Shark Bay Prawn Managed Fishery (Western Australia) management unit
Western King Prawns and Brown Tiger Prawns (the other key target species) overlap in their spatial distribution within Shark Bay. Western King Prawns are more resilient to fishing than Brown Tiger Prawns because they are less catchable (they are strongly nocturnal and readily bury) and have a protracted spawning period3,4. Therefore the rates of fishing that maintain the spawning biomass of Tiger Prawn are well below the rates that could result in Western King Prawn becoming recruitment overfished5. More than 40 years of catch-and-effort data support the assumption that this stock has never been reduced to levels considered to be recruitment overfished6, and current effort levels are below the level of effort previously applied to the stock. Analysis of catch-and-effort data from the 1970s to the 1990s provided no evidence of a stock–recruitment relationship for Western King Prawns5, suggesting that the spawning stock was never reduced to levels where this would become evident. Consequently, at the levels of effort exerted during that period (which covered most environmental variations that are likely to be encountered, including the Leeuwin Current, La Niña and El Niño), sufficient breeding stock will be available to ensure ongoing recruitment levels.
In addition, there is no significant correlation between spawning stock and recruitment indices derived from fishery-independent surveys of Western King Prawn for the range of spawning stocks observed since 2001. This is believed to reflect the maintenance of the spawning stock above levels that would result in recruitment overfishing (noting that there has never been a collapse of the Western King Prawn stock in Shark Bay). Similarly, there is no evidence of a declining trend in recruitment in fishery-independent survey indices since 2000 (unpublished data from the Department of Fisheries, Western Australia); the annual recruitment indices have been well above the target reference level each year (unpublished data from the Department of Fisheries, Western Australia), indicating that most of the recruitment variability is driven by environmental factors. The introduction of closures related to season, moon phase and area since the early 1990s provides further restrictions on the overall fishing effort, which increases protection for the breeding stocks of Western King Prawn5.
The fishery-independent recruitment surveys undertaken each year assess prawn abundance and size structure, and are used for catch predictions and management decisions, such as spatial–temporal opening of fishing areas.
Historical catch and catch rates from 1989 to 1998, when it was known that recruitment was not affected by fishing effort, were used as the basis for calculating the target catch range (950–1350 tonnes [t]) and mean target catch rate (21 kg per hour; range 16–29 kg per hour) for this stock7. The total commercial catch of 1139 t in 2013 was within the target catch range, and an overall mean catch rate of 31.7 kg/hr was slightly above the target. The above 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.
Exmouth Gulf Prawn Managed Fishery (Western Australia) management unit
For the Exmouth Gulf management unit, maintaining catches within historical ranges is also used to ensure that spawning stock and fishing mortality are kept at appropriate levels8. Production levels from the 1970s to the 1990s provide no evidence of a stock–recruitment relationship for Western King Prawn6. In 1983, the effort on Western King Prawn increased significantly as a result of the requirement to reduce effort on Tiger Prawn. The annual production of Western King Prawn increased on average by around 40 per cent as a result of this increased effort. Although it is assumed that this increased production would have decreased the overall spawning stock, it did not result in any decrease in production other than the normal variations seen in recruitment strength due to environmental factors; this suggests that the stock has never been reduced to levels at which this stock–recruitment relationship would become evident. The current effort levels are below this and therefore considered adequate to maintain breeding stocks. This indicates that, at current effort levels and with variations in environmental conditions, sufficient breeding stock will be available to ensure sufficient recruitment in the future.
Fishery-independent recruitment surveys are undertaken each year to assess the abundance and size structure of the stock, and are used for catch predictions and management decisions, such as spatial–temporal opening of fishing areas. In 2013, the Western King Prawn fishery-independent recruitment index was 60.5 kg/hr, which was well above the target (30 kg/hr).
Catch and catch rate levels from 1989 to 1998 have been used as the basis for calculating a target catch range of 350–500 t7 and a target catch rate of 12 kg/hr (range 8–14 kg/hr). The target catch range is being reviewed, following a decline in the level of effort for the fishery as a result of shifts in markets and targeting of larger prawns. The commercial catch for 2013 of 331 t was just below the target range, although the catch rate (19.3 kg/hr) was well above the target range. The above 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.
North Coast Prawn Managed Fisheries (Western Australia) management unit
The North Coast Prawn Managed Fisheries management unit is made up of four separate fisheries (see Table 1) but reported as one unit because of its minimal take. Western King Prawn forms part of total prawn landings in these multispecies prawn fisheries. Only in the Broome Prawn Managed Fishery is Western King Prawn the key target species. Current commercial catch compared with historical ranges is therefore used to assess the level of fishing mortality for these minor North Coast Prawn Managed Fisheries. Historical catch levels from periods when it is known that recruitment was not affected by fishing effort (1991 to 1998) have been used as the basis for calculating target catch ranges; collectively, the range is 65–295 t7 for the North Coast Prawn Managed Fisheries. Total commercial catch for 2013 was only 2 t, with the majority taken in the Broome Prawn Managed Fishery. The low catches are attributed to very low effort expended on this species in these fisheries because of the current low market value and high costs of fishing. The above 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 it is known that recruitment was not affected by fishing effort (1990 to 1999) 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 14–52 kg per day fished. Total commercial catch for 2013 was only 4 t7, which is below the target catch range and well below the long-term (20 years) average catch of 18 t. The 2013 catch rate of 47 kg per day was within the historical catch range, with the low landings reflecting low effort. The above evidence indicates that the biomass of the stock is unlikely to be recruitment overfished and that the current level of fishing mortality is unlikely to cause the stock to become recruitment overfished.
