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Western Australia is home to four stocks of Ballot’s Saucer Scallop, all of which are sustainable. The one stock in Queensland is classified as depleted.

Ballot’s Saucer Scallop in Australian waters are now classified as Ylistrum balloti (formerly Amusium balloti) following a recent revision of the genus Amusium [Mynhardt et al. 2014]. This species is distributed from Israelite Bay in Western Australia, across the tropics, to the southern coast of New South Wales. However, Ballot's Saucer Scallops only occur in high abundance in parts of this extensive range. Within these areas of higher abundance, scallop recruitment is also highly variable, both seasonally and spatially. In Western Australia, Ballot’s Saucer Scallop occur along most of the coast but given the vast length of this coastline and the potential for regional differences in recruitment, four separate management units have been established in this jurisdiction for those areas where Ballot's Saucer Scallop occur in commercial quantities.

The eastern Australian stock stretches from Innisfail in Queensland to Jervis Bay in New South Wales. In general, saucer scallops in the main fishing ground (latitude 22°–27° south) form a single stock, although there is some evidence to suggest that saucer scallop on the fishing ground east of K’gari (formerly Fraser Island), are less connected to those on the fishing grounds between Yeppoon and Hervey Bay [Dredge 2006; Wortmann et al. 2022]. No fishery for Ballot’s Saucer Scallop exists in New South Wales waters. The stock status classification presented here is based on information from the commercial fishery in southern Queensland where the majority of scallops on the east coast occur.

Here, assessment of stock status is presented at the management unit level—Shark Bay Scallop Managed Fishery, Abrolhos Islands and Mid-West Trawl Managed Fishery, South West Trawl Managed Fishery and South Coast Trawl Fishery (Western Australia); and East Coast Otter Trawl Fishery (Queensland).

East Coast Otter Trawl Fishery

In Queensland, the saucer scallop fishing year is defined as November of the preceding year to October of the named year and catch and effort is given in fishing year unless otherwise labelled. The annual catch of Ballot's Saucer Scallop declined from higher levels in 2001 when annual harvests of legal sized scallops were generally greater than or equal to 800 tonnes (t) meat weight to an average of 211 t over the last 5 years (2017–2022), prior to the closure in late 2021 [French 2023]. After the closure of the main fishing grounds, catch for this stock decreased to around 13 t in 2022. 

The most recent update to the stock assessment [French 2023] estimated that the spawning stock biomass of the southern inshore and offshore trawl regions in 2022 was 15% of 1956 unfished levels. The assessment indicated that biomass declined to 10% of unfished biomass between 1956 and 2016. The main fishing grounds will remain closed until spawning stock biomass reaches 30% of unfished levels [QDAF 2021]. 

Commercial-sized scallop density (number of legal-sized scallops per hectare in October) from a fishery-independent survey decreased from 45 to 10 scallops per hectare from 2021 to 2022 [French 2023]. Standardised catch rates were on average 5 baskets per boat per day (southern inshore and offshore) for November 2021–January 2022 and up to 17 baskets per day in February 2022. 

It is notable that scallop spawning success and survival is associated with environmental conditions, in particular sea surface temperatures (SST). Above-average winter SST are negatively associated with scallop catch rates during the next season [O’Neil et al. 2020]. However, high SST, like those observed in Western Australia in 2010–11 have not been observed in Queensland [Wortmann et al. 2022]. Environmental conditions may impact the recovery of this stock. Of importance, Wortmann et al. [2022] notes that if natural mortality increases with SST, then it may affect target reference points used for managing fishing effort. The above evidence indicates that the biomass of this stock is likely to be depleted and that recruitment is likely to be impaired.

A long-term decline in the annual number of scallop harvesting days has been evident since 1997, when the stock was first considered to be overfished and scallop replenishment areas (SRAs) were first introduced. There are six SRAs located off Yeppoon, Bustard Head and Hervey Bay. The SRAs operated on a rotational system from the early 2000s and were permanently closed in January 2017 due to depletion. Following this, the main fishing grounds were permanently closed in late 2021. The closure was in response to the low biomass levels found in consecutive stock assessments, the 2022 stock assessment proposed a catch of zero t and estimated that it would take 10 years to rebuild to 40% of unfished biomass [Wortmann et al. 2022]. The 2022 harvest of around 13 t is below the 234 t that represents equilibrium harvest at 15% biomass [French 2023]. The above evidence indicates that adequate management measures have been put in place to allow the stock to recover from its recruitment impaired state but have not yet resulted in measurable improvement.

