Ballot's Saucer Scallop (2020)

Ylistrum balloti

  • Mervi Kangas (Department of Primary Industries and Regional Development. Western Australia)
  • Anthony Roelofs (Department of Agriculture and Fisheries, Queensland)

Date Published: June 2021

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

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Stock Status Overview

Stock status determination
Jurisdiction Stock Stock status Indicators
Queensland East Coast Otter Trawl Fishery Depleted

Stock assessment, estimated biomass, abundance survey, CPUE, catch, effort. test

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Stock Structure

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. Over this extensive species range, Ballot's Saucer Scallops only occur in high abundance in parts of this range.  Scallop recruitment is also highly variable, both seasonally and spatially within these higher abundance areas.  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. No fishery for Ballot’s Saucer Scallop exists in New South Wales waters. The stock classification presented here is based on information from the commercial fishery in central and southern Queensland (latitude 22°–27° south) where higher abundances of scallops 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).

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Stock Status

East Coast Otter Trawl Fishery

In Queensland, the annual catch of Ballot's Saucer Scallop has been declining since 2001 when annual harvests of legal sized scallops were generally ≥ 800 t meat weight. Annual harvests since 2011 have been mostly ≤ 400 tonnes. Harvest  in the 2018 and 2019 fishing years were 163 tonnes and 246 tonnes (meat weight) respectively for the stock in the main fishing grounds between Yepoon and Hervey Bay [Wortmann et al. 2020]. Total harvest from the overall East Coast Otter Trawl Fishery increased to 281 t meat weight in 2019 from a historical low level of 134 t in 2017 [QFISH 2020]. 

The most recent update to the stock assessment [Wortmann et al. 2020] estimated that the spawning biomass of the East Coast biological stock of Ballot's Saucer Scallop in 2019 was 17 per cent of unfished levels in 1956. Commercial-sized scallop density (number of legal sized scallops per hectare in October) from a fishery-independent survey had also decreased from 93 to 56 scallops per hectare from 2018 to 2019, although this was slightly higher than 2017 (38 scallop per hectare). 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. Effort in 2019 was nearly 86 per cent lower than in 1997, however it is only 32 per cent lower than the previous 10 year average [QFISH 2020]. A shift in fleet composition towards more efficient vessels has increased fishing power since 2000 [Campbell et al. 2012] and fishing pressure is high relative to the available biomass. Spatial and temporal closures introduced in late 2016 to reduce fishing pressure and a no take closure period for scallops from May-October have resulted in minor reductions in annual effort. Further changes were implemented in 2019 including a restriction on total effort on the stock (118 635 effort units) and an extension of the scallop no-take period by 1 month to include November. Additional reforms are currently being considered for the 2020–21 fishery season including a further restriction on effort and extended closure periods. Recommendations from the most recent assessment suggest that reducing the total effort cap to 80 000 effort units would allow the stock to rebuild to BMSY in approximately 10 years [Wortmann et al. 2020]. However at the current effort cap, the stock assessment forecasts it would take approximately 20 years to reach BMSY levels (42 per cent of unfished biomass). 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.


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

Species Longevity / Maximum Size Maturity (50 per cent)
Ballot's Saucer Scallop

Maximum of 4 years and 140 mm SH 

At ~1 year of age and 85–90 mm SH 

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

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Fishing methods
Management methods
Method Queensland
Limited entry
Seasonal closures
Size limit
Spatial closures
Vessel restrictions
Commercial 276.89t
Indigenous No catch
Recreational No catch

Queensland – Indigenous (management methods) for more information see https://www.daf.qld.gov.au/business-priorities/fisheries/traditional-fishing

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Catch Chart

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

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  1. Campbell, AB, O’Neill, MF, Leigh GM, Wang Y-G & Jebreen, EJ 2012, Reference points for the Queensland scallop fishery, final report to the Fisheries Research and Development Corporation, project 2009/089, Queensland Department of Employment, Economic Development and Innovation.
  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. Gaughan, DJ and Santoro K (eds) 2020, State of the fisheries and aquatic resources report 2018/19, Department of Primary Industries and Regional Development, Western Australia.
  4. Heald, D 1978, A successful marking method for the saucer scallop Amusium balloti (Bernardi), Australian Journal of Marine and Freshwater Research, 29: 845–851.
  5. 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.
  6. 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..
  7. 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.
  8. QFish, Department of Agriculture and Fisheries, www.qfish.gov.au
  9. 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.
  10. 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.
  11. 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.

Downloadable reports

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