|Scientific Name:||Mustelus antarcticus|
|Species Authority:||Günther, 1870|
|Red List Category & Criteria:||Least Concern ver 3.1|
|Assessor(s):||Walker, T.I. (SSG Australia & Oceania Regional Workshop, March 2003)|
|Reviewer(s):||Fowler, S., Cavanagh, R.D. & Kyne, P.M. (Shark Red List Authority)|
Mustelus antarcticus is a highly abundant southern Australian endemic with relatively high productivity (longevity 16 years, low age at maturity, eight year generation period, and up to 38 pups per litter). It is harvested over its entire range, but about two-thirds of the catch is taken from Bass Strait. There is no population fragmentation. Mandatory adoption of middle-sized mesh-sizes in the fishery and the large area closure of all Victoria waters to shark fishing provide effective protection of large breeding females. Age-based fishery assessment models indicate that current catch levels are sustainable and that, while the number of births is closely related to the number of maternal animals, recruitment to the fishery at age two years is remarkably stable for a wide range of population sizes. In Bass Strait, South Australia and Western Australia, stock assessments indicate that biomass has been 40 to 55% of initial biomass for most of the past two decades, with less than 20% change in population size over the three generation period. A steady decline in fishing effort since the mid-1980s and adoption of a total allowable catch (TAC) during 2000 has led to a steady increase in abundance of mature and maternal animals in the population. Biomass is above the level required to provide the maximum sustainable yield. This species is therefore updated from the 2000 assessment of Conservation Dependent to Least Concern.
|Range Description:||M. antarcticus is endemic to southern Australia from about Port Stephens in New South Wales (32°S) to about Geraldton in Western Australia (28°S). The species is demersal, occurring mainly on the continental shelf from the shore to about 80 m depth, but also on the upper slope down to 350 m. Very similar (possibly the same) species occur on the east and west coasts of Australia between latitudes of about 17° and 30°S in depths between 120 and 400 m (Last and Stevens 1994).|
Native:Australia (New South Wales, South Australia, Tasmania, Victoria, Western Australia)
|FAO Marine Fishing Areas:||
Indian Ocean – eastern; Pacific – southwest; Pacific – western central
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||Tagging (Walker 1983, Walker et al. 2000), genetic (MacDonald 1988, Gardner and Ward 1998) and morphometric (Heemstra 1973) studies indicate the presence of three genetic stocks of M. antarcticus. One ranges along the southern coast of Australia from Bunbury in the west to Eden (Bermagui based on tag data) in the east, a second is located off New South Wales in the region from Newcastle to Clarence River, and a third is located off Queensland near Townsville. Shark fisheries mainly harvest animals from the stock on the south coast.|
|Habitat and Ecology:||
Female M. antarcticus reach a longer total length (185 cm) than the males (148 cm) (T. I. Walker, Marine and Freshwater Resources Institute, Victoria, Australia, unpublished data), and reach a maximum weight of 24.8 kg (Walker 1983). Tagging and ageing studies indicate that the species has a maximum life span of about 16 years (Moulton et al. 1992).
The species exhibits aplacental viviparity with uterine compartments. Ovulation occurs October to mid-December in Bass Strait and off South Australia (Walker 1996) and November to February off Western Australia (Lenanton et al. 1990). Pregnant sharks carry 1 to 38 young, and large mothers carry more embryos than smaller ones. The length at first maturity and the proportion of sharks longer than this length found to be pregnant increases from east to west (Walker 1996). In Bass Strait about half of the population of large female sharks breed each year whereas off South Australia (Walker 1994a) and Western Australia (Lenanton et al. 1990) most breed each year. The sex ratio of embryos is 1:1 and mean length at birth is about 33 cm (Walker 1983). The young are usually born in shallow coastal areas.
