Northern Prawn Fishery (Commonwealth) Brown Tiger Prawn management unit
Brown and Grooved Tiger Prawn stocks are assessed as part of the annual integrated bioeconomic model undertaken for the Northern Prawn Fishery (NPF)1. The base-case estimate of spawner stock size for Brown Tiger Prawn at the end of 2010 was 165 per cent (range 109–165 per cent) of the spawner stock size at maximum sustainable yield (SMSY)1. On this basis, the management unit is not considered to be recruitment overfished.
In 2010, effort (1175 boat days) was below the level that would achieve MSY (EMSY; 4723 boat days)1. This level of effort is unlikely to cause the management unit to become recruitment overfished.
On the basis of the evidence provided above, Brown Tiger Prawn in the Northern Prawn Fishery management unit is classified as a sustainable stock.
Northern Prawn Fishery (Commonwealth) Grooved Tiger Prawn management unit
The base-case estimate of spawner stock size for Grooved Tiger Prawn at the end of 2010 was 142 per cent of SMSY (range 130–143 per cent)1. On this basis, the management unit is not considered to be recruitment overfished.
In 2011, effort (3928 boat days) was below the estimate of EMSY (12 063 boat days)1. This level of effort is unlikely to cause the management unit to become recruitment overfished.
On the basis of the evidence provided above, Grooved Tiger Prawn in the Northern Prawn Fishery management unit is classified as a sustainable stock.
Torres Strait Prawn Fishery (Commonwealth) Brown Tiger Prawn management unit
The most recent assessment uses two separate modelling approaches, producing two separate estimates of MSY and EMSY2. Commercial catch of this stock has been below the mean estimates of MSY (606 tonnes [t] and 676 t) for the past five seasons (2006–10), and effort has been below the estimates of EMSY (8245 and 9197 fishing nights) for the past seven seasons (2004–10)3. This level of catch and effort is unlikely to cause the management unit to become recruitment overfished.
Some components of the assessment were updated in 20074; this indicated that biomass in 2006 was 60–80 per cent of the unfished (1980) level. This was considerably higher than biomass that supports MSY (BMSY), estimated to be around 28–38 per cent of the unfished level2,4. As a result of the 2006 biomass estimate and low levels of catch and effort since that estimate, the management unit is not considered to be recruitment overfished.
On the basis of the evidence provided above, Brown Tiger Prawn in the Torres Strait Prawn Fishery management unit is classified as a sustainable stock.
New South Wales
Uncertainty exists around the stock structure. Tiger Prawns caught in New South Wales are at the edge of their geographic range, and catches are very low5. Hence, no stock assessment has been completed. Insufficient information is available to confidently classify the status of this stock; as a result, the management unit is classified as an undefined stock.
East Coast Otter Trawl Fishery (Queensland) Brown and Grooved Tiger Prawn management unit
Brown and Grooved Tiger Prawns are recorded as 'Tiger Prawns' by Queensland commercial fishers. The most recent assessment of Tiger Prawn fishing effort (2004) estimated the EMSY at 19 618 fishing days. From 2001 to 2007, effort for Tiger Prawns decreased by 75 per cent and, since 2007, effort has been below EMSY6. This level of fishing effort is unlikely to cause the management unit to become recruitment overfished.
The most recent assessment estimated that the biomass in 2003 was 137 per cent of the unfished (1988) level7. In addition, the recent East Coast Otter Trawl Fishery ecological risk assessment found that there is a low risk of Brown Tiger Prawns being overfished at 2010 effort levels6. The management unit is not considered to be recruitment overfished.
On the basis of the evidence provided above, Tiger Prawns in the East Coast Otter Trawl Fishery management unit are classified as a sustainable stock.
Shark Bay Prawn Managed Fishery (Western Australia) Brown Tiger Prawn management unit
Standardised catch per unit effort data are used as an indicator of abundance, and can be used to monitor changes in stock levels from year to year. The average commercial catch and catch rate are compared with a 10-year (1989–98) reference point8.
This Brown Tiger Prawn management unit is also assessed each year using fishery-independent recruitment and spawning stock surveys. These methods are the primary means for assessing stock status. Recruitment surveys provide an index of annual recruitment and are also the basis of an annual Brown Tiger Prawn catch prediction.
A spawning stock–recruitment relationship exists for Brown Tiger Prawns9–11, and the maintenance of adequate spawning stock (using a threshold catch rate) is the key management objective. Brown Tiger Prawns are managed to reference levels (catch rates) and accompanying decision rules.
A mandatory closure of the Brown Tiger Prawn spawning area is enforced, either to a catch rate threshold or on a set date (around June–July), whichever is sooner, to protect the spawning stock. The fishery operates on a real-time management basis: commercial catch rates are monitored nightly to ensure that the Brown Tiger Prawn spawning areas are closed at the appropriate time. As fishing ceases in this area, fishery-independent surveys are then conducted to verify catch rates.
The 2010 spawning stock surveys showed a mean catch rate of 27.1 kg/hour in the Brown Tiger Prawn spawning area. This is within the target threshold range of 25–30 kg/hr12, indicating that the biomass of this management unit is unlikely to be recruitment overfished. With respect to fishing mortality, the assessment also set a target catch range for the 2010 season of 400–700 t. Total catch (423 t) was within the target catch range and below the average catch over the past 15 years (540 t)12. This evidence indicates that 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, Brown Tiger Prawn in the Shark Bay Prawn Managed Fishery management unit is classified as a sustainable stock.
Exmouth Gulf Prawn Managed Fishery (Western Australia) Brown Tiger Prawn management unit
Stock assessments for this management unit are undertaken using similar methods to those used in the Shark Bay Prawn Managed Fishery (Western Australia). Three standardised Brown Tiger Prawn spawning stock surveys were carried out from August to October 2010, with an average catch rate of 36.6 kg/hour, well above the target threshold level of 25 kg/hour. This evidence indicates that the management unit is unlikely to be recruitment overfished. The projected commercial catch from fishery-independent surveys for 2010 was 270–410 t, and the long-term target catch range is 250–550 t. Total commercial catch for 2010 was 388 t, which was within both the projected and target catch range and below the average catch rate of 446 t (averaged over the previous eight years). This evidence indicates that 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, Brown Tiger Prawn in the Exmouth Gulf Prawn Managed Fishery management unit is classified as a sustainable stock.
Onslow Prawn Managed Fishery (Western Australia) Brown Tiger Prawn management unit
Stock assessments for this management unit are undertaken using similar methods as for other Western Australian Brown Tiger Prawn stocks; however, fishery-independent surveys are not undertaken. Historical commercial catch levels from periods when recruitment is known not to have been affected by fishing effort (1989–98) have been used as the basis for calculating commercial target catch ranges (10–120 t)12. Total commercial catch for 2010 was 27 t, within the target range but below the long-term (25 years) average catch of 50 t. The current level of fishing mortality is unlikely to cause the management unit to become recruitment overfished.
Since 2006, a maximum of three boats per year have operated in this fishery, and catch rates varied between 4 and 18 kg/hour between 2006 and 2009. In 2010, the catch rate was 17 kg/hour, which is within the range seen during these low-effort years. The management unit is not considered to be recruitment overfished.
On the basis of the evidence provided above, Brown Tiger Prawn in the Onslow Prawn Managed Fishery management unit is classified as a sustainable stock.