Blue Swimmer Crab Portunus armatus (formerly Portunus pelagicus)

Danielle Johnstona, Stephen Wescheb, Craig Noellc and Daniel Johnsond


Blue Swimmer Crab

Table 1: Stock status determination for Blue Swimmer Crab

Jurisdiction

Western Australia

Stock

Shark Bay

(SBCIMF, SBPMF)

Cockburn Sound

(CSCMF)

Peel–Harvey Estuary

(PHECF)

Western Australian north coast

(EGPMF, NBPMF, PDCF)

Western Australian south-west coast

(EF, JASDGDLMF, MBDCF, SCEMF, SCRCF, SWTMF, WSCMF)

Stock status

Environmentally limited

Environmentally limited

Sustainable

Sustainable

Sustainable

Indicators

Catch, CPUE, fishery-independent juvenile and breeding stock abundance

Catch, CPUE, fishery-independent juvenile and residual index, egg production index

Catch, CPUE

Catch, CPUE

Catch


CPUE = catch per unit effort; CSCMF = Cockburn Sound (Crab) Managed Fishery (Western Australia); EF = Estuaries Fisheries (Condition) (Western Australia); EGPMF = Exmouth Gulf Prawn Managed Fishery (Western Australia); JASDGDLMF = Joint Authority Southern Demersal Gillnet and Demersal Longline Managed Fishery (Zone 1 and Zone 2) (Western Australia); MBDCF = Mandurah to Bunbury Developing Crab Fishery (Western Australia); NBPMF = Nickol Bay Prawn Managed Fishery (Western Australia); PDCF = Pilbara Developmental Crab Fishery (Western Australia); PHECF = Peel–Harvey Estuary Crab Fishery (Area 2 of West Coast Estuarine Managed Fishery) (Western Australia); SBCIMF = Shark Bay Crab (Interim) Managed Fishery (Western Australia); SBPMF = Shark Bay Prawn Managed Fishery (Western Australia); SCEMF = South Coast Estuarine Managed Fishery (Western Australia); SCRCF = Swan and Canning Rivers Crab Fishery (Area 1 of West Coast Estuarine Managed Fishery) (Western Australia); SWTMF = South West Trawl Managed Fishery (Western Australia); WSCMF = Warnbro Sound Crab Managed Fishery (Western Australia)

Table 1 continued

Jurisdiction

Queensland

South Australia

New South Wales

Stock

North-eastern Australian

(BSCF, ECOTF)

Spencer Gulf

(BCF, MSF)

Gulf St Vincent

(BCF, MSF)

West coast

(MSF)

South-eastern Australian

(EGF, OTF)

Stock status

Sustainable

Sustainable

Transitional–recovering

Undefined

Undefined

Indicators

Catch, CPUE, fishery-independent juvenile abundance

Fishery-independent legal-sized and pre-recruit abundance

Fishery-independent legal-sized and pre-recruit abundance

Catch

Catch, CPUE


BCF = Blue Crab Fishery (South Australia); BSCF = Blue Swimmer Crab Fishery (Queensland); CPUE = catch per unit effort; ECOTF = East Coast Otter Trawl Fishery (Queensland); EGF = Estuary General Fishery (New South Wales); MSF = Marine Scalefish Fishery (South Australia); OTF = Ocean Trawl Fishery (New South Wales)


Stock Structure

Blue Swimmer Crab is distributed in Australia from Cape Naturaliste in 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. While most chapters in the Status of key Australian fish stocks reports consider a single fishery to be a management unit, the term ‘management unit’ in this chapter can also describe a compilation of multiple fisheries.

In Western Australia, stock delineation of Blue Swimmer Crab is unknown; for this state, reporting of stock status is therefore at the management unit level2,3. There are three major management units off the Western Australian coast between Cape Naturaliste and Nickol Bay (Shark Bay, Cockburn Sound and Peel–Harvey Estuary). The two other Western Australian management units discussed in this chapter each comprise several minor fisheries.

In South Australia, research has identified three separate biological stocks of Blue Swimmer Crab—in Spencer Gulf, in Gulf St Vincent and on the coastline west of the Eyre Peninsula4,5; the latter is referred to as the ‘west coast’ biological stock. Stock structure on the east coast of Australia is uncertain, involving overlapping stocks or a semicontinuous 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 each of the above cases where biological stock delineation is known, reporting is at the biological stock level.


