Table 1: Stock status determination for Gummy Shark
Jurisdiction |
Commonwealth, New South Wales, South Australia, Tasmania, Victoria, Western Australia |
New South Wales |
Stock |
Southern Australian
(CIF, ITF, JASDGDLF, LACF, MSF, OF, OTF, OTLF, PPBF, SESSF, SF, WCDGDLF, WPF) |
Eastern Australian (OTF, OTLF) |
Stock status |
|
|
Sustainable |
Undefined |
Indicators |
Biomass, catch |
None |
CIF = Corner Inlet Fishery (Victoria); ITF = Inshore Trawl Fishery (Victoria); JASDGDLF = Joint Authority Southern Demersal Gillnet and Demersal Longline Managed Fishery; LACF = Lakes and Coorong Fishery (South Australia); MSF = Marine Scalefish Fishery (South Australia); OF = Ocean Fishery (Victoria); OTF = Ocean Trawl Fishery (New South Wales); OTLF = Ocean Trap and Line Fishery (New South Wales); PPBF = Port Phillip Bay Fishery (Victoria); SESSF = Southern and Eastern Scalefish and Shark Fishery (Commonwealth); SF = Scalefish Fishery (Tasmania); WCDGDLF = West Coast Demersal Gillnet and Demersal Longline Managed Fishery (Western Australia); WPF = Western Port Fishery (Victoria)
Gummy Shark (Mustelus antarcticus) is distributed throughout the temperate waters of Australia, from at least Port Stephens in New South Wales to Geraldton in Western Australia (including Tasmania)1–2. Other species of Gummy Shark may overlap the extremities of the distribution of
M. antarcticus, but are not included in this assessment. The most recent research on biological stock structure for M. antarcticus3 suggested that there is most likely one biological stock in southern Australia (extending from Bunbury in Western Australia to Jervis Bay in New South Wales) and a second biological stock in eastern Australia (extending from Newcastle to the Clarence
River in New South Wales). Previous studies have suggested an additional biological stock off the
Queensland coast, but this has since been proposed as a separate species (Mustelus walkeri)3. The southern Australian biological stock is considered to comprise four separate subpopulations for formal stock assessment purposes: the continental shelf of Bass Strait, Tasmania, South Australia
and Western Australia. The first three are assessed by the Commonwealth within an integrated assessment by the Shark Resource Assessment Group (SharkRAG)4. The fourth is assessed separately by Western Australia5. Reporting of status is undertaken at the biological stock level. Status determination for the southern Australian biological stock considers information compiled in both the Commonwealth and Western Australian assessments.
Southern Australian biological stock
The Commonwealth assessment uses pup production as an indicator of biomass, due to the close relationship between the number of pups and both the number and length of females. The most recent assessment4 treats Bass Strait, South Australia and Tasmania as separate subpopulations, with no movement of animals between these regions and no density-dependent effects of one population on another. Estimated pup production in 2010, as a proportion of the unfished level of pup production (1927) for Bass Strait, ranged between 0.34 and 0.73 across model configurations. The estimated level of pup production across model configurations was 0.58 to 1.20 for South Australia and 0.68 to 0.86 for Tasmania. From these results, this part of the biological stock is not considered to be recruitment overfished.
SharkRAG's recommended biological catch for the three subpopulations combined was 1836 tonnes (t)6. This was used to determine a total allowable catch (TAC) of 1717 t for the 2010–11 season. Catch in 2010–11 was 1512 t, less than the TAC. This level of fishing mortality is not expected to cause this part of the biological stock to become recruitment overfished.
The Western Australian assessment uses age-structured modelling to estimate spawning stock biomass. The most recent assessment5 concludes that biomass in 1997–98 was 42.7 per cent of the unfished (1975) level. Reductions in demersal gillnet fishing effort since then should ensure that biomass has remained above this level. Therefore, this part of the biological stock is not considered to be recruitment overfished.
An increase in catch per unit effort (CPUE) occurred between the mid-1990s and 2005–06. This was probably the result of reductions in demersal gillnet fishing effort in Western Australia from 1992 onwards, leading to increases in breeding stock biomass. However, recent declines (from 2007–08) in CPUE need to be closely monitored until an updated stock assessment model for this part of the biological stock is completed (an updated assessment is expected within three years). Despite the recent decline in CPUE, the current level of fishing mortality is considered unlikely to cause this part of the biological stock to become recruitment overfished5.
