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MORETON BAY BUGS

Thenus parindicus, Thenus australiensis, Thenus spp.

  • Brad Zeller (Department of Agriculture and Fisheries, Queensland)
  • James Larcombe (Australian Bureau of Agricultural and Resource Economics and Sciences)
  • Mervi Kangas (Department of Fisheries, Western Australia)

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Stock Status Overview

Stock status determination
Jurisdiction Stock Fisheries Stock status Indicators
Commonwealth Northern Prawn Fishery NPF Sustainable Catch
Commonwealth Torres Strait Prawn Fishery TSPF Sustainable Catch
NPF
Northern Prawn Fishery (CTH)
TSPF
Torres Strait Prawn Fishery (CTH)
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Stock Structure

Reef Bug (Thenus australiensis) and Mud Bug (T. parindicus) are known collectively as ‘Moreton Bay Bugs’. Moreton Bay Bugs are distributed along the tropical and subtropical coast of Australia from northern New South Wales to Shark Bay in Western Australia2. No studies have been carried out on the biological stock structure of Australian Moreton Bay Bugs. The two species have overlapping distributions; may be trawled together; are undifferentiated in the catch; and are assessed together.

Given the uncertainty in biological stock structure, here assessment of stock status is presented at the management unit level—Queensland and Commonwealth; and the jurisdictional level—Western Australia.

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Stock Status

Northern Prawn Fishery

Northern Prawn Fishery (Commonwealth) trawl surveys were used to estimate the biomass of Moreton Bay Bugs in the Gulf of Carpentaria, from which an estimate of acceptable biological catch was derived3. This assessment estimated the annual acceptable biological catch for Moreton Bay Bugs in the fishery at 1887 tonnes (t) (95 per cent confidence interval 1716–2057 t). Annual commercial catches have remained well below this (catch peaked at 120 t in 1998). Catches were 59 t in 2014 and 77 t in 2015. The above evidence indicates the biomass of this stock is unlikely to be recruitment overfished.

Fishing mortality has been low in recent years, and ecological risk assessments4 have indicated that the risk of stock depletion of Moreton Bay Bugs is low. A trigger catch limit of 100 t is also in place. If this limit is reached then additional analysis will be conducted to ensure that there are no sustainability concerns with the harvest level. Fishing mortality of juveniles is also reduced by regulating the size at which Moreton Bay Bugs may be retained, and spawning potential is protected through prohibiting retention of egg bearing females. Given the low level of catch in recent years compared to estimates of acceptable biological catch, the stock is unlikely to become recruitment overfished.

On the basis of the evidence provided above, the Northern Prawn Fishery (Commonwealth) management unit is classified as a sustainable stock.

Torres Strait Prawn Fishery

No formal stock assessment exists for Moreton Bay Bugs in the Torres Strait Prawn Fishery (Commonwealth) (TSPF) management unit. Assessment of seabed and associated biodiversity in the Torres Strait5,6 estimated the 2007 Moreton Bay (Reef) Bug biomass at 124 t, only 19 per cent of which was located within the area exposed to prawn trawling (based on the 2005 footprint of the fishery using vessel monitoring system data). The biomass of Mud Bugs was estimated to be 151 t. Only 18 per cent of biomass was located in areas exposed to prawn trawling. With the decline in fishing effort in recent years, fishing mortality is also likely to have declined. Fishing mortality of juveniles is also reduced by regulating the size at which Moreton Bay Bugs may be retained, and spawning potential is protected through prohibiting retention of egg bearing females. Research has found that Mud Bug egg production is maintained at the minimum size limit of 75 mm CW7.The above evidence indicates the biomass of this stock is unlikely to be recruitment overfished.

The Torres Strait assessment of seabed and associated biodiversity5 indicated that Moreton Bay Bugs are unlikely to have been exposed to high levels of fishing pressure in the Torres Strait Protected Zone. In 2013–15 annual catch of Moreton Bay Bugs averaged 23 t, which is estimated to be less than 10 per cent of available biomass, most of which inhabits extensive areas outside of fished areas. Trawl operations in the TSPF cover only a small proportion—approximately 20 per cent6—of the Torres Strait Protected Zone. Lower fishing effort has resulted in reduced spatial coverage of the fishery in recent years. The above evidence indicates that 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 Torres Strait Prawn Fishery (Commonwealth) management unit is classified as a sustainable stock.

