Ballot's Saucer Scallop

Ylistrum balloti

  • Mervi Kangas (Department of Fisheries, Western Australia)
  • Brad Zeller (Department of Agriculture and Fisheries, Queensland)

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Stock Status Overview

Stock status determination
Jurisdiction Stock Fisheries Stock status Indicators
Queensland East Coast Otter Trawl Fishery ECOTF Overfished Catch, catch rate
East Coast Otter Trawl Fishery (QLD)
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Stock Structure

Ballot’s Saucer Scallops in Australian waters are now classified as Ylistrum balloti (formerly Amusium balloti) following a recent revision of the genus Amusium1. This species is distributed from Esperance in Western Australia, across the tropics, to the southern coast of New South Wales. Ballot’s Saucer Scallops occur along most of the coast of Western Australia, but given the vast length of this coastline and the potential for regional differences in recruitment, four functionally independent management units have been established in this jurisdiction.

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).

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 for Western Australia; and East Coast Otter Trawl Fishery for Queensland.

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Stock Status

East Coast Otter Trawl Fishery

In Queensland, the most recent quantitative assessment8 estimated that the spawning biomass of the East Coast biological stock in 2015 may be as low as five to six per cent of the unfished level (1977). Average monthly catch rates from January 2015–April 2016 (seven baskets per boat day) were the lowest in the 39-year catch record. Annual landings of Ballot’s Saucer Scallop by the East Coast Otter Trawl Fishery in 2014 and 2015 were also near historical lows, at 280–300 t9. The stock is considered to be recruitment overfished.

Although fishing effort has reduced in recent years, standardised catch rates have not improved9. Ballot’s Saucer Scallop stocks occasionally show marked annual variation in recruitment due to changes in environmental conditions10. Productivity of this species can be influenced by factors such as river flow and temperature11 and the low rainfall in the region over the last three years may have also constrained recruitment. A number of management measures were introduced in late 2016 to reduce fishing pressure, including spatial and temporal closures. The current level of fishing pressure is expected to allow the stock to recover from its recruitment overfished state; however, measurable improvements in biomass are yet to be detected.

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

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Ballot’s Saucer Scallop biology12–15

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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Distribution of reported commercial catch of Ballot’s Saucer Scallop

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Fishing methods
Otter Trawl
Management methods
Method Queensland
Limited entry
Rotational closures
Size limit
Spatial closures
Vessel restrictions
Active vessels
127 in ECOTF
East Coast Otter Trawl Fishery (QLD)
Commercial 1.54Kt in ECOTF
Indigenous No catch
Recreational No catch
East Coast Otter Trawl Fishery (QLD)

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Catch Chart

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

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Effects of fishing on the marine environment

  • Habitat effects of Western Australian and Queensland Ballot’s Saucer Scallop fisheries are considered low risk, with trawl vessels generally sweeping a small proportion of the designated trawl area (six per cent in the Great Barrier Reef Marine Park [GBRMP])16. Furthermore, the physical impact of this gear on the sandy habitat that supports scallops is negligible within Western Australian Scallop fisheries17, and intermediate to low in the Queensland East Coast Otter Trawl Fishery (ECOTF) within the GBRMP16, where an estimated 45 per cent of the stock biomass and its associated benthic biota are protected from fishing impacts through permanent closures16,18. Rotational and temporal closures in the ECOTF also play a role in alleviating fishing pressure on the maturing stock and maintaining benthic assemblages.
  • Food chain effects of Western Australian Ballot’s Saucer Scallop fisheries are deemed low risk, with the total biomass taken by these operations being small. The high natural recruitment variability and therefore Ballot’s Saucer Scallop stock abundance2 also means that few predators will have become highly dependent on this species19. Trawl-related risks to ecological processes within GBRMP are low18.
  • Bycatch reduction devices (grids) are mandatory mitigation measures to minimise fishing impacts in the Shark Bay Scallop Managed Fishery and the Abrolhos Islands and Mid-West Trawl Managed Fishery, as are turtle excluder devices in the East Coast Trawl Fishery. These gear modifications are effective in limiting bycatch of larger species such as turtles, sharks, rays and sea snakes20,21. Square mesh codends decrease bycatch of smaller aquatic organisms22 and their use was mandated in 2015 for vessels towing scallop gear in the ECOTF. Compliance monitoring of bycatch reduction devices and vessel activities (through vessel monitoring systems) occurs in each management area.
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Environmental effects on Ballot's Saucer Scallop

