Mobula thurstoni | UAE National Red List of Marine Species: Reef-building corals, cartilaginous fishes and select bony fishes

Taxa
Mobula thurstoni | (Lloyd, 1908)
Location
Countries in Assessment
United Arab Emirates
Country ISO code(s)
ARE
Does the assessment cover a marine EEZ area(s)?
Off
Scope (Assessment)
National
Taxon
Taxonomic Group
Vertebrates
Taxonomic Group Level 2
Fishes
Assessed taxon level
Species
Taxon distribution as listed in assessment
The Bentfin Devil Ray occurs in UAE waters on the Sea of Oman coast. It is excluded from the Arabian Gulf. Elsewhere, it is distributed in tropical, subtropical, and temperate waters of the Indian Ocean from the Red Sea to India, Sri Lanka, and the Maldives (Couturier et al. 2012, Notarbartolo di Sciara et al. 2017).
Habitats and Ecology
Ecological system type
Terrestrial system
No
Freshwater system
No
Marine system
Yes
Habitat
Habitat details as listed in assessment
The Bentfin Devil Ray is usually pelagic or epipelagic in shallow, productive, neritic waters of &lt;100 m depth (Notarbartolo di Sciara 1988, Croll et al. 2016), although it is also caught in offshore pelagic waters (Mas et al. 2015), and around seamounts in the Mid-Atlantic Ridge (Mendonça et al. 2012). Segregation by size and sex is seasonal, with all size classes and sexes appearing together during the summer months (Notarbartolo di Sciara 1988). The species is observed either solitarily or in small groups (2-“6 individuals); it is not a schooling species (Notarbartolo di Sciara 1988). Maximum size is reported to at least 189 cm disc width (DW) and both females and males are estimated to mature at around 154 cm disc width (DW), while size at birth is estimated at 65-“85 cm DW (Notarbartolo di Sciara 1988, Last et al. 2016). Size at 50% maturity was estimated at 153.8 cm DW for males (White et al. 2006b). The mode of reproduction is matrotrophic viviparity. Embryos obtain nutrients initially via 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 after a 12-month gestation period (Wourms 1977, Notarbartolo di Sciara 1988). It is estimated that the maximum intrinsic population growth rate (r<sub>max</sub>) of devil rays is similar to manta rays, and these productivity rates are among the lowest of all chondrichthyans (Dulvy et al. 2014, Pardo et al. 2016). Mating, parturition, and early life history are reported to take place in the shallow water during summer and perhaps early autumn (Notarbartolo di Sciara 1988).For the Spinetail Devil Ray (up to 310 cm DW), Cuevas-Zimbrón (2012) estimated age at maturity to be 5-“6 years and a minimum lifespan of 14 years, giving a generation length of 10 years. While accurate age at maturity and longevity information is unavailable for the Bentfin Devil Ray, it can be inferred according to the smaller maximum size that it would be close to but slightly shorter than that of its congener. As there are not enough data to estimate an exact generation length for this species, an approximate, suspected generation length is used. A midway point of 7.5 years between a very conservative low of five years, and the larger Spinetail Devil Ray's 10-year generation length is suspected to be the approximate generation length for the Bentfin Devil Ray until more accurate information becomes available.
Is there a map available in assessment?
Yes
Assessed status
Asessment status in full
Vulnerable
Assessment status abreviation
VU
Assessment status criteria
A2d
Assessment rationale/justification
In UAE waters, the Bentfin Devil Ray occurs only in the Sea of Oman in inshore and offshore waters. This species is not targeted or valued in markets of the UAE and capture of this species is totally banned in the UAE. When captured in the Sea of Oman, it is typically discarded alive, and significant declines are not suspected there at this time. It is a component of the bycatch in several fisheries (e.g., Pakistan), and is directly targeted in Sri Lanka and India. Its low productivity causes it to be susceptible to rapid population declines, and declines have recently been confirmed from Pakistan (over the past three years). It is especially susceptible to exploitation (target and bycatch) in many largely unregulated gill net, longline and trawl fisheries that operate within its range outside and surrounding UAE waters. Some management measures are now in place in the Arabian Sea region, although domestic fisheries are likely to continue. Though data specifically from the UAE are not available, individuals in the UAE are a component of a larger, interconnected and migratory population that occurs broadly in the north-western Indian Ocean. It is inferred that declines reported in the Arabian Sea region are representative of its status in the UAE. There is no information to confirm that this species is breeding in the UAE and no information confirming the likelihood of a cease in immigration from outside the region, despite ongoing threats and recorded declines. Based on recorded levels of exploitation, it is suspected to have declined by 30-50% over the past three generation lengths, or about 23 years. It is listed as Vulnerable A2d.
About the assessment
Assessment year
2019
Assessors/contributors/reviewers listed
UAE National Red List Workshop
Affliation of assessor(s)/contributors/reviewers listed on assessment
Government
IGO
Assessor affiliation specific
Government|IGO
Criteria system
Criteria system specifics
IUCN v3.1
Criteria system used
IUCN
Criteria Citation
IUCN. 2012. IUCN Red List Categories and Criteria: Version 3.1, Second edition. IUCN, Gland, Switzerland and Cambridge, UK. iv + 32pp pp. And IUCN. 2012. Guidelines for Application of IUCN Red List Criteria at Regional and National Levels: Version 4.0. Gland, Switzerland and Cambridge, UK: IUCN. iii + 41pp.
Endemism
Endemic to region
Not_assigned
Endemism Notes
Is an endemic?: Not_assigned
Conservation
Threats listed in assessment
Information pertaining to threats specific to the UAE are unavailable. This species is impacted by target (for fins and their valuable meat) and bycatch fisheries that are active elsewhere in its range. Manta rays are easy to target because of their large size, slow swimming speed, aggregation behaviour and predictable habitat use.
Conservation Measures

Conservation measures:
Conservation measures notes:
Required conservation measures:

Scientific Name Kingdom Phylum Class Order Family Genus
Mobula thurstoni Animalia Chordata Chondrichthyes Myliobatiformes Mobulidae Mobula