Stock Status

Shark Bay management unit

The Shark Bay fishery for Blue Swimmer Crab expanded rapidly between 2000 and 2010. In 2010, it was Australia’s highest producing Blue Swimmer Crab fishery, with landings of 828 tonnes (t) (collectively caught by the dedicated crab trap sector and as byproduct by the trawl sector). In late 2011, the crab stock in Shark Bay was found to be at historically low levels as a result of recruitment failure and the mortality of adult stock. This was attributed to the unprecedented environmental conditions that were experienced in Shark Bay during late 2010 to early 2011: the marine heatwave in summer 2010–11, and two flooding events, with associated increased turbidity, in December 2010 and February 2011. These events also affected a number of fish stocks in the Gascoyne region. The low stock abundance of Blue Swimmer Crabs was confirmed by a fishery-independent trawl survey in November 2011 and by the very low commercial crab trap catch rates experienced at that time (less than 1 kg per trap-lift). Above-average water temperatures continued in the summers of 2011–12 and 2012–13.

The decline in abundance led to a voluntary closure of both the trap and trawl commercial sectors of the crab fishery in April 2012. This was followed by intensive monitoring of the resource and its recovery, using a combination of fishery-independent trawl- and trap-based surveys. These surveys were designed to target key deepwater trawl grounds and inshore trapping grounds that historically have been used to target crabs. Only a partial recovery of the crab stock in Shark Bay occurred during 2012 and 2013, with improved biomass levels of legal (equal to or greater than 135 mm carapace width) and sublegal (less than 135 mm carapace width) crabs in 2013, as well as strong recruitment pulses. However, these levels remain well below target levels for spawning biomass and recruitment, and there is insufficient evidence to suggest that stock biomass has recovered above the limit reference point. Nevertheless, the data provided some confidence for a limited commercial fishing season in 2013–14, based on a total allowable commercial catch (TACC) of 400 t.

A formal catch allocation within the commercial sectors was made in June 2013 (trap sector—66 per cent, prawn trawl sector—33.8 per cent, scallop trawl sector—0.2 per cent). The fishery is also being transitioned from an interim status to a fully managed status, which will incorporate a system of individual transferable quotas of entitlement, to apply across all three commercial sectors in Shark Bay. It is envisaged that the new management plan will be implemented in early 2015.

The above evidence indicates that spawning stock biomass has decreased to a point at which average recruitment levels are significantly reduced. This is primarily a result of substantial environmental changes, rather than overfishing, so the stock cannot be classified as recruitment overfished. Fisheries management has responded appropriately to the environmental change in productivity, and the evidence indicates that the current level of fishing pressure will allow the stock to continue to recover.

On the basis of the evidence provided above, the management unit is currently classified as an environmentally limited stock.

Cockburn Sound (Crab) Managed Fishery (Western Australia) management unit

Historically, variations in recruitment of Blue Swimmer Crabs in Cockburn Sound have depended on environmental conditions, which have resulted in large fluctuations in stock abundance and the annual commercial catch6. A shift by commercial fishers from using set nets to traps in the mid-1990s resulted in a marked increase in mean annual crab landings. Following a series of high catches (250–350 t) in the late 1990s, the catch declined significantly7,8. Fishery-independent surveys indicated that low recruitment was generated by high fishing pressure, combined with poor environmental conditions, which reduced the spawning stock to low levels and required the closure of the fishery in December 20066–8. Recovery of the spawning stock and subsequent recruitment was slower than expected; fishery-independent trawl surveys indicated that the strength of recruitment and the spawning stock biomass did not improve sufficiently to reopen the fishery until December 2009. The fishing season for 2010 was restricted to 3.5 months to ensure that the catch level and size/sex composition would enable continued recovery of the spawning stock biomass. At this time, the fishery was considered as transitional–recovering.