The blunt, flattened teeth of gummy sharks are more suited to crushing rather than cutting their prey. They prey on a wide variety of demersal species from areas of sandy and, to a lesser extent, rocky substrate. Studies of stomach contents show that gummy sharks in Bass Strait feed on at least 95 species and that squid and octopus contribute most weight (36%) to their diet. Crustaceans contribute 25% by weight and teleost fish 11%. The remaining 28% consist of 12 other classes of organism and unidentifiable material (Walker 1996). These animals do not exhibit well defined migration patterns, but tag data indicate that some large females leave Bass Strait and move to waters off South Australia and Western Australia. Movements rates from South Australia to Bass Strait are much lower (Walker et al. 2000).
In the Australian Southern Shark Fishery, Mustelus antarcticus and Galeorhinus galeus have been targeted in oceanic waters since the mid-1920s and possibly earlier in inshore areas. Baited hooks attached to bottom-set longlines was the principal fishing method until the early 1970s when the method was replaced by bottom-set gillnets.
Today the main threat to populations of M. antarcticus are from targeting widely across southern Australia with gillnets of 6 to 6½-inch mesh-size off South Australia, Victoria and Tasmania of 6½ to 7-inch mesh-size off Western Australia. In Bass Strait (Walker 1994, 1998), South Australia (Walker 1994b), and Western Australia (Simpfendorfer 1999), stock assessment indicates that the level of biomass was 40 to 55% of initial biomass for most of the past two decades. A steady decline in fishing effort since the mid-1980s and adoption of a total allowable catch during 2000 led to a steady increase in abundance. There is negligible targeting for M. antarcticus off New South Wales and south of Bass Strait off Tasmania. In accordance with the FAO Code of Conduct for Responsible Fishing, the biomass is above the level required to provide the maximum sustainable yield.
Application of age-based fishery assessment models, allowing for age- and density-dependent natural mortality and incorporating information on growth and reproduction of the species and on selectivity of gillnets indicates that current catch levels are sustainable and shows that while the number of births is closely related to the number of maternal animals, recruitment to the fishery at age two years is remarkably stable for a wide range of population sizes (Walker 1992, 1994a,b, 1998). For this species, there are advantages in harvesting the middle-sized sharks and in protecting the large older sharks for breeding purposes and for protecting the young animals to improve the yield from growth. This is achieved by gillnets of mesh-size ranging 6 to 6½ inches (Walker 1998, 1999).
Minor threats include fishing with long-lines, trawls, and other methods.
|Conservation Actions:||Management measures in this fishery include limited entry for the use of gillnets and longlines (since 1984) and, for all fishing sectors, Total Allowable Catches (TAC) (since 2000) and various input controls. Limits apply to length of net (since 1988) (initially 6,000 m but subsequently reduced to 4,200 m) and depth of net (20-meshes). Various 4 to 6 week closed seasons have been in place to protect pregnant animals of Galeorhinus galeus during October to December (1953 to 1967 and 1993 to 1994). There is a legal minimum mesh-size of 6 inches (since 1975) and a legal maximum length of 6.5 inches (since 1997) for gillnets for most of the fished area. Closed areas to commercial gillnetting in inshore waters of Tasmania have been variously implemented since 1954 to protect newborn, juvenile and pregnant G. galeus on nursery areas. A more extensive closed area was adopted during 1988 when all Victorian proclaimed waters (inside three-mile limit) were closed to the use of shark gillnets and longlines. Legal minimum lengths were phased in by the States and Commonwealth during 1949 and the early 1950s and remain current. During 2002, the TAC for M. antarcticus was 1,750 tonnes for the Southern Shark Fishery, 86 tonnes for the South East Trawl Fishery, and 28 tonnes for the Great Australia Bight Trawl Fishery.|
|Citation:||Walker, T.I. (SSG Australia & Oceania Regional Workshop, March 2003) 2003. Mustelus antarcticus. The IUCN Red List of Threatened Species. Version 2015.2. <www.iucnredlist.org>. Downloaded on 01 July 2015.|