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Stock Status Overview
|Tasmania||Giant Crab Fishery (Tasmania)||GCF||Overfished||Percentage of egg production relative to unfished level, CPUE|
- Giant Crab Fishery (TAS)
Giant Crab is considered to be a single biological stock from Western Australia to Tasmania because the species occurs in a continuous distribution across this range. The larval duration is around 50 days, with larval release occurring along the edge of the continental shelf. The shelf is a high current area, facilitating dispersal. Oceanographic modelling has indicated that Giant Crab dispersal occurs over large spatial scales1–3. Commercial catches off Tasmania occur in two distinct areas, although video sampling has shown that Giant Crab occurs at non-commercial densities between these areas3.
Both previous Status of Australian Fish Stocks reports on Giant Crab provided an overall assessment for this biological stock. However, there have been significant changes in the relative performance of the various fisheries operating across this stock since 2014. New information indicates that the stock is now considered overfished in Tasmania and sustainable at the opposite, Western Australian, end of its range. With current understanding of Giant Crab population dynamics, it was not possible to reconcile these differences and determine a single stock status for the entire Southern Australian stock. Management arrangements vary across jurisdictions (for example, size limits) and the fishing fleets in each jurisdiction consist of a small number of vessels with very different characteristics, resulting in different patterns of exploitation.
These factors, combined with the need for more information to assess the status of Giant Crab in some jurisdictions, have resulted in this status report providing different status determinations for Giant Crab at the jurisdictional level—Western Australia and South Australia; and the management unit level—Giant Crab Fishery (Victoria) and Giant Crab Fishery (Tasmania).
The Southern Australian biological stock has components in Western Australia, Victoria, Tasmania and South Australia. Each jurisdiction assesses the part of the biological stock that occurs in its waters. Historically, the Victorian and Tasmanian fisheries have constituted the bulk of the Giant Crab Fishery; however, both these states have had substantial reductions in total allowable commercial catch (TACC) over the past decade.
Giant Crab Fishery (Tasmania)
A length-based model has been developed to estimate annual levels of biomass and egg production. The model is based on data that include catch and effort data from commercial fisheries7. This model was used to develop the current sex-specific size limits to afford greater protection to mature female crabs, which are also protected whilst berried and through female spawning closures. Nevertheless, egg production has decreased to an estimated 14 per cent of unfished levels8. This is inadequate relative to benchmarks in most crustacean fisheries9. CPUE has decreased continually since the inception of the Tasmanian fishery. Due to its slow growth and longevity, Giant Crab is particularly susceptibility to becoming recruitment overfished. The above evidence indicates that the stock is likely to be recruitment overfished.
With the objective of increasing abundance and catch rates, the TACC for the Tasmania has been reduced in several steps from 104 t in 2003–04 to 38.3 t in 2014–15. The TACC has been routinely under-caught by approximately 10 per cent because of limited quota trading and leasing. Since the 2012–13 quota year this under-catch has increased to approximately 40 per cent, which is partly attributable to changes in regulation relating to the unloading of Giant Crab interstate, low beach price and low CPUE4. The ongoing decline in catch rates, despite substantial TACC and even more substantial catch reductions, indicates that the Tasmanian TACC has not been reduced to a sufficient level to allow for recovery. To address this issue, for the 2017/18 season the Giant Crab TAC has been reduced to 20.7 t, with additional measures to maintain an average annual catch of 15 t. The stock assessment model indicates this will provide significant future biomass increases. The above evidence indicates that fishing pressure at the 2015 level is expected to prevent the stock recovering from a recruitment overfished state.
On the basis of the evidence provided above, Giant Crab Fishery (Tasmania) management unit is classified as an overfished stock.
Giant Crab biology1,3,4
|Species||Longevity / Maximum Size||Maturity (50 per cent)|
|Giant Crab||30+ years; >200 mm CL ; ~10 kg||125–140 mm CL, depending on region|
Distribution of reported commercial catch of Giant Crab
|Giant Crab Trap|
|Giant Crab Trap|
|Giant Crab Trap|
|Commercial||21.10t in GCF|
- Giant Crab Fishery (TAS)
a Western Australia, Victoria, Tasmania and South Australia Tasmanian and West Coast Deep Sea Crustacean Fishery (Western Australia) data are for the 2015 calendar year; South Australian data are from quota holders in the 2014–15 fishing season (October 2014–May 2015), Victorian data are for the 2014–15 fishing season (November 2014–September 2015) and South Coast Deep Sea Crustacean Fishery (Western Australia) data are for the 2014–15 financial year.
