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

Taxa
Brevitrygon walga | (Müller & Henle, 1841)
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
Taxonomic Notes
Last et al. (2016a) placed Himantura heterurus, H. imbricata, H. javaensis, and H. walga within the new genus Brevitrygon, previously confused with other dwarf whiprays (Brevitrygon species) (Last et al. 2016b). There remains considerable taxonomic confusion over 'B. walga' with different forms across its range. These may turn out to represent a series of different species.
Taxon distribution as listed in assessment
The Scaly Whipray occurs throughout UAE waters. It is restricted to the Arabian Sea region, although its true distribution is unclear due to significant taxonomic issues, and research is urgently required to resolve this. Forms apparently consistent with the illustration in Last et al. (2016) appear to be present in eastern Iran waters of the Sea of Oman (F. Owfi unpub. data). However, specimens from the northern Arabian Gulf (hereafter referred to as the 'Gulf') (Kuwait and Iran; previously reported as Himantura imbricata) appear notably different (A.B.M. Moore unpub. data) and more consistent with the Bengal Whipray (Brevitrygon imbricata), a species that Last et al. (2016) report only from the Bay of Bengal region. Additional variation is evident in India. Until taxonomy is resolved, the forms are treated as a single species for the purposes of this assessment.
Habitats and Ecology
Ecological system type
Terrestrial system
No
Freshwater system
No
Marine system
Yes
Habitat
Habitat details as listed in assessment
This species is very common in shallow and intertidal waters over soft substrates mostly to 30 m, but occasionally 40 m (K.V. Akhilesh pers. comm. 05/02/2017). It is a very small species, only growing to 32 cm disc width (DW). Data from the H. imbricata form show that males mature about 18 cm DW and females by at least 23 cm DW (Moore et al. 2012). It is born at 7-10 cm DW (Last et al. 2016). No data on litter size is available, but given the small size, it is likely to be low. Similarly, no data on frequency of breeding or on ageing are available. Generation length is estimated from the similar-sized Speckled Maskray (Neotrygon picta) from Australia that matures at 3-4 years and reaches a maximum age of 18 years, yielding a generation length of ~11 years (Jacobsen and Bennett 2010).
Is there a map available in assessment?
Yes
Assessed status
Asessment status in full
Near Threatened
Assessment status abreviation
NT
Assessment status criteria
A2cd
Assessment rationale/justification
The Scaly Whipray occurs throughout UAE shallow waters, and can be common. Within the Arabian Sea region, it is regularly caught in shallow water trawls and is normally discarded at sea in the western part, but landed in considerable numbers in the eastern part (i.e., India). This species is not targeted or valued in markets of the UAE, trawling has been banned there since 1980, and recently conducted surveys indicate it remains common in the area. It is, however, discarded in large numbers and it is unknown how impactful this threat is to the species. 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. Based on recorded levels of exploitation and decline in habitat quality, it is suspected to have declined by 20-30% over the past three generation lengths, or about 33 years. It is listed as Near Threatened, nearly meeting the thresholds for Vulnerable A2cd.
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 bycatch fisheries that are active elsewhere in its range. Marine habitats in the Gulf are experiencing high levels of disturbance and quickly deteriorating due to major impacts from development activities (including dredging and reclamation), desalination plants, industrial activities, habitat destruction through the removal of shallow productive areas and major shipping lanes (Sheppard et al. 2010).
Conservation Measures

Conservation measures:
Conservation measures notes:
Required conservation measures:

Scientific Name Kingdom Phylum Class Order Family Genus
Brevitrygon walga Animalia Chordata Chondrichthyes Myliobatiformes Dasyatidae Brevitrygon