Blue Swimmer Crab
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Stock Status Overview
|South Australia||Gulf St. Vincent||BCF||Sustainable||Fishery-independent legal-sized and pre-recruit abundance|
|South Australia||Spencer Gulf||BCF, MSF||Sustainable||Fishery-independent legal-sized and pre-recruit abundance|
|South Australia||West Coast||MSF||Undefined||Catch|
- Blue Crab Fishery (SA)
- Marine Scalefish Fishery (SA)
Blue Swimmer Crab is distributed in Australia from the south coast of Western Australia, north to the Northern Territory, across Queensland, down the east coast and to the New South Wales–Victoria border. They are also found in the warmer waters of the South Australian gulfs1.
In Western Australia, Blue Swimmer Crab is fished in numerous fisheries across five regions. The stock delineation between these regions is unknown2,3. Stock structure on the east coast of Australia is uncertain, involving overlapping stocks or a semi-continuous stock2. Due to the geographic separation between the major fishing grounds for Blue Swimmer Crab in New South Wales and Queensland, they are managed as two separate biological stocks. In South Australia, research has identified three separate biological stocks of Blue Swimmer Crab—in Spencer Gulf, Gulf St Vincent and on the coastline west of the Eyre Peninsula4,5.
Here, assessment of stock status is presented at the management unit level—Shark Bay Crab Managed Fishery, Cockburn Sound (Crab) Managed Fishery, Peel-Harvey Estuary Crab Fishery (Area 2 of West Coast Estuarine Managed Fishery), Western Australian north coast and Western Australian south-west coast (Western Australia); and at the biological stock level—north-eastern Australia (Queensland), south-eastern Australia (New South Wales), and the Spencer Gulf, Gulf St Vincent and West coast (South Australia).
In South Australia, TACC levels have been set since 1996 that aim to harvest Blue Swimmer Crab resources within ecologically sustainable limits and protect the species from becoming recruitment overfished. Since 1999–2000, exploitation rates have been limited by setting the TACC at a level below the maximum historical catch for the fishery. A LMS of 110 mm CW is enforced, at which size crabs are approximately 14–18 months old and sexually mature. Females produce at least two batches of eggs each season18.
The primary measures of status for the Spencer Gulf biological stock are the relative abundance of legal-sized and pre-recruit crabs, as indicated by catch rates in fishery-independent pot surveys that have been conducted in most years since 2002. Catch rates are compared with limit reference points that are defined in the South Australian Blue Crab Fishery Management Plan19. These reference points were set at the lower end of the observed range of relative catch rates in the reference period 2002–10, to ensure that relative abundance remains within the range of historical values during a period when the TACC was constant and considered to be harvested sustainably.
No survey was conducted in the Spencer Gulf fishing zone in 2015 because of a high abundance of pre-recruits in the 2014 survey, which permitted the option in the management plan to miss a survey. Relative abundance of legal-sized crabs in 2014 (10 crabs per pot-lift) was above the average for the 9-year reference period (6.9 crabs per pot-lift; range 5.1–9.1 crabs per pot-lift) and above the limit reference point (five crabs per pot-lift). Relative abundance of pre-recruits in 2014 (9.4 crabs per pot-lift) was above the average for the 9-year reference period (5.3 crabs per pot-lift; range 2.3–10.1 crabs per pot-lift) and above the limit reference point (two crabs per pot-lift). Given these abundance levels and the stable commercial catch history throughout the survey period14, the biological stock is not considered to be recruitment overfished.
During the 2014–15 season (1 July 2014–30 June 2015), the TACC was 381.7 t, and almost all of this (380.1 t) was landed. An additional 3 t was harvested by the Marine Scalefish fishery. This level of fishing mortality is unlikely to cause the biological stock to become recruitment overfished.
On the basis of the evidence provided above, the Spencer Gulf (South Australia) biological stock is classified as a sustainable stock.
Gulf St. Vincent
The process for determining the status of the Gulf St. Vincent biological stock is the same as for the Spencer Gulf stock, using a similar fishery-independent pot survey design, and the same definition and usage of limit reference points based on catch rate, as an index of abundance.
