Himantura leoparda

The Leopard Whipray (Himantura leoparda) is a recently described species of whipray closely related and similar in shape and dorsal disc pattern to the Reticulate Whipray (H. uarnak) and Bleeker’s Variegated Whipray (H. undulata). These three species are from the ‘uarnak’ species-complex, a subgroup of mainly reticulated, ocellated or spotted whiprays. The Leopard Whipray can be distinguished by its unique arrangement of midscapular denticles and the leopard-like markings on the dorsal surface of adults and large specimens. Juveniles of the three species are born at different sizes and vary slightly in colour patterns and denticle shapes (Manjaji-Matsumoto and Last 2008, Last and Stevens 2009). Taxonomic work is currently ongoing to more clearly define the sister species relationships (Peter Last pers. comm. 2010).

The Leopard Whipray (Himantura leoparda) is possibly widely distributed in the Indo-West Pacific in mainly coastal inshore waters. It is currently known to range from Malaysia to the Japanese Archipelago and south to northern Australia, however there are ongoing taxonomic issues that are being investigated; the outcomes of which may affect the known distributional range. Its biology is poorly known, partly due to confusion with other members of the ‘uarnak’ species-complex. This species is commercially valuable throughout Southeast Asia where it is taken as utilised bycatch in a range of commercial and artisanal fisheries including demersal trawl and tangle/gill nets, dropline and longline fisheries, and Danish seine fisheries. In recent decades, demersal fishing pressure has increased in both capacity and effort and is intense throughout this species’ inshore range in Southeast Asia. Fishing pressure is also very heavy in the Arafura Sea region; previously more than 600 trawlers operated and although the numbers of currently active trawlers is unclear, there are still high levels of Indonesian trawl fishing in the area. This level of exploitation is of great concern to the sustainability of Leopard Whipray populations in the Arafura Sea outside the Australian Fishing Zone. This species’ preference for inshore coastal waters means it is also threatened by extensive habitat degradation and destructive fishing practices throughout a large part of its range. Although species-specific data are not available, given the species’ high levels of exploitation, extensive habitat degradation and its large size, significant population declines are suspected to have occurred and are likely to be ongoing in Southeast Asia.

Conversely, this species has refuge from fishing pressure in northern Australia, where fishing pressure is light, bycatch mitigation measures are in place and it is not commercially utilised and consequently is considered at low risk. While fisheries in northern Australia remain well managed this species is assessed as Least Concern regionally in Australia. Globally, it is assessed as Vulnerable on the basis of suspected declines as a result of high levels of exploitation and habitat degradation in large areas of its range. These assessments should be revisited if and when there is any new taxonomic and distributional information as this may affect the fishing pressure to which this species is exposed.

The Leopard Whipray is possibly widespread in the Indo-West Pacific. Its distributional range is based on current knowledge, however there are ongoing taxonomic issues that are being investigated and the outcomes of these may affect the known distributional range. It is currently known to range from Malaysia to the Japanese Archipelago and south to northern Australia (where it occurs from Coral Bay, Western Australia to the Torres Strait, Queensland) (Manjaji-Matsumoto and Last 2008, Last and Stevens 2009). It is currently thought to be absent from the western Indian Ocean.

There is no species-specific information about populations or trends for the Leopard Whipray, 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. It is not possible to estimate the proportion of the global population occurring within the Australian region as there is little information on the population structure of this species, however an estimated 15% of the Leopard Whipray’s known distributional range is in the Australian region.

The Leopard Whipray is demersal on soft substrates and is mainly inshore and coastal though it also occurs on the continental shelf to at least 70 m depth (White et al. 2006, Manjaji and Last 2008). The biology of this species is poorly known, partly due to confusion with other species of the ‘uarnak’ species-complex; attains about 140 cm disc width (DW); born at about 20 cm DW. Males mature at 70–94 cm DW (White and Dharmadi 2007, Last and Stevens 2009). Reproduction is viviparous and the diet is unknown but likely comprises small fishes and crustaceans (White et al. 2006).

As there is no information on this species’ maximum age and age at maturity, generation length was inferred as 20 years based on data for the congener, the Blackspotted Whipray (Himantura astra). Female Blackspotted Whiprays are reported to have a maximum age of 29 years and an age at maturity of nine years (Jacobsen and Bennett 2011). These were used to calculate a generation length of 19 years based on the equation: generation length = (((29-9)/2)+9). The maximum size of the Leopard Whipray is considerably larger (~140 cm DW) than that of the Blackspotted Whipray (80 cm DW) so it is possible the generation length of the Leopard Whipray could be greater than 20 years.

The threats to the Leopard Whipray are many of those faced by other Himantura species within its range. However, the Leopard 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 outside Australian waters (Manjaji and White 2004).

In Indonesia and across large parts of its distribution, the Leopard 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 et al. 2006). In Southeast Asia, this species is commercially valuable, with most specimens caught as bycatch landed and sold. The Leopard 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 the Leopard Whipray and/or other Himantura species, given that the Leopard 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.