Based on improving abundances of juveniles (0+ years) and residuals (1+ years), and egg production levels in 2010, 2011 and 2012, management restrictions were eased. This included lengthening the season to 6 months (December–June) and decreasing in the minimum size to the pre-closure size limit of 130 mm carapace width, while retaining the 20 per cent reduction in trap numbers9. However, catch did not improve significantly, remaining at around 50 t, with catch rates declining significantly through each of the 2010, 2011 and 2012 fishing seasons, from 1.1 kg per trap-lift to 0.5 kg per trap-lift. In 2013, despite a slight increase in catch to 62 t, fishery-independent trawl surveys indicated that there had been low recruitment, with levels similar to those preceding the closure in 2006. Although egg production (based on mature female abundance) in 2012 was acceptable, a very low proportion of berried females observed during commercial monitoring and fishery-independent trawl surveys between September 2012 and January 2013 may explain the very low recruitment observed in 2013. These low numbers of berried females may be attributed to a lack of growth and moulting of a large cohort of sublegal crabs that occurred over summer 2011–12. The role of the 2010–11 heatwave in the recruitment failure is not clear; some preliminary evidence suggests that crabs in Cockburn Sound were in poor nutritional condition, possibly due to a lack of prey. On this basis, an adaptive management approach was undertaken for the 2013–14 season, with the fishery closing early as a result of a very low stock biomass and low egg production.

The above evidence indicates that spawning stock biomass is likely to have decreased to a point at which average recruitment levels have been significantly reduced. This is primarily a result of substantial environmental changes, rather than overfishing, so the stock cannot be classified as recruitment overfished. Fisheries management has responded appropriately to the environmental change in productivity, and the evidence indicates that the current level of fishing pressure will allow the stock to continue to recover.

On the basis of the evidence provided above, the management unit is classified as an environmentally limited stock.

Peel–Harvey Estuary Crab Fishery (Western Australia) management unit

The gradual conversion from targeting Blue Swimmer Crabs using gillnets to using hourglass traps in the Peel–Harvey Estuary between the mid-1990s and early 2000s resulted in an increase in annual crab catches, largely as a result of the increased efficiency of the traps. Conversion to traps increased crab fishing in autumn and winter, but most (62 per cent) of the catch and the highest catch rates are still taken between December and March10. Commercial catch levels have generally ranged between 50 and 100 t annually. A recreational survey conducted in the Peel–Harvey Estuary during 2007–08 estimated that the recreational take accounted for an additional 110–180 t, approximately 60–70 per cent of the total catch10.

Since complete gear conversion in 2001, annual commercial catch rates have fluctuated between 0.7 and 1.4 kg per trap-lift, but have generally remained above 1 kg per trap-lift. In 2010, catch per unit effort (CPUE) was 1.17 kg per trap-lift9,10, and the stock was not considered to be recruitment overfished. In 2013, a catch of 107 t and a CPUE of 1.4 kg per trap-lift were the highest on record. The high catch and CPUE are within target ranges and well above threshold reference levels, indicating that the stock is currently fished at sustainable levels. The biomass of this stock is therefore unlikely to be recruitment overfished. The breeding stock in this region has additional protection because the size at maturity (86–98 mm carapace width) is well below the legal minimum size (127–130 mm). Spawning occurs outside the estuary following flushing of crabs from the estuary during winter, providing the spawning stock with further spatial protection. The protection offered by minimum size limits also ensures that fishing mortality is unlikely to cause the management unit to become recruitment overfished.

On the basis of the evidence provided above, this management unit is classified as a sustainable stock.

Western Australian north coast management unit

The Western Australian north coast management unit is made up of a dedicated minor developing crab trap fishery and crab taken as byproduct in prawn trawl fisheries. Catch for these crab fisheries in 2013 ranged from 0.5 t in the Exmouth Gulf Prawn Managed Fishery and 7 t as byproduct in the same fishery to 16 t in the Pilbara Developmental Crab Fishery, with relatively low effort over large spatial areas. Catch and catch-rate data for the dedicated crab trap fishery (Pilbara Developmental Crab Fishery) indicate that stocks are fished at sustainable levels. The above evidence indicates that the biomass in this management unit is unlikely to be recruitment overfished and that current levels of fishing mortality are unlikely to cause the management unit to become recruitment overfished.

On the basis of the evidence provided above, the management unit is classified as a sustainable stock.

Western Australian south-west coast management unit

The Western Australian south-west coast management unit is made up of a number of dedicated minor crab trap and gillnet fisheries, as well as crab taken as byproduct in other net and trawl fisheries. Catch for these crab fisheries in 2013 ranged from less than 0.1 t in the Joint Authority Southern Demersal Gillnet and Demersal Longline Managed Fishery to 29 t in the Warnbro Sound Crab Managed Fishery and 32 t in the South Coast Estuarine Managed Fishery. Catch and catch-rate data for dedicated crab trap (Warnbro Sound Crab Managed Fishery, Mandurah to Bunbury Developing Crab Fishery) and gillnet (Swan and Canning Rivers Crab Fishery) fisheries indicate that stocks are fished at sustainable levels. The above evidence indicates that the biomass in this management unit is unlikely to be recruitment overfished and that current levels of fishing mortality are unlikely to cause the management unit to become recruitment overfished.

