|Scientific Name:||Dasyatis fluviorum|
|Species Authority:||Ogilby, 1908|
|Red List Category & Criteria:||Vulnerable A2bcd+3cd+4bcd ver 3.1|
|Assessor/s:||Kyne, P.M., Pollard, D.A. & Bennett, M.B. (SSG Australia & Oceania Regional Workshop, March 2003)|
|Reviewer/s:||Cavanagh, R.D. (Shark Red List Authority) & Pogonoski, J.|
Dasyatis fluviorum is recorded from the east and north coasts of Australia and the southern coast of New Guinea. Very little is known of its biology and ecology. Once common, there is considerable anecdotal evidence of a significant range contraction and decline in abundance for this species in the waters of New South Wales and southern Queensland, Australia. Historic accounts report that D. fluviorum was an extremely common species in the bays and estuaries of southern Queensland and New South Wales. It has not been reported from Port Jackson and Botany Bay, New South Wales, where it was once common, since the 1880?s and is now uncommon anywhere along the central and northern coast of New South Wales. The southern limit of the species is uncertain. The species also appears to be declining in the estuaries of southern Queensland, where it was also once common. This decline is probably the combined result of a number of threatening processes, including, bycatch in commercial fisheries, persecution by shellfish farmers, destruction of incidental catches by recreational fishers and during some commercial fishing activities, and habitat degradation and loss due to foreshore development. The species appears particularly vulnerable to such human activities due to its reliance on shallow tidal and mangrove habitats, particularly within estuaries and rivers. D. fluviorum is assessed as Vulnerable (VU A2bcd+3cd+4bcd) given its decline in range and abundance, decline in quality of habitat and continuing threats. Habitat protection, fisher education and research are priorities for its recovery.
|Range Description:||Dasyatis fluviorum has a subtropical to tropical distribution in Australian waters from New South Wales (NSW) north to at least the central Queensland coast, and west from Cape York in Queensland to Darwin in the Northern Territory. Its occurrence north of Proserpine (around 20°30'S) to Cape York, Queensland, requires verification (Pogonoski et al. 2002, Jeff Johnson, pers. comm.). It is also recorded from southern New Guinea, off both Papua New Guinea and Indonesian Irian Jaya. Its occurrence off the northern coast of New Guinea has not been verified (Last and Stevens 1994). This species is reported from FAO Fisheries Areas 71 (Western Central Pacific) and 81 (Southwest Pacific). As well as being reported from marine and estuarine waters, it is known to ascend rivers to beyond the tidal limit (Whitley 1940). Historically, the southern extent of its range in NSW was Botany Bay and Port Jackson (33°51'S), however it has not been reported there since the 1880s (Pogonoski et al. 2002). Its southern range extent is uncertain, but may now be Forster (32°10'S) (Last and Stevens 1994). Although Gray et al. (1990) report the species from the Hawkesbury River (33º34'S), this report can not be verified (J. Pogonoski, pers. comm.).|
Native:Australia (New South Wales, Northern Territory, Queensland); Indonesia (Irian Jaya); Papua New Guinea
|FAO Marine Fishing Areas:||
Pacific – southwest; Pacific – western central
|Range Map:||Click here to open the map viewer and explore range.|
|Habitat and Ecology:||
This species is reported from mangrove-fringed rivers and estuaries, and offshore to at least 28 m depth, but more commonly in shallow inshore waters (Last and Stevens 1994, Pogonsoki et al. 2002). As well as being reported from marine and estuarine waters, it is known to ascend rivers to beyond the tidal limit (Whitley 1940). However, the species appears to be rather habitat specific, and appears to be common only at a number of suitable locations. Dasyatis fluviorum is reported to reach a disc width (DW) of 120 cm. Young are born at 11 cm DW (Last and Stevens 1994). The species is reported to be a major predator of shellfish, including farmed oysters (Whitley 1940, Last and Stevens 1994) however, detailed dietary assessments are unavailable. Individuals move over mudflats with the incoming tide to feed, and in Moreton Bay, southern Queensland, have been found to consume numerous soldier crabs (Mictyris longicarpus) (P. Kyne, pers. obs).
