|Scientific Name:||Dipturus australis|
|Species Authority:||(Macleay, 1884)|
Raja australis Macleay, 1884
|Red List Category & Criteria:||Vulnerable A2bd+4bd ver 3.1|
|Assessor(s):||Stevens, J.D. & Valenti, S.V.|
|Reviewer(s):||Gibson, C. & Pogonoski, J. (Shark Red List Authority)|
The Sydney Skate (Dipturus australis) occurs on the continental shelf of eastern Australia between Moreton Bay (Queensland) and Jervis Bay (New South Wales), at depths of 22-325 m. The species attains about 50 cm total length. This was once one of the most common skates on the continental shelf off eastern Australia, however there is evidence that it has declined significantly in areas of its range. Fishery independent surveys off southern New South Wales (NSW) have shown that catch rates for "skates" combined have declined by 83% between 1976/1977 and 1996/1997. The Sydney Skate was the dominant species in the upper depth zone surveyed (200-275 m). This species is impacted on the NSW trawl grounds, in the southern part of its range, but also occupies large areas of lightly or non-trawled bottom off central and northern NSW. Therefore the species is assessed as Vulnerable based on past and continuing population declines estimated at >30% globally, reflecting its distribution outside of heavily fished areas too. Population trends should be monitored and the species may prove to qualify for a higher category in the future.
|Range Description:||Southwest Pacific: continental shelf of eastern Australia between Moreton Bay (Queensland) to at least Tathra (New South Wales, c. 36 45) (Last and Stevens 1994, K. Graham pers. comm. 2008).|
Native:Australia (New South Wales, Queensland)
|FAO Marine Fishing Areas:||
Pacific – southwest
|Range Map:||Click here to open the map viewer and explore range.|
The most common skate on the continental shelf of central eastern Australia. Fishery independent surveys off southern New South Wales have shown that catch rates have declined by 83% between 1976/1977 and 1996/1997 for grouped "skates" (Graham et al. 1997, Graham et al. 2001). Eight species of skates were recorded during this study, with data pooled into four depth zones. The principle species captured in the deeper depth zones (330-605 m depth), on all trawl grounds were Dipturus gudgeri and Dipturus sp. B. In the upper depth zone (200-275 m), catches mainly comprised D. australis, but also included Raja sp. A and C and Dipturus whitleyi (Graham et al. 2001). Catch data were pooled for all species and mean catch rates calculated for the mix of species combined. In 1976-77, mean catch rates for skates were similar on all grounds (range 32-33 kg h-1) but were substantially lower in 1996-97 (range 4-8 kg h-1). Declines in the upper depth zone, where D. australis comprised the majority of catch, where greatest off Eden, in the southern survey areas.
There are limited species-specific fisheries catch data for skates, with most being lumped into the category "rays". Batoid sales and landing data from major markets, such as Sydney and Melbourne, are also limited, with only major categories such as "Rajids" recorded.
|Habitat and Ecology:||This skate occurs on the continental shelf at depths of 50-180 m (Last and Stevens 1994). They reach about 50 cm total length (TL) and adult males and females are similar in size. Males mature at 43-48 cm TL (Last and Stevens 1994). A bottom-dwelling species that probably feeds on invertebrates (including small to large crustaceans, cephalopods) and demersal bony fish. Like other skates, reproduction is oviparous and the species deposits eggs in large, quadrangular egg cases. The biology of Dipturus australis is virtually unknown.|
Presumably, taken as bycatch of trawl fisheries operating in the area, such as the Commonwealth Trawl Sector of the Southern and Eastern Scalefish and Shark (SESS) fishery. This fishery has operated since the 1900s and targets a number of teleost species such as tiger flathead, jackass morwong, eastern school whiting, John Dory etc.
These target species are under quota management, but sustainable catch levels for Sydney skate will be much lower than for the more productive teleost species. Independent surveys off southern New South Wales show catch rates for "skates" combined have declined by 83% over 20 years (Graham et al. 2001). Commercial trawling on the upper slope off NSW began in 1968 and by the early 1980s more than 100 trawlers between 15-25 m were operating off NSW, landing about 15,000 t of fish per year. About 60 of these trawlers regularly fished on the upper slope. By the end of the 1990s, the number of trawlers regularly fishing the NSW slope grounds had reduced to about 40 (Graham et al. 2001).
D. australis is still impacted on NSW trawl grounds but also occupies large areas of lightly or non-trawled bottom off central and northern NSW (K. Graham pers. comm. 2007).
Most skates caught off southeastern Australia used to be discarded, but most of the larger ones would now be retained for the local market. In 2005, 29% of Dipturus australis were retained based on observer monitored catches (ISMP data) More recently, increasing management of major commercial species has resulted in fishers looking for alternate species to market, including skates and rays. At the Melbourne wholesale fish market the only separate sales figures for batoids are for skates (Family Rajidae). For the year 2002, 43 tonnes of "flaps" were sold which equates to 134 tonnes live weight. At the Sydney market, batoids are sold under a number of categories. Common names make it difficult to determine the exact species but most appear to be myliobatids, rhinobatids, rhynchobatids and smaller amounts of dasyatids.
None specific to Sydney skate. Trawl fisheries in the area are under quota management.
Fisheries management in Australia is starting to move from single species management to ecosystem management and all fisheries now have Bycatch Action Plans and have to be assessed for ecological sustainability. They are required to meet certain certification standards if they are to continue operating.
|Citation:||Stevens, J.D. & Valenti, S.V. 2009. Dipturus australis. The IUCN Red List of Threatened Species. Version 2015.2. <www.iucnredlist.org>. Downloaded on 30 June 2015.|
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