Himantura undulata

Until recently Bleeker’s Variegated Whipray (Himantura undulata) included the recently described species, the Leopard Whipray (H. leoparda) (Last and Stevens 1994, 2009). These two species are often confused with the Reticulate Whipray (H. uarnak) and the Honeycomb Whipray (H. fava) (White et al. 2006). All of these whiprays are from the ‘uarnak’ species-complex, a subgroup of mainly reticulated, ocellated or spotted whiprays. Bleeker’s Variegated Whipray juveniles of 50 cm disc width (DW) have a well developed main denticle band with inconspicuous primary denticles while the adults have a strong pattern of large ocelli and reticulations. Conversely, adults of the Reticulate Whipray have fine reticulations and small black spots, the Leopard Whipray have leopard like markings, while the Honeycomb Whipray have honeycomb reticulations that are widely spaced (White et al. 2006, Manjaji-Matsumoto and Last 2008).

Taxonomic work is currently ongoing to more clearly define the sister species relationships among the ‘uarnak’ species-complex (Peter Last pers. comm. 2010). Manjaji (2004) considers Bleeker’s Variegated Whipray to be a senior synonym of the Honeycomb Whipray (Manjaji-Matsumoto and Last 2008).

Bleeker’s Variegated Whipray occurs in the Indo-West Pacific from India to eastern Indonesia, though its distribution is poorly defined as this range is based on current knowledge of this species. There are ongoing taxonomic issues that are being investigated and the outcomes of these may affect the known distributional range. There are no confirmed records of this species from Australia (Last and Stevens 2009, Last et al. 2010).

This species is caught regularly in Indonesia, but rarely in Malaysia (Manjaji and White 2004). There is no species-specific information about populations or trends, however in a large part of its range there is heavy fishing pressure and extensive habitat degradation, and it is suspected that significant population declines have occurred and are ongoing.

The threats to Bleeker’s Variegated Whipray are many of those faced by other Himantura species within its range. Bleeker’s Variegated Whipray may be more vulnerable than some of its congeners due to its large size at maturity and maximum size and its preference for inshore coastal waters that are heavily fished and degraded in many parts of its range (Manjaji and White 2004).

In Indonesia and across large parts of its distribution, Bleeker’s Variegated Whipray is caught by demersal trawl and tangle/gill nets, dropline and longline fishing, Danish seine fishing gear, and coastal artisanal fisheries (Manjaji and White 2004, White and Dharmadi 2007, Last et al. 2010). This species is commercially valuable, with most specimens caught as bycatch landed and sold. Bleeker’s Variegated Whipray is important in the gill and tangle net fisheries in Indonesian waters, which likely also includes adjacent waters. These fisheries, along with trawl fishing are particularly intensive in the Arafura Sea region (W. White pers. comm. 2010). In 2004, it was reported that more than 600 trawlers operated in the Arafura Sea and that catches in inshore waters had declined with vessels travelling further south to maintain catches (Manjaji and White 2004). Although the numbers of trawlers currently operating is unclear this intensive fishing pressure still continues; high levels of Indonesian trawl fishing in the Arafura Sea adjacent to the Australian Fishing Zone have recently been reported (Heazle and Butcher 2007, Northern Territory Government 2009) and thus the level of exploitation of this species could be extremely high.

In recent decades, demersal fishing pressure has increased in both capacity and effort in many areas of this species’ inshore range. 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). On standardized trawl surveys conducted over this 20 year period in the Gulf of Thailand, the abundance (biomass) of the major trawl bycatch groups was recorded. The group ‘rays’ showed a large reduction in biomass over this period and an ecosystem model fitted to the bycatch data indicated that ‘rays’ were one of the groups most severely impacted by the initial increase in fishing pressure (Pauly et al. 2005). Species-specific catch data are not available, but Indonesian landings of ‘Rays, stingrays, mantas, nei’ (nei = not elsewhere included) increased from ~10,000 t in 1975 to 58,000 t in 2004 (FAO 2009).

This species’ preference for inshore coastal waters means it is also threatened by extensive habitat degradation, including pollution and clearing, and destructive fishing practices. Large coastal areas, in particular mangroves, have been lost in Indonesia and Malaysia through land conversion for urban development, shrimp farms and agriculture. Across Indonesia and Malaysia from 1980 to 2005, the area of mangroves was reduced by >30% (FAO 2007).

Although data are available mostly only for grouped ‘rays’ and not specifically for Bleeker’s Variegated Whipray and/or other Himantura species, given that Bleeker’s Variegated Whipray is a large species with a preference for shallow waters where threats from coastal fisheries and habitat degradation are highest, significant declines are suspected to have occurred in Southeast Asia, the northern Indian Ocean and elsewhere in areas of high exploitation (Manjaji and White 2004).

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