While published estimates of size at sexual maturity are lacking, of 12 males examined from Moreton Bay, the smallest mature individual was 45 cm DW. All individuals of greater size than this were mature. The smallest mature female from seven individuals examined was 43 cm DW (unpublished data). Sexual maturity was determined by methods outlined in Bass et al. (1973). There is no available information on the reproductive biology (including fecundity or gestational period), age and growth, natural mortality or detailed behavioural ecology of this species.
Once common, there is considerable anecdotal evidence of a significant contraction and decline in abundance for this species in the waters of NSW and southern Queensland. A number of threatening processes can be identified as acting on the species, which have, and still are, probably combining to cause the current population trend. While Dasyatis fluviorum is not utilized commercially (Last and Compagno 1999), it is taken as bycatch in inshore commercial fisheries, including demersal prawn trawl fisheries in NSW and Queensland (P. Kyne, pers. obs.). The species readily takes cut fish baits and is therefore prone to capture by inshore line fishing (recreational and commercial). Incidental capture by recreational fishers is also likely to be a significant threat to the species as fishers often destroy any stingray catches (Pogonoski et al. 2002, P. Kyne, pers. obs.). Decline in southern Queensland waters is also thought to be a result of the reclamation of large areas of shallow muddy tidal bays and mangroves for the development of urban areas, canal estates and marinas. For example, over 20% of the original mangrove habitat of Moreton Bay in southern Queensland has been lost to such development since European settlement (Greenwood 1993).
This stingray has been reported to feed voraciously on farmed oysters (Whitley 1940, Last and Stevens 1994), and subsequent persecution by commercial shellfish farmers in NSW and southern Queensland estuaries has probably been another factor contributing to the species? apparent decline. Furthermore, the practice of "spiking" incidentally caught stingrays (using a metal bar or stick with a sharpened point attached to pierce the animal?s chondrocranium and remove it from nets, sorting trays, etc.) continues in many commercial fishing situations and may be a potentially significant source of mortality.
No information is available on the species? current status in New Guinean waters, although in that locality it is likely to face pressure from subsistence fishing activities and the effects of pollution from mining and other land-based activities.
Dasyatis fluviorum is listed as Near Threatened, using the previous IUCN Red List system in the Conservation Overview and Action Plan for Australian threatened and potentially threatened marine and estuarine fishes published by Environment Australia (Pogonoski et al. 2002). This report emphasises, however, that there is significant concern for this species and that it needs to be closely monitored to ensure that its conservation status is not raised into the Vulnerable category in the near future (Pogonoski et al. 2002). Here, however, the species meets the criteria for a Vulnerable listing.
Pogonoski et al. (2002) recognise critical habitat for D. fluviorum as relatively shallow mangrove and estuarine areas and suggest that habitat protection is required as a recovery objective. While D. fluviorum is likely to occur in a number of Marine Protected Areas in NSW and Queensland waters, the zoning plans for these parks and reserves restrict fishing activities in only small areas and do not generally protect sufficient areas of the habitat of this species.
The species is still relatively common in some southern Queensland estuaries and bays (Hervey Bay, parts of Moreton Bay), and these areas may be important for habitat protection (they are however, also heavily fished both commercially and recreationally and face development pressure).
Education of commercial fishers, aquaculturists and recreational fishers is a priority to halt the destruction of incidental catches of the species.
|Citation:||Kyne, P.M., Pollard, D.A. & Bennett, M.B. (SSG Australia & Oceania Regional Workshop, March 2003) 2003. Dasyatis fluviorum. In: IUCN 2012. IUCN Red List of Threatened Species. Version 2012.2. <www.iucnredlist.org>. Downloaded on 24 May 2013.|
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