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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. Two are classified as depleted – the Tasmanian Scallop Fishery and Victoria’s Ocean 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. Prompted by poor catches during the mid-to late-2000s, fishery independent surveys of historically fished scallop beds in 2009 [Harrington et al. 2010] and 2012 [Semmens and Jones 2012] found low scallop densities and negligible recruitment. Consequently, the TAC for the 2010–11, 2011–12 and 2012–13 fishing seasons was set at zero. 

A TAC of 135 t has been set since this time 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 135 t TAC has been harvested each year during this period, although more recently in 2020–21 there have been much improved catches (by < 5 of the 91 licence holders so total is confidential) taken from a relatively concentrated area proximal to the Bass Strait Central Zone.

A further abundance survey covering the historical fishing grounds in eastern Victoria was undertaken in late December 2017 and early January 2018 [Koopman et al. 2018]. Results from this survey have indicated a continued low level of abundance and recruitment throughout the fishery. Whilst the survey did locate a very small number of beds containing commercially available scallops, they were not at a level or density considered sufficient to provide ongoing recruitment to the fishery.

The scallop bed containing the highest abundance of adult scallops greater than the legal minimum length of 80 mm located during the survey had an estimated biomass of 386 t. The density of this bed was estimated at 0.5 individuals per m². Aligning with the Bass Strait Central Zone Commercial Scallop fishery harvest strategy [AFMA 2014] an area containing a minimum abundance estimate of 1 500 t adult spawning stock of high density (above 0.2 individuals per m²) is recognised as being sufficient to maintain ongoing recruitment in a scallop fishery.

The above evidence indicates that the biomass of this stock is likely to be depleted and that recruitment is likely to be impaired. The above evidence indicates that 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. Environmental factors appear to have prevented such recovery rather than the effects of fishing and a cautious approach has been implemented to support recovery. If the most recent increase in catch is followed by more years of sustained improvement in future catches across a broader range of the fishing grounds, and if future surveys show spawning stock densities to be consistently above an average of above 0.2 individuals per m², then the classification could be revised accordingly.

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 Port Phillip Bay Commercial Scallop dive fishery in 2014, the year after the single exclusive license was issued, and effort increased gradually over the next two years reaching a maximum in 2016 and 2017. 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 exact amount is 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 naturally fluctuates by several orders of magnitude, which has been well documented in Port Phillip Bay [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 (<60 t) within the context of the total abundance, which was estimated to be >11 000 t in 2015 [Gwyther 2015] i.e. ~0.5% of the total biomass. As a result, 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 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].

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 catch is presented for 2017.

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. Native title holders are also exempt from the need to obtain a recreational fishing licence under the provisions of the Commonwealth’s Native Title Act 1993.

Commercial catch of Commercial Scallop - note confidential catch not shown.

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