|Scientific Name:||Glaucostegus typus (Anonymous [Bennett], 1830)|
Rhinobatos typus Anonymous [Bennett], 1830
Rhinobatos batillum Whitley, 1939
Rhinobatus armatus Gray, 1834
|Taxonomic Source(s):||Anonymous [Bennett], E. T. 1830. Class Pisces. In: Lady Stamford Raffles (ed.), Memoir of the life and public services of Sir Thomas Stamford Raffles, pp. 686-694. John Murray, London.|
|Taxonomic Notes:||Some recent changes in the systematics of Rhinobatus have elevated the subgenus Glaucostegus to full generic status and placed this genus into a family of its own: Glaucostegidae (Compagno 2005, Last et al. 2016).|
|Red List Category & Criteria:||Vulnerable A2bd+3bd+4bd ver 3.1|
|Assessor(s):||White, W.T. & McAuley, R.B.|
|Reviewer(s):||Fowler, S.L., Kyne, P.M. & Cavanagh, R.D.|
This is an amended version of the 2003 assessment to accommodate recent taxonomic revision of the genus Rhinobatus, and the former subgenus Glaucostegus being raised to genus level.
Glaucostegus typus is taken by multiple artisanal and commercial fisheries throughout its range both as a target species and as bycatch. Flesh is sold for human consumption in Asia and the fins from large animals fetch particularly high prices, creating a significant incentive for bycatch to be retained. Very little is known about the biology or population status of this species. Given its susceptibility to capture by multiple fishing gear types, including trawl nets, gillnets and hooks and its high value fins, it is probable that numbers have been locally reduced by fishing throughout its range. Local population depletion can be inferred from Indonesia where the target gillnet fishery fleet for rhinids and rhynchobatids has declined significantly, reportedly due to declining catch rates. Therefore, globally this species meets the criteria of Vulnerable A2bd+3bd+4bd due to the apparent population decline outlined above and the remaining very high level of exploitation in South East Asia. Furthermore, destruction of habitat, e.g., mangrove areas, and high level of fishing pressure in areas such as Papua (e.g., Merauke) may be having a deleterious effect on juveniles of this species that utilize such inshore regions.
There are no target fisheries for G. typus in Australia but it is a known bycatch of demersal trawl fisheries in the region. The introduction of Turtle Exclusion Devices (TEDs) in the Australian Northern Prawn Trawl Fishery in 2000 and the implementation of various elasmobranch-finning prohibitions, has probably led to a recent reduction in captures by this sector. However, given the population declines throughout South East Asia and the high value placed on fins (even in Australia) the Australian population may meet the criteria of Vulnerable A2d, but more detailed catch data is required and it is thus assessed as Near Threatened in Australian waters.
|Previously published Red List assessments:|
|Range Description:||Glaucostegus typus is widely distributed in the Indo-Pacific (Last and Stevens 1994, Compagno and Last 1999). Another species, G. granulatus, co-occurs with this species at the western extremity of its range but has not been positively identified from the Australia and Oceania Region (Last and Stevens 1994).|
Native:Australia (New South Wales, Northern Territory, Queensland, Western Australia); Bangladesh; India; Indonesia; Malaysia; Singapore; Sri Lanka; Viet Nam
|FAO Marine Fishing Areas:|
Indian Ocean – western; Indian Ocean – eastern; Pacific – western central; Pacific – southwest
|Range Map:||Click here to open the map viewer and explore range.|
|Current Population Trend:||Decreasing|
|Habitat and Ecology:||Juveniles of G. typus occur inshore, e.g., mangrove systems and estuaries, and around atolls, whilst adults are found in the deeper waters of the continental shelf to about 100 m (Last and Stevens 1994). This species has also been reported to be able to live and breed permanently in freshwater. |
Glaucostegus typus is reported to attain at least 270 cm in length (Last and Stevens 1994). Although no published information is available on size at maturity and reproductive biology of this species, specimens examined from Shark Bay (Western Australia) showed that females and males appear to mature at between 155 and 175 cm total length (TL), and young are born at approximately 38 to 43 cm TL (W. White, unpublished data). There does not appear to be a distinct seasonal reproductive cycle with newborn young found in most months of the year (W. White, unpublished data).
This species is a major predator of crustaceans, with an examination of the diets showing that more than 90% of food ingested belongs to juveniles of either the blue swimmer crab (Portunus pelagicus) or the western king prawn (Melicertus latisulcatus) (W. White, unpublished data). Juveniles also utilize shallow sand flats as nursery areas and move into mangrove areas and sand flats at high tide to feed.
There is no published information on the age at maturity, longevity and natural mortality of this species.
The fins from G. typus are widely considered as being amongst the most valuable of elasmobranchs (i.e., white-fin) and there is a significant incentive for fishers to remove the fins from large individuals when they are taken as either target catch or bycatch. Glaucostegus typus is commonly landed as bycatch in fisheries in Indonesia (Bentley 1996, Chen 1996, W. White personal observation). Fisheries targeting the rhynchobatids in eastern Indonesia, e.g., Aru Islands and Merauke (Papua), often catch this species but generally in low numbers.
Since juveniles of this species inhabit shallow sand flats and mangrove estuaries (Last and Stevens 1994, W. White unpubl. data), intensive fishing pressures, e.g., gill, trap and seine nets, in such inshore areas throughout Indonesia, e.g., Merauke (Papua), are most likely having a high level of impact on this species.
Such threats to this species in the Australia and Oceania region appear to be more confined to eastern Indonesia (e.g., Papua). There are no target fisheries for G. typus in Australia but it is a known bycatch of demersal trawl fisheries in the region (Stobutzki et al. 2000, Stephenson and Chidlow in prep.). In northern Australia, this species constitutes a minor component of the catch in the northern prawn trawl fishery and since the introduction of compulsory turtle excluder devices (TEDs) in this fishery in the year 2000, the number of large individuals of such elasmobranchs retained have been further reduced (Stobutzki et al. 2002). There is also likely to be only limited fishing pressure on juvenile G. typus in inshore regions in northern Australia.
|Conservation Actions:||Further research into the population structure, biology and ecology of G. typus is required to assess the extent to which fishing pressure, particularly in relation to finning, and habitat destruction is influencing this species within its range. Improved species composition data from all fisheries that take shovelnose rays and guitarfish is necessary.|
|Citation:||White, W.T. & McAuley, R.B. 2016. Glaucostegus typus. The IUCN Red List of Threatened Species 2016: e.T41849A104018648.Downloaded on 17 February 2018.|