  • Strong La Niña events that are typically associated with strong Leeuwin Currents and warm sea surface temperatures often result in below-average Ballot’s Saucer Scallop recruitment and may necessitate the closure of the Shark Bay Scallop Managed Fishery and/or the Abrolhos Islands and Mid-West Trawl Managed Fishery23–26. Between 2012–15, fishery closures in these two fisheries occurred due to a marine heat wave event in 2010–11 (associated with a strong La Niña) that resulted in mortality of breeding stock and subsequent very poor recruitment for a number of years6,7,27,28. Further research continues into understanding recruitment variation (including the collapse) of Ballot’s Saucer Scallop stocks in Western Australia.
  • Environmental variables affecting the Queensland east coast Ballot’s Saucer Scallop stock productivity have also been the subject of recent research. Highly significant correlations were found between November catch rates and several oceanographic variables, including chlorophyll densities and seabed temperature anomalies in the preceding June and August, respectively11. While the precise causal mechanisms of these associations remain uncertain, concerns have arisen that current stock assessment procedures may not adequately account for these and other environmental factors11.
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  1. 1 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.
  2. 2 Fletcher, WJ and Santoro, K (ed.s) unpublished, State of the fisheries and aquatic resources report 2015/16, Western Australian Department of Fisheries, Perth.
  3. 3 Joll, LM and Caputi, N 1995, Environmental influences on recruitment in the Saucer Scallop (Amusium balloti) Fishery of Shark Bay, Western Australia, ICES Journal of Marine Sciences Symposium, 199: 47–53.
  4. 4 Kangas, M, Sporer, E, Brown, S, Shanks, M, Chandrapavan, A and Thomson, A 2011, Stock assessment for the Shark Bay Scallop Fishery, Fisheries research report 226, Western Australian Department of Fisheries, Perth.
  5. 5 Caputi, N, de Lestang, S, Hart, A, Kangas, M, Johnston, D and Penn, J 2014, Catch predictions in stock assessment and management of invertebrate fisheries using pre-recruit abundance—case studies from Western Australia, Reviews in Fisheries Science & Aquaculture, 22: 36–54.
  6. 6 Caputi, N, Kangas, M, Hetzel, Y, Denham, A, Pearce, A and Chandrapavan, A 2016, Management adaptation of invertebrate fisheries to an extreme marine heat wave event at a global warming hotspot, Ecology and Evolution, 6: 3583–3593.
  7. 7 Caputi, N, Feng, M, Pearce, A, Benthuysen, J, Denham, A, Hetzel, Y, Matear, R, Jackson, G, Molony, B, Joll, L and Chandrapavan, A 2014, Management implications of climate change effect on fisheries in Western Australia: part 1, Fisheries research report, Fisheries Research and Development Corporation project 2010/535, Western Australian Department of Fisheries, Perth.
  8. 8 Yang, WH, Wortmann, J, Robins, JB, Courtney AJ, O’Neill, MF and Campbell, MJ 2016, Quantitative assessment of the Queensland Saucer Scallop (Amusium balloti) Fishery, The University of Queensland Centre for Applications in Natural Resource Mathematics and the Queensland Department of Agriculture and Fisheries.
  9. 9 Queensland Department of Agriculture and Fisheries unpublished, Queensland Stock Status Assessment Workshop, 14–15 June 2016, Brisbane, Species Summary Pages, Queensland DAF, Brisbane.
  10. 10 Welch, DJ, Saunders, T, Robins, J, Harry, A, Johnson, J, Maynard, J, Saunders, R, Pecl, G, Sawynok, B and Tobin, A 2014, Implications of climate change on fisheries resources of northern Australia. Part 1: vulnerability assessment and adaptation options, Fisheries Research and Development Corporation project 2010/565, March 2014, James Cook University.
  11. 11 Courtney, AJ, Spillman, CM, Lemos, R, Thomas, J, Leigh GM and Campbell, AB 2015, Physical oceanographic influences on Queensland reef fish and scallops, final report FRDC 2013/020, Department of Agriculture and Fisheries, Queensland, Centre of Australian Weather and Climate Research, Australian Government Bureau of Meteorology, Centre for Applications in Natural Resource Mathematics, School of Mathematics and Physics, University of Queensland.
  12. 12 Orensanz, JM, Parma, AM, Turk, T and Valero, J 2006, Dynamics, assessment and management of exploited natural populations, in SE Shumway and GJ Parson (ed.s), Scallops: biology, ecology and aquaculture, Developments in aquaculture and fisheries science, 35: 765–868.
