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Blue Swimmer Crab

Portunus armatus

  • Danielle Johnston (Department of Fisheries, Western Australia)
  • Anna Garland (Department of Agriculture and Fisheries, Queensland)
  • Crystal Beckmann (South Australian Research and Development Institute)
  • Daniel Johnson (Department of Primary Industries, New South Wales)

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Stock Status Overview

Stock status determination
Jurisdiction Stock Fisheries Stock status Indicators
New South Wales South-Eastern Australia EGF, OTF Sustainable Catch, CPUE
EGF
Estuary General Fishery (NSW)
OTF
Ocean Trawl Fishery (NSW)
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Stock Structure

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).

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Stock Status

South-Eastern Australia

Blue Swimmer Crabs occur in coastal and estuarine waters along the length of the New South Wales coastline. New South Wales Blue Swimmer Crab populations are at the southern end of the species distribution along the east coast and have a limited spawning period (November–February), rather than the year-round spawning that occurs in more northern latitudes14. A LMS of 60 mm carapace length is enforced for both male and female crabs. Female crabs close to the LMS are sexually mature, and are capable of producing one–three batches of eggs within a season14.

The most recent estimate of the recreational harvest of Blue Swimmer Crabs in New South Wales was approximately 51 000 crabs (27 t) during 2013–1415. The annual recreational harvest of Blue Swimmer Crabs in New South Wales was previously estimated to lie between 150 and 310 t based on the results of the offsite National Recreational and Indigenous Fishing Survey16 and onsite surveys undertaken by New South Wales Department of Primary Industries. Commercial catches of this species have tended to fluctuate around a long-term average of about 144 t over the period 2000–15. Nominal catch rates of Blue Swimmer Crabs by the main fishing methods in the Estuary General Fishery have remained relatively steady and have been above long-term averages for the past 5 years. Five estuaries account for 95 per cent of commercial Blue Swimmer Crab landings in New South Wales (192 t in 2015), the most important being Wallis Lake (167 t in 2015). Catch rates in Wallis Lake appear stable and within historic levels indicating a stable level of biomass in this area. Since the transition to daily reporting in 2009–10, annual commercial catch rates (kg per day) for fish trapping, the method that accounts for around 95 per cent of commercial landings (159 t in 2015) have fluctuated between 16.5 and 40.1 kg per day, but have generally remained above 23 kg per day. In 2015, total landings from Wallis Lake (167 t) and CPUE (40.1 kg per day) were 75 and 36 per cent higher than 5-year averages, respectively. The length compositions of the commercial landings for this species have been stable since monitoring commenced in 200917. Nominal effort levels (in the number of fisher days) over the past 5 years have remained steady, and are well below historical levels. The minimum legal length for both commercial and recreational fishers and spatial closures in New South Wales reduces fishing pressure on the spawning stock.

The above evidence indicates that the biomass of this stock is unlikely to be recruitment overfished and the current level of fishing pressure is unlikely to cause the stock to become recruitment overfished.

 

On the basis of the evidence provided above, the South-eastern Australian (New South Wales) biological stock is classified as a sustainable stock.

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Biology

Biology
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
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Distributions

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Tables

Fishing methods
New South Wales
Commercial
Coastal, Estuary and River Set Nets
Mesh Net
Otter Trawl
Blue Swimmer Crab Trap
Fish Trap
Recreational
Dip Net
Blue Swimmer Crab Trap
Management methods
Method New South Wales
Commercial
Gear restrictions
Limited entry
Protection of egg-bearing females
Size limit
Spatial closures
Spatial zoning
Vessel restrictions
Indigenous
Section 31 (1)(c1), Aboriginal cultural fishing authority
Recreational
Bag limits
Gear restrictions
General recreational licence or fishing boat licence (not species specific)
Protection of egg-bearing females
Size limit
Spatial closures
Active vessels
New South Wales
130 in EGF, 51 in OTF
EGF
Estuary General Fishery (NSW)
OTF
Ocean Trawl Fishery (NSW)
Catch
New South Wales
Commercial 185.39t in EGF, 6.90t in OTF
Indigenous Unknown
Recreational 27 t (2013–14)
EGF
Estuary General Fishery (NSW)
OTF
Ocean Trawl Fishery (NSW)

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.

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Catch Chart

Commercial catch of Blue Swimmer Crab - note confidential catch not shown.

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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.
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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.
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References

  1. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 13 Queensland Department of Agriculture and Fisheries 2016, Queensland Stock Status Assessment Workshop 2016, 14–15 June 2016, Brisbane, Queensland DAF, Brisbane.
  14. 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. 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. 16 Henry GW, Lyle JM 2003, The national recreational and Indigenous fishing survey. Fisheries Research and Development Corporation, Canberra.
  17. 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. 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. 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. 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. 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. 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. 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. 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. 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. 26 Giri, K. and Hall, K 2015, South Australian recreational fishing survey. Fisheries Victoria Internal Report Series No. 62.

Archived reports

Click the links below to view reports from other years for this fish.