|Scientific Name:||Mobula thurstoni|
|Species Authority:||(Lloyd, 1908)|
Mobula lucasana Beebe & Tee-Van, 1938
|Red List Category & Criteria:||Near Threatened ver 3.1|
|Assessor(s):||Clark, T.B., Smith, W.D. & Bizzarro, J.J.|
|Reviewer(s):||Kyne, P.M., Notarbartolo-di-Sciara, G., Fowler, S.L. & Compagno, L.J.V. (Shark Red List Authority)|
Mobula thurstoni is probably circumglobal in all temperate and tropical seas, but its distribution is not completely defined. It is usually pelagic in shallow, neritic waters (<100 m). Mobula thurstoni is highly susceptible to gillnets and is known to be landed in Indonesia, México and the Philippines and likely elsewhere across its range. It is a component of the inshore pelagic tuna gillnet fishery in Indonesia where the flesh and gill rakers are utilised. The high value of gill rakers, which are dried and exported for the Asian medicinal market has resulted in recent dramatic increases in fishing for mobulids in Indonesia with targeting now occurring. In the Gulf of California, México, the species is landed in directed artisanal elasmobranch fisheries and as bycatch. In the Philippines the species was historically targeted in a mixed mobulid fishery, and while a ban on fishing for devil rays is presently in place, enforcement is insufficient and landings still occur. Information on catches is not available from other parts of its range, but it is likely being captured elsewhere, certainly in Southeast Asia where target fisheries for whale sharks and manta rays operate. While little species composition data is available, limiting the assessment of current fishing pressures on populations, increased targeting and catches in Indonesia, which may mirror increases elsewhere, is cause for great concern and requires urgent international conservation measures as the species is unlikely to be able to tolerate present levels of exploitation. Its large size (to 180 cm disc width) and fecundity of a single pup per litter emphasizes the limited reproductive potential and low productivity of this species. Mobula thurstoni is assessed as Near Threatened globally, but Vulnerable throughout Southeast Asia where catches and demand are increasing. Vulnerable listings may also be warranted elsewhere if future studies show declines in populations where fished.
|Range Description:||Probably circumglobal in tropical and subtropical waters, but thus far confirmed from scattered locations in the Indian, Pacific and Atlantic Oceans.|
Native:Australia (Queensland); Brazil; Chile; Costa Rica; Côte d'Ivoire; Ecuador; El Salvador; Eritrea; Guatemala; Honduras; India; Indonesia; Japan; Mexico; Nicaragua; Oman; Philippines; Senegal; South Africa; Thailand
|FAO Marine Fishing Areas:||
Atlantic – eastern central; Atlantic – southeast; Atlantic – southwest; Indian Ocean – eastern; Indian Ocean – western; Pacific – eastern central; Pacific – southeast; Pacific – western central
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||Reported to be uncommon (Compagno and Last 1999).|
|Habitat and Ecology:||
The species is usually pelagic in shallow, neritic waters (<100 m) (Notarbartolo-di-Sciara 1988).
The mode of reproduction in the species is aplacental viviparity. Embryos obtain nutrients initially by yolk, then through absorption of enriched uterine fluid from the mother (Wourms 1977). Only the left ovary is functional and litter size is one pup (Wourms 1977, Notarbartolo-di-Sciara 1988). Size at birth is estimated at 65-85 cm DW (Notarbartolo-di-Sciara 1988). Both females and males from the Gulf of California, México are estimated to mature at 150 cm DW (Notarbartolo-di-Sciara 1988). Mating, parturition, and early life history are reported to take place in the shallow water during summer and perhaps early fall (Notarbartolo-di-Sciara 1988). The southern Gulf of California is apparently an important feeding and mating ground. Segregation by size and sex is seasonal, with all size classes and sexes appearing together during the summer months (Notarbartolo-di-Sciara 1987). Observed either solitarily or in small groups (2-6); not a schooling species (Notarbartolo-di-Sciara 1988).
Diet is highly specialized with the euphausid Nyctiphanes simplex accounting for the vast majority of observed prey items but mysids (Mysidium spp.) are also common. Diet varied with season with mysids dominant from December through March and euphausids during the warmer months (Notarbartolo-di-Sciara 1988).
Life history parameters
Age at maturity (years): Unknown.
Size at maturity (disc width): 150 cm DW (Notarbartolo-di-Sciara 1988) (male & female).
Longevity (years): Unknown.
Maximum size (disc width): 180 cm DW (Notarbartolo-di-Sciara 1987).
Size at birth: 65 to 85 cm DW (Notarbartolo-di-Sciara 1988).
Average reproductive age (years): Unknown.
Gestation time: 12 months (estimated) (Michael 1993).
Reproductive periodicity: Unknown.
Average annual fecundity or litter size: 1 pup/litter (Notarbartolo-di-Sciara 1988).