  13. 13 Heald, D 1978, A successful marking method for the saucer scallop Amusium balloti (Bernardi), Australian Journal of Marine and Freshwater Research, 29: 845–851.
  14. 14 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.
  15. 15 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.
  16. 16 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.
  17. 17 Pears RJ, Morison, AK, Jebreen, EJ, Dunning, M, Pitcher, CR, Courtney, AJ, Houlden, B and Jacobsen, IP 2012, Ecological risk assessment of the East Coast Otter Trawl Fishery in the Great Barrier Reef Marine Park: data report, Great Barrier Reef Marine Park Authority, Townsville
  18. 18 Laurenson, LJB, Unsworth, P, Penn, JW and Lenanton, RCJ 1993, The impact of trawling for saucer scallops and western king prawns on the benthic communities in coastal waters off south western Australia, Fisheries research report No. 100, Department of Fisheries, Western Australia, 93 pp.
  19. 19 Pitcher, CR, Doherty, P, Arnold, P, Hooper, J, Gribble, N, Bartlett, C, Browne, M, Campbell, N, Cannard, T, Cappo, M, Carini, G, Chalmers, S, Cheers, S, Chetwynd, D, Colefax, A, Coles, R, Cook, S, Davie, P, De’ath, G, Devereux, D, Done, B, Donovan, T, Ehrke, B, Ellis, N, Ericson, G, Fellegara, I, Forcey, K, Furey, M, Gledhill, D, Good, N, Gordon, S, Haywood, M, Jacobsen, I, Johnson, J, Jones, M, Kinninmoth, S, Kistle, S, Last, P, Leite, A, Marks, S, McLeod, I, Oczkowicz, S, Rose, C, Seabright, D, Sheils, J, Sherlock, M, Skelton, P, Smith, D, Smith, G, Speare, P, Stowar, M, Strickland, C, Sutcliffe, P, Van der Geest, C, Venables, W, Walsh, C, Wassenberg, T, Welna, A and Yearsley, G 2007, Seabed biodiversity on the continental shelf of the Great Barrier Reef World Heritage Area, Australian Institute of Marine Science, CSIRO, Queensland Museum, Queensland Department of Primary Industries and CRC Reef Research Centre, task final report, CSIRO Marine and Atmospheric Research.
  20. 20 Kangas, M, McCrea, J, Fletcher, W, Sporer, E and Weir, V 2006, Shark Bay Scallop Fishery, ESD report series 2, Western Australian Department of Fisheries, Perth.
  21. 21 Kangas, M and Thomson, A 2004, Implementation and assessment of bycatch reduction devices in the Shark Bay and Exmouth Gulf trawl fisheries, FRDC Project No. 2000/189, Department of Fisheries, Government of Western Australia, North Beach.
  22. 22 Courtney, AJ, Campbell, MJ, Roy, DP, Tonks, ML, Chilcott, KE and Kyne, PM 2008, Round scallops and square-meshes: a comparison of four codend types on the catch rates of target species and bycatch in the Queensland (Australia) Saucer Scallop (Amusium balloti) Trawl Fishery, Marine and Freshwater Research 59: 849–864.
  23. 23 Roy, D and Jebreen, E 2011, Extension of Fisheries Research and Development Corporation funded research results on improved bycatch reduction devices to the Queensland East Coast Otter Trawl Fishery, final report to the Fisheries Research and Development Corporation, project 2008/101, FRDC, Canberra.
  24. 24 Joll, LM and Caputi, N 1995, Geographic variation in the reproductive cycle of the Saucer Scallop, Amusium balloti (Bernardi, 1861) (Mollusca: Pectinidae), along the Western Australian coast, Marine and Freshwater Research, 46: 779–792.
  25. 25 Caputi, N, Penn, JW, Joll, LM and Chubb, CF 1998, Stock–recruitment–environment relationships for invertebrate species of Western Australia, in GS Jamieson and A Campbell (ed.s) Proceedings of the North Pacific Symposium on Invertebrate Stock Assessment and Management, Canadian Special Publication of Fisheries and Aquatic Sciences, 125: 247–255.
  26. 26 Lenanton, RC, Caputi, N, Kangas, M and Craine, M 2009, The ongoing influence of the Leeuwin Current on economically important fish and invertebrates off temperate Western Australia—has it changed? Journal of the Royal Society of Western Australia, 92(2): 111–127.
  27. 27 Pearce, A, Lenanton, R, Jackson, G, Moore, J, Feng, M and Gaughan, D 2011, The “marine heat wave” off Western Australia during the summer of 2010/11, Fisheries Research Report 222, Western Australian Department of Fisheries, Perth.
  28. 28 Caputi, N, Feng, M, Pearce, A, Benthuysen, J, Denham, A, Hetzel, Y, Matear, R, Jackson, G, Molony, B, Joll, L and Chandrapavan, A 2015, Management implications of climate change effect on fisheries in Western Australia, part 2: case studies, FRDC Project No. 2010/535, Fisheries Research Report No. 261, Department of Fisheries, Western Australia.

Archived reports

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