|Scientific Name:||Himantura dalyensis|
|Species Authority:||Last & Manjaji-Matsumoto, 2008|
|Taxonomic Notes:||The Freshwater Whipray (Himantura dalyensis) is a recently described species which was previously referred to as Himantura chaophraya Monkolprasit & Roberts, 1991 (for example, in Last and Stevens 1994). Himantura chaophraya was considered to occur in Southeast Asia and in northern Australia. However, Last and Manjaji-Matsumoto (2008) consider the Australian form to be distinct from the Southeast Asian form, and they described the former as H. dalyensis. They also clarified the correct name for the Southeast Asian species as H. polylepis (Bleeker, 1852). Thus, the name H. chaophraya is invalid.|
|Red List Category & Criteria:||Least Concern ver 3.1|
|Reviewer(s):||Walls, R.H.L. & Dulvy, N.K.|
|Facilitator/Compiler(s):||Kyne, P.M. & Walls, R.H.L.|
The Freshwater Whipray (Himantura dalyensis) is a poorly known species, which is possibly endemic to fresh and estuarine waters of tropical northern Australia, although its range is not fully mapped and its occurrence in New Guinea requires investigation. There may be minimal exchange between rivers where it occurs, and so separate subpopulations may exist across northern Australia. The ecology of this uncommon, large (reaching 124 cm disc width, but more commonly <100 cm disc width) stingray is poorly known; there is a lack of information on life history parameters. Similarly, there is a lack of concrete information available on threats to this species. Freshwater elasmobranchs are generally of conservation concern given the coupling of the usual biological limitations of the group with the physical constraints of their environment which limits their ability to evade both habitat alteration/degradation and exploitation. The restricted geographic range of this whipray, the fact that it is not particularly common, and the presumed limited interchange between rivers, increases the species’ inherent sensitivity. Details are required on how several potentially threatening processes may be affecting this ray, namely: commercial fishing (the species’ range overlaps with net fisheries, however it is not very susceptible to capture in gillnets), recreational fishing (parts of its range are extremely popular for recreational fishing, an activity that continues to grow in northern Australia), impoundments and artificial barriers (which have the capacity to affect movements and alter habitat availability, and which may become more common as pressure mounts to develop northern Australia), and broader-scale catchment practices. More remote parts of the species’ range may provide some refuge from fishing, as does river systems closed to commercial fishing. At this time, although the inherent sensitivity of this ray and the existence of future potential threatening processes can be recognized, there is no support for it meeting a threatened category. Depending on future development of rivers the status of this species could change rapidly, but for now it is assessed as Least Concern.
|Previously published Red List assessments:||
|Range Description:||The Freshwater Whipray is possibly endemic to estuarine and freshwater environments of northern Australia, although it may also occur in the Fly River Basin of Papua New Guinea (Last and Manjaji-Matsumoto 2008, Last and Stevens 2009). It has been recorded from the Ord, Fitzroy, and Pentecost Rivers in Western Australia; the Victoria, Daly, Adelaide, South Alligator, and Roper Rivers in the Northern Territory; and the Mitchell, Gilbert, Normanby, and Wenlock Rivers in Queensland (Thorburn et al. 2003, Last and Manjaji-Matsumoto 2008, Last and Stevens 2009, P.M. Kyne, unpubl. data). However, its range is not fully mapped, and it has been suggested that it may occur in most large tropical rivers of northern Australia (Last and Stevens 2009). The Daly River (Northern Territory) and Normanby River (Queensland) systems have been identified as sites of significance for the species, given abundances relative to other systems (Thorburn et al. 2003).|
Native:Australia (Northern Territory, Queensland, Western Australia)
|FAO Marine Fishing Areas:||
Indian Ocean – eastern; Pacific – western central
|Lower depth limit (metres):||6|
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||There is no information available on the population size or trends for this whipray. It is possible that separate subpopulations exist in each of the different river systems in which the species occurs, particularly given that some of these are widely separated, minimising exchange between them. Although its exact status is unknown, it was considered to be uncommon by Larson et al. (2004).|
|Current Population Trend:||Unknown|
|Habitat and Ecology:||
The Freshwater Whipray occurs in freshwater and estuarine habitats. It has been recorded in both tidal and non-tidal reaches of rivers in waters of <30 ppt salinity (usually <10 ppt) and frequents both turbid and clear waters (Thorburn et al. 2003). It has not been recorded from euhaline marine waters (Pogonoski et al. 2002, Last and Manjaji-Matsumoto 2008). Thorburn et al. (2003) documented the species on sparsely covered finer substrates (sand and silt) in the main channel of rivers, to a maximum depth of 3.5 m, although it generally occurred in shallow waters of 0.3–1.0 m. Maximum recorded depth of capture in Northern Territory rivers was 5.6 m (P.M. Kyne, unpubl. data). Maximum recorded size is 124 cm disc width (DW), but most specimens have been <100 cm DW; an 88 cm DW male was adolescent, but exact sizes at maturity are not known for either sex (Thorburn et al. 2003, Last and Manjaji-Matsumoto 2008, Last and Stevens 2009). Thorburn et al. (2003) noted that several individuals are often encountered together, suggesting some sort of aggregation behaviour or concentration in suitable habitat. Most aspects of the species’ ecology and biology are unknown, including reproductive biology (although it is known to be viviparous). There is a lack of knowledge regarding its full habitat requirements. A small number of tagged whiprays in the Wenlock River in Queensland showed a high degree of site fidelity to a <8 km stretch of river, and sexual differences in wet season movement patterns with females remaining in the same river stretches, but males moving downstream to brackish waters (Campbell et al. 2012).
