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Australia has four stocks of Commercial Scallop. Two are sustainable – the Bass Strait Central Zone Scallop Fishery and the Port Phillip Bay Dive Scallop Fishery. One is classified as depleted (Victoria’s Ocean Scallop Fishery), and one is classified as a recovering stock (the Tasmanian Scallop Fishery).

There are several Commercial Scallop bed regions fished commercially in Commonwealth, Victorian and Tasmanian waters. Commercial Scallops in Port Phillip Bay (Victoria) and D’Entrecasteaux Channel (Tasmania) are genetically distinct from conspecifics in most other locations in south-eastern Australia [Woodburn 1990; Semmens et al. 2015; Ovenden et al. 2016]. Beds in north-eastern Bass Strait are also genetically distinct to adjacent Bass Strait beds and may not contribute to wider recruitment based on biophysical models of larval movement [Ovenden et al. 2016].  

Here, assessment of stock status is reported at the management unit level—Bass Strait Central Zone Scallop Fishery (Commonwealth), Ocean Scallop Fishery (Victoria), Port Phillip Bay Dive Scallop Fishery (Victoria) and Tasmania Scallop Fishery.

Ocean Scallop Fishery

The Victorian Scallop (Ocean) Fishery extends out from the coastline to 20 nautical miles. Since the commercial fishery began in the 1970s, catches have varied greatly from year to year. Historical catch and CPUE information would suggest the scallop stocks in coastal eastern Victorian waters (off Lakes Entrance) became heavily depleted during the 2000s, although no formal quantitative stock assessment was undertaken at that time (Koopman et al, 2023). No current depletion estimate is available for Commercial Scallops in the Victorian Ocean Scallop Fishery stock.  

Prompted by poor catches during the mid-to late-2000s, fishery independent surveys of historically fished scallop beds were undertaken during 2009 [Harrington et al. 2010] and 2012 [Semmens and Jones 2012], revealing only very low densities of scallops and negligible recruitment. Consequently, the TACC for the 2010–11, 2011–12 and 2012–13 fishing seasons was set at zero. A TACC of 136.5 t was set for the 2013–14 and 2014–15 seasons. For the 2015–16 to 2020–21 seasons, the TACC remained set at 135 t to allow limited exploratory fishing to take place to locate viable scallop beds and determine if there has been any stock recovery. Only a small portion of the TACC was caught each year during most of this period, although effort was much lower than that during the early 2000s.

In 2017 another broad area survey was undertaken [Koopman et al. 2018], again revealing only very small patches and low densities of scallops, negligible recruitment and no commercially viable scallop beds. These results suggested that there had been virtually no recovery of the stock at that stage. Catches increased during the 2020–21 season (caught by fewer than 5 of the 91 licence holders, so total catch is confidential), taken from a relatively concentrated area near to the Bass Strait Central Zone.

Evidence of some recent recruitment and a potentially viable scallop bed prompted a survey of the “Tarwhine bed”, south-east of Lakes Entrance during 2020 [Koopman et al. 2021]. At that time, this bed had commercially viable densities of large (greater than 80mm) scallops and an estimated biomass of about 8,000 t of legal-sized scallops. Half of this bed (named as the Tarwhine east stratum in subsequent surveys) was closed to commercial fishing and the other half (Tarwhine west stratum) supported a commercial catch of 662 t over 112 days fished during the 2021–22 season.

Results of the 2022 pre-season survey [Koopman et al. 2022] supported that the Tarwhine Bed (east and west strata combined) remained commercially viable, with 8,759 t of legal-sized scallops.  Other than the Tarwhine bed, there was little evidence of recovery of historical beds, with the Clonmel bed in the south showing only a low biomass. During the 2022–23 season, catches reported from the fishery were lower than the previous year with significantly fewer days fished.

The most recent survey (the 2023 pre-season survey) revealed a decrease in biomass on the Tarwhine bed by about 50% to 4,280 t [Koopman et al. 2023]. This reduction in biomass occurred in both the area of the bed that had been closed to commercial fishing (Tarwhine east) and the area that was open to fishing (Tarwhine west). The low level of catch in the fishery during the 2022–23 season indicates that the reduction in biomass was unlikely due to fishing. Results revealed no signs of new recruitment, and there are no known developing beds elsewhere in the fishery. The 2023–24 TACC has been set at 135 t.

The above evidence indicates that the biomass of this stock is likely to be depleted and that recruitment is likely to be impaired. Current fishing mortality is constrained by management to a level that should allow the stock to recover from its recruitment impaired state; however measurable improvements are yet to be detected.  

