East Coast Otter Trawl Fishery (Queensland) management unit
No formal stock assessments exist for Moreton Bay Bugs in the East Coast Otter Trawl Fishery (Queensland). Areas open to trawling in the Great Barrier Reef Marine Park contribute approximately 88 per cent of the east coast commercial catch of Moreton Bay Bugs. However, components of the biomass of the eastern Queensland populations of Moreton Bay Bugs have been within permanent closures associated with the Great Barrier Reef Marine Park since the mid 1980s. Research3 estimated that closures in the Great Barrier Reef Marine Park included 54 per cent of the estimated biomass of T. australiensis and 45 per cent of the estimated biomass of T. parindicus in 20053. In addition, the catch per unit effort (CPUE) for Moreton Bay Bugs has shown an increasing trend over the past 10 years4. Given this level of historical protection and the trends in CPUE, Moreton Bay Bugs in this management unit are unlikely to be recruitment overfished.
T. australiensis and T. parindicus mature at approximately 5.2 and 5.8 cm carapace length, respectively. Hence conservative minimum legal size limits (7.5 cm carapace length) should allow Moreton Bay Bugs to spawn before they enter the fishery, provided that undersized animals caught survive post-capture. Square-mesh codends protect juveniles of both species from fishing mortality in the fishery4. These measures, combined with spatial closures, mean that fishing mortality is unlikely to cause Moreton Bay Bugs in this management unit to become recruitment overfished.
On the basis of the evidence provided above, the East Coast Otter Trawl Fishery (Queensland) management unit is classified as a sustainable stock.
North-western Australia (Western Australia) management unit
No formal stock assessments exist for Moreton Bay Bugs in north-western Australia. Moreton Bay Bugs are not specifically targeted in north-western Australia, and current commercial catch levels are low. Insufficient information is available to formally assess the status of this management unit. As a result, the north-western Australia management unit is classified as an undefined stock.
Northern Prawn Fishery (Commonwealth) management unit
An assessment of byproduct species in the Gulf of Carpentaria within the Northern Prawn Fishery (Commonwealth) was conducted in 20105. 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). This is well in excess of historical annual commercial catches (catch peaked at 120 t in 1998). As a result, Moreton Bay Bugs in the Northern Prawn Fishery management unit are unlikely to be recruitment overfished.
Fishing mortality has been low in recent years, and ecological risk assessments have suggested that the risk of stock depletion of Moreton Bay Bugs is low. A trigger limit of 100 t is also in place. If this limit is reached in a season, further analysis will be conducted to ensure that there are no sustainability concerns with the harvest level of Moreton Bay Bugs. Given the low level of catch in recent years, the Northern Prawn Fishery (Commonwealth) management unit 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 (Commonwealth) management unit
No formal stock assessment has been carried out for Moreton Bay Bugs in the Torres Strait Prawn Fishery (Commonwealth). Moreton Bay Bugs are a byproduct species within this fishery, taken while targeting prawns. Trawl operations in the Torres Strait Prawn Fishery (Commonwealth) cover a small proportion—approximately 20 per cent6—of the Torres Strait Protected Zone. The coverage of the fishery is likely to have declined in recent years as a result of declining effort. Reported commercial catches of the species have been decreasing over the past decade. In 2010, approximately 4 t of Moreton Bay Bugs were reported. There is a minimum size limit for Moreton Bay Bugs of 7.5 cm carapace length in the Torres Strait Prawn Fishery (Commonwealth) that should provide an opportunity for individuals to spawn before they are retained by fishers, provided that animals survive post-capture.
A recent assessment of the seabed and associated biodiversity of the Torres Strait7 indicates that Moreton Bay Bugs are unlikely to have been exposed to high levels of fishing pressure in the Torres Strait Protected Zone. The assessment estimated that biomass of T. australiensis in 2007 was 124 t, 19 per cent of which was located within the area exposed to prawn trawling (2005 footprint of the fishery using vessel monitoring system data). The biomass of T. parindicus was estimated to be 151 t, with 18 per cent located in areas exposed to prawn trawling.
The current low levels of commercial catch and effort, and the protection offered by the minimum size limit, mean that it is unlikely that Moreton Bay Bugs in this management unit will become recruitment overfished. This being the case, it is also unlikely that the management unit is overfished.
On the basis of the evidence provided above, the Torres Strait Prawn Fishery (Commonwealth) management unit is classified as a sustainable stock.
Figure 2: Commercial catch of Moreton Bay Bugs in Australian waters, 2000–10 (calendar year)
On average, East Coast Otter Trawl Fishery (Queensland) landings make up 95 per cent of the Australian Moreton Bay Bug commercial catch. In 2000 and 2001, catches were low compared with more recent catches; this was mainly the result of the East Coast Otter Trawl Fishery (Queensland) adjusting to management changes accompanying the introduction of a statutory management plan for the fishery in November 1999. A number of factors, including extensive spatial and temporal closures, mandatory use of compliant bycatch reduction devices, and more detailed catch-and-effort recording requirements, may have reduced the reported Moreton Bay Bug catch. Since 2001, annual landings in the East Coast Otter Trawl Fishery (Queensland) have averaged 429 t, ranging from 222 to 484 t. Fishing effort in the East Coast Otter Trawl Fishery (Queensland) decreased steadily from 2001 to 2008, but has steadied in recent years.