*

MUD CRABS (2020)

Scylla spp., Scylla serrata, Scylla olivacea

  • Thor Saunders (Department of Industry, Tourism and Trade, Northern Territory)
  • Daniel Johnson (Department of Primary Industries, New South Wales)
  • Danielle Johnston (Department of Primary Industries and Regional Development, Western Australia)
  • Lisa Walton (Department of Agriculture and Fisheries, Queensland)

You are currently viewing a report filtered by jurisdiction. View the full report.

Toggle content

Summary

Two species of Mud Crabs are found in Australian waters: Giant Mud Crab and Orange Mud Crab. All six stocks are sustainable.

Toggle content

Stock Status Overview

Stock status determination
Jurisdiction Stock Stock status Indicators
Northern Territory Arnhem-west Northern Territory Management Unit Sustainable Catch, effort, catch rate
Northern Territory Western Gulf of Carpentaria Sustainable Catch, effort, catch rate, biomass, fishing mortality
Toggle content

Stock Structure

Two species of Mud Crabs are found in Australian waters: Giant Mud Crab (Scylla serrata) and Orange Mud Crab (S. olivacea). The former constitutes more than 99 per cent of the commercial catch of Mud Crabs in the Northern Territory and Queensland, and the entire commercial catch in New South Wales. The species composition in the Kimberley Developing Mud Crab Fishery (Western Australia) is uncertain but is known to vary considerably between locations.

The life history and biology of Giant Mud Crab in the Northern Territory and Queensland are well documented [Heasman 1980, Hill et al. 1984, Hill 1994, Knuckey 1999, Alberts-Hubatsch 2015] but, with some exceptions [Butcher et al. 2003, Butcher 2004, Alberts-Hubatsch et al. 2014], corresponding information from Western Australia and New South Wales is scarce. There are no published accounts on the biology of Orange Mud Crab in Australian waters. Hence, all catch, and biological information presented here refers to the Giant Mud Crab (S. serrata), unless otherwise stated.

Genetic evidence suggests that there are at least two biological stocks of Giant Mud Crab in Australian waters: one to the west and another to the south east of the Torres Strait [Gopurenko and Hughes 2002], referred to as the Northern Australian and East Coast biological stocks, respectively.

Female Giant Mud Crab in northern Australia migrate up to 95 km offshore to release their eggs [Hill 1994], which average around 4.5 million per individual [Mann et al. 1999]. Coupled with a planktonic larval stage that can last for several weeks [Nurdiani and Zeng 2007], this reproductive strategy may facilitate significant gene flow between areas (depending on local oceanography). However, there have been significant changes in the relative performance of some fisheries operating across these stocks since 2014, suggesting that, despite larval connectivity, there are different exploitation rates on components of the adult stock in different areas. These changes, combined with different management arrangements for each of the four jurisdictions that harvest Giant Mud Crab, and (in some cases) the need for more information on local population dynamics, and fine-scale stock structure, have resulted in this status report providing status determinations for Giant Mud Crab at the level of fishery management units: Kimberley Developing Mud Crab Fishery (Western Australia); Arnhem-West Mud Crab Fishery (Northern Territory), Western Gulf of Carpentaria (Northern Territory); Gulf of Carpentaria (Queensland), East Coast (Queensland); and the Estuary General Fishery (New South Wales).

Toggle content

Stock Status

Arnhem-west Northern Territory Management Unit

The Arnhem-West Northern Territory (AWNT) management unit encompasses all NT waters outside of the Gulf of Carpentaria. This unit includes the Darwin region that supports a substantial non-commercial harvest of Mud Crabs. The estimates of the harvest by recreational and Indigenous fishers within the AWNT indicate that their combined take accounted for around 40 per cent of the overall harvest within this management unit during 2000 - 2001 [Henry and Lyle 2003, Coleman 2004]. A more recent, non-Indigenous, resident-only angler survey confirmed the significance of the recreational harvest in this region (23 per cent) [West et al. 2012]. However, a lack of annual catch estimates for recreational and Indigenous fishers means that the assessment presented here is primarily based on data from commercial logbooks.