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Biology

Moreton Bay Bug biology16,17

Biology
Species Longevity / Maximum Size Maturity (50 per cent)
MORETON BAY BUGS ~7 years T. australiensis: Males 106 mm CW , Females 124 mm CW T. parindicus: Males 87 mm CW, Females 103 mm CW T. australiensis (Female): 82 mm CW T. parindicus (Female): 75 mm CW
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Distributions

Distribution of reported commercial catch of Moreton Bay Bugs

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Tables

Fishing methods
Commonwealth
Commercial
Otter Trawl
Management methods
Method Commonwealth
Commercial
Effort limits
Limited entry
Retention of females with eggs prohibited
Size limit
Spatial closures
Vessel restrictions
Active vessels
Commonwealth
51 in NPF, 23 in TSPF
NPF
Northern Prawn Fishery (CTH)
TSPF
Torres Strait Prawn Fishery (CTH)
Catch
Commonwealth
Commercial 77.63t in NPF, 27.88t in TSPF
Indigenous No catch
Recreational No catch
NPF
Northern Prawn Fishery (CTH)
TSPF
Torres Strait Prawn Fishery (CTH)

a Commonwealth – Recreational The Commonwealth Government does not manage recreational fishing. Recreational fishing in Commonwealth waters is managed by the states or territory immediately adjacent to those waters, under their management regulations.
b Commonwealth – Indigenous The Commonwealth Government does not manage non-commercial Indigenous fishing (with the exception of the Torres Strait). In general, non-commercial Indigenous fishing in Commonwealth waters is managed by the states or territory immediately adjacent to those waters. In the Torres Strait, both commercial and non-commercial Indigenous fishing is managed by the Torres Strait Protected Zone Joint Authority (PZJA) through the Australian Fisheries Management Authority (Commonwealth), Department of Agriculture Fisheries and Forestry (Queensland) and the Torres Strait Regional Authority. The PZJA also manages non-Indigenous commercial fishing in the Torres Strait.
c Queensland – Indigenous In Queensland, under the Fisheries Act 1994, Indigenous fishers are able 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 can be obtained through permits.

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Catch Chart

Commercial catch of Moreton Bay Bugs

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Effects of fishing on the marine environment

  • The impact of trawling on habitats is managed in the Queensland and Western Australian fisheries which harvest Moreton Bay Bugs. In Queensland, the Great Barrier Reef Marine Park (GBRMP) occupies 63 per cent of the East Coast Otter Trawl Fishery18, 34 per cent of which is open to trawling5, but effort is highly aggregated, occurring within only a small fraction (six per cent) of the open area9. South of the GBRMP, the fishery operates in only 10 per cent of the area open to trawling19. In Western Australia, extensive permanent and temporary closures result in the fleet operating in only seven per cent of the Shark Bay region, less than 30 per cent of the Exmouth Gulf, and less than three per cent of the north coast region. Fishing operations are restricted to areas of sand and mud, where trawling has minimal long-term physical impact20–23. The Northern Prawn Fishery (Commonwealth) (NPF) also uses a system of closures (spatial and seasonal) to manage the fishery, as well as other input controls (for example limited entry, gear restrictions). A total of 2.1 per cent of the total managed area of the fishery is subject to permanent closures, while 8.3 per cent is subject to seasonal closures24. The Torres Strait Prawn Fishery (Commonwealth) (TSPF) also employs spatial and temporal closures which are used to protect small prawns, but also important habitat areas like breeding populations of turtles25.
  • Although the incidental capture of byproduct and bycatch species by trawling can lead to a range of indirect ecosystem effects26, studies in Queensland and Western Australia, found no significant difference in biodiversity or overall distribution patterns of seabed biota between trawled and non-trawled areas12,22. An assessment of trawl-related risk in the GBRMP found that the East Coast Otter Trawl Fishery (Queensland) (Qld ECOTF), posed no more than an intermediate risk of overfishing species assemblages exposed to trawling9. The spatial contraction and/or temporal reduction in effort in these jurisdictions (see above) are likely to have mitigated somewhat the ecosystem impacts of trawling. Similarly, the Commonwealth fisheries have undergone varying levels of ecological risk assessment. In the NPF, the ecological risk management report identifies priority species at high risk. However, no target or protected species have been assessed as high risk because of the fishery27. An ecological risk assessment has also been conducted for the TSPF and identified nine species where trawling has had a negative impact on their biomass28.
  • The use of bycatch reduction devices (BRDs) in trawling can significantly reduce bycatch—by more than 50 per cent by weight in some fisheries29. In the Qld ECOTF the mandatory use of BRDs from 1999 and of turtle excluder devices (TEDs) from 2001, largely eliminated capture of most large bycatch species, including turtles, sharks and rays30. BRDs and TEDs became mandatory in NPF in 2001. Use of TEDs in the NPF reduced turtle bycatch from 5 700 individuals per year (before 2001) to approximately 30 per year (after 2001)4. The introduction of TEDs in the Western Australian trawl fisheries in 2003 reduced turtle bycatch by at least 95 per cent31. BRDs and TEDs have been mandatory in the Shark Bay and Exmouth Gulf prawn fisheries since 2003 and in all northern Western Australian prawn fisheries since 2005. All prawn trawlers operating in Western Australia now must use BRDs, including TEDs, secondary fish exclusion devices and hoppers to increase survival of returned fish. Commitment to continuous improvement in bycatch mitigation has facilitated increased use of best practice TEDs and BRDs in the Qld ECOTF since 2008. Reduced impact of trawling and a general absence of high risk of overfishing bycatch species has been acknowledged in recent ecological risk assessments of the fishery9,10.
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Environmental effects on MORETON BAY BUGS

