Spencer Gulf biological stock
In South Australia, total allowable commercial catch (TACC) levels have been set since 1996 that aim to harvest Blue Swimmer Crab resources within ecologically sustainable limits and protect the species from overfishing. 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 is enforced, measured across the carapace from the base of the largest spines. Crabs close to the minimum legal size in Spencer Gulf (and in Gulf St Vincent—see below) are approximately 14–18 months old and sexually mature, and females have produced at least two batches of eggs within one season7.
The primary measure for biological stock status in Spencer Gulf is the relative abundance of (a) legal-sized and (b) pre-recruit crabs obtained during fishery-independent pot surveys, which have been conducted annually since 2002. Relative abundance is compared with limit reference points that are defined in the South Australian Blue Crab Fishery Management Plan8. The limit reference points were set at the lower end of the observed range of relative abundances from 2002 to 2010,
to ensure that relative abundance remains within the range of historical values during a period when the TACC was harvested sustainably. Relative abundance of legal-sized crabs in 2010 (8.9 crabs per pot-lift) was above the 9-year average (6.9 crabs per pot-lift; range 5.1–9.0 crabs per pot-lift) and above the limit reference point (5.0 crabs per pot-lift). Relative abundance of pre-recruits in 2010
(8.0 crabs per pot-lift) was above the 9-year average (5.3 crabs per pot-lift; range 2.3–10.1 crabs
per pot-lift) and above the limit reference point (2.0 crabs per pot-lift). Given these abundance levels and the stable commercial catch history throughout the survey period5, the biological stock is not considered to be recruitment overfished.
In 2009–10, the TACC was 377 tonnes (t), and almost all of this (376.6 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 is classified as a sustainable stock.
Gulf St Vincent biological stock
The primary measure for biological stock status in Gulf St Vincent is the relative abundance of (a) legal-sized and (b) pre-recruit crabs obtained during fishery-independent pot surveys, which have been conducted annually since 2002. Relative abundance is compared with limit reference points that are defined in the South Australian Blue Crab Fishery Management Plan8. The limit reference points were set at the lower end of the observed range of relative abundances from 2002 to 2010,
to ensure that relative abundance remains within the range of historical values during a period when the TACC was harvested sustainably. Relative abundance of legal-sized crabs in 2010 (3.1 crabs per
pot-lift) was close to the 9-year average (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 2010 (7.3 crabs per pot-lift) was well above the 9-year average (4.4 crabs per pot-lift; range 0.4–10.7 crabs per pot-lift) and the limit reference point (1.5 crabs per pot-lift). Given these abundance levels and the stable commercial catch history throughout the survey period5, the biological stock is not considered to be recruitment overfished.
In 2009–10, the TACC was 241.9 t, and only 158.5 t (66 per cent) 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 is classified as a sustainable stock.
West coast biological stock
Blue Swimmer Crabs are captured in low quantities (generally <50 t annually) on the west coast, as part of the Marine Scalefish Fishery. Fishers target a range of species, and effort patterns generally reflect changes in seasonal abundance of the species captured and their market prices. As for the gulf fisheries, a minimum legal size of 11 cm is enforced, under the assumption that growth rates and size at sexual maturity are similar for the west coast. Given these circumstances, it is unlikely that the west coast Blue
Swimmer Crab biological stock is recruitment overfished. However, insufficient information is available to confidently classify the status of this biological stock.
On the basis of the evidence provided above, the biological stock is classified as an undefined stock.
Shark Bay Crab (Interim) Managed Fishery (Western Australia) management unit
The fishery for Blue Swimmer Crab in Shark Bay has expanded over the past 10 years to become Australia's highest producing Blue Swimmer Crab fishery. In 2010, commercial landings of Blue Swimmer Crab from the trap sector of the fishery and as byproduct of the prawn trawl fishery totalled 828 t. This is an increase of 1 per cent over the 2009 season9. Despite this increased catch, the mean annual catch per unit effort (CPUE) since 2001 has shown no clear trend, ranging between
1.4 and 1.8 kg/pot-lift. In 2010, it was 1.5 kg/pot-lift, which is well above the management threshold value of 1.0 kg/pot-lift. The management unit is not considered to be recruitment overfished.
Male Blue Swimmer Crabs in Shark Bay become sexually mature at 11.5 cm carapace width, whereas females become sexually mature below 10 cm carapace width. The commercial minimum size of
13.5 cm carapace width should ensure adequate egg production for Blue Swimmer Crab stocks under typical environmental conditions. It should also ensure that female Blue Swimmer Crabs are exposed to negligible fishing pressure and have an opportunity to breed before they recruit into the fishery. The protection offered by minimum size limits ensures that fishing mortality is 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.
Cockburn Sound Crab Fishery (Western Australia) management unit
Historically, variations in recruitment in Cockburn Sound have largely depended on environmental conditions, which have resulted in large fluctuations in both stock abundance and the annual commercial catch10. A shift by commercial fishers from using set nets to using traps in the mid-1990s resulted in a marked increase in mean annual crab landings. Following a series of high catches in the late 1990s (250–350 t), the catch declined significantly11–12. 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 closure of the fishery in December 200611–12. Recovery of the spawning stock and subsequent recruitment were slower than expected; fishery-independent trawl surveys indicated that the strength of recruitment and spawning stock biomass did not improve sufficiently to reopen the fishery until December 20099. The fishing season for 2010 was restricted to 3.5 months to ensure that the catch level and catch composition
were consistent with enabling continued recovery of the spawning stock biomass. The catch levels and season length in future years will continue to be based on survey results, to ensure that the level of fishing mortality is such that the management unit can continue to recover from its recruitment overfished state.