The most recent stock assessment based on the model used in Grubert et al. [2019] estimated the biomass in 2019 as a proportion of the biomass at Maximum Sustainable Yield (B2019/BMSY) was 1.23, indicating that the stock is currently above the target reference level. The above evidence indicates that the biomass of the stock is unlikely to be depleted and that recruitment is unlikely to be impaired.

The same stock assessment estimated that fishing mortality in 2019 as a proportion of that to achieve MSY (F2019/FMSY) was 0.8 indicating that overfishing is not occurring. Consequently, this level of fishing mortality is unlikely to cause the stock to become recruitment impaired. 

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

Western Gulf of Carpentaria

The Western Gulf of Carpentaria management unit (WGOC) has accounted for more than 70 per cent of the commercial harvest of Mud Crabs in the Northern Territory over the past 20 years. There are no records indicating the presence of Orange Mud Crab within this management unit [Keenan et al. 1998, Atlas of Living Australia 2021] so the catch of Mud Crabs in this region is assumed to consist entirely of Giant Mud Crab. A survey of Northern Territory anglers in 2009–2010 estimated that the harvest of Giant Mud Crab by resident anglers within the WGOC is less than five per cent of the overall harvest of Scylla spp. by this sector across the Northern Territory [West et al. 2012]. However, the sporadic collection of recreational harvest data for this species within this management unit means that the assessment presented here is based on data from commercial logbooks.

In addition to fisheries impacts, the GOC has a unique environment that has had a recent period of drought Duke et al. [2017] and a series of extreme ocean warming events [Benthuysen et al. 2018]. The culmination of these factors probably contributed significantly to the commercial catch in 2016 declining to a  low level (51 t) [NTG 2018]. However, this historical low catch was followed by a substantial increase in 2017 (185 t). This increase is attributed to above average rainfall during the 2016–17 monsoon season, recovery of juvenile nursery areas and a return to average sea surface temperatures that year [COA BOM 2017, IMOS 2018] highlighting the resilience of this species.

The most recent stock assessment based on the model used in Grubert et al. [2019] estimated the biomass in 2019 as a proportion of the biomass at Maximum Sustainable Yield (B2019/BMSY) was 0.6. While this value would be low for many species, the biomass in this management unit has increased substantially from the low levels in 2016 (B2016/BMSY = 0.32) demonstrating that Mud Crab stocks can rebuild very quickly under favourable environmental conditions. The above evidence indicates that the biomass of this stock is unlikely to be depleted and that recruitment is unlikely to be impaired.

Moreover, the same stock assessment estimated that fishing mortality in 2019 as a proportion of that to achieve MSY (F2019/FMSY) was 0.73 indicating that overfishing is not occurring. Consequently, this level of fishing mortality is unlikely to cause the stock to become recruitment impaired.

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

Toggle content

Biology

Giant Mud Crab biology [Heasman 1980, Knuckey 1999, Butcher et al. 2003, Jebreen et al. 2008, Grubert and Lee 2013]

Biology
Species Longevity / Maximum Size Maturity (50 per cent)
MUD CRABS 3–4 years, 230 mm CW, but rarely exceeds 200 mm CW in most areas Varies by sex and location but generally 120–150 mm CW 
Toggle content

Distributions

Distribution of reported commercial catch of Mud Crabs
Toggle content

Tables

Fishing methods
Northern Territory
Commercial
Crab Trap
Indigenous
Spearfishing
Hook and Line
Cast Net
Traps and Pots
Recreational
Spearfishing
Hand collection
Hook and Line
Traps and Pots
Charter
Traps and Pots
Management methods
Method Northern Territory
Commercial
Effort limits
Gear restrictions
Limited entry
Protection of berried females
Protection of soft-shelled crabs
Size limit
Spatial closures
Spatial zoning
Recreational
Gear restrictions
Possession limit
Protection of berried females
Size limit
Spatial closures
Spatial zoning
Vessel limits
Catch
Northern Territory
Commercial 125.54t
Charter 1.1 t
Indigenous 69 t (2000–01)
Recreational 29 t (2015)

Western Australia – Indigenous (catch) The estimate of the Indigenous harvest tonnage of Mud Crabs in Western Australia has been revised down as the weight multiplier previously used to calculate this value (1.34 kg per crab) is now considered unrealistically high given that the average weight of harvested Mud Crabs in Western Australia was recently estimated at 0.65 kg.

