Giant manta ray (Manta birostris)

TAXONOMY AND NAMING

Class : Chondrichthyes
Order : Myliobatiformes
Clade : Neoselachii
Family : Mobulidae
Genus/species : Mobula birostris
Common names :
English : Giant manta ray
Spanish : Mantarraya
French : Raie manta

Giant Manta Ray (Mobula birostris)©Andrea Marshall

ANATOMY AND MORPHOLOGY

The Mobulidae family are planktivorous elasmobranchs comprised of manta and devil rays (ten extant species), with a circumglobal range ; all are recognised by the cephalic lobes used for feeding, a stingless tail, and wing-like pectoral fins. The oceanic manta ray, attains a maximum disc-width of 680 cm, but averages between 400 – 500 cm. Mantas are filter feeders. Their frontal lobes help driving water to their mouths where planktonic organisms are filtered.

BEHAVIOUR AND LIFE HISTORY

Like other elasmobranchs, the Giant manta has long gestation periods and low fecundity, which makes them highly vulnerable to any kind of exploitation such as fishing. In addition, a low rate of exchange of individuals between populations is suggested, which makes it even more vulnerable.

Mobulid rays are capable of making significant movements across broad geographic ranges throughout pelagic and coastal waters. Although populations appear to be fragmented, and across ocean-basin travels are likely to be rare, records of individual large-scale movements across jurisdictional borders and into the open ocean support the fact that the species are capable of large movements.

DISTRIBUTION AND ABUNDANCE

Oceanic manta rays inhabit areas of high productivity across tropical, sub-tropical and temperate waters. They are observed along coastlines, islands, offshore pinnacles and seamounts, or observed surface-feeding both inshore and offshore.

When National Marine Fisheries Service examined all the available scientific and commercial information for a critical habitat designation for giant manta rays in 2019, sightings were rare throughout the U.S. Caribbean.

Giant manta ray (Manta birostris) geographic range©IUCN red list

THREATS

M. birostris is considered highly susceptible to anthropogenic threats. Being a mobile, pelagic species that is often observed feeding near the surface ; mantas are highly susceptible to direct and by-catch fishing incidents. The greatest threat facing all mobulid species are fisheries, either as targets or bycatch. The demand for this species has grown in recent years. Mantas that use to be considered bycatch are now kept and processed. An illegal market has been also identified mostly to export manta and mobula parts to Asian markets.

Aside from their consumptive use in the gill plate trade and as meat (for bait and local consumption), manta rays are the focus of highly lucrative ecotourism “swim-with” experiences. Manta rays can be disturbed by divers’ poor buoyancy or divers approaching too close to the station, which in turn, can also cause damage to the fragile coral ecosystem.

Critical juvenile habitats (often shallow, more protected areas of the reef) are vulnerable to anthropogenic pressures, including pollution and habitat or coastal erosion. Increased anthropogenic activity in coastal regions results in species’ heightened exposure to boat traffic and strikes, mooring lines, and fishing activities, marine debris and storm water runoff. Climate change is an increasing stressor to oceanic manta rays. Manta rays show sensitivity to large-scale climatic variability.

ABUNDANCE AND CONSERVATION STATUS

Giant Manta Ray was reviewed as a species displaying a strong decline especially in areas with heavy fishing pressure. Rapid local declines have been noted in sightings records and landings where they are targeted or caught as bycatch ; these range from 71 to 95% declines over 13- to 21-year periods (all less than one generation length of 29 years). It is suspected that the Giant Manta Ray has undergone a population reduction of 50–79% over the past three generation lengths (87 years) and a reduction in area of occupancy due to suspected local and regional extinctions. In areas where Giant Manta Ray are protected, the sighting trends appear stable.

In 2020, Manta birostris was classified as “Endangered” due to a suspected population decline of 50–79% over the past three generations, and a reduction in area of occupancy due to suspected local and regional extinctions.

SPAW Protocol : yes since 2017_Annex III

CITES : yes_Annex II

CMS : yes_Annex I

Bibliography
Proposal for the uplisting of the giant manta ray from Annex III to Annex II of the SPAW Protocol