If you are a diver or snorkeler, you may have had the privilege to cross paths with the mysterious manta ray (Manta spp.). These large, graceful and harmless creatures are good at leaving one with a sense of awe and amazement as they glide silently through the water on their triangular pectoral fins, dwarfing most creatures in their path. Besides their large size and preference for being in the water column (as opposed to the ocean bottom), a good way to tell mantas from other rays is their distinctive forward fins or cephalic lobes. These are long flaps that flare into a tunnel when the manta is feeding; they help direct water into the manta’s mouth so it can filter its favorite food: zooplankton, shrimp and sometimes small fish. When not feeding, mantas often roll these fins up, giving the appearance of horns.
Until recently, mantas that hang out near reefs and mantas in the open ocean were considered the same species, Manta birostris. However, in 2009 it was discovered these were actually two species of manta ray1. There is the giant oceanic manta, M. birostris and the reef manta, M. alfredi. The oceanic manta is larger than the reef manta, with a maximum wingspan of 7 m and weighing up to 2 tons. The reef manta, though not as large, still has a very respectable maximum wingspan of 5 m and can weigh up to 1.4 tons.1 Mantas are also very smart, boasting the largest brain to body ratio of any fish! If you are lucky, one may decide to come over and check you out while diving.
Both manta species can be found worldwide between 40ºN and 40ºS, although their populations appear highly fragmented and sparse2. They can live several decades but are slow to reproduce, producing only one pup (called a burrito) every two to three years2,3. This means that when populations are depleted, they will take a long time to rebuild. Right now the greatest threat to manta rays is from fishing. They are targeted for their gill rakers and as food, or captured as bycatch3. As a result, the IUCN lists mantas as vulnerable on their Red List2,3.
Where to find mantas
In Australia, we are lucky to have both the oceanic and reef mantas occur in our waters, although the reef manta is the most commonly sighted. Populations of the reef manta extend from Perth in Western Australia around the north, and all the way to the Solitary Islands in New South Wales4. It is the reef manta we usually see on the reefs off of Queensland and New South Wales. They travel less than the oceanic mantas and can often be spotted at a favorite cleaning station. In case you haven’t seen one before, cleaning stations are usually rocks or coral bommies where small fish live that will eat the parasites, dead skin and bacteria off of larger marine animals. Some observers estimate mantas can spend between 2 to 8 hours a day at cleaning stations! And when a good cleaning station is found, word tends to get out, with some stations attracting large aggregations of mantas.
Manta cleaning station at Lady Elliot Island.
So when is the best time to see mantas? In Queensland and Northern New South Wales, the reef mantas have seasonal preferences. They hang out in the southern Great Barrier Reef near Lady Elliot Island year round, with their numbers peaking in the winter. From mid-spring to mid-autumn many move south and are commonly seen off the SE Queensland coast, near North Stradbroke Island. And from late summer to mid-autumn they are also in Byron Bay.4 Increased food availability is likely one of the main drivers for their movements.5
Although reef mantas are a common sight off Queensland, little was known about their population biology and ecology before a research project called Project Manta took shape in 2007. The project started at The University of Queensland, Brisbane, with industry support from Earthwatch Institute, Lady Elliot Island Eco Resort, and Manta Lodge and Scuba Centre. Since that time, Project Manta has expanded to cover all of Australia, teaming up with researchers from Murdoch and Deakin Universities, Ningaloo Marine Interactions in Coral Bay, WA and receiving generous support from ARC Linkage grants, Austral Fisheries and TG Kailis Marine Conservation Fund.
The project involves a large citizen science component, where photos from divers and snorkelers are used to help identify individual mantas, estimate population sizes and migration routes. As a result of this project, many knowledge gaps in the basic life history of the reef manta have been filled in such as their distribution, population size, and feeding ecology. Recent findings from this project include an expansion of the previously known range of oceanic mantas to off the coast of Tasmania.6 However, there is still a lot that remains to be learned, and continued monitoring of these gentle giants is needed to ensure populations are still around for generations to come.
How you can help
If you are a diver or snorkeler, you can help Project Manta learn more about mantas and be an active part of this exciting research. All you need is an underwater camera. Mantas can be identified by unique pigmentation markings on their underside. If in the water with a manta, try to get a photo or video of the underside that includes these three target areas:
- Between the gill slits
- The belly
- The pelvic fins
If you are in the water with a manta, please observe these guidelines to avoid stressing them out:
- Leave plenty of space for mantas to maneuver
- Stay low (close to the seafloor), whilst remaining mindful of your surroundings so not to damage the reef
- Be calm and patient – let the manta see you before approaching
- Keep at least 3 m between you and the manta – let the manta come to you of its own free will
- Avoid using a flash when photographing them
- Avoid touching or attempting to ride mantas – this removes their protective mucus coat
- Be mindful of your bubbles if diving – these can startle or make a manta feel trapped
- Continue to learn more about these magnificent creatures and share your new knowledge with friends and family!
1 Marshall, A. D., Compagno, L. J. V. & Bennett, M. B. Redescription of the genus Manta with resurrection of Manta alfredi (Krefft, 1868) (Chondrichthyes; Myliobatoidei; Mobulidae). Zootaxa 2301, 1-28, (2009).
2 Couturier, L. I. E. et al. Biology, ecology and conservation of the Mobulidae. J. Fish Biol. 80, 1075-1119, (2012).
3 Marshall, A. et al. Manta alfredi The IUCN Red List of Threatened Species 2011, e.T195459A8969079, (2011).
4 Couturier, L. I. E. et al. Distribution, site affinity and regional movements of the manta ray, Manta alfredi (Krefft, 1868), along the east coast of Australia. Mar Freshwater Res 62, 628-637, (2011).
5 Jaine, F. R. A. et al. When Giants Turn Up: Sighting Trends, Environmental Influences and Habitat Use of the Manta Ray Manta alfredi at a Coral Reef. PLoS ONE 7, e46170, (2012).
6 Couturier, L. I. E., Jaine, F. R. A. & Kashiwagi, T. First photographic records of the giant manta ray Manta birostris off eastern Australia. PeerJ 3, e742, (2015).