Northern Territory — Charter (management methods) In the Northern Territory, charter operators are regulated through the same management methods as the recreational sector but are subject to additional limits on license and passenger numbers.

Northern Territory – Indigenous (management methods) The Fisheries Act 1988 (NT), specifies that “…without derogating from any other law in force in the Territory, nothing in a provision of this Act or an instrument of a judicial or administrative character made under it limits the right of Aboriginals who have traditionally used the resources of an area of land or water in a traditional manner from continuing to use those resources in that area in that manner”.

Queensland – Indigenous (management methods) for more information see https://www.daf.qld.gov.au/business-priorities/fisheries/traditional-fishing

New South Wales – Indigenous (management methods)https://www.dpi.nsw.gov.au/fishing/aboriginal-fishing

New South Wales – Recreational (Catch) Murphy et al. [2020].

Active Vessels The number of active exemption holders (for Western Australia), licences (for the Northern Territory and Queensland) or businesses (for New South Wales) are shown here because the number of active vessels is not an appropriate measure of effort in Australian Mud Crab fisheries. Licensing arrangements also vary significantly between jurisdictions.

Toggle content

Catch Chart

Commercial catch of Mud Crabs - note confidential catch not shown
Toggle content

References

  1. Alberts-Hubatsch, H 2015, Movement patterns and habitat use of the exploited swimming crab Scylla serrata (Forskål, 1775), PhD thesis, University Bremen, Germany.
  2. Alberts-Hubatsch, H, Lee SY, Diele, K, Wolff, M and Nordhaus, I 2014, Microhabitat use of early benthic stage mud crabs, Scylla serrata (Forskål, 1775), in eastern Australia. Journal of Crustacean Research, 34: 604–610.
  3. Atlas of Living Australia website. Species page: https://bie.ala.org.au/species/urn:lsid:biodiversity.org.au:afd.taxon:628cd52f-10b6-4f23-8a76-9caff511b775#tab_recordsView. Accessed 20 January 2021
  4. Benthuysen, JA, Oliver, ECJ, Feng, M and Marshall, AG 2018, Extreme marine warming across tropical Australia during austral summer 2015–2016. Journal of Geophysical Research: Oceans, 123: 1301–1326.
  5. Brown, IW 2010, Taking female Mud Crabs (Scylla serrata): assessment of risks and benefits, FRDC final report 2009/031, Queensland Government Department of Employment, Economic Development and Innovation, Deception Bay.
  6. Butcher PA, Boulton AJ, Macbeth WG and Malcolm HA (2014) Long-term effects of marine park zoning on giant mud crab Scylla serrata populations in three Australian estuaries, Marine Ecology Progress Series 508: 163–176.
  7. Butcher, PA 2004, Mud Crab (Scylla serrata) and marine park management in estuaries of the Solitary Islands Marine Park, New South Wales, PhD thesis, University of New England, Armidale.
  8. Butcher, PA, Boulton, AJ and Smith, SDA 2003, Mud Crab (Scylla serrata: Portunidae) populations as indicators of the effectiveness of estuarine marine protected areas, In JP Beumer, A Grant and DC Smith (eds.), Aquatic protected areas: what works best and how do we know? Proceedings of the world congress on aquatic protected areas, Australian Society for Fish Biology, Cairns, Queensland, 421–427.
  9. COA BOM (Commonwealth of Australia, Bureau of Meteorology) 2017, Northern Territory wet season October to April 2016–17: wetter than average.
  10. COA BOM (Commonwealth of Australia, Bureau of Meteorology) 2018, Regional Water Information.
  11. Coleman, APM 2004, The national recreational fishing survey: the Northern Territory, Fishery report 72, Northern Territory Department of Business, Industry and Resource Development, Darwin.
