Blue Swimmer Crab (2023)
Portunus armatus
Date Published: June 2023
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Summary
Australia has ten stocks of Blue Swimmer Crab across WA, Qld, NSW and SA. Eight of those stocks are sustainable with one stock in WA classified as depleted and one stock In South Eastern Australia classified as depleting.
Stock Status Overview
Jurisdiction | Stock | Stock status | Indicators |
---|---|---|---|
South Australia | Gulf St. Vincent | Sustainable | Fishery-independent legal-sized relative catch rate |
South Australia | Spencer Gulf | Sustainable | Fishery-independent legal-sized relative catch rate |
South Australia | West Coast | Sustainable | Catch, CPUE |
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 gulfs [Kailola et al. 1993].
In Western Australia, Blue Swimmer Crab is fished in numerous fisheries across five regions. The stock delineation between these regions is unknown [Chaplin et al. 2001; Chaplin et al. 2008]. Stock structure on the east coast of Australia is uncertain, involving overlapping stocks or a semi-continuous stock [Chaplin et al. 2001]. Using a high-resolution oceanographic model coupled with a Lagrangian particle tracking framework to simulate larval dispersal, Hewitt et al. 2022 suggest populations of Blue Swimmer Crab in NSW and Queensland appear to constitute demographically separate stocks, supporting the current assessment and management at the state level. 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 Peninsula [Bryars and Adams 1999; Dixon and Hooper 2011].
Here, assessment of stock status is presented at the biological stock level—North-Eastern Australia (Queensland), South-Eastern Australia (New South Wales), Spencer Gulf, Gulf St Vincent and West coast (South Australia), and at the management unit level—Shark Bay, Cockburn Sound, Peel-Harvey Estuary, Western Australian North Coast and Western Australian South-West Coast (Western Australia).
Stock Status
Gulf St. Vincent
IIn the South Australian gulfs, access to take Blue Swimmer Crabs is provided via a Blue Crab Fishery (BCF) or a Marine Scalefish Fishery (MSF) licence endorsed with quota entitlements. The MSF licence holders predominantly use hoop and drop nets while the pot fishing sector of the BCF uses specifically designed crab pots. Determination of stock status is based on a fishery-independent pot survey with trigger and limit reference points based on survey catch rate, as indices of relative biomass and fishing mortality [PIRSA 2020]. The TACC levels have been set since 1996 to limit Blue Swimmer Crab catches within ecologically sustainable limits set in the management plans [PIRSA 2020]. Since 1999–2000, exploitation rates have been limited by setting the TACC at levels below the maximum historical catch for the fishery. Throughout South Australia, a legal minimum size (LMS) of 110 mm carapace width (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 season [Kumar et al. 2003].
The most recent stock assessment reported that 195.1 t was harvested, which represented 72% of the TACC (269.66 t) in the 2021–22 season [Beckmann and Hooper 2023]. In 2022, legal sized fishery independent survey CPUE was 5.4 kg crabs per pot-lift, which was above the trigger (1.7 kg crabs per pot-lift) and target (2.5 kg crabs per pot-lift) reference points [Beckmann and Hooper 2023]. The above evidence indicates that the biomass of this stock is unlikely to be depleted and that recruitment is unlikely to be impaired. Furthermore, the above evidence indicates that the current level of fishing mortality is unlikely to cause the stock to become recruitment impaired.
On the basis of the evidence provided above, the Gulf St. Vincent biological stock is classified as a sustainable stock.
Spencer Gulf
In the South Australian gulfs, access to commercially harvest Blue Swimmer Crabs is provided via a Blue Crab Fishery (BCF) or a Marine Scalefish Fishery (MSF) licence endorsed with quota entitlements. The MSF licence holders predominantly use hoop and drop nets while, the pot fishing sector of the BCF uses specifically designed crab pots. Determination of stock status is based on a fishery-independent pot survey with trigger and limit reference points based on survey catch rate, as an index of relative biomass and fishing mortality [PIRSA 2020]. The TACC levels have been set since 1996 to limit Blue Swimmer Crab catches within ecologically sustainable limits set in the management plans [PIRSA 2020]. Since 1999–2000, exploitation rates have been limited by setting the TACC at levels below the maximum historical catch for the fishery. Throughout South Australia, a legal minimum size (LMS) of 110 mm carapace width (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 season [Kumar et al. 2003].
The most recent stock assessment reported that 326.3 t was harvested, which represented 86% of the TACC (381.67 t) for the 2021–22 season [Beckmann and Hooper 2023]. In 2022, legal sized fishery independent survey CPUE was 4.1 kg crabs per pot-lift, which was above the trigger reference point (2.4 kg crabs per pot-lift) [Beckmann and Hooper 2023]. The above evidence indicates that the biomass of this stock is unlikely to be depleted and that recruitment is unlikely to be impaired. Furthermore, the above evidence indicates that the current level of fishing mortality is unlikely to cause the stock to become recruitment impaired.