Annual rate of population increase: Unknown.
Natural mortality: Unknown.
Mobula thurstoni is vulnerable to pelagic and demersal gillnets together with purse seines and juveniles could be incidentally captured in trawl fisheries. It is taken, either as bycatch or as a target species in Indonesia, México and the Philippines. Catches have also been reported from Brazil (Gadig et al. 2003). While information is available on these areas it is likely to be landed in other countries also, such as in West Africa and particularly in Southeast Asia where pressure on the marine environment is considerable and where mobulid gill rakers are a high value product.
Mobula thustoni is a caught in the inshore pelagic tuna gillnet fisheries of Indonesia and is also taken by purse seine in that country. The high value of gill rakers in some areas, e.g., Pelabuhanratu in West Java (W. White pers. comm.), is driving a dramatic increase in the catch of mobulids in Indonesia where some fishers are now targeting devil rays. When shark catches are lower (off-season, December to March) fishers are landing more mobulids as an alternative (W. White pers. comm.). The flesh is also utilized both for human consumption and as bait and chum for longlines.
The species is caught in artisanal drift and demersal gillnet fisheries and directly targeted using harpoons in the Gulf of California. Notarbartolo-di-Sciara (1988) reported fishery data from a mixed mobulid fishery with M. thurstoni making up 58% of the catch. Mean daily capture of M. thurstoni from 20 fishing vessels ("pangas") in Bahia de la Ventana from March to July, 1983 was: March: 0.38, April: 0.69, May: 5.00, June: 5.10, July: 0.56. One M. thrustoni was observed among 129 mobulids landed at Punta Arena de la Ventana, Baja California Sur, México in June 2001 (J. Bizzarro pers. obs.). There is still an active mobulid fishery in the southwest Gulf of California, south of La Paz and devil rays are also landed in nearshore artisanal elasmobranch fisheries throughout the Gulf of California. Although available published research is centered around the southern Gulf of California, these rays are landed by artisanal fisheries throughout the region.
Mobula thurstoni comprised 54% of the Philippine mobulid fishery from March 2001 to March 2002 (Bureau of Fisheries and Aquatic Resources, unpublished study), which may reflect its relative importance in other target fisheries in the Southeast Asia region. There is currently a ban on fishing for manta rays in the Philippines, but the effectiveness of this ban is questionable due to limited enforcement ability and mobulids are still being taken illegally.
Gadig et al. (2003) reported M. thurstoni taken by artisanal fishers employing gillnets on the southern coast of São Paulo of Brazil, noting that the small size of artisanal fishing boats precludes the landing of large mobulids and individuals are usually discarded.
Mobula thurstoni is not likely to be able to tolerate high catch levels, given its low reproductive potential. Increasing catches of mobulids in Indonesia, which may mirror increases elsewhere, is of great concern.
Additional research is needed to quantify the extent of target and non-target fisheries take for this species throughout its range. Because of its large size, migratory behavior, extremely low fecundity and large size at maturity, this species is likely highly vulnerable to fishing pressure. However, available life history information is limited and more research is required to make a more accurate assessment of the threat posed by fisheries. Current landings in the Gulf of California need to be documented and compared with catch rates observed in the 1980s (Notarbartolo-di-Sciara 1988).
In México, a moratorium on the issue of elasmobranch fishing permits was issued in 1993, but no formal management plan has been implemented for Mobula thurstoni specifically or most other chondrichthyans. However, legislation is currently being developed in México to establish national elasmobranch fishery management.
Elasmobranch landings in most parts of the world generally lack species-specific details (for example in México, batoids are broadly grouped as "manta raya"). Improved clarity in catch records would provide a basis for detecting potential trends in effort and landings.
In the Philippines, fishing for mobulids was banned in 1998, however it was lifted in 1999 to study the fishery. The ban was put back in place in 2002, and currently it is illegal to fish for any Manta or Mobula in Philippine waters. However, enforcement is insufficient and mobulids are still being taken illegally.
Elasmobranch fisheries are generally unmanaged throughout Central America and Southeast Asia and indeed elsewhere in the range of this species, and attempts to regulate fisheries in these regions would greatly improve conservation of M. thurstoni and other chondrichthyans.
The development and implementation of management plans (national and/or regional e.g., under the FAO International Plan of Action for the Conservation and Management of Sharks: IPOA-Sharks) are required to facilitate the conservation and sustainable management of all chondrichthyan species across the regions where this ray occurs.
The vulnerability of mobulids and increasing catches requires urgent international conservation measures. These will need to focus on harvest and trade management.
|Citation:||Clark, T.B., Smith, W.D. & Bizzarro, J.J. 2006. Mobula thurstoni. The IUCN Red List of Threatened Species. Version 2014.2. <www.iucnredlist.org>. Downloaded on 20 October 2014.|