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Mustelus antarcticus 

Scope: Global
Language: English
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Taxonomy [top]

Kingdom Phylum Class Order Family
Animalia Chordata Chondrichthyes Carcharhiniformes Triakidae

Scientific Name: Mustelus antarcticus
Species Authority: Günther, 1870
Common Name(s):
English Gummy Shark, Sweet William
Taxonomic Source(s): Eschmeyer, W.N., Fricke, R. and Van der Laan, R. (eds). 2016. Catalog of Fishes: genera, species, references. Updated 2 May 2016. Available at: http://researcharchive.calacademy.org/research/ichthyology/catalog/fishcatmain.asp. (Accessed: 2 May 2016).

Assessment Information [top]

Red List Category & Criteria: Least Concern ver 3.1
Year Published: 2016
Date Assessed: 2015-04-15
Assessor(s): Walker, T.I.
Reviewer(s): Simpfendorfer, C. & Dulvy, N.K.
Facilitator/Compiler(s): Kyne, P.M., Walls, R.H.L., Simpfendorfer, C. & Chin, A.
Justification:
The Gummy Shark (Mustelus antarcticus) is a highly abundant endemic species off southern Australia with relatively high productivity (longevity: 16 years, low age at maturity: 5 years for females, 4 years for males; 10-year generation length; and, up to 57 pups per litter). It is exploited over its entire range, but about two-thirds of the catch is taken from Bass Strait in southeast Australia. Mandatory adoption of middle-sized mesh-sizes in the fishery and the large area closure of all Victorian 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 2 years is remarkably stable over a wide range of population sizes. In Bass Strait, South Australia and Western Australia, stock assessments indicate that biomass has been 40–55% 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 the 2000s 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 assessed as Least Concern.
Previously published Red List assessments:

Geographic Range [top]

Range Description:

The Gummy Shark is endemic to southern Australia from about Geraldton in Western Australia (latitude 28°S) to about Port Stephens in New South Wales (32°S), including Tasmania (Last and Stevens 2009). 

Countries occurrence:
Native:
Australia (New South Wales, South Australia, Tasmania, Victoria, Western Australia)
FAO Marine Fishing Areas:
Native:
Indian Ocean – eastern; Pacific – southwest
Additional data:
Estimated area of occupancy (AOO) - km2:1000000Continuing decline in area of occupancy (AOO):No
Extreme fluctuations in area of occupancy (AOO):NoEstimated extent of occurrence (EOO) - km2:1000000
Continuing decline in extent of occurrence (EOO):NoExtreme fluctuations in extent of occurrence (EOO):No
Continuing decline in number of locations:No
Extreme fluctuations in the number of locations:No
Lower depth limit (metres):350
Range Map:Click here to open the map viewer and explore range.

Population [top]

Population:The range of the Gummy Shark appears presently to cover two genetically distinct sub-stocks: one extending from Geraldton to Jervis Bay in New South Wales (latitude 35°S) (southern sub-stock) and the other from Jervis Bay to Port Stephens (eastern sub-stock). The large southern sub-stock provides for a major target shark fishery over the full range of its distribution, whereas the small eastern sub-stock provides small catches for a range of fisheries over its range. Most of the available biological and fishery information for the species is from the southern sub-stock.

Tagging (Brown et al. 2000, Walker et al. 2000), genetic (MacDonald 1988, Gardner and Ward 1998) and morphometric (Heemstra 1973) studies initially indicated the presence of three genetic sub-stocks of the Gummy Shark. One ranged along the southern coast of Australia from Bunbury in the west to Eden (Bermagui based on tag data) in the east, a second was located off New South Wales in the region from Newcastle to Clarence River, and a third was located off Queensland near Townsville. Subsequent analyses of the tag data indicate that the south coast sub-stock extends north to Jervis Bay in New South Wales (Walker 2007). Two species of Mustelus closely related to the Gummy Shark (White and Last 2008, Boomer et al. 2012) occur more northerly on the western (M. stevensi) and eastern (M. walkeri) coasts of Australia. It is likely that the third sub-stock referred to as occurring near Townsville by Gardner and Ward  (1998) is M. walkeri (White and Last 2008) and the second sub-stock referred to as occurring in the region from Newcastle to Clarence River is either, based on their much smaller size (Ken Graham, pers. comm.), a distinct sub-stock or separate species.
Current Population Trend:Stable
Additional data:
Number of mature individuals:500000Continuing decline of mature individuals:No
Extreme fluctuations:NoPopulation severely fragmented:No
No. of subpopulations:2Continuing decline in subpopulations:No
Extreme fluctuations in subpopulations:NoAll individuals in one subpopulation:No

Habitat and Ecology [top]

Habitat and Ecology:The Gummy Shark is demersal, occurring mainly on the continental shelf from the shore to about 80 m depth (Walker and Gason 2009), but also on the upper slope down to 350 m. Female Gummy Shark reach a longer total length (TL) (185.2 cm) and greater body mass (24.8 kg) than males (148.2 cm TL, 13.5 kg) (Walker 2007). Tagging and ageing studies indicate that the species has a maximum life span of about 16 years (Moulton et al. 1992).

