White-edge freshwater whipray  (Himantura signifer)

Classified as Endangered (EN) on the IUCN Red List (1).

Very little is known about this mysterious ray, as just ten specimens have been identified and studied in museums (1). Named for the pale margin of its disc-shaped body (2), the white-edge freshwater whipray is light grey in colour on the upper surface (3), and the underside is very pale, which aids camouflage amongst the river bed and water surface respectively. Two pale spots are visible on the ray's upper surface, each one positioned between an eye and a spiracle (2), a small opening which allows water to pass over the gills whilst the ray is still. Characteristic of the Himantura genus, this whipray also has a long, slender tail. Male white-edge freshwater whiprays differ from females by the possession of a pair of claspers, which are used to transfer sperm to the female during mating (2) (3).

The white-edge freshwater whipray is thought to have a limited range in four tropical river systems within South East Asia. The few specimens identified have come from Thailand, Malaysia and Indonesia (1) (2).

Primarily occurring in tropical freshwater habitats, the white-edge freshwater whipray glides across sandy river and estuary bottoms (1) (2). However, studies have revealed that this species also enters brackish water at some time in its life (4).

Little is known about the life history and ecology of the white-edge freshwater whipray, as few individuals have been studied. Its diet consists of crustaceans and shellfish dwelling on the river bed (2). Reproduction is ovoviviparous, a method of reproduction in which the young, known as pups, develop within eggs that remain inside the female’s body until they hatch; the female then gives birth to live young (2).

As with many ray species, a sharp spine on the tail is used for defence and can cause painful and potentially fatal injuries for enemies, including humans (2).

Like a number of other freshwater ray species, the white-edge freshwater whipray is under threat, primarily by habitat loss and degradation, as habitat is cleared to make way for new residential and industrial sites. Where this building occurs in river catchment areas, alteration to the water supply and flow can negatively affect the freshwater habitat of this species (5).

The clearance of forests can also have enormous impacts on the surrounding freshwater habitats and their inhabitants. Without the protective layer of the forest canopy, more rain reaches the ground and quickly runs into the rivers, resulting in floods downstream during monsoon periods. Conversely, without the forest to soak up rainfall and slowly release it into nearby streams, drought can occur in the upper reaches of streams during dry periods (6). Dams are constructed to try and prevent flooding downstream; however, these barriers have a negative impact on the white-edge freshwater whipray by splitting and isolating populations (1) (5).

Development can also cause pollution, which drastically impacts the nearby rivers. This includes industrial waste, sewage and agricultural chemical build up, as well as silt run-off from mining (1) (5). In addition, the white-edge freshwater whipray is known to be eaten in Thailand (3), and the intense fishery industry in much of this species’ range threatens populations through bycatch. It is also captured to satisfy demand for the aquarium market (7).

A conservation project was initiated by the Thai government in the 1990s, consisting of a breeding programme to boost populations upstream of dams (1). However, this was unfortunately put on hold in 1996 and no definite conservation measures for this species have been in place since (1).

Hope for this little-known ray is likely to come from successful management and conservation of tropical freshwater ecosystems as biodiversity hotspots, rather than species-specific measures. However, this is a tough challenge, involving national policy change and continued research (8).

View information on this species at the UNEP World Conservation Monitoring Centre.