Manta Ray Research Program 2001- National Geographic & Lady Elliot Island
What we know about Manta Rays
The Manta Ray, the next largest marine species on the Great Barrier Reef following the whales and the whale sharks, can equally be described as both charismatic and 'mega'. They grow to 5 metres in width and weigh several hundred kgs. They are a not-to-be-forgotten experience for any snorkeller or diver who is fortunate enough to see one while underwater. Divers often come into contact with these animals on an ad hoc basis and there are many references to swimming with mantas in the popular literature.
There have been no studies to date about the ecology or populations dynamics of this remarkable species of ray. There is little information about their current status, and world-wide there is next to no information about these creatures.
Possible threats to the species in Australia have not been catalogued, however threats are most likely to be in the form of activities or processes that impact on water quality or disturb habitat. They are not recorded as any significant form of by-catch from commercial fishing operations in Australia, although other rays species are occasionally caught in trawl nets.
This is possibly due to the fact that:
- Manta rays are an active swimmer, occupying all parts of the water column, particularly mid water and near surface - whereas bottom dwelling and more sedentary species of rays would be more susceptible to capture by trawl operations
- Manta rays may have little affinity for open deep water and prefer areas in contact with coastal or reef/island features, areas where trawlers do not work. While little is known about the current status of manta rays in Australia it is assumed because their distribution appears to cover a broad geographic area and there are few identified threats, that their populations are secure. Manta rays are not currently protected by any fisheries legislation in Australia.
The average Manta Ray
|3 - 7 metres|
||1000 - 1300 kg|
||Ovoviviparous (babies are wrapped in a thin-shell that hatches inside the mother)|
||Plankton (Filter feeders)|
(Dimensions based on mature male)
Sonic Tags (Underwater Sonic transmitters) make it possible to have a better understanding of movements of individual animals on an ongoing basis.
An underwater receiver, or a series of receivers, can be located at strategic locations along the reef slope. They will record when a tagged animal is within a certain distance from the receiver. This signal is constant as long as the animal remains within the reach of the transmitter. Once the animal moves beyond the transmission distance the signal will cease. (See diagram on the right)
Similar transmitters are currently being used in the Coral Sea as part of a home range study of reef sharks at Osprey Reef.
At Lady Elliot Island, sonic transmitters be attached to three manta rays. the range will be somewhere between 500 and 1000 metres
Size of the transmitter is 48mm long x 16mm diameter. The tags will be delivered via a hand spear apparatus by divers on scuba gear, and the tags will be inserted in the fleshy area on the back of the animal. Similar methodology has been used for tagging white pointer sharks in the Spencer Gulf area of South Australia.
It is expected that apart from the initial 'fright' of being jabbed with the tag, disturbance to the animals will be minimal. Field work for this part of the project was undertaken in early May 2001.
One of the largest, yet least-known of fishes, the manta ray is found mainly in tropical waters throughout the world. Australian Geographic staff writer Liz Ginis travelled to Lady Elliot Island on the Great Barrier Reef with photographer Mark Spencer in Manta ray to follow an Australian Geographic-sponsored study of the manta's behaviour and movements.
Great Barrier Reef Marine Park Authority marine biologist, Mark Simmons and Australian Geographic photo-journalists spent several weeks on Lady Elliot Island capturing data and images of these naturally inquisitive, marine creatures, that can grow up to nine metres (29 feet) in diameter (equal to the length of two family cars bumper to bumper).
Research into the anatomy of the manta ray has concluded that this graceful creature has one of the largest brains of all fishes - which explain the inquisitive nature of these creatures.
The research program also found that the reef surrounding Lady Elliot Island is a permanent home to a 40 strong population of manta rays.
The photographic story now graces the cover of Australian Geographic (Issue 66 - out now). Copies are available through Australian Geographic Retail stores in Australia (price $14.95).
The Research Project
Manta rays are an enigma; little to nothing is known of their range, breeding cycle, migratory habits and social behaviour. Through this research we hope to shed light on all of these things.
This project is a population ecology and home range study of the manta rays from the Lady Elliot Island area using photo-id techniques and underwater tracking systems. Analysis will also be undertaken of social interactions within the species. Observations will also be made, where possible, of human/manta interactions in order to better develop guidelines for interacting with these animals
The Research Team
Mark Simmons has nearly 20 years experience working with Australia's native flora and fauna, particularly on the Great Barrier Reef. For six of those years he worked as a Marine Parks Ranger with the Queensland National Parks & Wildlife Service, which allowed him to specialise in underwater research, monitoring and photography. Contact Mark Simmons
If you have a question about this research project, send it via email to Mark at Great Barrier Reef Marine Park Authority.