Balmain Bug Ibacus alticrenatus, I. brucei, I. chacei, I. peronii

East Coast biological stock

This cross-jurisdictional, multispecies biological stock has components in New South Wales and Queensland. Each jurisdiction assesses the part of the biological stock that occurs in its waters. The status presented here for the entire biological stock has been established using evidence from both jurisdictions.

In New South Wales, Balmain Bugs (true Balmain Bugs and Smooth Bugs) are trawl target species, and have been assessed in terms of their commercial catch rates and length compositions in landings. Median catch rates (kg/day of trawling) have fluctuated but show no overall trends, while the size compositions in landings have remained stable for both species. The above evidence indicates that the biomass of this part of the stock is unlikely to be recruitment overfished. Current landings are at historically low levels as a result of a large reduction in fishing effort, with the number of days fished in 2013 being less than 30 per cent of those fished in 2000. This reduction in fishing effort, in combination with stable size compositions in landings, strongly suggests that fishing mortality is constrained in New South Wales waters. The above evidence indicates that the current level of fishing pressure is unlikely to cause this part of the stock to become recruitment overfished.

In Queensland, Balmain Bug fishing mortality is managed by a prohibition on taking egg-bearing females, conservative minimum legal sizes (which were updated in 2009), and mandatory use of turtle excluder devices since the early 2000s—these have been shown to reduce the incidental catch rates of scyllarid lobsters, including Balmain Bugs^2,3. In addition, the spawning stock is partly protected from fishing during an annual seasonal closure. Although nominal catch rates have declined since 2011, and the 2013 catch was relatively low⁴, this is likely to be an indication of the more conservative minimum legal sizes for I. chacei and fisher behaviour, rather than declining abundance. Fishers harvest Balmain Bug as low-value byproduct of fishing for Eastern King Prawn. Given their low value, it is suspected that Balmain Bug fishing mortality is also likely to be low.

Balmain Bugs were considered in a recent species risk assessment of the Queensland East Coast Otter Trawl Fishery, based on a qualitative method that combines biological resilience properties with fishery impact susceptibility⁵. It found a low risk of the Queensland part of the east coast Balmain Bug stock becoming recruitment overfished at the 2009 effort level south of the Great Barrier Reef Marine Park⁶, where the majority (83 per cent, on average) of catch is taken. Fishing effort has declined in that area by 10 per cent since 2011, further reducing the risk of the stock becoming recruitment overfished. The risk of recruitment overfishing within the Great Barrier Reef Marine Park was intermediate to high⁷, based on perceived differences between this area and the area south of the Great Barrier Reef Marine Park, in terms of fishery interaction throughout the Balmain Bug life cycle, marketability and access to refugia. Fishing effort in the Great Barrier Reef Marine Park has declined by 23 per cent since 2009, also reducing risk for this part of the stock.

The above evidence indicates that the biomass of the Queensland part of the stock is unlikely to be recruitment overfished and the current level of fishing pressure is unlikely to cause this part of the stock to become recruitment overfished.

On the basis of the evidence provided above, the entire biological stock is classified as a sustainable stock.