  • There are suggestions that ocean acidification, changes in ocean current patterns (for example, strengthening of the East Australian Current), and increased intensity of tropical storms associated with climate change may affect food availability, larval survival, dispersion and settlement patterns, abundance of Moreton Bay Bugs, and the distribution and level of catches in the East Coast Otter Trawl Fishery (Queensland)32. Increased rainfall and sea level rise have been identified33 as key impacts of climate change in the region of the Northern Prawn Fishery (Commonwealth). These impacts have the potential to modify the geographical distribution of Moreton Bay Bug stocks.
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References

  1. 1 Burton, TE and Davie, PJF 2007, A revision of the shovel-nosed lobsters of the genus Thenus (Crustacea: Decapoda: Scyllaridae), with descriptions of three new species, Zootaxa, 1429: 1–38.
  2. 2 George, RW and Griffin, DJG 1972, The shovel nosed lobsters of Australia, Australian Natural History, September 1972, 227–231.
  3. 3 Milton, DA, Fry, GC, Kuhnert, P, Tonks, M, Zhou, S, and Zhu, M 2010, Assessing data poor resources: developing a management strategy for byproduct species in the Northern Prawn Fishery, final report to the Fisheries Research and Development Corporation, project 2006/008.
  4. 4 Griffiths, S, Kenyon, R, Bulman, C, Dowdney, J, Williams, A, Sporcic, M, and Fuller, M 2007, Ecological risk assessment for the effects of fishing: report for the Northern Prawn Fishery, report for the Australian Fisheries Management Authority, Canberra.
  5. 5 Pitcher, CR, Haywood, M, Hooper, J, Coles, R, Bartlett, C, Browne, M, Cannard, T, Carini, G, Carter, A, Cheers, S, Chetwynd, D, Colefax, A, Cook, S, Davie, P, Ellis, N, Fellegara, I, Forcey, K, Furey, M, Gledhill, D, Hendriks, P, Jacobsen, I, Johnson, J, Jones, M, Last, P, Marks, S, McLeod, I, Sheils, J, Sheppard, J, Smith, G, Strickland, C, Van der Geest, C, Venables, W, Wassenberg, T, and Yearsley, G 2007, Mapping and characterisation of the biotic and physical attributes of the Torres Strait ecosystem, CSIRO/QM/QDPI CRC Torres Strait Task final report.
  6. 6 Turnbull, C and Rose, CL 2007, Towards ecologically sustainable management of the Torres Strait Prawn Fishery, CRC Torres Strait Task T1.5 final report, Department of Primary Industries and Fisheries, Queensland.
  7. 7 Courtney, AJ 2002, The status of Queensland’s Moreton Bay Bug (Thenus spp.) and Balmain Bug (Ibacus spp.) stocks, Queensland Government, Department of Primary Industries, Brisbane.
  8. 8 Fletcher, WJ and Santoro, K (eds) 2015, Status Reports of the Fisheries and Aquatic Resources of Western Australia 2014/15, The State of the Fisheries. Western Australian Department of Fisheries, Perth.
  9. 9 Pears, RJ, Morison, AK, Jebreen, EJ, Dunning, M, Pitcher, CR, Courtney, AJ, Houlden, B, and Jacobsen, IP 2012, Ecological risk assessment of the East Coast Otter Trawl Fishery in the Great Barrier Reef Marine Park: Technical Report, Great Barrier Reef Marine Park Authority, Townsville.
  10. 10 Queensland Department of Agriculture and Fisheries 2016, unpublished, An ecological risk assessment of the East Coast Trawl Fishery in Southern Queensland Including the River and Inshore Beam Trawl Fishery, Queensland Government, Department of Agriculture, Fisheries and Forestry, Brisbane.