  12. Duke, NC, Kovacs, JM, Griffiths, AD, Preece, L, Hill, DJE, van Oosterzee, P, Mackenzie, J, Morning, HS and Burrows, D 2017, Large-scale dieback of mangroves in Australia. Marine and Freshwater Research 68:1816–1829.
  13. Froese, R. Demirel, N and Winker, H 2019, Simple User Guide for CMSY+ and BSM (CMSY_2019_9f.R) published online at http://oceanrep.geomar.de/33076/
  14. Froese, R. Demirel, N. Gianpaolo, C. Kleisner, KM and Winker, H 2017, Estimating Fisheries Reference Points from Catch and Resilience. Fish and Fisheries 18: 506-526.
  15. Gopurenko, D and Hughes JM 2002, Regional patterns of genetic structure among Australian populations of the mud crab Scylla serrata (Crustacea: Decapoda): evidence from mitochondrial DNA, Marine and Freshwater Research, 53: 849–857.
  16. Grubert MA, Walters CJ, Buckworth, RC and SS Penny. In press, Simple modelling to inform harvest strategy policy for a data moderate crab fishery. Marine and Coastal Fisheries.
  17. Grubert, M, D Johnson, D Johnston, and M Leslie 2016, Mud Crabs. in Status of Australian Fish Stocks Reports 2016.
  18. Grubert, M. A., Walters, C. J., Buckworth, R. C., & Penny, S. S. (2019). Simple Modeling to Inform Harvest Grubert, M. A., Walters, C. J., Buckworth, R. C., & Penny, S. S. (2019). Simple Modelling to Inform Harvest Strategy Policy for a Data-Moderate Crab Fishery. Marine and Coastal Fisheries, 11(2), 125-138.
  19. Grubert, MA and Lee, HS 2013, Improving gear selectivity in Australian Mud Crab fisheries, Fishery report 112, Northern Territory Government Department of Primary Industry and Fisheries, Darwin.
  20. Haddon, M. Punt, A and Burch, P 2018, simpleSA: A package containing functions to facilitate relatively simple stock assessments. R package version 0.1.18.
  21. Heasman, MP 1980, Aspects of the general biology and fishery of the Mud Crab Scylla serrata (Forskål), in Moreton Bay, Queensland, PhD thesis, University of Queensland, Brisbane.
  22. Henry, GW and Lyle, JM (eds.) 2003, The national recreational and Indigenous fishing survey, Fisheries Research Development Corporation project 99/158, Australian Government Department of Agriculture, Fisheries and Forestry, Canberra.
  23. Hill, BJ 1994, Offshore spawning by the portunid crab Scylla serrata (Crustacea Decapoda), Marine Biology, 120: 379–384.
  24. Hill, BJ, Williams, MJ and Dutton, P 1982, Distribution of juvenile, subadult and adult Scylla serrata on tidal flats in Australia, Marine Biology, 69: 117–120.
  25. Hyland, SJ, Hill, BJ and Lee, CP 1984, Movement within and between different habitats by the portunid crab Scylla serrata. Marine Biology, 80: 57–61.
  26. Ikhwanuddin, M, Azmiea, G, Juariah, HM, Zakaria, MZ and Ambak, MA 2011, Biological information and population features of mud crab, genus Scylla from mangrove areas of Sarawak, Malaysia. Fisheries Research 108: 299–306.
  27. Integrated Marine Observing System 2018, IMOS OceanCurrent: Surface Currents and Temperature. Up to date ocean information around Australia.
  28. Jebreen, E, Helmke, S, Lunow, C, Bullock, C, Gribble, N, Whybird, O and Coles, R 2008, Fisheries long term monitoring program—Mud Crab (Scylla serrata) report: 2000–2002, PR08-3498, Queensland Government Department of Primary Industries and Fisheries, Brisbane.
  29. Johnston, D, Yeoh, D, Harris, D and Fisher, E 2020b. Blue Swimmer Crab (Portunus armatus) and Mud Crab (Scylla serrata and Scylla olivacea) Resources in the North Coast and Gascoyne Coast Bioregions, Western Australia. Fisheries Research Report No. 306. Department of Primary Industries and Regional Development, Western Australia. 156pp.
