Banana Prawn Penaeus merguiensis (formerly Fenneropenaeus merguiensis)¹

Northern Prawn Fishery (Commonwealth) management unit

Recruitment of White Banana Prawns in the Northern Prawn Fishery (Commonwealth) is thought to be largely determined by seasonal conditions, particularly rainfall⁴. As a result, a reliable stock–recruitment relationship has not been established. No formal stock assessment exists for this stock.

The harvest strategy for White Banana Prawns in the Northern Prawn Fishery (Commonwealth) is designed for the capture of larger prawns and to allow for sufficient escapement to ensure adequate spawning biomass (based on historical data), preventing growth and recruitment overfishing, and providing higher returns by minimising the capture of small prawns. This is achieved through season-length, the end of which is dictated by catch-rate thresholds ⁵. The harvest strategy is designed to perform under conditions of substantial variation in biomass, which are largely independent of fishing. Although fishing mortality is thought to be high for White Banana Prawns in some years⁶, the species is thought to be resilient to fishing pressure.

In 2013, total reported commercial landings were 2713 tonnes (t); this is substantially below the landings in recent years and below the average catch of the preceding 10 years (2004 to 2013) of 4105 t. These catch levels indicate that a smaller than average biomass was available in 2013. Effort expended on White Banana Prawns in the Northern Prawn Fishery (Commonwealth) in 2013 was 2192 vessel-days, less than the 10-year average (2002 to 2012) of approximately 2858 vessel-days.

The recent history of commercial catches of White Banana Prawns, which have been harvested in accordance with the harvest strategy and with a substantially reduced fishing fleet (compared with historical levels), indicates that the management unit is unlikely to be recruitment overfished⁷. The comparatively low effort indicates that fishing mortality is unlikely to cause the management unit to become recruitment overfished⁷.

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

East coast (Queensland) management unit

The most recent quantitative assessment of the east coast (Queensland) management unit was based on catch-and-effort data from 1988 to 2004, and estimated an average annual maximum sustainable yield (MSY) of 802 t³. Although there appears to be no long-term trend in total annual catch in relation to the MSY, there is evidence that the size of year-to-year variations may be increasing (for example, record high total catch in 2011, record low total catch in 2012 and the second highest total catch in 2013)⁸. From 2009 to 2013, annual catches have been variable in substocks where the majority (95 per cent) of the catch was taken⁸. The above evidence indicates the biomass of the management unit is unlikely to be recruitment overfished.

Although fishing mortality is likely to be at or near the upper sustainable limit for some substocks, recent ecological risk assessments found that there was a low risk of the management unit becoming recruitment overfished at 2009 effort levels^9,10. Since 2009, there has been a 16 per cent decrease in effort directed at White Banana Prawn (days when White Banana Prawn was caught), indicating that, despite an increase in fishing power in the East Coast Otter Trawl Fishery fleet (0.4 to 3.1 per cent per year)¹¹, fishing pressure on the management unit is not increasing. The above evidence indicates that the current level of fishing pressure is unlikely to cause the management unit to become recruitment overfished.

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

Exmouth Gulf Prawn Managed Fishery (Western Australia) management unit

Banana Prawn landings are generally low (or zero) in this fishery, but in 2013 landings (74 t) were the highest recorded since the fishery started. This is likely to be attributable to favourable environmental conditions for White Banana Prawn (moderate rainfall in December–March for 3 years and warmer than average water temperatures). In 2012, a total of 33 t of White Banana Prawn was landed, indicating a higher than average abundance of spawning stock in that year. This is likely to have resulted in improved recruitment in 2013. The management unit is not considered to be recruitment overfished, and the current level of fishing mortality is unlikely to cause the management unit to become recruitment overfished.

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

Nickol Bay Prawn Managed Fishery (Western Australia) management unit

Historical commercial catch levels from 1989 to 1998 have been used as the basis for calculating target catch ranges. The target catch range is 40–220 t ¹². Annual commercial catch projections for the fishing season are based on wet-season rainfall (December–March). The commercial catch projection for the 2013 fishing season was 120–180 t. Total commercial catch for 2013 was 106 t, which is within the target catch range but slightly below the 2013 projected catch range. Six boats fished in 2013, for a total effort of 178 vessel-days.

On the basis of annual trends in landings and effort since 1980 and, more recently, annual catch rates and the outputs of stock production models and a biomass dynamics model (unpublished work by the Western Australian Department of Fisheries), the White Banana Prawn stock in Nickol Bay is currently being fished at a sustainable level. Key evidence to support this is as follows:

• There has been no marked declining trend in overall landings across the entire time series, despite very marked reductions in effort in recent years. Catches have typically fluctuated within the lower half of the catch target range.
• Although catches have declined somewhat in recent years, the level of reduction is consistent with the level of effort reduction, according to the outputs of stock production models.
• There has been no decline in peak catch rates in recent years in the two main fishing grounds.
• There has been a declining trend in fishing mortality due to low fishing levels, as estimated by a biomass dynamics model.
• In recent years, the levels of spawning biomass have been high relative to the estimated unfished level, as determined from the biomass dynamics model.

Therefore, the management unit is not considered to be recruitment overfished, and the current level of fishing mortality is unlikely to cause the management unit to become recruitment overfished.

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

Kimberley Prawn Managed Fishery (Western Australia) management unit

Historical commercial catch levels from 1989 to 1998 have been used as the basis for calculating target catch ranges. The range in the Kimberley Prawn Managed Fishery (Western Australia) is 200–450 t¹². Annual commercial catch projections for the fishing season are based on January and February rainfall levels in Kalumburu and Derby, and the annual total landings¹². The commercial catch projection for the 2013 fishing season was 230–350 t. Total commercial catch for 2013 was 144 t, which is well below the target catch range and projected catch range. The management unit operates under an upper-limit effort cap of 1500 vessel-days (based on historical effort levels); only 314 vessel-days were fished in 2013.

On the basis of annual trends in landings and effort since 1980 and, more recently, catch rates, the White Banana Prawn stock is currently being fished at a sustainable level. Key evidence to support this is as follows:

• There has been no marked declining trend in landings across the entire time series.
• Landings have been maintained at relatively low levels of effort compared with historical levels.
• Fishing effort (vessel-days) in the past 5 years has been well below the levels that provided the highest catches in the history of the fishery.
• In recent years, estimated levels of stock biomass have been high, and estimated levels of fishing mortality have been low, as determined from a preliminary biomass dynamic model.
• There has been a marked increase in annual mean catch rates, apparently associated with a change in the economics of fishing since about 2005, which led to a marked reduction in the number of fishers harvesting the available stock.

The management unit is not considered to be recruitment overfished, and the current level of fishing mortality is unlikely to cause the management unit to become recruitment overfished.

In the current economic conditions, fishers are aiming to optimise returns by maximising their efficiency (with the majority fishing only when catch rates are high), and targeting larger and higher-quality prawns (by fishing later in the year). These conditions are conducive to conservative harvesting of the resource. Permanent closures have been introduced in all the major rainfall catchments, as well as temporal closures in two of the catchment areas (known as 'size management fish grounds') to protect smaller prawns and their habitats.

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