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31.01.12

THE CONSERVATION COLUMN: Project Manta

Dr Kathy Townsend, Earthwatch scientist and chief investigator for Project Manta, Moreton Bay Research Station, University of Queensland, talks about her work with manta rays, from ascertaining behavioural patterns to protecting their future...

Manta ray - the name brings to mind an image of a large, graceful creature that seems to fly, rather than swim, through the water. Their beauty is featured in almost every marine documentary and divers spend thousands of dollars for the privilege of being in the water with them. With this in mind, you may be surprised by how little is know of these iconic creatures.

With a wing-span reaching between five and seven metres across, these gentle giants are closely related to sting rays, but without the stinging barb or crushing teeth. They are the largest bodied plankton-feeding species that forages in the warm waters of Australia’s Great Barrier Reef.

It was only two years ago that scientists discovered that there are two species of manta rays. Prior to that, it was thought that there was a single species only. This is equivalent to discovering a new species of elephant, and excited the marine biology community.

The oceanic manta (or Manta birostris) was the name originally given to the entire group. Ironically, it turned out that the newly described species, the reef manta (Manta alfredi), is the most common species and the one we most often see in Australian waters.

Unfortunately, very little is known about the biology of either species. Basic questions remain unanswered. Questions like: how long do they live? How often do they reproduce? At what age do they reach sexual maturity? How many of them are there? How many young do they produce? And how fast do they grow?

We know that mantas can be found around North Stradbroke Island, off Brisbane during the summer months, but then they disappear in the winter months. This leads us to questions of conservational importance such as: Why do they undergo seasonal migrations? How far do they go? Do they cross international boundaries?

 

While large, mantas are also graceful

 

Movement across international boundaries is a big concern, with manta rays and their relatives being targets for fisheries in south-east Asian waters. Mantas and their relatives are harvested for their gill rakers (known as Peng Yu Sai) for use in traditional Chinese medicine. The industry has been estimated to be worth over US$11.3m per year. Due to this increasing pressure on populations, both species of manta rays have now been listed as vulnerable on the IUCN red list for endangered species.

The lack of basic biological data on these beautiful, yet vulnerable creatures in Australia inspired “Project Manta”, a multidisciplinary team of academics from the University of Queensland and CSIRO (the Commonwealth Scientific and Industrial Research Organisation).
With help from industry partners, Earthwatch volunteers and recreational divers, Project Manta is creating a photographic identification database. With over 500 individuals identified so far, we are using the information to estimate population sizes, habitat usage, growth rates, reproductive rates, sex-ratios and to piece together a snap-shot of broad movement patterns.

Project Manta has also invested heavily in tracking technology, using state of the art acoustic and satellite tags to determine broad scale movement patterns of mantas. The tracks generated by the satellite tags are overlaid on oceanographic features such as sea surface temperatures and chlorophyll a concentrations (which is a proxy for the manta’s favourite food source - plankton). By combining these three pieces of information, we not only find out where the mantas are going but more importantly why.

The connection between manta ray movement patterns, food and oceanographic features is important to understand, as plankton abundance is predicted to be heavily impacted by climate change. Mantas are large bodied creatures, and disruptions to their food sources will affect them on many levels. As such, manta rays are currently acting as the canary in the cage for our precious marine environment.

For more information or to find out how you can help Kathy and her team in their vital research visit the Project Manta expedition page on the Earthwatch website.

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