Shark Bay Prawn Managed Fishery (Western Australia) management unit
Western King Prawns are the most resilient of the prawn species taken in this fishery. Therefore, the rates of fishing that maintain the spawning biomass of Tiger Prawns are well below the rates that could result in recruitment overfishing of Western King Prawns3. More than 40 years of catch-and-effor
data support the assumption that this management unit has never been reduced to levels considered to be recruitment overfished4 and current effort levels are below those previously exerted. Analysis
of catch-and-effort data in the 1970s to the 1990s provided no evidence of a stock–recruitment relationship for Western King Prawns4, suggesting that the Western King Prawn in this management unit was never reduced to levels where it would become evident. Consequently, at the levels of
effort exerted during that period (which allowed for environmental variations that are likely to occur, including Leeuwin Current variations, and La Niña and El Niño events), sufficient breeding stock will be available to ensure ongoing recruitment levels. Furthermore, the introduction of seasonal, moon and area closures since this period further restricts the overall fishing effort, which increases protection for breeding populations of Western King Prawns. Therefore, historical catch and catch rates from the period (1989–98) when recruitment was known not to be affected by fishing effort were used as the basis for calculating target catch ranges for this management unit (1100–1600 tonnes [t])5 and mean catch rate (21 kg/hour; range 16–29 kg/hour).
The target catch range is currently being reviewed due to declines in the level of effort and shifts to targeting larger prawns. Total commercial catch for 2010 was 1122 t, with a catch rate of 27.5 kg/ hour; these are within historical target ranges. This evidence indicates that the biomass of Western King Prawn in this management unit is unlikely to be recruitment overfished, and 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, the management unit is classified as a sustainable stock.
Exmouth Gulf Prawn Managed Fishery (Western Australia) management unit
Maintaining catches within historical ranges is used to ensure that the spawning stock and fishing mortality are kept at appropriate levels for the Exmouth Gulf management unit6. Production levels from the 1970s to the 1990s provide no evidence of a stock–recruitment relationship for Western King Prawns4. In 1983, the effort on Western King Prawns increased significantly, due to the requirement to reduce effort on Tiger Prawns. As a result, the annual production of Western King Prawns improved by around 40 per cent, on average. Although it would be expected that this increased production would have decreased the overall spawning stock, there was no decline
in production other than the normal variations seen in recruitment strength associated with environmental factors. This suggests that Western King Prawn in this management unit has never been reduced to levels where the stock–recruitment relationship would become evident. This indicates that, at current effort levels and with variations in environmental conditions, sufficient breeding stock will be available to ensure adequate recruitment in the future.
Catch and catch-rate levels from 1989 to 1998 have been used as the basis for calculating a target catch range of 350–500 t5 and a catch rate of 12 kg/hour (range 8–14 kg/hour). The target catch range is currently being reviewed due to declines in the level of effort and shifts to targeting larger prawns. The commercial catch for 2010 of 254 t reflects these changes, although the catch rate
(9.8 kg/hour) was within the target range. This evidence indicates that the biomass of Western King Prawn in this management unit is unlikely to be recruitment overfished, and 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, the management unit is classified as a sustainable stock.
North coast prawn managed fisheries (Western Australia) management unit
The north coast prawn managed fisheries management unit is made up of four separate fisheries but reported as one unit because of minimal catch. Western King Prawns form part of total prawn landings in these multispecies prawn fisheries. Only in the Broome Prawn Managed Fishery (Western Australia) are Western King Prawns the key target species. Current commercial catch compared with historical ranges is therefore used to assess the level of fishing mortality for these fisheries. Historical catch levels from periods when recruitment was known not to be affected by fishing effort (1991–98) have been used as the basis for calculating target catch ranges; these are 65–295 t5 for the north coast prawn fisheries combined. Total commercial catch for 2010 was less than 10 t, well below the target catch range and the long-term (20-year) average combined catch of 140 t. For the Broome Prawn Managed Fishery (Western Australia), the catch rate in 2010 was 24 kg/hour, within the target catch-rate range (19–43 kg/hour). The low catches are attributed to very low effort expended in
these fisheries, as a result of the current low market value of Western King Prawns and high costs of fishing. This evidence indicates that the biomass of the management unit is unlikely to be recruitment overfished, and 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, the management unit is classified as a sustainable stock.
South West Trawl Managed Fishery (Western Australia) management unit
Historical catch and catch-rate ranges are used to assess spawning stock and fishing mortality for the small prawn fisheries in the south-west region of Western Australia. Historical catch levels from periods when recruitment was known not to be affected by fishing effort (1990–99) have been used as the basis for calculating target catch ranges and catch rates. The target catch range is 10–40 t,
and the target catch rate is 14–52 kg/day. Total commercial catch for 2010 was 12 t5, which is within the target catch range and below the long-term (20-year) average catch of 18 t. The 2010 catch
rate was 60 kg/day, which is higher than the historical catch range. This evidence indicates that the biomass of the management unit is unlikely to be recruitment overfished, and 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, the management unit is classified as a sustainable stock.
Spencer Gulf Prawn Fishery (South Australia) management unit
The primary measures for stock status in Spencer Gulf are the average catch rates obtained during fishery-independent surveys conducted in February, April and November, which are used as indices of relative biomass. Since the fishery has maintained a long and stable history of commercial
catches and recruitment7, the performance indicators for relative biomass aim to maintain survey catch rates within historical ranges. Mean catch rates for surveys conducted in February, April and November 2010 were 143 kg/hour, 214 kg/hour and 136 kg/hour, respectively8. These were above the limit reference points of 120 kg/hour, 160 kg/hour and 95 kg/hour, respectively8. This evidence indicates that the biomass is unlikely to be recruitment overfished. Combined with stable commercial catches, this suggests 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, the management unit is classified as a sustainable stock.
Gulf St Vincent Prawn Fishery (South Australia) management unit
The primary measures for stock status in Gulf St Vincent are the average catch rates obtained during fishery-independent surveys conducted in December, March, April and May, which are used as indices of relative biomass. Since surveys were first conducted, in December 2004, the fishery
has maintained stable recruitment9. It is considered that maintaining survey catch rates above the historical minimum levels will ensure adequate egg production. Mean catch rates for surveys conducted in March, April, May and December 2010 were 57 kg/hour, 73 kg/hour, 70 kg/hour and
50 kg/hour, respectively9. These are above the historical lows of 45 kg/hour, 41 kg/hour, 45 kg/ hour and 35 kg/hour, respectively. This evidence indicates that the biomass of the management unit is unlikely to be recruitment overfished. Combined with levels of commercial catch in 2010
that were below the historical average, 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.
West Coast Prawn Fishery (South Australia) management unit
The West Coast Prawn Fishery harvests from an oceanic stock that experiences large fluctuations in recruitment and commercial catch10. The primary measures for stock status on the west coast are
the total commercial catch and the average catch rates obtained during fishery-independent surveys conducted in February, June and November, which are used as indices of relative biomass. The
fishery suffered a prolonged period of stock collapse from 2002 to 200711.
Comparisons of mean commercial catch and survey catch rates during this period provide the basis for assessment of status. During 2010, commercial catch (89 t) was higher than during the period
of collapse (2002–07; mean = 16 t), but lower than during the previous period of stable catches (1995–2001; mean = 145 t)11. Mean survey catch rate (47 kg/hour) was also higher than during the period of collapse (mean = 30 kg/hour)11, suggesting a recovering stock. Commercial catch
and effort were low in 2010, in the historical context. This level of fishing mortality should allow this management unit to recover from its recruitment overfished state.
On the basis of the evidence provided above, the management unit is classified as a transitional–recovering stock.