The species exhibits limited matrotrophic aplacental viviparity with uterine compartments. Synchronous ovarian and parturition cycles are mostly annual west and biennial east of Kangaroo Island (longitude 138°E). Ovulation and parturition peak during November–December and the gestation period is ∼12 months. Largest ovarian follicle diameter ranges from 15 to 28 mm at ovulation, and mean wet mass gain is 10-fold from in utero egg (∼10 g) to full-term embryo (∼100 g) at ∼33 cm TL born usually in shallow coastal waters. The sex ratio of embryos in utero is 1:1, and litter size (1 to 57 embryos) rises curvilinearly with maternal length. Length at which 50% of females are mature or maternal, estimated before the biasing effects of high length-selective fishing mortality, are 110.5 cm TL and 112.9 cm TL (age ~5 years), respectively (Walker 2007). Parturition, mating and ovulation occur form early November to early February off Western Australia (Lenanton et al. 1990).

This species does 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).
Systems:Marine
Generation Length (years):10
Movement patterns:Not a Migrant
Congregatory:Congregatory (year-round)

Use and Trade [top]

Use and Trade: This species is utilized for its meat.

Threats [top]

Major Threat(s): Historically, Gummy Shark and Tope (Galeorhinus galeus) have been targeted in continental shelf waters since the mid-1920s by the Shark Gillnet Sector and Shark Hook Sector of the Southern and Eastern Scalefish and Shark Fishery of southern Australia, and possibly earlier in inshore areas. Baited hooks attached to bottom-set longlines were the principal fishing method until the early 1970s when the method was replaced by bottom-set gillnets. 

Currently, the main threat to stocks of the Gummy Shark are from targeting widely across southern Australia with gillnets of 6 to 6½-inch mesh-size off South Australia, Victoria and Tasmania and of 6½ to 7-inch mesh-size off Western Australia. In Bass Strait (Walker 1994a,b, 1998, 2010; Pribac et al. 2005), South Australia (Walker 1994b, 2010; Pribac et al. 2005), 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 the Gummy Shark off New South Wales and south of Bass Strait off Tasmania (Walker and Gason 2009). 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 2 years is remarkably stable for a wide range of population sizes (Walker 1992, 1994a,b, 1998, 2010; Pribac et al. 2005). 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, 2010).

Climate change threats to the Gummy Shark are highly uncertain. The most productive region for fisheries is Bass Strait where water temperatures are coolest. Whilst warming of these waters might reduce productivity in terms of yield per unit area of substrate to levels characteristic of other regions, warming water might trigger a change from the biennial reproductive cycle presently characteristic of Bass Strait to an annual cycle characteristic of the other regions (Walker 2007), which may increase pup production and hence productivity of the population and yield from the fishery.

Conservation Actions [top]

Conservation Actions:

Management measures in the fishery targeting Gummy Shark 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 Tope (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 gillnet fishing in inshore waters of Tasmania have been variously implemented since 1954 to protect newborn, juvenile and pregnant Tope on nursery areas. A more extensive closed area was adopted during 1988 when all Victorian proclaimed waters (inside the 3 nm 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 the Gummy Shark was 1,750 tonnes for the Shark Gillnet Sector and Shark Hook Sector, 86 tonnes for the South East Trawl Sector, and 28 tonnes for the Great Australia Bight Trawl Sector.

Several recent general management measures benefit the conservation of the Gummy Shark:

  • Restructuring of the Southern and Eastern Scalefish and Shark Fishery during 2006–07 through buy-back of Commonwealth fishing licences (Penney et al. 2014) and implementation of markedly reduced overall fishing effort with progressive reductions in Total Allowable Catches (TACs), particularly in southern NSW (Walker and Gason 2007).
  • The Commonwealth has adopted spatial closures to the Shark Gillnet Sector in South Australia for Australian Sea Lion (Neophoca cinerea). The first such closure was adopted at the Pages Islands (largest sea lion colony) and around Kangaroo Island in 2003, and since 2011 up to 50 such closures have applied under temporary legislation (Penny et al. 2014). Existing closures have been retained and became permanent from the beginning of the 2015–16 fishing season (Georgeson et al. 2015). 
  • Implementation of the Management Plan (operational since 1 July 2013) for the South-East Commonwealth Marine Reserves Network (proclaimed in 2007) prohibits demersal otter trawl and Danish seining, and in some areas all other fishing methods, in 14 Commonwealth marine reserves (including one at Macquarie Island) covering ~388,464 km2 over a diverse range of temperate marine environments on the continental shelf, continental slope, and abyssal plain. Stretching from the far south coast of New South Wales, around Tasmania and Victoria, and west to Kangaroo Island off South Australia, the Network provides several refuges over the entire depth range of the Gummy Shark (Anonymous 2013). The Management Plan for the South-West Commonwealth Marine Reserves Network (not yet implemented as of February 2016) is similarly expected to provide further refuges for the Gummy Shark.


Citation: Walker, T.I. 2016. Mustelus antarcticus. The IUCN Red List of Threatened Species 2016: e.T39355A68634159. . Downloaded on 09 December 2016.
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