  11. 11 Queensland Department of Agriculture and Fisheries, unpublished, Queensland Stock Status Assessment Workshop, 14–15 June 2016, Species Summary Pages, Brisbane.
  12. 12 Pitcher, CR, Doherty, P, Arnold, P, Hooper, J, Gribble, N, Bartlett, C, Browne, M, Campbell, N, Cannard, T, Cappo, M, Carini, G, Chalmers, S, Cheers, S, Chetwynd, D, Colefax, A, Coles, R, Cook, S, Davie, P, De’ath, G, Devereux, D, Done, B, Donovan, T, Ehrke, B, Ellis, N, Ericson, G, Fellegara, I, Forcey, K, Furey, M, Gledhill, D, Good, N, Gordon, S, Haywood, M, Jacobsen, I, Johnson, J, Jones, M, Kinninmoth, S, Kistle, S, Last, P, Leite, A, Marks, S, McLeod, I, Ozkowicz, S, Rose, C, Seabright, D, Sheils, J, Sherlock, M, Skelton, P, Smith, D, Smith, G, Speare, P, Stowar, M, Strickland, C, Sutcliffe, P, Van der Geest, C, Venables, W, Walsh, C, Wassenberg, T, Welna, A, and Yearsley, G 2007, Seabed biodiversity on the continental shelf of the Great Barrier Reef World Heritage Area, AIMS/CSIRO/QM/QDPI CRC Reef Research Task final report.
  13. 13 Hill, B, Blaber, S, Wassenberg, T, and Milton, D 1998, Composition and Fate of Discards, in I Poiner, J Glaister, R Pitcher, C Burridge, T Wassenberg, N Gribble, B Hill, S Blaber, D Milton, D Brewer, and N Ellis (eds), The Environmental Effects of Prawn Trawling in the Far Northern Section of the Great Barrier Reef Marine Park: 1991-1996, CSIRO Division of Marine Research, Cleveland.
  14. 14 Courtney, AJ, Campbell, MJ, Roy, DP, Tonks, ML, Chillcott, KE and Kyne, PM 2008, Round scallops and square meshes: a comparison of four codend types on the catch rates of target species and by-catch in the Queensland (Australia) saucer scallop (Amusium balloti) trawl fishery, Marine and Freshwater Research, 59: 849–864.
  15. 15 Zeller, B, Kangas, M, and Larcombe, J, 2014, Moreton Bay Bug Thenus australiensis, T. parindicus, in M Flood, I Stobutzki, J Andrews, C Ashby, G Begg, R Fletcher, C Gardner, L Georgeson, S Hansen, K Hartmann, P Hone, P Horvat, L Maloney, B McDonald, A Moore, A Roelofs, K Sainsbury, T Saunders, T Smith, C Stewardson, J Stewart and B Wise (eds) 2014, Status of key Australian fish stocks reports 2014, Fisheries Research and Development Corporation, Canberra.
  16. 16 Jones, CM 1988, The biology and behaviour of bay lobsters, Thenus spp. (Decapoda: Scyllaridae), in northern Queensland, Australia, PhD thesis, University of Queensland, Brisbane.
  17. 17 Courtney, AJ 1997, A study of the biological parameters associated with yield optimisation of Moreton Bay Bugs, Thenus spp., final report (project 92/102), Queensland Department of Primary Industries, Brisbane.
  18. 18 Huber, D, 2003, Audit of the Management of the Queensland East Coast Trawl Fishery in the Great Barrier Reef Marine Park Report, Great Barrier Reef Marine Park Authority, May 2003.
  19. 19 Coles, R, Grech, A, Dew, K, Zeller, B and McKenzie, L, 2008, A preliminary report on the adequacy of protection provided to species and benthic habitats in the east coast otter trawl fishery by the current system of closures, Queensland Department of Primary Industries and Fisheries, Brisbane.