On the basis of the evidence provided above, the management unit is classified as a transitional–recovering stock.
Peel–Harvey Estuary Crab Fishery (Western Australia) management unit
Commercial catch levels have been in the range of 50–90 t annually. A recreational survey in the Peel–Harvey Estuary during 2007–08 estimated that the recreational catch accounted for an additional 110–180 t—approximately 60–70 per cent of the total catch9. The commercial effort has been stable for the past 14 years, and CPUE over this period has varied between 0.9 and 1.5 kg/pot-lift, with no overall upward or downward trend. In 2010, CPUE was 1.17 kg/pot-lift9. The management unit is not considered to be recruitment overfished.
The breeding stock in this region is protected by the setting of legal minimum size limits (12.7–13.0 cm carapace width) well above the size-at-maturity (8.6–9.8 cm carapace width) and restricted effort levels in the commercial fishery. Additionally, spawning occurs outside the estuary following flushing of crabs from the estuary during winter, providing the spawning stock with added spatial protection, since the stock is not targeted outside the estuary. The protection offered by minimum size limits ensures that fishing mortality is 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.
New South Wales biological stock
Blue Swimmer Crabs occur in coastal and estuarine waters along the length of the New South Wales coastline. Recreational landings are not well documented but are thought to be significant, and occur throughout the range. Five estuaries account for 95 per cent of commercial landings (the most important being Wallis Lake). Commercial landings and catch rates from crab potting have declined in recent years; the reasons for these declines are being investigated. Recreational landings are likely to be greater than commercial catch, but no recent estimates are available.
Insufficient information is available to confidently classify the status of this biological stock; as a result, the biological stock is classified as an undefined stock.
Queensland Blue Swimmer Crab biological stock
Blue Swimmer Crabs are found in coastal and estuarine waters along the entire Queensland coast, but are fished mainly in the southern part of Queensland. Since 2003, the CPUE of commercial pot harvest has been relatively stable (approximately 45 kg/day), and did not trigger the annual limit reference point in 2010. CPUE of commercial trawl harvest has also remained relatively stable since
2000 (approximately 6.5 kg/day)13. The biological stock is unlikely to be recruitment overfished.
Temporary and permanent spatial closures within the Great Barrier Reef Marine Park ensure that a substantial proportion of the Blue Swimmer Crab biomass is protected from depletion. Additionally, the management arrangements in Queensland prohibit the take of female Blue Swimmer Crabs. A minimum legal size limit ensures that a proportion of male Blue Swimmer Crabs have an opportunity to spawn before recruitment into the fishery13. The protection offered by spatial closures, minimum size limits and prohibition of female catch ensures that fishing mortality is unlikely to 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.
In New South Wales, annual commercial landings of Blue Swimmer Crab were relatively stable, at
150–200 t, from the 1970s until 2007–08. Since then, reported landings have been about 100 t per year. Since 2000, significant changes have taken place in the management of New South Wales estuarine commercial fisheries, following the creation of a number of 'recreational only' fishing areas, and the number of fishers licensed in the Estuary General Fishery (New South Wales) has declined
as a result of the associated buyback of licences. Recreational landings of Blue Swimmer Crabs are now likely to be greater than commercial landings and are estimated to be 150–310 t per year18.
In Queensland, the fishery is predominantly a commercial fishery, with 82 per cent of the total harvest taken by commercial fishers in 2009 (based on a 2005 recreational catch estimate)19. The reported commercial catch was highest between 2001 and 2004, and both the catch and the number of
fishing days decreased in 2005. The catch was relatively stable until 2010, when the annual reported commercial pot catch of Blue Swimmer Crabs decreased, from 717 t in 2009 to 514 t in 201013. The number of active pot licences in the fishery decreased from 180 in 2009 to 145 in 2010, and fishing effort days decreased by 2800 days from 2009 to 2010.
Catches from the west coast of South Australia ranged from 9 to 56 t between 2000 and 2010. Commercial catches from Spencer Gulf (South Australia) and Gulf St Vincent (South Australia) increased annually from 1983–84 to 1995–96 before the introduction of a TACC. The TACC was initially set at 520 t for the 1996–97 fishing season, representing a 29 per cent decrease in the catch. Over
the next four seasons, the TACC gradually increased until it reached 626.8 t in 2000–01, where it has remained since. The TACC was not fully caught until 2007–08, mainly because of quota being held and not caught by less efficient hoop-net fishers. Currently, pot fishers hold 99.9 per cent of the TACC in Spencer Gulf (South Australia) and Gulf St Vincent (South Australia).
In Western Australia, the recent catches in the Cockburn Sound Crab Fishery have been low because of management actions (fishery closures) to rebuild the stock in this region. The annual catch in the Peel–Harvey Estuary Crab Fishery (Western Australia) had been slowly increasing from
50 t to 90 t since 2000, but in the past two years it has declined due to a relatively higher proportion of undersized crabs and low body weights of legal-sized crabs. The annual catch in the Shark Bay Crab (Interim) Managed Fishery (Western Australia) has increased from 500 t to more than 800 t
over the past five years, as the level of retention of crabs by the trawl fleet has increased in response to improvements in markets and prices.