On the basis of the evidence provided above, the Spencer Gulf biological stock is classified as a sustainable stock.
West Coast
On the West Coast of South Australia, access to take Blue Swimmer Crabs is provided via a Marine Scalefish Fishery (MSF) licence. MSF licence holders predominantly use hoop and drop nets. The West Coast zone is not subject to the quota management system and is managed separately to the BCF. This zone of the fishery operates under the Management Plan for the MSF [PIRSA 2018] that specifies general performance indicators assessed in Smart et al. [2023].
Catches continued to decline during 2000s and early 2010s, dropping to a low of 31.2 t in 2016, and have since increased to 58 t in 2021–22 [Smart et al 2023]. The primary indices of biomass and fishing mortality for the West Coast biological stock are the commercial CPUE and catch trends. Comparison of recent CPUE and catch trends to values in the past decade is considered to provide a reliable proxy for relative biomass and fishing mortality. These historical values have been stable at relatively high levels, indicating that the biomass of this stock was unlikely to be depleted or that recruitment was unlikely to be impaired in the past decade. The total targeted effort was 1,059 fisher days in 2021–22 which produced a CPUE (targeted crab net effort) by fisher day of 58 kg.fisher/day. The CPUE in 2021–22 was the lowest since 2017–18 (51 kg.fisher/day) and was similar to the previous ten-year average (60 kg.fisher/hr). The above evidence indicates that the biomass of this stock is unlikely to be depleted, that recruitment is unlikely to be impaired and that the current level of fishing mortality is unlikely to cause the stock to become recruitment impaired.
On the basis of the evidence provided above, the West Coast biological stock is classified as a sustainablestock.
Biology
Blue Swimmer Crab Biology [de Lestang et al. 2003a,b; Sumpton et al. 2003]
Species | Longevity / Maximum Size | Maturity (50 per cent) |
---|---|---|
Blue Swimmer Crab | 3–4 years, ~ 200 mm CW | Varies among locations, 6–14 months, 86–110 mm CW |
Tables
South Australia | |
---|---|
Commercial | |
Unspecified | |
Blue Swimmer Crab Trap | |
Recreational | |
Diving | |
Coastal, Estuary and River Set Nets |
Method | South Australia |
---|---|
Commercial | |
Gear restrictions | |
Limited entry | |
Protection of egg-bearing females | |
Size limit | |
Spatial closures | |
Spatial zoning | |
Temporal closures | |
Total allowable catch | |
Recreational | |
Bag limits | |
Boat limits | |
Gear restrictions | |
Protection of egg-bearing females | |
Size limit | |
Spatial closures |
South Australia | |
---|---|
Commercial | 57.99t |
Indigenous | Unknown |
Recreational | 251 t (2021–22) |
Western Australia – Recreational (Catch). Boat-based recreational catch in 2017–18 [Ryan et al. 2019]. Does not include scoop netting and other methods of recreational fishing.
Queensland – Indigenous (Management Methods). for more information see: https://www.daf.qld.gov.au/business-priorities/fisheries/traditional-fishing
Queensland – Commercial (Catch). Queensland commercial and charter data have been sourced from the commercial fisheries logbook program. Further information available through the Queensland Fisheries Summary Report https://www.daf.qld.gov.au/business-priorities/fisheries/monitoring-research/data/queensland-fisheries-summary-report
Queensland – Commercial (Management Methods). Harvest strategies available at: https://www.daf.qld.gov.au/business-priorities/fisheries/sustainable/harvest-strategy
Queensland – Recreational Fishing (Catch). Data are based at the whole of Queensland level and derived from statewide recreational fishing surveys. Where possible, estimates have been converted to weight (tonnes) using best known conversion multipliers. Conversion factors may display regional or temporal variability. In the absence of an adequate conversion factor, data presented as number of fish.
New South Wales – Indigenous (Management Methods). (https://www.dpi.nsw.gov.au/fishing/aboriginal-fishing)
New South Wales – Recreational (Catch) . Recreational catch estimate of 20 t t is based on (i) an estimated recreational catch of 42,200 Blue Swimmer Crabs by NSW resident recreational anglers in 2019–20 [Murphy et al. 2021]; and (ii) an assumed mean weight of kept Blue Swimmer Crabs of 0.225 kg/crab.
Catch Chart
Commercial catch of Blue Swimmer Crab - note confidential catch not shown.
References
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