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Reef Bug and Mud Bug, collectively known as Moreton Bay Bugs, are sustainable species distributed along the tropical and subtropical coast of Australia.

Reef Bug (Thenus australiensis) and Mud Bug (Thenus 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 Australia [George and Griffin 1972]. The two species have overlapping distributions but display relatively strong habitat partitioning. Reef Bugs typically prefer deeper areas with coarser sediments, while Mud Bugs inhabit mainly shallow inshore areas with finer sediments [McMillan et al. 2023]. In the Queensland East Coast Otter Trawl Fishery (ECOTF), where around 80% of total landings occur, the two species have been differentiated in the catch since 2021. Modelling of species distributions combined with harvest locations indicated that the proportion of Reef Bugs comprising total landings increased from around 67% of landings in the ECOTF in 1988 (at the beginning of logbook records) to 93% in 2021 [McMillan et al. 2023]. This reflects a shift to targeted fishing for the larger, more valuable Reef Bugs, while Mud Bugs remain an incidentally caught species in the ECOTF. In other fisheries, both species are undifferentiated in the catch and are assessed together. Genetic population structure of Reef Bugs, which dominate landings in the ECOTF, supportsa single biological stock on Queensland’s east coast [McMillan et al. 2024]. No studies have been carried out on the biological stock structure of Moreton Bay Bugs in other fisheries.

Given the uncertainty in biological stock structure, here assessment of stock status is presented at the management unit level—Northern Prawn Fishery (Commonwealth), Torres Strait Prawn Fishery (Commonwealth) and East Coast Otter Trawl Fishery (Queensland); and the jurisdictional level—Western Australia.

Western Australia

No formal stock assessment exists for Moreton Bay Bugs in Western Australia. Moreton Bay Bugs are not targeted in Western Australia but are landed occasionally as a by-product species of prawn and scallop trawl fisheries, so directed fishing effort is low. In 2022, the combined Western Australian fisheries landings of Moreton Bay Bugs was 6 t, which is low but within the historical catch range. Combined fishery landings have been at or below 10 t in nine out of the last 10 years. The spatial coverage of Western Australian fisheries that retain Moreton Bay Bugs is limited compared with the large area across which Moreton Bay Bugs are distributed in north-western Western Australia. Substantial Moreton Bay Bug biomass is protected within the extensive network of fishery closures in place from Shark Bay to Napier Broome Bay [Newman et el. 2023]. The above evidence indicates that the biomass of this stock is unlikely to be depleted, 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 Western Australian jurisdictional stock is classified as a sustainable stock.

Moreton Bay Bug biology [Courtney 1997; Jones 1988]

Commonwealth – Recreational. The Australian 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. 

Commonwealth – Indigenous. The Australian 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.

Commonwealth – Commercial (Management Methods/Catch). Data provided for the Commonwealth align with 2021–22 financial year.

Queensland – Indigenous (Management Methods). For more information see https://www.daf.qld.gov.au/business-priorities/fisheries/traditional-fishing

Queensland – Commercial (Catch) Commercial data have been sourced from the commercial fisheries logbook program. Further information available through the 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 are available at: https://www.daf.qld.gov.au/business-priorities/fisheries/sustainable/harvest-strategy  

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2. 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.
3. 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.
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