|Scientific Name:||Himantura polylepis|
|Species Authority:||(Bleeker, 1852)|
|Infra-specific Taxa Assessed:|
Himantura chaophraya Monkolprasit & Roberts, 1990
Trygon polylepis Bleeker, 1852
H. chaophraya was described in 1990 from Thailand, but it did not take into account the description by Bleeker in 1852 of H. polylepis. Recent work by Last and Manjaji-Matsumoto (2008) comparing material from the holoytpe of polylepis (Java, Indonesia) with material from the Chao Phraya (Thailand), Sabah (Malaysia) and from India confirmed that polylepis is the senior name.
In the recent description of Himantura dalyensis from Australia (formerly thought to be chaophraya but considered to be restricted to Australia and possibly New Guinea and Papua New Guinea; W. White pers. comm. 2011; P. Last pers. comm. 2011), Last and Manjaji-Matsumoto (2008), clarified that H. polylepis (the type locality for which is in Java, Indonesia) is a senior synonym and recognised this as the valid species name, thus making H. chaophraya a junior synonym.
This species requires further taxonomic research and it is possible that populations in the Mekong and other drainages may also pertain to other species (W. Rainboth, pers. comm.). Significant differences in the DNA and amino acid sequences were found between Thai and Indian specimens (Sezaki et al. 1999; see Martin 2005), suggesting evolutionary divergence between sub-populations.
|Red List Category & Criteria:||Endangered A2bcd ver 3.1|
|Assessor/s:||Vidthayanon, C., Baird, I. & Hogan, Z.|
|Reviewer/s:||Ng, H.H., Rainboth, W. & Allen, D.|
|Contributor/s:||Hadiaty, R.K., Musick, J.A., Compagno, L.J.V., Fowler, S.L., Britz, R., Vishwanath, W., Cook, S.F. & Kyne, P.M.|
This species is recorded from several rivers in Southeast Asia and is probably unrecorded in others, however the potential for exchange between these subpopulations is thought to be very limited, and the continued presence and taxonomic status of other sub-populations requires confirmation. There appear to be no recent records from the Ganges/Brahmaputra, Ayeyarwaddy or Salween basins, and there are few recent known records from Sabah and none from Sarawak.
The species has been and continues to be adversely affected in much of its range by a number of factors including fisheries, and habitat degradation or destruction. The species is taken by fishermen on the rivers in Central Thailand and the Mekong. In Thailand, Thai fishermen reported 25 individuals of this species in their catch in 1992, but by 1993 the reported landings had dropped to three specimens, a decline of 88% in one year (Cook and Compagno 1994). In the Maeklong and Bangpakong rivers in central Thailand, fishing pressure is increasing due to capture for aquariums and sportfishing. Anecdotal information from fishermen suggest that catches have gone from a catch of 2-3 fish per day to one fish every 2-3 days, a significant decline (N. Chansue pers. comm.). In Cambodia, fishers ( reported a 62% decline in the catch of this species since 1980 (Z. Hogan, unpublished data). The average size of an individual fish has also fallen from 23.2kg in 1980 to 6.9kg in 2006. At the same time, the maximum size of a fish reported in an average season dropped from 175kg in the 1980’s to 60kg in recent times. Seven fishers in central Thailand reported that they can no longer catch the species in their area (Z. Hogan, unpublished data).
Populations appear to be healthier in the upper Cambodia Mekong (where fishers regularly catch the species and report population declines of 30-50%) and less healthy in the Tonle Sap Lake/Kampong Cham/Prey Veng areas where fishermen report declines of 50-95%. C. Vidthayanon (pers. comm.) observed numerous specimens in markets in Stung Treng (Cambodia) in 2006. Although the species is still harvested in significant numbers in many areas where it occurs, catch data and local knowledge indicates a significant decline over the past 20-30 years. Past and future harvest, habitat degradation, and future habitat modification due to dam building are likely to continue to negatively impact this large-bodied, long-lived species. Population trends in other parts of the species range (e.g., India, Malaysia and Indonesia) are not known, but there are very few recent records from Malaysia and Indonesia.
A population decline of at least 30-50% can be inferred from data from the rivers of central Thailand and catch rates in Cambodia, therefore the species is assessed as Endangered A2bcd. Recruitment rates (at one pup per season) are low, and the capacity for populations to recover in the face of continuing threats is limited.
Future threats to the species include the development of mainstream dams on the Mekong River. The species habitat and reproductive success would be greatly impacted if these dams were to be developed.
Further research and survey is required to confirm the presence, population trend, and taxonomic status of populations of the species from all parts of its range, especially India, Bangladesh, Myanmar, Viet Nam, parts of Indonesia and Malaysia, and Papua New Guinea.
|Range Description:||The species is known from several disjunct freshwater localities in south and southeast Asia, from India to eastern Indonesia (Last et al. 2010), although the presence and taxonomic status of some of the reported populations requires confirmation.