This stock was previously considered in 2012–13 to be recruitment overfished. However, relative catch rate of legal-sized crabs in 2015 (5.4 crabs per pot-lift) was above the average for the 9-year reference period (3.2 crabs per pot-lift; range 1.6–4.7 crabs per pot-lift) and above the limit reference point (1.5 crabs per pot-lift). Relative abundance of pre-recruits in 2015 (5.8 crabs per pot-lift) was above the average for the 9-year reference period (4.4 crabs per pot-lift; range 0.4–10.7 crabs per pot-lift) and above the limit reference point (1.5 crabs per pot-lift). During the 2014–15 season (1 July 2014–30 June 2015), 196.4 t was landed, equivalent to 100 per cent of the TACC (196.1 t). In response to low relative abundances of pre-recruit and legal-size crabs in the 2013 survey, a 20 per cent reduction in the TACC was maintained during the 2014–15 season. A 50 per cent reduction in recreational bag and boat limits has also remained in place since 2013–14 to promote stock recovery. The stock response to these actions appears to be positive with an increase in the abundance of pre-recruit and legal-size crabs during the 2014 and 2015 surveys20. This level of fishing pressure is unlikely to cause the stock to become recruitment overfished.
Taking into account the management arrangements to promote stock recovery, and the measurable improvements in the abundance of pre-recruits in the fishery-independent survey, increases in the abundance of legal-sized and pre-recruit crabs in the 2015 survey indicate that the stock has recovered from its recruitment overfished state.
On the basis of the evidence provided above, the Gulf St. Vincent (South Australia) biological stock is classified as a sustainable stock.
Blue Swimmer Crabs are harvested in low quantities (generally less than 60 t per year) on the west coast of South Australia as part of the Marine Scalefish Fishery. Fishers in this fishery target a range of species, and effort patterns generally reflect changes in seasonal abundance of the various species and their market prices.
As for the Spencer Gulf and Gulf St. Vincent biological stocks, a minimum legal size of 110 mm CW for Blue Swimmer Crab is enforced, under the assumption that growth rates and size at sexual maturity are similar for the West coast stock.
During the 2014–15 season (1 July 2014–30 June 2015), 41 t was landed from the West coast over 608 boat days. The 2014–15 catch rate was 68 kg per boat dayand catch rate has remained around this level since 2002–03 (range: 53–78 kg per boat day). Given the multispecies nature of the Marine Scalefish Fishery, and the sustained low annual catches of Blue Swimmer Crabs in the fishery, it is unlikely that the West coast biological stock is recruitment overfished; however, insufficient information is available to classify its status.
On the basis of the evidence provided above, the West coast (South Australia) biological stock is classified as an undefined stock.
|Species||Longevity / Maximum Size||Maturity (50 per cent)|
|Blue Swimmer Crab||3 - 4 years; ~ 200 mm CW||Varies among locations; 6–14 months; 86–98 mm CW|
|Blue Swimmer Crab Trap|
|Coastal, Estuary and River Set Nets|
|Protection of egg-bearing females|
|Total allowable catch|
|Protection of egg-bearing females|
|6 in BCF, 33 in MSF|
- Blue Crab Fishery (SA)
- Marine Scalefish Fishery (SA)
|Commercial||41.70t in MSF|
|Recreational||376 t (Dec 2013–Nov 2014)|
- Marine Scalefish Fishery (SA)
a Queensland – Indigenous (management methods) Under the Fisheries Act 1994 (Qld), Indigenous fishers in Queensland are entitled to use prescribed traditional and non-commercial fishing apparatus in waters open to fishing. Size and possession limits, and seasonal closures do not apply to Indigenous fishers. Further exemptions to fishery regulations may be applied for through permits.
b New South Wales – Indigenous (management methods) Aboriginal Cultural Fishing Interim Access Arrangement - allows an Indigenous fisher in New South Wales to take in excess of a recreational bag limit in certain circumstances, for example, if they are doing so to provide fish to other community members who cannot harvest themselves. Aboriginal cultural fishing authority - the authority that Indigenous persons can apply to take catches outside the recreational limits under the Fisheries Management Act 1994 (NSW), Section 37 (1)(c1), Aboriginal cultural fishing authority.
c Western Australia – Recreational (catch) Boat-based recreational catch from 1 May 2013–30 April 2014 24.
Commercial catch of Blue Swimmer Crab - note confidential catch not shown.
Effects of fishing on the marine environment
- Because the commercial catch of crabs generally represents a relatively small proportion of the biomass, which is renewed annually, these fisheries are unlikely to have significant impacts on the food chain.
- Fishing with traps results in limited habitat disturbance because it is generally conducted over sand habitats that are resilient.
- Although part of the Blue Swimmer Crab catch in the Shark Bay Crab (Interim) Managed Fishery (Western Australia) is harvested during otter trawling operations for prawns in Shark Bay, this activity is highly regulated and restricted to a small proportion of the area.
Environmental effects on Blue Swimmer Crab
- There is some evidence to suggest that the distribution of Blue Swimmer Crab is extending further south in both of South Australia’s gulfs5,20, possibly as a response to climate change.
