Shark Bay Scallop Managed Fishery (Western Australia) management unit
The Shark Bay Scallop Managed Fishery (Western Australia) management unit employs a constant escapement policy to ensure carryover of spawning biomass to subsequent breeding seasons. Generally, catch rate target levels (400–450 kg meat weight per day) are used to limit fishing mortality during the key spawning period (April–June). Ceasing the take of scallops can be triggered by reaching this level, or during May, irrespective of catch rate2.
Catch predictions for 2013 (based on fishery-independent surveys3,4 in November 20122) were extremely low for both Denham Sound (10 tonnes [t]) and northern Shark Bay (20 t). These low yield predictions necessitated that the entire stock be protected to maximise spawning success, and the fishery remained closed (it was also closed for the 2012 season). Despite fishery closures in both 2012 and 2013, the spawning stock remains at record low levels, and poor recruitment is likely in 2014 even if environmental conditions improve. This decline in productivity appears to be due to several years of suppressed recruitment caused by record high water temperatures, associated with very strong La Niña climate events and a strong Leeuwin Current5.
A small area containing juvenile scallops was recently identified in Denham Sound and closed to prawn trawling in 2013 to provide additional protection of the spawning stock. This closure will also enable comparisons of scallop recruitment in areas closed and open to fishing, and demonstrate the relative impacts of natural phenomena and harvesting.
In summary, the stock biomass within this management unit has fallen to a level at which there is a significant risk of recruitment failure. Recent annual surveys indicate low scallop abundance, with catch predictions below the target level for resumption of fishing. This reduction has not been due to overfishing or lack of appropriate fisheries management; the low stock biomass is the result of a series of poor recruitment events associated with sustained unfavourable environmental conditions dating back to late 2010. The fishery has now been closed for several years to provide maximum protection to all remaining stock. Fisheries management has responded appropriately to the environmental change in productivity, with a complete cessation of fishing since November 2012.
On the basis of the evidence provided above, the management unit is classified as an environmentally limited stock.
Abrolhos Islands and Mid-West Trawl Managed Fishery (Western Australia) management unit
The Abrolhos Islands and Mid-West Trawl Managed Fishery (Western Australia) management unit is regulated in a similar manner to the Shark Bay Scallop Managed Fishery. The impact on the spawning biomass is limited by:
- fishing after the peak spawning period
- setting the duration of fishing according to catch predictions (based on pre-season surveys)
- closing the fishery at a minimum catch rate threshold (250 kg meat weight per day)
- not opening sections of the fishery if scallop abundance is considered too low2.
Annual pre-season surveys indicate very low recruitment since 2011. The 2012 abundance estimate was the lowest since 1997, most likely due to high water temperatures associated with the very strong La Niña climate events and strong Leeuwin Current, combined with poor recruitment in previous years. Consequently, the fishery was not opened in 2012.
Predicted catches for 2013 and 2014 were also below the target range (95–1830 tonnes [t] whole weight), and the fishery remains closed at the time of writing. It may take several years of favourable conditions for the stock to recover. Consideration is being given to intervention measures such as translocation, and release of hatchery-produced spat, to aid in rebuilding the spawning stock.
In summary, the stock biomass within this management unit has fallen to a level at which there is a significant risk of recruitment failure. Recent annual surveys indicate low scallop abundance, and catch predictions are below the target level for resumption of fishing. This reduction has not been due to overfishing or lack of appropriate fisheries management; the low stock biomass is the result of a series of poor recruitment events associated with sustained unfavourable environmental conditions dating back to late 2010. The fishery has now been closed for several years to provide maximum protection to all remaining stock. Fisheries management has responded appropriately to the environmental change in productivity, with a complete cessation of fishing since June 2011.
On the basis of the evidence provided above, the management unit is classified as an environmentally limited stock.
South West Trawl Managed Fishery (Western Australia) management unit
The South West Trawl Managed Fishery (Western Australia) management unit is a comparatively small, low-activity fishery in which effort is related to the abundance of scallops in any given year, which can be highly variable. The few vessels that actively operate in the fishery cover only a small proportion of its area, and the limited harvest is unlikely to adversely impact the breeding stock2. This modest level of fishing mortality is unlikely to cause the stock to become recruitment overfished, and the stock is unlikely to be recruitment overfished.
On the basis of the evidence provided above, the management unit is classified as a sustainable stock.
South Coast Trawl Fishery (Western Australia) management unit
The South Coast Trawl Fishery (Western Australia) management unit is a comparatively small, low-activity fishery in which effort is related to the abundance of scallops in any given year, which can be highly variable. The few boats (up to four) that are licensed to operate in the fishery cover only a small proportion of its area, and the limited harvest is unlikely to adversely impact the breeding stock2. This modest level of fishing mortality is unlikely to cause the stock to become recruitment overfished, and the stock is unlikely to be 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
The most recent quantitative assessment of the east coast biological stock applied two groups of models to commercial catch and catch-rate data (spanning the years 1977 to 2009) from the East Coast Otter Trawl Fishery (Queensland). The first group of models predicted a maximum sustainable yield (MSY) of 546 t, and the second group an MSY of 683 t. The catch in 2013 (504 t) fell short of both estimates, as did the average catch over the previous 5 years (538 t). However, annual catches have been highly variable since 1997 (when rotational area closures—scallop replenishment areas—were introduced), exceeding the upper MSY estimate (683 t) in 9 out of the past 17 years6.
Catch rates in the east coast biological stock have generally increased since 1999, with two notable exceptions: 2011 and 20126. Scallop stocks often show marked annual variations in recruitment due to changes in a range of environmental conditions7. The decline in catch rates in 2011–12 was probably environmentally driven, as it coincided with major coastal flooding8. The precise causal mechanism of this anomaly is the subject of current research. The fishery recovered in 2013, with the overall catch rate exceeding the 1993 historical high6. The evidence above suggests that the biomass of this biological stock is unlikely to be recruitment overfished.
Although one group of 2009 stock assessment models suggested that the biomass of this stock may have been below the biomass at MSY (BMSY) in the past, the other group of models did not9. Given that 45 per cent of the stock biomass is protected within the Great Barrier Reef Marine Park10, and the relative efficacy of the rotational management system, the risk of the stock becoming recruitment overfished at 2009 effort levels is considered to be low to intermediate11,12.
In 2013, fishing effort, in terms of trawling time and the number of active vessels, was below the previous 4-year averages by 21 per cent and 9 per cent, respectively, and close to historical lows6. The fishing mortality rate in 2013 is therefore considered to be less than that in 2009. Likely causes of the recent decline in scallop fishing effort include depressed export prices, increased operational costs, and greater profit margins in other fisheries (such as Eastern King Prawn).
Fishing pressure on this biological stock is managed by rotational area closures, temporal closures, a 9 cm shell height minimum size limit, and a ban on daytime trawling. In 2013, roughly 23 per cent of vessels catching Saucer Scallop in the East Coast Otter Trawl Fishery used square-mesh codends to reduce discard mortality of undersized product13. The evidence above indicates that the current level of fishing mortality is unlikely to cause the east coast biological stock to become recruitment overfished.
On the basis of the evidence provided above, the management unit is classified as a sustainable stock.
Figure 1: Distribution of reported commercial catch of Saucer Scallop in Australian waters, 2013 (calendar year)
Figure 2: Commercial catch of Saucer Scallop in Australian waters, 2000 to 2013 (calendar years)