On the basis of the evidence provided above, the management unit is classified as a sustainable stock.

North-eastern Australian biological stock

The two fisheries that target the north-eastern Australian biological stock of Blue Swimmer Crab operate primarily in southern Queensland, in an inshore and an offshore area. Before 1998, the major Blue Swimmer Crab fishery area was the inshore area, in and around Moreton Bay. Catch, effort and catch rates increased in the offshore area in 1998 when the fishery expanded into this region, which previously was lightly fished. Offshore catch and catch rate peaked in 2003, when the offshore catch contributed 75 per cent of the total catch in the fishery.

Since 2003, catch and effort have declined almost as rapidly as they increased. By 2013, they were at levels similar to those before the expansion. This rise and subsequent fall of catch and effort in the offshore area is of concern, and indicates a decline in fishable biomass for the offshore area and the biological stock as a whole. The catch and catch rates for the whole biological stock have shown a declining trend in recent years11, with total recorded catch in 2013 being the lowest since 1997. A formal stock assessment is in progress to better determine current biomass levels for the whole biological stock. Fishery-independent recruitment surveys11 show that recruitment has remained stable in the inshore area over the past 5 years, although limit reference points have not been established yet. The declining catch rate trend, driven by the offshore component, indicates that the biomass is likely to be declining. However, the biomass of the stock is not yet considered to be recruitment overfished.

Spatial closures within the Moreton Bay, Great Sandy Strait and Great Barrier Reef marine parks ensure that a substantial proportion of the Blue Swimmer Crab biomass is protected from fishing mortality. Management arrangements in Queensland prohibit the take of female crabs, and a minimum legal size limit ensures that a high proportion of male Blue Swimmer Crabs have an opportunity to mate before recruitment into the fishery. Blue Swimmer Crab biomass is believed to be linked to strength and duration of freshwater flow events, but no data are available to quantify the impact of environmental factors on natural mortality in recent years. It is unclear what effect the declining biomass in the offshore fishery area will have on stock recruitment, but current protection should be sufficient to ensure that fishing mortality will not cause the biological stock to become recruitment overfished.

On the basis of the evidence provided above, the biological stock is classified as a sustainable stock.

Spencer Gulf biological stock

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, the TACC has been set at a level below the maximum historical catch for the fishery. A minimum legal size of 11 cm carapace width is enforced. Crabs close to the minimum legal size are approximately 14–18 months old and sexually mature, and females produce at least two batches of eggs within one season12.

The primary measure of status for the Spencer Gulf biological stock is the relative abundance of legal-sized and pre-recruit crabs obtained in fishery-independent pot surveys, which have been conducted in most years since 2002. Relative abundance is compared with limit reference points that are defined in the South Australian Blue Crab Fishery management plan13. These reference points were set at the lower end of the observed range of relative abundances in the reference period 2002 to 2010, 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 2013 because of a high abundance of pre-recruits in the 2012 survey, which permitted the option in the management plan to skip a survey. Relative abundance of legal-sized crabs in 2012 (9.2 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 (5 crabs per pot-lift). Relative abundance of pre-recruits in 2012 (8.8 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 (2 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.

In 2012–13, the TACC was 381.7 t, and almost all of this (377.4 t) was landed. 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 biological stock in this management unit is classified as a sustainable stock.

Gulf St Vincent biological stock

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.

Relative abundance of legal-sized crabs in 2013 (1.4 crabs per pot-lift) was below the average for the 9-year reference period (3.2 crabs per pot-lift; range 1.6–4.7 crabs per pot-lift) and just below the limit reference point (1.5 crabs per pot-lift). Relative abundance of pre-recruits in 2013 (1.2 crabs per pot-lift) was below the average for the 9-year reference period (4.4 crabs per pot-lift; range 0.4–10.7 crabs per pot-lift) and just below the limit reference point (1.5 crabs per pot-lift), although it was above the abundance in 2012 (0.8 crabs per pot-lift). Although the limit reference point was not developed to explicitly define the level below which the stock is recruitment overfished, the above evidence indicates that the biomass of this stock may be recruitment overfished.