In Thailand it is known from the Chao Phraya, Nan, Mekong, Bangpakong (Bang Pakong), Tachin and Tapi (Tapee) rivers. It is recorded from the mainstream of the Mekong in Lao PDR, Viet Nam and Cambodia. It is possibly present as far upstream on the Mekong as Chiang Khong in northern Thailand, where unidentified stingrays have been seen (Z. Hogan, pers. comm.).
In Indonesia it is recorded from the Mahakam basin in Kalimantan (Monkolprasit and Roberts 1990), and from Java (the holotype locality; given as "Jakarta [Batavia]", most likely from the Ciliwung River drainage). C. Leh (pers. comm.) reported anecdotal records of the species being collected by locals in the Kapuas River at Pontianak, Kalimantan, and the Kapuas was connected to the Lupar River in Sarawak in geological times, however extensive survey along the length of the Kapuas River in 1997 (C. Lim. pers. comm.) did not record the species. There are no recent records of the species from Java and recent surveys of both the Ciliwung and Cisidane drainages (R.K. Hadiaty, pers. comm.) have reported a very high level of decline in fish diversity; further survey in coastal areas is required to confirm the species presence.
While this species was reported from Sarawak by Kottelat et. al. (1993) and by Roberts (1989), it is largely unknown in Sarawak, and the species has not been recorded there in the last 25 years (C. Leh pers. comm. 2011). Extensive recent survey in the Rajang River in Sarawak by Parenti and Lim (2005) did not report the species. Specimens have been collected from the Kinabatangan (Fyler and Caira 2006) and Buket (in 1997; Yano et al. 2005) rivers in Sabah. Last et al. (2010) consider it to be probably common in the Kinabatangan River, but rarely caught, and found in coastal and marine and brackish habitats in other parts of Indonesia. No specimens of the species are held by the Sarawak Museum, and the conclusion by C. Leh (pers. comm.) is that the status of the species in Sabah and Sarawak is largely unknown and that there is insufficient data the species. There do not appear to be records from Brunei Darussalam (a survey in the Belalong River in the early 1990's in the Temburong National Park by the Earl of Cranbrook did not report the species) or from Singapore (Chong Ving Ching, pers. comm.).
It was reported to be present in Myanmar, but there is no information is available on its distribution there; its presence in Myanmar rivers requires confirmation, and R. Britz (pers. comm.) has not seen nor is aware of any records from Myanmar. It is also recorded as present in India (as Trygon fluviatilis Annandale, 1909) but there appear to be no recent records. The identification of the records from the Ganges and the Bay of Bengal require confirmation (Last and Manjaji-Matsumoto 2008). Sezaki et al. (1999) compared specimens from India and Thailand and found significant molecular differences.
Records from Australia pertain to H. dalyensis (Last and Manjaji-Matsumoto 2008), which may also occur in most of the large rivers of tropical Australia; records from New Guinea (Fly River) most likely also refer to dalyensis, but this requires study of material to confirm. Records of the species from Papua New Guinea also require taxonomic confirmation, and are probably also dalyensis (P. Last pers. comm. 2011).
The species has also been recorded in estuarine waters. Despite records of this species from estuarine waters, there is only a possibility that it may be able to transit marine waters between riverine systems, most of its populations are thought likely to be geographically isolated.
Native:Cambodia; India; Indonesia (Kalimantan); Lao People's Democratic Republic; Malaysia (Sabah, Sarawak); Thailand; Viet Nam
|FAO Marine Fishing Areas:||
Indian Ocean – eastern; Pacific – western central
|Range Map:||Click here to open the map viewer and explore range.|
The population has generally declined as a result of pollution and fishing pressure, and is locally uncommon. In some parts of the range (e.g., Mae Khlong in Thailand, Stung Treng in Cambodia (C. Vidthayanon, pers. comm.) the species occurs in fish markets occasionally. WWF (2010) report that populations of the species are suffering less than other very large fish in the Mekong from overfishing and pollution, possibly because of the depth of the river these species inhabit as well as the fact that they are difficult to catch.
The species is taken by fishermen on the rivers in Central Thailand and the Mekong. In 1992, Thai fishermen reported 25 individuals of this species in their catch, but by 1993 the reported landings had dropped to three specimens, a decline of 88% in one year (Cook and Compagno 1994). However C. Vidthayanon (pers. comm.) observed numerous specimens in markets in Stung Treng (Cambodia) in 2006. Population trends in other parts of the species range (e.g., India, Malaysia and Indonesia) are not known, but there are very few recent records from Malaysia and Indonesia.
In the Maeklong and Bangpakong rivers in central Thailand, fishing pressure is increasing due to capture for aquariums and sportfishing. Anecdotal information from fishermen suggest that catches have gone from a catch of 2-3 fish per day to one fish every 2-3 days, a significant decline (N. Chansue pers. comm.). In Cambodia, fishers (age 40 years an older, n = 36) report a 62% decline in the catch of this species since 1980 (Z. Hogan, unpublished data). The average size of an individual fish has dropped from 23.2kg in 1980 to 6.9kg in 2006. At the same time, the maximum size of a fish reported in an average season dropped from 175kg in the 1980’s to 60kg in recent times. Average catch per fish has dropped from 306.2kg per season to 27.6kg per season in 2006. Seven fishers report that they can no longer catch stingray in their area (Z. Hogan, unpublished data).