|Use and Trade:||
This species is a component of Indigenous fisheries for food, but available evidence (including community surveys of river resource use in the Northern Territory and Western Australia) suggests that it is taken only in small numbers (Marcus Finn, CSIRO, pers. comm., 2010). Any exploitation by Indigenous communities would be consumed at the local level.The species is not a target of commercial fisheries. The extent to which recreational fishers retain this species for food is unknown but is probably negligible.
There has been a small take of this species for public displays (namely the Territory Wildlife Park outside Darwin in the Northern Territory which has an interactive exhibit housing the Freshwater Whipray). Collection of individuals from the wild will likely continue in the future when replacement animals are required.
There is little concrete information available on threats facing the Freshwater Whipray. Freshwater elasmobranchs are generally of conservation concern given the coupling of the usual biological limitations of the group with the physical constraints of their environment which limits their ability to evade both habitat alteration/degradation and exploitation (Compagno and Cook 1995). Broader-scale catchment practices may also affect the species’ habitat through such activities as overgrazing, land clearing, and mining. The restricted geographic range of the species, the fact that it is not particularly common, and the presumed limited interchange between rivers increases the species’ inherent sensitivity.
Impoundments and artificial barriers on rivers may have caused reductions in habitat available for the species, thus possibly altering its range. Although poorly known, migrations and movement patterns have certainly been affected by these barriers, which can limit or completely restrict movements. Thorburn et al. (2004) noted a concentration of the Largetooth Sawfish (Pristis pristis) and the Bull Shark (Carcharhinus leucas) below Camballin Weir on the Fitzroy River, which acted as an obstacle to upstream movement during the lower water levels of the dry season. Similarly, the Freshwater Whipray is easily observed immediately downstream of Beeboom Crossing on the Daly River, which is impassable to upstream moving elasmobranchs for much of the year (P.M. Kyne, pers. obs.). Impoundments and artificial barriers on rivers may become more common in the future as pressure mounts to develop northern Australia.
During the dry season, when water levels are at their seasonal low, some freshwater elasmobranchs become isolated in disconnected pools, and this may make them more susceptible to capture as they are concentrated in or restricted to smaller areas. Any human-induced reduction in dry season water levels (for example, through water extraction for agriculture or other purposes) may increase this susceptibility to capture as well as reduce available habitat.
It is not known how fishing activities, both recreational and commercial, have affected this species both historically and presently. Parts of its range are extremely popular recreational fishing locations, such as the Daly and Fitzroy Rivers, and elasmobranchs are a bycatch of recreational fishing for Barramundi (Lates calcarifer) (Thorburn et al. 2003). In some areas of these rivers (for example the Douglas-Daly Region of the Daly River which is close to Darwin and easily accessible) recreational fishing activity is considerable. Given the general difficulty and danger of handling stingrays, some fishers who do unintentionally hook this species may cut their line to release the animal. Post-release stress and injuries caused by the remaining line and hook may result in subsequent mortality, although this has not been determined. Thorburn et al. (2003) observed discarded Freshwater Whipray at a site on the Fitzroy River, a result of unwanted catch from recreational fishing (the Largetooth Sawfish and the Bull Shark were also found at the site). Discarded elasmobranchs have been observed at other popular fishing spots on other rivers (P.M. Kyne, pers. obs.), and this highlights that mortality (without utilization) does occur from recreational fishing.