In 2012–13, the TACC was 245.1 t, but only around half (53 per cent—129.0 t) was landed. In response to low relative abundances of pre-recruit crabs in the 2012 survey, a 6-month closure, a 20 per cent reduction in the TACC, and a 50 per cent reduction in recreational bag and boat limits were put in place for the 2013–14 season to promote stock recovery. Although the stock response to these actions will not be known until the stock assessment for the 2013–14 season is available (in 2015), supplementary fishery-dependent pot-sampling data from January to June 2013 indicated an increase in the abundance of pre-recruit crabs14.

Taking into account the management arrangements to promote stock recovery, and the small but measurable improvements in the abundance of pre-recruits in the fishery-independent survey and supplementary fishery-dependent sampling in 201314, increases in the abundance of legal-sized and pre-recruit crabs in the 2014 survey would also be required to demonstrate further recovery of the stock. The above evidence indicates that the current level of fishing pressure should allow the stock to recover from its recruitment overfished state.

On the basis of the evidence provided above, the biological stock is classified as a transitional–recovering stock.

West coast biological stock

Blue Swimmer Crabs are harvested in low quantities (generally less than 50 t annually) 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 11 cm for Blue Swimmer Crab is enforced, under the assumption that growth rates and size at sexual maturity are similar for the west coast.

In 2013, 58 t was landed from the west coast. 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 biological stock is currently classified as an undefined stock.

South-eastern Australian biological stock

Blue Swimmer Crab occurs in coastal and estuarine waters along the New South Wales coastline. Recreational landings are not well documented but are thought to be significant, and occur throughout the range15. Five estuaries account for 95 per cent of commercial landings (the most important being Wallis Lake). 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 latitudes16. Commercial landings and catch rates from crab trapping have declined in recent years, and the majority of the catch is now reported from fish traps. Recreational landings are likely to be greater than the commercial catch, but no recent estimates are available. Insufficient information is available to confidently classify the status of this stock.

On the basis of the evidence provided above, the biological stock is classified as an undefined stock.


Table 2: Blue Swimmer Crab biology17-19

Longevity and maximum size

3–4 years; ~ 200 mm CW

Maturity (50%)

Varies among locations, 6–14 months; 86–98 mm CW

CW = carapace width


Figure 1: Distribution of reported commercial catch of Blue Swimmer Crab in Australian waters, 2013 (calendar year)
Figure 1: Distribution of reported commercial catch of Blue Swimmer Crab in Australian waters, 2013 (calendar year)



Table 3: Main features and statistics for Blue Swimmer Crab fisheries in Australia, 2013 (calendar year)

Jurisdiction

Western Australia

Queensland

South Australia

New South Wales

Fishing methods

Commercial

Crab trap

Gillnet

Haul net

Otter trawl

Recreationala

Crab trap

Drop net

Diving

Scoop net/dip net

Hook and line

Indigenous

Traditional apparatus

Management methods

Commercial

Limited entry

Spatial zoning

Vessel restrictions

Gear restrictions

Effort limits

Size limits

Protection of female crabs

Protection of egg-bearing females

Spatial closures

Temporal closures

Total allowable catch

✓ (SBCIMF only)

✓ (ECOTF only)

Recreational

Size limits

Protection of female crabs

Protection of egg-bearing females

General recreational licence or fishing boat licence (not species specific)

Spatial closures

Boat limits

Bag limits

Gear restrictions

Indigenousa,b

Gear restrictions

Section 37(1)(c1), Aboriginal cultural fishing authority

Active vessels

1 in EF

4 in CSCMF

6 in EGPMF

1 in JASDGDLMF

2 in MBDCF

2 in NBPMF

1 in PDCF

10 in PHECF

3 in SBCIMF

18 in SBPMF

23 in SCEMF

1 in SCRCF

2 in SWTMF

1 in WSCMF

121 in BSCF

211 in ECOTF

6 in BCF

33 in MSF

130 in EGF

51 In OTF

Catch

Commercial

<0.5 t in EF

61 t in CSCMF

7 t in EGPMF

<0.1 t in JASDGDLMF

11 t in MBDCF

<0.5 t in NBPMF

16 t in PDCF

107 t in PHECF

56 t in SBCIMF

16 t in SBPMF

32 t in SCEMF

8 t in SCRCF

1 t in SWTMF

29 t in WSCMF

342 t in BCSF

42 t in ECOTF

513 t in BCF

62 t in MSF

99 t in EGF

5 t in OTF

Recreational

97 t statewidec (2011–12)20

157 t (2005)21

284 t (2007–08)22

223 t statewide (2000)