On the basis of the evidence provided above, the entire biological stock is classified as a sustainable stock.
Eastern Australian biological stock
Available information indicates that there is little catch of Gummy Shark (<50 t per year) from
the eastern Australian biological stock7–8. No information has been identified to facilitate a status determination. Hence, the status of the biological stock is classified as an undefined stock.
Table 2: Gummy Shark biology6,9–11
Longevity and maximum size |
16 years; 185 cm TL (24.8 kg total body mass) |
Maturity (50%) |
Females: 5 years, ~85 cm TL Males: ~4 years, ~80 cm TL |
TL = total length
Figure 1: Distribution of reported commercial catch of Gummy Shark in Australian waters, 2010
Note: Catch may include some species other than Mustelus antarcticus.
- Fishing is primarily undertaken using demersal gillnets and demersal longlines.
- Management of Tasmanian, South Australian and Victorian subpopulations is undertaken
by the Australian Government under Offshore Constitutional Settlement arrangements. The Western Australian subpopulation is managed by the Western Australian Government on behalf of a joint authority, comprising the Western Australian and Australian governments. A range of management controls have been implemented across the fisheries that target Gummy Shark:
- Input controls include gear restrictions, individual transferable effort limits within a total allowable effort range, and spatial and temporal closures.
- Output controls include individual transferable quotas within a TAC. Size and bag limits apply for all recreational fishers in all states.
- The number of commercial vessels that reported catch of Gummy Shark in 2010 was 124 in Commonwealth fisheries, 197 in South Australia, fewer than 20 in Tasmania, 93 in Victoria, 147 in New South Wales and 26 in Western Australia.
- The total amount of Gummy Shark caught commercially in Australia in 2010–11 was approximately 2207 t, comprising 1511 t in the Commonwealth, 150 t in South Australia, 8 t in Tasmania, 21 t in Victoria, 50 t in New South Wales and 467 t in Western Australia. Annual
recreational harvest is thought to be minimal. In New South Wales, less than 10 t of recreational catch is thought to be taken annually12. In Western Australia, recreational shark catch is considered to be less than 5 per cent of the total commercial catch. Indigenous catch across Australia is understood to be negligible.
Figure 2: Commercial catch of Gummy Shark in Australian waters, 2000–2010 (calendar year)
In the early 1970s, the introduction of monofilament gillnets (which are more effective than hooks at catching Gummy Shark) and concerns over mercury content in other large shark species saw Gummy Shark become the most commonly commercially targeted shark species in southern Australia. Commonwealth catch peaked in 1992–93 at 2435 t. In 1997, an upper mesh size limit of
165 mm was introduced. Individual transferable quotas were introduced in 2001. Commonwealth commercial catch has remained relatively stable since this time.
In Western Australia, commercial catch has remained fairly constant for the past 10 years. However, in 2009, the Department of Fisheries Western Australia transitioned the fishery to a more explicit effort management system, with the objectives of removing excessive latent effort capacity and restricting effort within fisheries targeting Gummy Shark to 2001–02 levels.
- Interactions with marine mammals (Australian Sea Lions, Australian Fur Seals, New Zealand Fur Seals and dolphins) in some gillnet fisheries continue to be a major issue. Mitigation actions that have been implemented include spatial closures, increased monitoring and implementation of the Australian Sea Lion Management Strategy in the Southern and Eastern Scalefish and Shark Fishery13.
- Offal management strategies, introduced in April 2011, include requirements for gillnet operators to remove any biological materials from nets before they are set. This has been effective in reducing seabird interactions in other fisheries14.
- Dolphin interactions in the Commonwealth gillnet sector have recently been identified as an issue, based on the increased monitoring associated with Australian Sea Lions14. The Australian Fisheries Management Authority has closed the area where most interaction has occurred and increased observer coverage to 100 per cent in adjacent areas.
- Sea level rise and changes in sea temperature associated with climate change are of potential concern to Gummy Shark biological stocks, since the habitats they use as nursery and feeding grounds are potentially prone to the effects of climate change15.
a Australian Bureau of Agricultural and Resource Economics and Sciences
b South Australian Research and Development Institute
c Institute for Marine and Antarctic Studies, Tasmania
d Department of Fisheries, Western Australia
e Department of Primary Industries, New South Wales
f Department of Primary Industries, Victoria