On the basis of the evidence provided above, the Ocean Scallop Fishery (Victoria) management unit is classified as a depleted stock.

Port Phillip Bay Dive Scallop Fishery

Fishing commenced in the Scallop Dive (Port Phillip Bay) Fishery in 2014, the year after the single exclusive license was issued, and effort increased gradually over the next two years. Effort then decreased slightly in 2018. Catch has followed a similar trend, increasing from 2014 through to highs in 2016 and 2017, but decreased substantially in 2018 (as there is only one licence holder the amounts are confidential). CPUE increased from 2014 to 2016, with nominal CPUE reaching 93 kg/hr, and remained relatively stable in 2017. In 2018, however, nominal CPUE almost halved to 54 kg/hr, as a consequence of the slight decline in effort coupled with a large decline in the total catch landed. Importantly, the standardised results were higher but followed a similar pattern, indicating that bias in the data was consistent over time and that the somewhat symmetrical pattern of increase followed by decrease reflected the actual biomass [Conron et al. 2020].

Commercial Scallop abundance in Port Phillip Bay is naturally patchy and can fluctuate by several orders of magnitude, which has been well documented in Port Phillip Bay where it was reported that the now disbanded dredge fishery landed as much as 2,000 t of meat weight in any one year [Coleman 1998]. As a result, the decrease in CPUE observed in 2018 is not necessarily a sign of overfishing and is unlikely to be so given the very conservative landings (less than 60 t) within the context of the total abundance, which was estimated to be more than 11,000 t in 2015 [Gwyther 2015] i.e., approximately 0.5% of the total biomass. As a result, while information has not been provided to assess the spatial concentration of effort, it is likely that the decrease in CPUE observed in 2018 is largely due to naturally lower scallop abundance, which has resulted in a decrease in CPUE and consequently fishing effort as fishers are receiving lower returns for their effort. As time progresses it will become apparent how the natural variation in scallop abundance affects the dive fishery, but at present, given the very conservative landings, it is highly unlikely that the Port Phillip Bay Commercial Scallop dive fishery will cause recruitment impairment and the stock can be considered as sustainable [Conron et al. 2020]. Less than 15 days of fishing has taken place in any one year since 2021–22 and while the catch is confidential, it is likely to be very small compared to the TAC (60 t).

The above evidence indicates that the biomass of this stock is unlikely to be depleted, recruitment is unlikely to be impaired, and the current level of fishing mortality is unlikely to cause the stock to become recruitment impaired.

On the basis of the evidence provided above, the Port Phillip Bay Dive Scallop Fishery (Victoria) management unit is classified as a sustainable stock.

Commercial Scallop biology [Young et al. 1989; Woodburn 1990; Semmens et al. 2015; Ovenden et al. 2016]

Distribution of reported commercial catch of Commercial Scallop

Commonwealth – Commercial (Catch). Data provided for the Commonwealth align with the Commonwealth Bass Strait Central Zone Scallop Fishery for 2021.

Commonwealth – Recreational. The Australian Government does not manage recreational fishing in Commonwealth waters. Recreational fishing in Commonwealth waters is managed by the state or territory immediately adjacent to those waters, under its management regulations. Recreational fishing sectors in the Indian Ocean are South Australia, Victoria and Western Australia. Recreational sectors in the Pacific Ocean are New South Wales, Queensland and Tasmania.

Commonwealth – Indigenous. The Australian Government does not manage non-commercial Indigenous fishing in Commonwealth waters, with the exception of the Torres Strait. In general, non-commercial Indigenous fishing in Commonwealth waters is managed by the state or territory immediately adjacent to those waters. Indigenous fishing sectors in the Indian Ocean are South Australia, Victoria and Western Australia.

Victoria – Commercial (Catch). (a) To protect commercial confidentiality of data, the catch in the Ocean Scallop Fishery (Victoria) and Port Phillip Bay Dive Scallop Fishery (Victoria) cannot be reported because there are fewer than five licence holders; and (b) In Victoria, the reporting period is fishing season, which runs from 1 April–30 March.

Victoria – Indigenous (Management Methods). A person who identifies as Aboriginal or Torres Strait Islander is exempt from the need to obtain a Victorian recreational fishing licence, provided they comply with all other rules that apply to recreational fishers, including rules on equipment, catch limits, size limits and restricted areas. Traditional (non-commercial) fishing activities that are carried out by members of a traditional owner group entity under an agreement pursuant to Victoria’s Traditional Owner Settlement Act 2010 are also exempt from the need to hold a recreational fishing licence, subject to any conditions outlined in the agreement. 

Commercial catch of Commercial Scallop - note confidential catch not shown

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