On the basis of the evidence provided above, the management unit is classified as a sustainable stock.
East Coast Otter Trawl Fishery (Queensland) management unit
A recent ecological risk assessment of the East Coast Otter Trawl Fishery (Queensland) found a low risk of Western King Prawn becoming recruitment overfished as a result of 2009 fishing pressure levels9,10. Nominal fishing effort in the Great Barrier Reef Marine Park has declined by 23 per cent since 200911, suggesting that the risk of the management unit becoming recruitment overfished has not increased. The long-term catch rate is stable11. Catch declined steadily from 2004 to 2006, following the introduction of new closures in the Great Barrier Reef Marine Park, where more than 90 per cent of the Western King Prawn catch is taken11. From 2007 to 2013, catch was variable, but the 2011 catch was the lowest on record11. A key indicator of risk from trawling is the percentage of available biomass closed to trawling. Research estimated that, in 2005, a large proportion of the Western King Prawn biomass (41 per cent) within the Great Barrier Reef Marine Park was unavailable to trawl capture as a result of permanent closures9. These closures remain in place, isolating a large part of the biomass from fishing pressure. The above evidence indicates that the biomass of this management unit is unlikely to be recruitment overfished and 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.
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 yearly in February, April and November, which are used as indices of relative biomass. Mean catch rates for surveys conducted in February, April and November 2010 were 100 kg/hr, 171 kg/hr and 113 kg/hr, respectively12. The February mean catch rate was below the lower threshold of 120 kg/hr; the April mean catch rate was above the lower threshold of 160 kg/hr; and the November mean catch rate was above the lower threshold of 95 kg/hr. Fleet catch cap decision rules resulted in a 450 t pre-Christmas catch cap (fished in November and December)13. The lower thresholds for relative biomass aim to maintain survey catch rates within historical ranges13, rather than providing a reference below which the stock is considered to be recruitment overfished. Therefore, although the February mean catch rate was below the lower threshold, it is assumed to be above sustainable limits12. On balance, the mean catch rates across all three surveys indicate that the biomass is unlikely to be recruitment overfished. Combined with the fishery maintaining a long and stable history of recruitment and commercial catches14 (generally between 1600 and 2400 t), the above 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, 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, which are used as indices of relative biomass. Traditionally, four surveys were conducted each fishing year, in December, March, April and May; however, the number of surveys was reduced to two (April and May) in 2011–12. The fishery was closed in 2012–13 and 2013–14, primarily for economic reasons and, secondarily, reflecting concerns about biological sustainability; therefore, no survey results were available for 2013. The most recent surveys were conducted in 2012, when mean catch rates in April and May were 42 kg/hr and 43 kg/hr, respectively (unpublished data from the South Australian Research and Development Institute). Despite being among the lowest on record, these survey catch rates were similar to those from 2004 to 2006, which were followed by increases in survey catch rate and commercial catch. Because of a combination of poor economic performance, low mean survey catch rates in 2012, and consecutive declines in annual catch to the lowest since the fishery was closed in 1991–92 and 1992–93, the fishery was closed in November 2012. This evidence indicates that, although the biomass was not considered to be recruitment overfished, fishing pressure was moving the stock in the direction of becoming recruitment overfished. Management arrangements are currently being developed to address the economic and biological concerns associated with reopening of the fishery.
On the basis of the evidence provided above, the management unit is classified as a transitional–depleting 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 catch15. The primary measures for stock status on the west coast are the total commercial catch and the annual average catch rate from fishery-independent surveys (conducted yearly in February, June and November), which are used as an indicator of relative biomass. The fishery suffered a prolonged period of stock collapse from 2002 to 200715.
Comparisons of mean commercial catch and survey catch rates during this period provide the basis for assessment of status. The 2013 commercial catch of 148 t was higher than in the previous 5 years (2008 to 2012; mean = 125 t), more than nine times higher than during the period of collapse (2002 to 2007; mean = 16 t) and marginally higher than in the previous period of stable catches (1995 to 2001; mean = 145 t)16. The mean survey catch rate in 2013 of 57 kg/hr was higher than the annual mean of the previous 5 years (2008 to 2012; mean = 52 kg/hr) and almost double the annual mean during the period of collapse (2002 to 2007; mean = 30 kg/hr)15,16, suggesting that the stock has fully recovered. The above evidence indicates that the biomass is unlikely to be recruitment overfished and 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.