  30. Keenan CP, Davies PJF and Mann DL 1998, A revision of the genus Scylla de Haan, 1833 (Crustacea: Decapoda: Brachyura: Portunidae). The Raffles Bulletin of Zoology ,46: 217–245.
  31. Knuckey, IA 1999, Mud Crab (Scylla serrata) population dynamics in the Northern Territory, Australia and their relationship to the commercial fishery, PhD thesis, Northern Territory University, Darwin.
  32. Mann, D, Asakawa, T and Blackshaw, A 1999, Performance of mud crab Scylla serrata broodstock held at Bribie Island Aquaculture Research Centre, In CP Keenan and A Blackshaw (eds), Mud Crab aquaculture and biology, Proceedings of an international scientific forum held in Darwin, Australia, 101–105, ACIAR Proceedings No. 78.
  33. Martell, S, and Froese, R. 2013, A simple method for estimating MSY from catch and resilience. Fish and Fisheries 14:504–514.
  34. Murphy, J.J., Ochwada-Doyle, F.A., West, L.D., Stark, K.E. and Hughes, J.M., 2020. The NSW Recreational Fisheries Monitoring Program - survey of recreational fishing, 2017/18. NSW DPI - Fisheries Final Report Series No. 158.
  35. Northrop, A, O'Neill, M, F and Robins, J 2019 Towards an initial quota for the Queensland mud crab fishery. Department of Agriculture and Fisheries. Brisbane, Queensland.
  36. NTG (Northern Territory Government) 2017, Management Framework for the Northern Territory Mud Crab Fishery 2017. Northern Territory Department of Primary Industry and Resources, Darwin.
  37. NTG (Northern Territory Government) 2018, Status of Key Northern Territory Fish Stocks Report 2016. Northern Territory Department of Primary Industry and Resources, Fishery Report 119, Darwin.
  38. Nurdiani, R and Zeng, CS 2007, Effects of temperature and salinity on the survival and development of Mud Crab, Scylla serrata (Forskål), larvae. Aquaculture Research, 38: 1529–1538.
  39. Pillans, S, Pillans, RD, Johnstone, RW, Kraft, PG, Haywood, MDE and Possingham, HP 2005, Effects of marine reserve protection on the Mud Crab Scylla serrata in a sex-based fishery in subtropical Australia. Marine Ecology Progress Series, 295: 201–213.
  40. QFish, Department of Agriculture and Fisheries, www.qfish.gov.au
  41. Ryan KL, Hall NG, Lai EK, Smallwood CB, Tate A, Taylor SM, Wise BS 2019. Statewide survey of boat-based recreational fishing in Western Australia 2017/18. Fisheries Research Report No. 297, Department of Primary Industries and Regional Development, Western Australia.
  42. Schiller, A 2011, Ocean circulation on the North Australian Shelf, Continental Shelf Research, 31: 1087–1095.
  43. Status of Australian Fish Stocks 2020 – NSW Stock status summary – Giant Mud Crab (Scylla serrata).
  44. 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.
  45. Taylor, S, Webley, J and McInnes, K 2012, 2010 statewide recreational fishing survey, Queensland Department of Agriculture, Fisheries and Forestry, Brisbane.
  46. The Atlas of Living Australia 2018, Spatial Data Portal.
  47. Walters, CJ 2007, User guide for stock assessment using GTGmodel. Fisheries Centre, University of British Columbia publication, 10 p.
  48. Webley, J, McInnes, K, Teixeira, D, Lawson, A and Quinn, R 2015, Statewide Recreational Fishing Survey 2013–14, State of Queensland, Department of Agriculture and Fisheries.
  49. West, LD, Lyle, JM, Matthews, SR and Stark, KE 2012, A survey of recreational fishing in the Northern Territory, 2009–10, Fishery report 109, Northern Territory Government Department of Resources, Darwin.
  50. 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, Fisheries final report series 149, New South Wales Government Department of Primary Industries, Sydney.
  51. Wolanski, E 1993, Water circulation in the Gulf of Carpentaria. Journal of Marine Systems 4: 401–420.

Downloadable reports

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