Earlier this week, the Giant Manta Ray and the Reef Manta Ray (the only two extant species of Manta rays) got some exciting news. Previously the Giant Manta Ray and the Reef Manta Ray were in the genus Manta, however DNA testing revealed they actually belong to the Mobula genus, a genus comprised of devil rays (White et al., 2017). If you missed the post all about the announcement, be sure to check it out: Big Changes for Genus Manta: Why Scientific Names Matter! Because of the recent news, I will be referring to the Giant Manta Ray by the new species name: Mobula birostris.
The Giant Manta Ray (Mobula birostris) belongs to the Mobulidae family, a subclass of elasmobranchii within the order Rajiformes. This family is a relatively small family of marine rays, however it is made up of the largest marine rays with very large, specialized pectoral fins that spread out like wings (Parker, 2008). The Giant Manta Ray has a body that is similar to a stealth jet. When the current is flowing, they are able to completely stop in the water and remain buoyant despite not having an air bladder like bony fishes (Perrine, 1997). Just like airflow over an airplane wing, when the water flows over the pectoral fin of the Giant Manta, lift is generated, keeping the Manta a float in the water column (Perrine, 1997).
Balshort, A. [Adri Balshort]. (30 December 2015). Komodo Manta Rays at reef cleaning station with fish picking off parasites [Video file]. Retrieved from https://www.youtube.com/watch?v=AXGsH2a8NZc
The Manta Rays (Giant and Reef) were once classified as a separate genus within the Mobulidae family due to their physical characteristics that make them appear different from devil rays. Manta rays have a larger mouth located at their snout tip rather than under their head like devil rays or eagle rays (Aetobatus narinari). Both species of Manta ray have short tails that lack a stinging barb. However some species of devil rays have a stinging barb, and eagle rays have short barb (Tricas, Deacon, Last, McCosker, Walker, & Taylor, 1997). Their heads are also bordered by two long lobe-like extensions of their pectoral fins called the cephalic lobes. These lobes are flexible and spiral around in front of their mouths to help funnel in plankton while filter feeding (Tricas et al., 1997).
Giant Manta Rays have a unique spot pattern that allows researchers to identify individuals in the field. Their bellies are typically pale or white to blend with the bright light from the surface above them. However each individual has a unique spot pattern on their bellies, like a finger print, that separate them from other individuals. Researchers have begun a photo-identification project to capture-recapture each individual and learn about their movements. This allows researchers to track individuals without the use of invasive tracking devices (Marshall & Pierce, 2012).
Giant Mantas are not the only species with unique patterns used in photo-ID projects. Several species present with unique spots or dorsal fin marking that allow for each individual to be cataloged and tracked for decades when GPS tagging methods typically only last 1-2 years. Photo-ID projects also allow for citizen scientists- like you- to get involved in on-going studies by submitting your own photos to sites ECOCEAN Global Whale Shark Database (Marshall & Pierce, 2012).
The IUCN Red List of Threatened Species has the Giant Manta Ray listed as Vulnerable. While the Giant Manta is found globally throughout circum-tropical to semi-tropical waters, the populations appear to be fragmented likely due to resources and habitat needs of this species (Marshall et al., 2011). In the last three generations (approximately 75 years) we have seen population declines of nearly 30% worldwide. Sustained fishing pressures, both caused by direct targeted pressure and bycatch, have been isolated as cause of population decline (Marshall et al., 2011).
However recent years has seen a shift in thinking. Ecotourism such as dive tourism with the Manta Rays have demonstrated that sustainable tourism that is carefully managed can significantly enhance the economic value of a species compared to the short-term returns of the fisheries industry (Marshall et al., 2011). There have been some arguments against ecotourism. For example, some have argued that sustained tourism could impact behavior on an individual or population level, or that an increased number of boats and tourists could critically impact the habitat these Mantas depend on (Marshall et al., 2011). While the ecotourism industry continues to grow, these potential impacts should be closely monitored.
Wing Span: Up to 16.5 feet (5 meters)
Weight: Up to 3,000 lbs (1,360 kg)
Habitat: Inshore, Close to Coast, Reef Fringes, Deep Water, Open Ocean
Depth: Often observed at the surface. Tracking has revealed depths as are as 3,300 feet (1,000 meters).
Gestation: 12 to 13 months
Litter Range: 1 to 2 pups per litter
Home Range: Tropical waters world wide
Diet: Plankton, Filter Feeder
IUCN Status: Vulnerable
(Marshall et al., 2011; Tricas, et al., 1997)
Hope you enjoyed our featured species of the week! If you missed last week’s installment, be sure to check out the Longnose Sawshark (Pristiophorus cirratus). Let me know what species you’d like to learn more about by leaving me a comment.
Featured Image Source
Aussie Divers Phuket (Photographer). (July 2015). Giant Manta Ray [Digital Image]. Retrieved from https://www.aussiediversphuket.com/
Marshall, A. D., & Pierce, S. J. (2012). The use and abuse of photographic identification in sharks and rays. Journal of fish biology, 80(5), 1361-1379.
Marshall, A., Bennett, M.B., Kodja, G., Hinojosa-Alvarez, S., Galvan-Magana, F., Harding, M., Stevens, G. & Kashiwagi, T. 2011. Manta birostris. The IUCN Red List of Threatened Species 2011: e.T198921A9108067.
Perrine, D. (1997). Mysteries of the sea. Lincolnwood, IL: Publications International.
Tricas, T.C.; Deacon, K.; Last, P.; McCosker, J.E.; Walker, T.I.; Tayloer, L. (1997). The Nature Company Guides: Sharks and Rays. (L. Taylor, Ed.). Hong Kong: The Nature Company, Time Life Books.
White, W. T., Corrigan, S., Yang, L., Henderson, A. C., Bazinet, A. L., Swofford, D. L., & Naylor, G. J. P. (2017). Phylogeny of the manta and devilrays (Chondrichthyes: mobulidae), with an updated taxonomic arrangement for the family. Zoological Journal of the Linnean Society, 82, 65–73. http://doi.org/10.1093/zoolinnean/zlx018