Market surveys and social media provide confirmation of the endangered giant freshwater whipray Urogymnus polylepis in Myanmar

Abstract The giant freshwater whipray Urogymnus polylepis is a threatened species that is vulnerable to riverine and coastal marine pressures. Despite its threatened status, the range of U. polylepis is still being determined. In this study, photographic evidence of U. polylepis in Myanmar was provided through market surveys (2017–2018) and social media (Sharks and Rays of Rakhine Facebook page, 2021). Urogymnus polylepis is exposed to fisheries and habitat degradation pressures in Myanmar; therefore, conservation management is likely needed to ensure populations persist into the future.

biodiversity, Chin State, Facebook, non-marine elasmobranchs, Rakhine, threatened species There is global concern about the deterioration of riverine environments. In the tropics, riverine environments have degraded through a range of human-induced activities, such as the construction of water retention structures (Grill et al., 2019); general land repurposing for agriculture; and residential, commercial and industrial development within catchments (Vörösmarty et al., 2010). These activities have collectively altered, fragmented and reduced the quality of available riverine habitat. Intensive inland fisheries (e.g., Ainsworth et al., 2021;Funge-Smith, 2018) and species introductions have additionally compounded these pressures, resulting in a freshwater crisis (Su et al., 2021;Tickner et al., 2020), with large fish species being particularly affected (He et al., 2019).
Among freshwater fishes, there is very little information on the conservation status of non-marine elasmobranchs (Grant et al., 2019). Elasmobranchs that use freshwater environments are either freshwater obligates (45 described species, Grant et al., 2019;Loboda et al., 2021) or euryhaline generalists (10 species), which use a range of freshwater, estuarine and marine habitats throughout their life history (Grant et al., 2019). In the Indo-Pacific, most non-marine elasmobranchs are threatened with extinction on the IUCN Red List of Threatened Species (hereafter IUCN Red List, IUCN. 2021). These species are, however, poorly studied, and fundamental information is still required on aspects of their biology and distribution.
The giant freshwater whipray Urogymnus polylepis is one of the largest ray species, attaining sizes of at least 223 cm disc width (Grant et al., 2021b). It is a euryhaline species with fragmented populations across Indonesia (Java, Kalimantan and Sumatra), Malaysia (Peninsular and Borneo), Brunei, the Mekong River basin (including Laos, Thailand, Vietnam and Cambodia), Thailand, Bangladesh and India (Grant et al., 2021b). Within this range, U. polylepis is exposed to intense small-scale (subsistence and artisanal) fisheries (e.g., Funge-Smith, 2018;Haque et al., 2021), as well as targeted recreational fisheries and harvest for ornamental aquaculture (e.g., Compagno & Cook, 2005).
Despite the charismatically large size of U. polylepis, its global range is still being determined. It is only recently that this species has been observed broadly throughout the island of Borneo (Windusari et al., 2019), Indonesia (Iqbal et al., 2020) and Peninsular Malaysia , and contemporary observations in India (Ishihara et al., 1998;Sen et al., 2020) and Bangladesh (Haque et al., 2021) have been limited following the historic description of the junior synonym Trygon fluviatilis (Annandale, 1910) from the lower Ganges River.
Although conspecific subpopulations across this range are presently considered to be U. polylepis, the possibility of some subpopulations being separate species remains. For example, large divergences in sequences of the cytochrome b gene have been found between populations in India and Thailand (Sezaki et al., 1999). landing site surveys and social media data collection. Landing site surveys were conducted over three seasons (rainy, cool and dry) between 2017 and 2018. These surveys aimed to obtain baseline biological information on shark and ray species in Rakhine State (i.e., presence, diversity, spatial distribution, sex and size and gear susceptibility). The authors followed the survey protocol outlined in the Wildlife Conservation Society (WCS) Field Manual for Shark and Ray Fisher, Trader & Market Based Surveys in Rakhine, Myanmar (Bicknel, 2017). All surveys were conducted in Myanmar language by native Myanmar speakers. At each landing site, the authors identified boats that had shark or ray landings and obtained verbal consent from the fishers to conduct the survey. Before recording any landings data, the authors obtained information related to boat details, gear type, target species and fishing activity. For each ray specimen, they recorded the species, disc length, disc width, weight and sex. They also took a photograph of each specimen to verify species identifications. From these market surveys, two records of U. polylepis were made from Sittwe Market in In sum, photographs of six specimens and one video of a large female with two pups were obtained from five locations (Figure 1; Table 1). Although the quality of photographic evidence varied, each of the specimens pictured ( Figure 2) were clearly very large, uniformly brown stingrays. The broadly oval-to-subcircular disc, broad snout with an enlarged narrow apical lobe and minute eyes are distinctive of U. polylepis (see Last et al., 2016). Five of these specimens were reportedly caught in riverine environments, but no catch location was available for the Sittwe Market observations. One pregnant female was observed in an upstream freshwater environment at Kinwa, Paletwa, in the Kaladan River. This female pupped two well-developed neonates upon capture (Figure 2l,m), supporting suggestions that parturition and nursery areas occur in freshwater environments for this species (Grant et al., 2019).  (Grant et al., 2019). F. signifer also has a ventral white margin on its disc and a pearl spine on the scapular region as juveniles (Compagno & Roberts, 1982;Last et al., 2016). The tail provides a distinguishing characteristic between neonate U. polylepis and F. signifer: U. polylepis has a dark-coloured tail, covered entirely in denticles, whereas F. signifer has a characteristically light-coloured tail that is sparsely covered in denticles beyond the caudal stings (Last et al., 2016).   (Table 1) the focus of these studies towards other taxa. A further reason may be due to the subsistence nature (i.e., fishing directly for household consumption) of inland fisheries in Myanmar, limiting the amount of catch that is sold in markets and thus more easily observable. Apart from fishing, riverine environments in Myanmar have been significantly degraded by land repurposing activities and potentially from mining pollutants (Grant et al., 2021a). In particular, deforestation of mangroves in the lower delta estuarine areas of the Ayeyarwady River and Rakhine State has increased dramatically in recent decades (Estoque et al., 2018).

T A B L E 1 Available information for records of Urogymnus polylepis in Rakhine and Chin States, Myanmar
Only four other non-marine elasmobranch species are known from Myanmar. The Chindwin cowtail ray Makararaja chindwinensis is known from only two recorded specimens in the Chindwin River tributary of the Ayeyarwady basin (Grant et al., 2021a); the Ganges River shark Glyphis gangeticus has not been observed in Myanmar since the description of the junior synonym Glyphis (Prionodon) siamensis in the late 19th century (Li et al., 2015); the largetooth sawfish Pristis pristis has limited available records in Myanmar, and its presence is considered "uncertain" (Dulvy et al., 2016), whereas only the bull shark Carcharhinus leucas is still regularly observed in marine catch landings (e.g., Howard et al., 2015). Considering the conservation status of these other non-marine elasmobranch species in Myanmar, the present range extension of U. polylepis is unlikely to provide a globally significant refuge for this species, as populations are exposed to a combination of fisheries and habitat degradation pressures.