- The decline in annual catches of Blue Swimmer Crab in Gulf St. Vincent (South Australia) in recent years has coincided with substantial increases in commercial catches of Snapper (Chrysophrys auratus). Trophodynamic modelling work is being done to investigate a potential causal relationship between the two species; Blue Swimmer Crab is known to be a major component of the diet of Snapper. This relationship is also apparent in the Cockburn Sound (Crab) Managed Fishery (CSCMF) in Western Australia where the recent decline in catch of Blue Swimmer Crabs has coincided with an increase in Snapper abundance.
- Climate change impacts on Western Australian Blue Swimmer Crab stocks are currently under investigation. For Shark Bay, average summer temperatures have returned within the historical range since the marine heat wave event of 2010–11, although the long-term decadal warming trend persists. The typical winter months in Shark Bay were August–October, which has more recently shifted forward to June–August. Furthermore, a unique phenomenon has been noted where there appears to be a cooling trend of the winter sea surface temperatures inside the bay that is in contrast to the warming trend outside the bay (unpublished data, Department of Agriculture and Fisheries, Queensland). Preliminary analysis suggests the cooling to be linked to a southward shift in the subtropical high pressure ridge (unpublished data, Hetzel, Y). The winter months represent the period of peak spawning of Blue Swimmer Crabs in Shark Bay and the changing water temperature could be affecting the timing of spawning.
- Recent poor recruitment and egg production in the CSCMF is not attributable to fishing pressure, since a conservative management approach has been taken since the fishery was reopened in 2009, following a 3-year closure. Reasons for the stock decline are being investigated and it appears that crab catch is strongly correlated with primary productivity (summer chlorophyll–a concentration), with stock declines over the past decade consistent with declines in primary productivity. This indicates that recent declines in stock are most likely driven by environmental influences, with catch unlikely to increase significantly until primary productivity increases. Temperature and predation also appear to play a key role in influencing catch levels. There has been some evidence of density dependent growth occurring in Cockburn Sound with growth rates declining in years when stock levels were high and increasing when stock levels were low as evidenced recently. This lack of growth may have facilitated the lower proportion of berried females during 2012 when there was a very large cohort of recruiting crabs, leading to poor spawning and recruitment in 20139.
- 1 Kailola, PJ, Williams, MJ, Stewart, PC, Reichelt, RE, McNee, A and Grieve, C 1993, Australian fisheries resources, Bureau of Resources and Fisheries Research and Development Corporation, Canberra.
- 2 Chaplin, J, Yap, ES, Sezmis, E and Potter, IC 2001, Genetic (microsatellite) determination of the stock structure of the blue swimmer crab in Australia, Fisheries Research and Development report, FRDC project 98/118, Murdoch University, Western Australia.
- 3 Chaplin, JA and Sezmis, E 2008, A genetic assessment of the relationships among the assemblages of the blue swimmer crab, Portunus pelagicus, in Cockburn Sound, the Swan River Estuary and Warnbro Sound, final report to the Department of Fisheries, Western Australia, Centre for Fish and Fisheries Research, Murdoch University.
- 4 Bryars, S and Adams, M 1999, An allozyme study of the blue swimmer crab, Portunus pelagicus (Crustacea: Portunidae), in Australia: stock delineation in southern Australia and evidence for a cryptic species in northern waters, Marine and Freshwater Research, 50: 15–26.
- 5 Dixon, CD and Hooper, GE 2011, Blue Crab (Portunus pelagicus) Fishery 2009/10, Stock assessment report to Primary Industries and Resources South Australia (Fisheries and Aquaculture), South Australian Research and Development Institute publication F2007/000729-7, SARDI research report series 531, SARDI, Adelaide.
- 6 de Lestang, S, Bellchambers, LM, Caputi, N, Thomson, AW, Pember, MB, Johnston, DJ and Harris, DC 2010, Stock– recruitment–environment relationship in a Portunus pelagicus fishery in Western Australia, in GH Kruse, GL Eckert, RJ Foy, RN Lipcius, B Sainte-Marie, DL Stram and D Woodby (eds), Biology and management of exploited crab populations under climate change, Alaska Sea Grant, University of Alaska, Fairbanks, doi: 10.4027/bmecpcc.2010.06.
- 7 Johnston, DJ, Harris, D, Caputi, N and Thomson, P 2011a, Decline of a blue swimmer crab (Portunus pelagicus) fishery in Western Australia—history, contributing factors and future management strategy, Fisheries Research, 109(1): 119– 130.
- 8 Johnston, D, Harris, D, Caputi, N, de Lestang, S and Thomson, A 2011b, Status of the Cockburn Sound Crab Fishery, Fisheries research report 219, Western Australian Department of Fisheries, Perth.
