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Description |
Geographic Range [top]
Range Description: Wide-spread distribution in the Indian and western Pacific Oceans, from South Africa to northern Australia (White et al. 2006, Compagno 1998, W. White and B.M. Manjaji pers. obs. 2007).
Western Indian Ocean: South Africa to India, including the Red Sea and Gulf. Eastern Indian Ocean: India to Indonesia and northern Australia.
Northwest Pacific: Taiwan, Ryukyu Islands, southern Japan. Western Central Pacific: Australia, Papua New Guinea, Malaysia and Indonesia.
Mediterranean Sea: The species is thought to be a Lessepsian immigrant, having entered the Mediterranean Sea from the Red Sea through the Suez Canal (Serena 2005).
Countries occurrence:
Native:
Australia (Northern Territory, Queensland, Western Australia); India; Indonesia; Japan (Nansei-shoto); Malaysia; Papua New Guinea (Papua New Guinea (main island group)); South Africa; Taiwan, Province of China; Thailand
FAO Marine Fishing Areas:
Introduced:
Indian Ocean – western; Indian Ocean – eastern; Mediterranean and Black Sea; Pacific – northwest; Pacific – western central
Range Map: Click here to open the map viewer and explore range.
Population [top]
Population: Uncommon throughout much of its range (B.M. Manjaji pers. obs. 2007), but appears to be common in parts of northern Australia (W. White. pers. obs. 2007).
Current Population Trend: Decreasing
Additional data:
?Population severely fragmented: No
Habitat and Ecology [top]
Habitat and Ecology: Often found off sandy beaches and in shallow estuaries and lagoons and may enter freshwater; also found in sandy areas of coral reefs. Also occurs offshore to depths of at least 50 m (White et al. 2006).
Reproduction is viviparous, with histotrophy. Attains at least 148 cm disc width (DW) (White and Dhamadi 2007) (up to 450 cm total length in Compagno 1998). Males mature at 82-84 cm DW and size at birth is 21-28 cm DW (White et al. 2006, White and Dharmadi 2007, Manjaji 2004). Fecundity is probably low; one pregnant female observed possessed two embryos (B.M. Manjaji pers. obs.).
Systems: Marine
Use and Trade [top]
Use and Trade: Flesh is used fresh or salted and dried for human consumption. In some areas, vertebrae is dried and exported; skins are dried and used for manufacturing items such as wallets, belts, shoes, handbags (high value) etc. most of which are exported e.g. Thailand (White et al. 2006).
Threats [top]
Major Threat(s): Himantura uarnak faces many of the same threats as other Himantura species within its range, however, its large size at maturity and maximum size and preference for shallow waters (which are being heavily utilised and degraded in many parts of its range), suggest that it may be more vulnerable than its congeners (B.M. Manjaji, Fahmi, W. White, pers. Obs. 2007).
This species is captured by demersal tangle net, bottom trawl and, to a lesser extent, longline fisheries in Indonesia (White et al. 2006) and across large parts of its range. Its inshore distribution overlaps with coastal artisanal and commercial fisheries throughout large areas of the Indian and western Pacific oceans.
It is taken in commercial gillnet fisheries off Indonesia, particularly in the fishery that targets rhynchobatid rays in the Arafura Sea, and retained (Last and Compagno 1999, W. White pers. obs. 2007). It is thought to be heavily impacted in this area, where more than 600 trawl vessels operate (W. White pers. obs. 2007). The Rhynchobatus species gillnet fishery catches large numbers of stingrays and Himantura uarnak is important in this fishery. Catches in inshore waters have declined and these vessels are having to travel longer and longer distances to sustain catches. The rhynchobatid fisheries are very intensive in this region, thus the level of exploitation is extremely high. There is also evidence that fisherman in these regions increasingly illegally fish in Australian waters (Chen 1996, W. White, unpubl. data).
In Sabah (Malaysia) and Indonesia, Himantura species are often caught and landed in the inshore fisheries (trawls and longlines) and are also taken by Danish seine fishing gear (M. Manjaji and Fahmi pers. obs. 2007). In Southeast Asia, most specimens caught as bycatch by commercial fisheries (especially trawlers) are landed and sold as food fish.
Demersal fishing pressure has increased in both effort and capacity in many areas of this species inshore range during recent decades. For example, demersal resources in the Gulf of Thailand went from being lightly exploited to severely over-exploited between 1973 and 1994 (Pauly et al. 2005). Available time series data for grouped biomass of "rays" for this area and period applied to an ecostystem model for the area, suggested that this group was one of the most severely impacted by the initial increase in fishing pressure, showing a steady declining trend (Pauly et al. 2005). Species-specific catch data are not collected, but aggregated landings data for "Rays, stingrays, mantas, nei" are reported to FAO by some countries. Indonesian landings increased from ~10,000 t in 1975 to almost 60,000 t in 2003. Data are not available for India, but data for Pakistan show that landings increased to a peak of 53,000 t as early as 1982, after which landings dropped to ~10,000 t in 1983 and have not risen above 21,000 t since (FAO 2008).
This species preference for inshore waters, shallow estuaries and lagoons means it is also threatened by extensive habitat degradation and loss of mangrove forest. It may also be affected by destructive fishing practices and pollution. Extensive areas of mangrove forest have been lost in Indonesia and Malaysia through conversion of land for shrimp farms, excessive logging, urban development and, to a lesser extent, conversion of land to agriculture or salt pans (FAO 2007). Between 1980 and 2005 combined overall mangrove area in Indonesia and Malaysia was reduced by >30% (FAO 2007).
Although species-specific data are not available, given that this is a large species with low fecundity and a preference for shallow waters (where threats from coastal fisheries and habitat degradation are greatest), significant declines are suspected to have occurred as a result of over-exploitation in fisheries in Southeast Asia, the northern Indian Ocean, and elsewhere in areas of high exploitation.
Conversely, this species has refuge from fishing pressure in areas such as northern Australia, where fishing pressure is light and bycatch mitigation measures are in place. Large specimens are caught as bycatch in the Australian Northern Prawn Trawl Fishery, but the introduction of Turtle Exclusion Devices (TEDs) and other exclusion devices is thought to have greatly reduced bycatch of this species.
Conservation Actions [top]
Conservation Actions: Further research is required on taxonomy, as is assessment of catches throughout its range.
In Malaysia, the Shark Specialist Group together with various government departments in Sabah and Sarawak States have initiated elasmobranch biodiversity studies since 1996 (Fowler et al. 2002). While the monitoring surveys should continue to ascertain the status and possible threats to this species here, as well as in other portions of its range (New Guinea and Indonesia), efforts in further research should be directed to also obtain the population, habitat and ecology and life history parameters. The fishery is largely unregulated (licenses being issued, but catches/ landings are not properly monitored), and presently there is no specific conservation actions in place to help address this problem.
Citation: Manjaji, B.M. & White, W.T. 2009. Himantura uarnak. The IUCN Red List of Threatened Species 2009: e.T161692A5481403. http://dx.doi.org/10.2305/IUCN.UK.2009-2.RLTS.T161692A5481403.en. Downloaded on 14 June 2016.
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Indo-West Pacific: Red Sea (and eastern Mediterranean via Suez Canal) to southern Africa and French Polynesia, north to Taiwan, south to Australia. Also in the Arafura Sea (Ref. 9819). Collected from the estuary of the River Ganges (Ref. 33178). This |
