between the two species lie in colour, skin texture and reproductive biology. The smaller of the two species is not migratory and is often encountered at coral reefs where they congregate to be cleaned by parasite-eating fish in locations such as Hawaii, the Maldives, Mozambique, Australia, Japan and the Island of Yap.

The more commonly known ray resides in the same areas year round making it particularly susceptible to fishing pressure. If resident rays continue to be fished unsustainably they face localised extinction.

The larger rays, migrants and ocean wanderers which makes conservation management difficult, are fished heavily particularly in southeast Asia, and thousands are killed each year.

Many fall victim to ghost nets and are killed alongside other marine creatures as by-catch. Rays are also threatened by habitat degradation, boat traffic and disturbance by divers.

This old image illustrates the size that giant manta rays can reach. This particular specimen was caught of the coast of New Jersey:

This is an image from one of my presentations on trawl fisheries when I worked for NOAA/NMFS. I cannot remember where I found the image (it may be a Greenpeace image), but it shows a manta ray as bycatch amongst some type of Scombridae species, possibly skipjack tuna. Note the Leatherback sea turtle (Dermochelys coriacea) in the background too.

On the Net: Save Our Seas Foundation – Manta Rays, Mozambique
On the Net: The American Elasmobranch Society

Image Found Here
Image Found Here

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