Indigenous

Unknown

Unknown

Unknown

Markets

Domestic

Export


BCF = Blue Crab Fishery (South Australia); BSCF = Blue Swimmer Crab Fishery (Queensland); CSCMF = Cockburn Sound (Crab) Managed Fishery (Western Australia); ECOTF = East Coast Otter Trawl Fishery (Queensland); EF = Estuaries Fisheries (Condition) (Western Australia); EGF = Estuary General Fishery (New South Wales); EGPMF = Exmouth Gulf Prawn Managed Fishery (Western Australia); JASDGDLMF = Joint Authority Southern Demersal Gillnet and Demersal Longline Managed Fishery (Zone 1 and Zone 2) (Western Australia); MBDCF = Mandurah to Bunbury Developing Crab Fishery (Western Australia); MSF = Marine Scalefish Fishery (South Australia); NBPMF = Nickol Bay Prawn Managed Fishery (Western Australia); OTF = Ocean Trawl Fishery (New South Wales); PDCF = Pilbara Developmental Crab Fishery (Western Australia); PHECF = Peel–Harvey Estuary Crab Fishery (Area 2 of West Coast Estuarine Managed Fishery) (Western Australia); SBCIMF = Shark Bay Crab (Interim) Managed Fishery (Western Australia); SBPMF = Shark Bay Prawn Managed Fishery (Western Australia); SCEMF = South Coast Estuarine Managed Fishery (Western Australia); SCRCF = Swan and Canning Rivers Crab Fishery (Area 1 of West Coast Estuarine Managed Fishery) (Western Australia); SWTMF = South West Trawl Managed Fishery (Western Australia); WSCMF = Warnbro Sound Crab Managed Fishery (Western Australia)

a In Queensland, under the Fisheries Act 1994, Indigenous fishers are entitled to use prescribed traditional and noncommercial 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 The Aboriginal cultural fishing authority is the authority that Indigenous persons can apply to to take catches outside the recreational limits under the New South Wales Fisheries Management Act 1994, section 37(1)(c1) (Aboriginal cultural fishing authority).

c Boat-based recreational catch from 1 March 2011 to 29 February 201220


Figure 2: Commercial catch of Blue Swimmer Crab in Australian waters, 2000 to 2013 (calendar years)
Figure 2: Commercial catch of Blue Swimmer Crab in Australian waters, 2000 to 2013 (calendar years)

Note: Western Australian data were not provided at the level of the individual stocks reported in the Blue Swimmer Crab chapter.




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.
  • Due to the efficiency of traps for targeting Blue Swimmer Crabs, generally little or no bycatch is recorded.

Environmental effects on Blue Swimmer Crab
  • In South Australia, marine park boundaries are likely to overlap with a small proportion of Blue Swimmer Crab fishing habitat when they come into effect in October 2014. This is likely to protect a portion of the stock but may increase the intensity of fishing in other areas.
  • There is some evidence to suggest that the distribution of Blue Swimmer Crab is extending further south in both of South Australia’s gulfs5,14. It is possible that this is related 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.
  • Climate change impacts on Western Australian Blue Swimmer Crab stocks are currently under investigation. For Shark Bay, it appears that the record low winter temperatures (during the peak spawning period) and the extreme marine heatwave event during the summer of 2010–11 had a detrimental impact on recruitment and survival of juvenile and adult stocks. The winter water temperatures have now returned to historical levels, but summer temperatures in 2011–12 and 2012–13 were still slightly above the historical mean, which is consistent with the observed partial recovery of the stock in 2013 and 2014.
  • Poor recruitment and egg production in the Cockburn Sound (Crab) Managed Fishery is not attributable to fishing pressure, since a conservative management approach has been taken since the fishery was reopened. Following the heatwave of 2010–11, a very large cohort of sublegal crabs did not moult over the 2011–12 summer, possibly because of competition between crabs for limited resources. This probably resulted in poor mating success during 2012 and low numbers of berried females during the 2012–13 spawning season, leading to the low recruitment in 2013. Preliminary evidence also suggests that crabs are in a poor nutritional condition, which may be contributing to low stock biomass.


a Department of Fisheries, Western Australia
b Department of Agriculture, Fisheries and Forestry, Queensland
c South Australian Research and Development Institute
d Department of Primary Industries, New South Wales