On the basis of the evidence provided above, the East Coast Otter Trawl Fishery (Queensland) management unit is classified as a depleted stock.

Ballot’s Saucer Scallop biology [Heald 1978; Dredge 1981; Williams and Dredge 1981; Joll 1989; Orensanz et al. 2006]

Commercial catch of Ballot’s Saucer Scallop - note confidential catch not shown

Queensland – Commercial (Catch). Queensland commercial and data have been sourced from the commercial fisheries logbook program. Further information available through the Queensland Fisheries Summary Report https://www.daf.qld.gov.au/business-priorities/fisheries/monitoring-research/data/queensland-fisheries-summary-report 

Queensland – Commercial (Management Methods). Harvest strategies are available at: https://www.daf.qld.gov.au/business-priorities/fisheries/sustainable/harvest-strategy  

Queensland – Commercial (Catch). Catch table data have been provided in financial year format.

Commercial catch of Ballot’s Saucer Scallop - note confidential catch not shown

1. Chandrapavan A, Kangas, M, and Caputi N, 2020, Understanding recruitment variation (including the collapse) of Ballot’s saucer scallop stocks in Western Australia and assessing the feasibility of assisted recovery measures for improved management in a changing environment, Fisheries Research Report No. 308, Department of Primary Industries and Regional Development, Western Australia.
2. Dredge, MCL 1981, Reproductive biology of the saucer scallop Amusium japonicum balloti (Bernardi) in central Queensland waters, Australian Journal of Marine and Freshwater Research 32: 775–787.
3. Dredge, MCL 2006, Saucer Scallop Resource of Shark Bay Harvest Strategy 2020-2025, Fisheries Management Paper 301:39 pp, Department of Primary Industries and Regional Development, Western Australia.
4. French, SM 2023, Stock Assessment of Ballot's saucer scallop (Ylistrum balloti) in Queensland, Australia, with data to October 2022, Technical Report. State of Queensland, Brisbane.
5. Heald, D 1978, A successful marking method for the saucer scallop Amusium balloti (Bernardi), Australian Journal of Marine and Freshwater Research, 29: 845–851.
6. Joll, LM 1989, History, biology and management of Western Australian stocks of the saucer scallop Amusium balloti, in MLC Dredge, WF Zacharin and LM Joll (ed.s), Proceedings of the Australasian scallop workshop, Hobart, Tasmania, pp 30–40.
7. Kangas, MI, Wilkin, S, Leaversuch, R, and Grounds, G 2023, Saucer Scallop Resource Status Report. In: State of the fisheries and aquatic resources report 2021/22: The State of the Fisheries eds. Newman, SJ, Wise, BS, Santoro KG and Gaughan DJ, Department of Primary Industries and Regional Development, Western Australia.
8. Mynhardt, G, Alejandrino, A, Puslednik, L, Corrales, J and Serb, JM 2014, Shell shape convergence masks biological diversity in gliding scallops: description of Ylistrum n. gen. (Pectinidae) from the Indo-Pacific Ocean, Journal of Molluscan Studies, 80: 400–411.
9. Orensanz, JM, Parma, AM, Turk, T and Valero, J 2006, Dynamics, assessment and management of exploited natural populations, in SE Shumway and GJ Parson (eds), Scallops: biology, ecology and aquaculture, Developments in aquaculture and fisheries science, 35: 765–868.
10. Queensland Department of Agriculture and Fisheries 2021, Fisheries (Saucer Scallop) Amendment Declaration 2021, Queensland.
11. Saucer Scallop Resource of Shark Bay Harvest Strategy 2020–2025, Fisheries Management Paper 301:39 pp, Department of Primary Industries and Regional Development, Western Australia.
12. Williams, ML and Dredge, MCL 1981, Growth of the saucer scallop, Amusium japonicum balloti Habe, in central eastern Queensland, Australian Journal of Marine and Freshwater Research, 32: 657–666.
13. Wortmann, J 2022, Stock Assessment of Ballot's saucer scallop (Ylistrum balloti) in Queensland, Australia. Technical Report, State of Queensland, Brisbane.
14. Wortmann, J, O’Neill, MF, Courtney AJ and MJ Yang, WH 2020, Stock assessment of Ballot’s saucer scallop (Ylistrum balloti) in Queensland, Technical Report. State of Queensland, Brisbane.