Sunday, 12 October 2008

Save Our Seas Foundation - Manta Rays: A new species?

Manta Rays: A new species? A second, and possibly third, species of manta ray has been discovered in the World’s oceans. This is the biggest news to date to come out of ray research, and its importance is the marine equivalent of discovering an unknown species of elephant. The discovery however, has implications that go far beyond the breaking news of scientific journals, as it will deeply affect real world conservation ideas and policies.

Andrea Marshall diving with a manta
Andrea studies a manta ray off Mexico.
For the past five years the Save Our Seas Foundation (SOSF) has sponsored Andrea Marshall, a PhD marine biologist in a quest to make advances in the scientific knowledge of these winged beauties of the sea, whose large triangular pectoral fins can span almost 8m in width and whose weight can reach over 2000kg. Manta rays, which are totally harmless and do not possess a stinging barb, are the largest of over 500 different species of rays and skates, and although divers have noted variations in physical appearance they were previously believed to be the same kind.

After suspecting the existence of a second species Andrea began studying other populations across the globe. Through genetic and morphological analysis she confirmed that there is indeed a second, and possibly a third, species of manta ray that exists across temperate, tropical and subtropical waters worldwide. The two species have mainly overlapping distributions, but their lifestyles differ greatly; one is migratory and the other is resident to particular areas along the coast.

Other differences between the two species lie in their colour, skin texture, reproductive biology, and the presence of a non-functioning type of sting on the tail of one of the species.

The smaller, more commonly known manta ray, resides in the same areas year round 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. Due to their residential nature they face a grave threat from unsustainable fisheries, as other manta rays will not replace a dwindling population, making their regional extinction a likely possibility.
Smaller manta ray species
The more common resident manta ray.
(Photo © Thomas Peschak)

Larger migrant manta ray
The larger species of manta ray.
(Photo © Andrea Marshall)
Far less is known about the larger species, as it appears to be more migratory and elusive, shying away from divers rather than seeking interaction as its smaller cousin often does. Andrea has only ever witnessed it arriving at sea-mounts or at particularly productive areas along the coastline to feed on plankton before disappearing into the blue once again. Little is known about its behaviour or migratory patterns, though it appears to be targeted heavily by fisheries, particularly in Southeast Asia, where thousands are killed each year.

The discovery of two distinct species has huge implications for the conservation management and protection of these mysterious gentle giants.

The larger, ocean wanderer knows no borders, making collaboration between countries on its protection essential, whereas protective measure within countries must be enforced to avoid resident manta ray populations crashing. Habitat degradation, harassment by boat traffic and even divers who interact with them at critical habitats such as cleaning stations and breeding areas are other threats these graceful animals face. They also fall victim to ghost nets and are killed alongside many other marine creatures as by-catch.

Andrea’s obsession with sharks travelled with her from the tender age of five until university when she discovered how little was known about their cartilaginous cousins, manta rays. Undeterred by the difficulties such research would involve she sold her belongings and in 2003 moved to a small coastal village in southern Mozambique, to become the first marine biologist to study manta rays off the African coast. Through her observations of the unique spot patterning on the ventral surface of each ray Andrea has identified over 900 individuals on a single reef, and she believes southern Mozambique may boast the largest known population of manta rays in the world.

Discoveries about the reproductive behaviour of these highly social and inquisitive creatures have also been an important outcome of Andrea’s research. Manta rays are now known to give birth to a single large offspring of about 1.4m after a year of gestation and, once reaching maturity at about 4m across, typically produce a pup every other year. Elaborate and sophisticated courtship displays are performed and they may communicate with one another using specific body posturing and perhaps sound.

Andrea Marshall talks about her discovery
Watch a video of Andrea Marshall talking about her discovery.
SOSF aims to learn more about the role of marine species, particularly sharks and rays, and through this knowledge it hopes to raise awareness and conserve the marine realm. Andrea’s many hours underwater have produced information critically needed for the protection of these threatened animals. We now know that there are at least two species, but we need to know a great deal more about their population structure and distribution so that we can devise and implement improved protection measures.
Learn more about Andrea's research project in Mozambique here.

Save Our Seas Foundation - Manta Rays: A new species?