|Scientific Name:||Hemitrygon laosensis (Roberts & Karnasuta,1987)|
Dasyatis laosensis Roberts & Karnasuta,1987
|Taxonomic Source(s):||Last, P.R., Naylor, G.J.P. and Manjaji-Matsumoto, B.M. 2016. A revised classification of the family Dasyatidae (Chondrichthyes: Myliobatiformes) based on new morphological and molecular insights. Zootaxa 4139(3): 345-368. http://doi.org/10.11646/zootaxa.4139.3.2.|
|Taxonomic Notes:||The genus Hemitrygon formerly was a junior synonym of Dasyatis (Kottelat, 2013); it was resurrected by Last et al. (2016) in their revision of the family Dasyatidae.|
|Red List Category & Criteria:||Endangered A2acde ver 3.1|
|Reviewer(s):||Kottelat, M., Gibson, C. & Juffe Bignoli, D.|
|Contributor(s):||Fowler, S.L., Compagno, L.J.V. & Musick, J.A.|
This is an amended version of the 2006 assessment to accommodate the recent change in genus name from Dasyatis to Hemitrygon.
This species is a freshwater species endemic to the Mekong basin. Records from the Chao Phraya basin in Thailand are thought to have been introduced specimens from the Mekong population. The parts of the Mekong where this species is found are under heavy bycatch fishing pressure, and it is being affected by habitat degradation which is directly affecting this species. A population decline of at least 50% has been observed over the last twenty years, and the decline is expected to continue. The species is considered to be "highly vulnerable" to impacts from mainstream dam development on the Mekong mainstream and associated tributaries, and if they were to be developed, the dams would have further severe impacts on the species reproductive success and recruitment. The species is assessed as Endangered due to recent population decline resulting from fishery bycatch, pollution from a range of sources, and the decline of suitable habitat.
|Previously published Red List assessments:|
|Range Description:||The species is considered to be endemic to the Mekong River from Stung Treng in Cambodia to Chiang Rai in northern Thailand (Vidthayanon 2002). It is possibly present in the lower part of the main tributaries, and might also be expected as far downstream as the Mekong delta (I. Baird pers. comm. 2011). Records from the Chao Phraya River near Chai Nat in Thailand (Compagno 2005) are considered to pertain to a population introduced for in situ breeding and were sourced from the Mekong population (C. Vidthayanon pers. comm. 2011).|
Native:Lao People's Democratic Republic; Thailand
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||This species is uncommon throughout its range. Population decline has been observed (from occurrence in markets) for the past twenty years, and almost absent from markets in Thailand in the last ten years, though fishers in southern Lao PDR do not consider it to be especially rare (I. Baird pers. comm. 2011). Fish sellers report that a specimen has not been landed for several years in Thailand, and a population decline of 50% is inferred to have occurred over the last twenty years. This decline in numbers is estimated to continue in the future, and will be exacerbated by mainstream dam development on the Mekong mainstream and tributaries.|
|Current Population Trend:||Decreasing|
|Habitat and Ecology:||This species is restricted to freshwater habitats. It is found in sandy and rocky bottoms in mainstreams and rapids. Little life history information is available for this species. The generation length is estimated at 15 years (C. Vidthayanon pers. comm. 2011).|
|Generation Length (years):||15|
|Movement patterns:||Full Migrant|
|Congregatory:||Congregatory (and dispersive)|
|Use and Trade:||Young are sufficiently small to be suitable for the aquarium trade, and they are taken from the wild for aquaria and scientific research. This species may be locally consumed but it is not a targeted species.|
The species is subject to heavy fishing pressures, being taken as bycatch in intensive fisheries. The species is also impacted by large-scale habitat degradation through dam-building and pollution from agricultural and industrial development, which has apparently drastically decreased fish diversity in the rivers where this species occurs. Its population is considered to have declined as a result and this decline in numbers is projected to continue (Compagno 2005). The development of mainstream dams on the Mekong, if they were to be developed, would have further severe impacts on the species reproductive success and recruitment (MRC 2009; WWF 2010). Barlow et al. (2008) consider the species to be "highly vulnerable" to impacts from mainstream dam development.
Young are sufficiently small to be suitable for the aquarium trade, and they have been taken from the wild for aquaria and scientific research.
There is no in situ protection for the species or its habitat (Compagno 2005). The Thai government started a project in the 1990s to breed this and other freshwater stingrays ex situ in captivity at Chai Nat above a dam on the Chao Phraya River to counter declines of freshwater rays in the river, and young were successfully bred. The breeding project ceased without specimens being released to the wild.
This species occurs in areas subjected to heavy fishing pressure; it is a utilised bycatch but is not specifically targeted. New dams built in the Mekong basin probably have impacted the habitat and movement of this species (Compagno 2005). Further research and protection is required for the species.
|Citation:||Vidthayanon, C. 2016. Hemitrygon laosensis. The IUCN Red List of Threatened Species 2016: e.T39407A104120090.Downloaded on 23 September 2017.|