  20. 20 Kangas, M, McCrea, J, Fletcher, W, Sporer, E and Weir, V 2006, Exmouth Gulf Prawn Fishery, ESD Report Series 1, Western Australian Department of Fisheries.
  21. 21 Kangas, M, McCrea, J, Fletcher, W, Sporer, E and Weir, V 2006, Shark Bay Prawn Fishery, ESD Report Series 3, Western Australian Department of Fisheries.
  22. 22 Kangas, M, Morrison, S, Unsworth, P, Lai, E, Wright, I and Thomson, A 2007, Development of biodiversity and habitat monitoring systems for key trawl fisheries in Western Australia, final report, Fisheries Research and Development Corporation project 2002/038, Fisheries Research Report 160, Fisheries Western Australia, North Beach.
  23. 23 Kangas, M, and Morrison, S 2013, Trawl impacts and biodiversity management in Shark Bay, Western Australia, Marine and Freshwater Research, 64: 1135–1155.
  24. 24 Dichmont, CM, Jarrett, A, Hill, F and Brown, M 2014, Harvest strategy for the Northern Prawn Fishery under input control, Australian Fisheries Management Authority, Canberra.
  25. 25 Flood, M and George, D 2013, Torres Strait Prawn Fishery, in Commonwealth Trawl and Scalefish Hook Sectors, in Woodhams, J, Vieira, S and Stobutzki, I (eds.), Fishery status reports 2012: status of fish stocks and fisheries managed by the Australian Government, Australian Bureau of Agricultural and Resource Economics and Sciences, Canberra.
  26. 26 Dayton, PK, Thrush, SF, Agardy, MT, and Hofman, RJ 1995, Environmental effects of fishing, Aquatic Conservation, Marine and Freshwater Ecosystems, 5: 205–232.
  27. 27 Australian Fisheries Management Authority 2012, Ecological risk management: Report for the Northern Prawn Fishery tiger and banana prawn sub-fisheries, report to the Australian Fisheries Management Authority, Canberra.
  28. 28 Turnbull, C, Furlani, D, Bulman, C and Dowdney, J 2007, Ecological risk assessment for the effects of fishing: report for the Torres Strait Prawn Fishery, report to the Australian Fisheries Management Authority, Canberra.
  29. 29 Raudzens, E 2007, At sea testing of the Popeye Fishbox bycatch reduction device onboard the FV Adelaide Pearl for approval in Australia’s Northern Prawn Fishery, Australian Fisheries Management Authority, Canberra.
  30. 30 Roy, D and Jebreen, E 2011, Extension of Fisheries Research and Development Corporation funded research results on improved bycatch reduction devices to the Queensland East Coast Otter Trawl Fishery, final report to the Fisheries Research and Development Corporation, project 2008/101.
  31. 31 Kangas, MI and Thomson, A 2004, Implementation and assessment of bycatch reduction devices in the Shark Bay and Exmouth Gulf trawl fisheries, final report, Fisheries Research and Development Corporation project 2000/189, Western Australian Department of Fisheries, Perth.
  32. 32 Morison, AK and Pears, RJ 2012, Assessment of the ecological vulnerability of the East Coast Otter Trawl Fishery to climate change: a brief synthesis of information and results of an expert workshop, Great Barrier Reef Marine Park Authority, Townsville.
  33. 33 Hobday, AJ, Poloczanska, ES, and Matear, RJ (eds.) 2008, Implications of climate change for Australian fisheries and aquaculture: a preliminary assessment, report to the Australian Government Department of Climate Change, Canberra.

Archived reports

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