b Victoria – Indigenous (management methods) In Victoria, regulations for managing recreational fishing are also applied to fishing activities by Indigenous people. Recognised Traditional Owners (groups that hold native title or have agreements under the Traditional Owner Settlement Act 2010 [Vic]) are exempt (subject to conditions) from the requirement to hold a recreational fishing licence, and can apply for permits under the Fisheries Act 1995 (Vic) that authorise customary fishing (for example, different catch and size limits, or equipment). The Indigenous category in Table 3 refers to customary fishing undertaken by recognised Traditional Owners. In 2014–15, there were no applications for customary fishing permits to access Giant Crab.c Victoria – Indigenous (management methods) Subject to the defence that applies under Section 211 of the Native Title Act 1993 (Cth), and the exemption from a requirement to hold a recreational fishing licence, the non-commercial take by indigenous fishers is covered by the same arrangements as that for recreational fishing.
Commercial catch of Giant Crab - note confidential catch not shown
Effects of fishing on the marine environment
- Bycatch in the Giant Crab fishery was sampled from more than 3000 traps. This research concluded that the fishery is of low risk to other species because of the small amount of trapping effort. Further, the majority of the bycatch consists of species (mainly Antlered Crab, Hermit Crab and Draftboard Shark) that do not have swim bladders and are returned to the sea with a high chance of survival8.
- The Giant Crab fishery is based mainly in habitats found along the edge of the continental shelf. This bryzoan turf habitat is formed from encrusting filter-feeding organisms growing on sandy and muddy sediments3. The risk to this habitat from Giant Crab fishing gear is considered to be low because gear is not dragged and has minimal drift, and the fishing footprint is insignificant relative to the size of the habitat area3.
- No interactions with protected species have been reported by observers or fishers targeting Giant Crab. Because Giant Crab is targeted in deep water, species that are distributed in coastal waters, such as juvenile seals and cormorants, are unlikely to interact with Giant Crab fishing operations8. Interaction rates with marine mammal species inhabiting offshore waters remain unquantified.
Environmental effects on Giant Crab
- Recruitment is not distributed evenly, and some areas appear to have higher juvenile abundance than others. This is not a function of habitat but appears to be related to larval drift and thus movement by ocean currents3. Changes in ocean currents resulting from climate change or upwelling events may affect this process and recruitment. Increases in ocean temperature may also potentially decrease larval development times.
Gardner, C 1998, First record of larvae of the Giant Crab Pseudocarcinus gigas in the plankton, Papers and Proceedings of the Royal Society of Tasmania, 132: 47–48.
Gardner, C and Quintana, R 1998, Larval development of the Australian Giant Crab Pseudocarcinus gigas (Lamarck, 1818) (Decapoda: Oziidae) reared in the laboratory, Journal of Plankton Research, 20(6): 1169–1188.
Williams, A, Gardner, C, Althaus, F, Barker, B and Mills, D 2009, Understanding shelf-break habitat for sustainable management of fisheries with spatial overlap, final report to the Fisheries Research and Development Corporation, project 2004/066, CSIRO Marine and Atmospheric Research, Hobart.
- 4 McGarvey, R, Matthews, JM and Levings, AH 1999, Yield-, value-, and egg-per-recruit of Giant Crab, Pseudocarcinus gigas, South Australian Research and Development Institute, Adelaide.
Fisheries Victoria, 2010, Giant Crab Management Plan, Second Edition, ISBN 978-1-74264-478-3,
- 6 Linnane, A, McGarve, R., Feenstra, J., McLeay, L. and Reilly, D 2016, Victorian Giant Crab Fisheries fishery status report—2014/2015 fishing year, Fishery status report to Fishery Stock Assessment Report: 2014/15 Season. ISBN 1 74146 111 1.
- 7 Gardner, C, Haddon, M, Hobday, D and McGarvey, R 2007, Development of the tools for long term management of the Giant Crab resource: data collection methodology, stock assessment and harvest strategy evaluation, final report to the Fisheries Research and Development Corporation, Canberra.
Emery, T., Hartmann, K. and Gardner, C 2015, Giant Crab stock assessment report 2013/14, IMAS, Hobart.
Fogarty, MJ and Gendron, L 2004, Biological reference points for American lobster (Homarus americanus) populations: limits to exploitation and the precautionary approach, Canadian Journal of Fisheries and Aquatic Sciences, 61(8): 1392–1403.
- 10 McLeay, L 2016, South Australian Giant Crab (Pseudocarcinus gigas) Fishery Status Report 2014/15. Fishery Status Report to PIRSA Fisheries and Aquaculture. South Australian Research and Development Institute (Aquatic Sciences), Adelaide. SARDI Publication No. F2011/000332-6. SARDI Research Report Series No. 895. 16pp.