Populations appear to be healthier in the upper Cambodia Mekong (where fishers regularly catch the species and report population declines of 30-50%) and less healthy in the Tonle Sap Lake/Kampong Cham/Prey Veng areas where fishermen report declines of 50-95%. Although the species is still harvested in significant numbers in many areas where it occurs, catch data and local knowledge indicates a significant decline over the past 20-30 years. Past and future harvest, habitat degradation, and future habitat modification due to dam building are likely to continue to negatively impact this large-bodied, long-lived species.
|Habitat and Ecology:||
This is mainly a freshwater species found in large rivers with a muddy or sandy bottom. There have been records of the species from estuarine waters. Martin (2005) considered it an obligate freshwater species, though Last et al. (2010) report records from coastal and marine and brackish habitats in parts of Indonesia. Based on catch data and tagging work, the species does appear to occur in both brackish and freshwater, but it is considered unlikely that that the species needs to move between brackish and freshwater to complete its life cycle (Z. Hogan pers. comm. 2011), however large numbers of pregnant females are seen in brackish waters, so estuaries could be a pupping ground at least for some populations.
It is possible that it may be able to transit marine waters between riverine systems. The movement pattern of the species within and between river systems is not known and requires further research.
It reaches a size of up to 200 cm disc width (DW) and 600 kg in weight (Thailand). Males mature by 110 cm DW. Young (a single pup) are born at about 30 cm DW (Last and Stevens 1994); recruitment is likely to be limited. Other life history parameters (age at maturity, average generation period and maximum lifespan in the wild) are unknown. Ovoviviparous, the fish gives birth to live young measuring 30 cm wide.
It is often observed at the water margin where it is thought to be feeding on earthworms (I. Baird, pers comm.; C. Vidthayanon, pers. comm.).
The species is taken by fishermen on the rivers in Central Thailand and the Mekong. The species is similarly occasionally caught incidentally in artisanal fisheries on the Kinabatangan River (Sabah, Malaysia) and presumably elsewhere over much of its range. In the Maeklong and Bangpakong Rivers in central Thailand, fishing pressure is increasing due to capture for aquariums and sportfishing. Harvest for aquariums is a potential problem because survival in captivity is low (N. Chansue, pers. comm.). When a display animal dies, a new animal is harvested from the wild population. Sportfishing may also be a serious threat: sport anglers now have the equipment necessary to catch very large stingrays and sport anglers do not always practice catch and release (N. Chansue, pers. comm.). Moreover, mortality from catch-and-release angling is not known. Some catch and release anglers use very invasive techniques such as gaffing and hanging for display. Harvest for aquariums and sportfishing has lead to a decline in populations.
Factors causing degradation of riverine environments in Thailand and elsewhere in Southeast Asia include forest loss and degradation leading to drought upstream and flooding downstream during monsoon conditions; dam construction for hydropower and flood control (which again leads to siltation and retention of agrochemicals and other pollutants behind impoundments); and the development of land adjoining riverine habitats, which leads to the degradation of water quality through the the movement of sediment and pollution (domestic, agricultural, and industrial).
On Java, Indonesia, the Ciliwung River, the likely type locality, has been very heavily impacted by urban and industrial development (R.K. Hadiaty, pers. comm.).
In addition, dams effectively isolate portions of the reproductive populations of the species. Proposed mainstream dams on the Mekong in Lao PDR and in Cambodia would severely the impact the species, by further fragmenting their habitat and populations, however the time frame of the construction of these dams is uncertain.
Pollution impacts the species in the Thai parts of its range especially (C. Vidthayanon, pers. comm.); in the Bangpakong River, 30 specimens were found dead in one day in 2008-9 as a result of a pollution incident.
The precipitous decline of riverine stingrays in Thai fresh waters led the Thai government to implement an experimental programme for captive propagation to try to stabilise populations while they attempt to improve river habitats. The authors of the 2005 assessment observed the project at Chai Nat, Suppraya Province, Central Thailand in December 1993, where healthy individuals of H. chaophraya ranging in size from 0.45-1.6 m DW and ranging from an estimated 50-500 kg were observed. There is ongoing work in Thailand to tag individuals the Mekong and Bangpakong rivers (C. Vidthayanon, pers. comm.).
Further research and survey work is very much needed to ascertain the presence, taxonomic status, population trends, and possible threats to this species in other portions of its known and potential range (e.g., India, Myanmar, Bangladesh and Indonesia). Combining population assessments from known river basin populations would allow a more accurate global estimate of population size and trends to be made.
Movement patterns are unknown and require research. A significant gap in our knowledge of this species is its habitat use and requirements, movement patterns, and migrations or residency patterns (W. White, pers. comm., 2011).
|Citation:||Vidthayanon, C., Baird, I. & Hogan, Z. 2011. Himantura polylepis. In: IUCN 2012. IUCN Red List of Threatened Species. Version 2012.2. <www.iucnredlist.org>. Downloaded on 23 May 2013.|
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