Given the morphology of the species, it is not as susceptible to capture in gillnets (which are used across northern Australia to target commercial species such as Barramundi) as other elasmobranchs such as sawfishes or sharks; it is however susceptible to capture by longline and handline (Thorburn et al. 2003, 2004). The extent of interactions with commercial fisheries targeting Barramundi is largely unknown. Given that this whipray has not been recorded in euhaline marine waters, there are likely no interactions where these fisheries operate in coastal marine waters. These fisheries do operate in some rivers and river mouths, for example the Northern Territory Barramundi Fishery can operate within a restricted number of rivers. However, as these fisheries use monofilament gillnets, interactions with this species are likely to be minimal. Field et al. (2008) did not record the species in the Northern Territory Barramundi Fishery, but gear considerations aside, they largely sampled outside known rivers of Freshwater Whipray occurrence.
Chin et al. (2010) classified the Freshwater Whipray as one of the most susceptible chondrichthyans to the effects of climate change in the Great Barrier Reef and adjacent regions of the Queensland east coast, where it occurs in the Normanby River. This assessment was a result of a high exposure to climate change factors (rising sea levels, rising temperature, changing freshwater input, etc.) within its riverine/estuarine habitat; and the species’ high sensitivity and low adaptive capacity given its relative rarity, habitat specificity, and restricted range (Chin et al. 2010).
The Freshwater Whipray is poorly known, and a priority is to conduct further field research to ascertain the full extent of its range across northern Australia (and verify if it occurs in New Guinea), its habitat use and requirements, its biological parameters, more details of its migration and movement patterns and residency, and the extent to which it is affected by various potentially threatening processes (particularly artificial barriers, fishing activities, land use, and the future potential alteration of flow regimes).
Within the Northern Territory, commercial fishing is prohibited in the Roper (since 1988) and Daly (since 1989) Rivers (Handley 2010). However, this is not a conservation action to aid in the protection of the river’s fauna or habitats, but rather it is to enhance recreational fishing and tourism opportunities. Recreational fishing pressure is high in some parts of the Daly River, particularly during the peak of the Barramundi season. Some other parts of the species’ range are more remote, and this may benefit the species by limiting access for fishing. However, a growing population, improvements in technology, larger recreational boats, greater access to the coast and an increase in fishing tour operators (Handley 2010) means that remote areas are now becoming more accessible.
Areas closed to both commercial and recreational fishing should be considered as a management tool for limiting pressure on the species (Thorburn et al. 2003). Even though the species occurs in some protected areas, such as Kakadu National Park (where it has been documented in the South Alligator River), recreational fishing is still permitted there. Education on the safe release of all freshwater elasmobranchs caught by recreational fishers, like that which has been conducted for sawfish and river sharks (Glyphis species) in parts of northern Australia, should be conducted through community engagement programs.
The middle reaches of the Daly River, in which this whipray occurs, are considered to be a site of national conservation significance by the Northern Territory Government, recognizing the special biodiversity values of the area (Harrison et al. 2009). This does not translate to actual regulatory or legislative protection of the river, but should theoretically guide management towards the conservation of biodiversity.
Compagno and Cook (2005) previously considered H. chaophraya to be globally Vulnerable A1bcde+2ce, but commented that its status in Australia is ‘probably favourable’. Pogonoski et al. (2002) stated ‘[Freshwater Whipray] should be assigned the conservation status of Vulnerable in Australian waters. It has been and will continue to be affected by the complex and synergistic effects of the restrictions of its obligate freshwater habitat, fishing pressure, and habitat alteration/destruction.’ While considerable declines in H. polylepis (the valid name for what was previously referred to as Southeast Asian H. chaophraya) have occurred throughout its Asian range (Compagno and Cook 2005), there is no data to support a Vulnerable listing in Australia for the Freshwater Whipray. While the inherent sensitivity of the species due to it probable life history characteristics, and the restrictions of its habitat, imply that it is of conservation concern, data are rapidly needed to accurately assess the species’ conservation status and it would be remiss to carry the previous global assessment of Vulnerable for ‘H. chaophraya’ from Compagno and Cook (2005) across to the Australian ‘H. dalyensis’. Information on threats and how these are affecting the species need to be urgently gathered.
Under the Territory Parks and Wildlife Conservation Act 2000, the Freshwater Whipray is listed as Data Deficient in the Northern Territory.
|Citation:||Kyne, P.M. 2015. Himantura dalyensis. The IUCN Red List of Threatened Species 2015: e.T195319A68627227. . Downloaded on 24 June 2016.|
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