- 9 Johnston, D, Marks, R and O’Malley, J 2016, West coast Blue Swimmer Crab Fishery status report, in WJ Fletcher (ed), Status reports of the fisheries and aquatic resources of Western Australia 2014/15: the state of the fisheries, Western Australian Department of Fisheries.
- 10 Johnston, D, Chandrapavan, A, Wise, B and Caputi, N 2014, Assessment of blue swimmer crab recruitment and breeding stock levels in the Peel–Harvey Estuary and status of the Mandurah to Bunbury Developing Crab Fishery, Fisheries research report 258, Western Australian Department of Fisheries, Perth.
- 11 Johnston, DJ, Smith, KA, Brown, JI, Travaille, KL, Crowe, F, Oliver, RK and Fisher, EA 2015, Western Australian Marine Stewardship Council Report Series No 3: West Coast Estuarine Managed Fishery (Area 2: Peel-Harvey) and Peel-Harvey Estuary Blue Swimmer Crab Recreational Fishery. Department of Fisheries, Western Australia. 284 pp.
- 12 Sumpton, W, Campbell, M, O’Neill, M, McLennan, M, Campbell A and Leigh, G 2015, Assessment of the blue swimmer crab (Portunus armatus) fishery in Queensland. Department of Agriculture and Fisheries, Brisbane.
- 13 Queensland Department of Agriculture and Fisheries 2016, Queensland Stock Status Assessment Workshop 2016, 14–15 June 2016, Brisbane, Queensland DAF, Brisbane.
- 14 Johnson, DD, Gray, CA and Macbeth, WG 2010, Reproductive biology of Portunus pelagicus in a south-east Australian estuary, Journal of Crustacean Biology, 30: 200–205.
- 15 West, LD, Stark, KE, Murphy, JJ, Lyle, JM and Ochwada-Doyle, FA 2016, Survey of Recreational Fishing in New South Wales and the ACT, 2013/14, NSW Fisheries Final Report Series 149.
- 16 Henry GW, Lyle JM 2003, The national recreational and Indigenous fishing survey. Fisheries Research and Development Corporation, Canberra.
- 17 Stewart, J, Hegarty, A, Young, C, Fowler, AM and Craig, J 2015, Status of Fisheries Resources in NSW 2013-14, NSW Department of Primary Industries, Mosman: 391pp. .
- 18 Kumar, MS, Xiao, Y, Venema, S and Hooper, G 2003, Reproductive cycle of the blue swimmer crab, Portunus pelagicus, off southern Australia, Journal of the Marine Biological Association of the United Kingdom, 83: 983–994.
- 19 Primary Industries and Regions South Australia 2012, Management plan for the South Australian Commercial Blue Crab Fishery, South Australian fisheries management series paper 58, PIRSA (Fisheries and Aquaculture), Adelaide.
- 20 Noell, CJ, Beckmann, CL and Hooper, GE 2014, Blue Crab (Portunus pelagicus) Fishery 2012/13, Fishery assessment report to Primary Industries and Regions South Australia (Fisheries and Aquaculture), South Australian Research and Development Institute (Aquatic Sciences) publication F2007/000729-10, SARDI research report series 757, SARDI, Adelaide.
- 21 de Lestang, S, Hall, NG and Potter, IC 2003a, Reproductive biology of the Blue Swimmer Crab, Portunus pelagicus (Decapoda: Portunidae) in five water bodies on the west coast of Australia, Fishery Bulletin, 101: 745–757.
- 22 de Lestang, S, Hall, NG and Potter, IC 2003b, Do the age compositions and growth of the crab Portunus pelagicus in marine embayments and estuaries differ?, Journal of the Marine Biological Association of the United Kingdom, 83: 1– 8.
- 23 Sumpton, W, Gaddes, S, McLennan, M, Campbell, M, Tonks, M, Good, N and Hagedoorn, W 2003, Fisheries biology and assessment of the blue swimmer crab (Portunus pelagicus) in Queensland, Queensland Department of Primary Industries and Fisheries Research and Development Corporation project 98/117.
- 24 Ryan, KL, Hall, NG, Lai, EK, Smallwood, CB, Taylor, SM, and Wise, BS 2015, State-wide survey of boat based recreational fishing in Western Australia 2013/14. , Fisheries research report 268, Western Australian Department of Fisheries, Perth.
- 25 Webley, J, McInnes, K, Teixeira, D, Lawson, A and Quinn, R 2015, 2013-14, Statewide Recreational Fishing Survey, Queensland Department of Agriculture and Fisheries, Brisbane.
- 26 Giri, K. and Hall, K 2015, South Australian recreational fishing survey. Fisheries Victoria Internal Report Series No. 62.