2008 was the year that scientists realised that the humble manta ray (Manta birostris) might not be a a solitary species as initially thought. First described by the naturalist Johann Julius Walbaum back in 1792, the manta ray grows in excess of 7.6m (>25ft) and weighs up to 2300kg (~5,000lbs) – about 4/5ths of the weight of a Hummer SUV.
Andrea Marshall, a PhD student at the University of Queensland has been studying the ecology of manta rays in Mozambique for over 5 years, and his since identified over 900 individuals. Using genetic and morphological markers, her research showed that there are at least two different species of manta ray: the smaller common manta ray (as in the above video clip) specific to coastlines and coral reefs around the globe, and a second larger species of manta ray that is more elusive, and has broad migratory habits.
As Andrea points out, manta populations are frequently small in size, and intense fishing pressure can threaten the stability of local populations in a few years. The more common manta ray is particularly susceptible to unsustainable localised fishing pressures due to their restricted migratory ranges, whilst the larger migratory species causes problems with population estimates and conservation management to it’s broad home range. Manta rays are in increasing danger from the effects of fishing, and cartilidge and branchial plates (the characteristic mandibles or ‘lobes’ that protrude from the mouth) are sold for upto $50USD per kilo in Asia.
I filmed the video at the top whilst on fieldwork in the central Great Barrier Reef last year. The two manta rays (the smaller ‘common’ type) were feeding on an upwelling of plankton off the edge of the reef crest, and were happy for us to swim between them without being disturbed. Visit the homepage of the the Manta Ray & Whale Shark Research Centre in Mozambique to read more about the conservation and protection of these amazing creatures, or check out their blog (“The latest news on the biggest fishes“) over at wordpress