Scallop, King, scallops

Pecten maximus

Method of production — Caught at sea
Capture method — Dredge
Capture area — North East Atlantic (FAO 27)
Stock area — Wales
Stock detail

Cardigan Bay

Picture of Scallop, King, scallops

Sustainability rating four info

Sustainability overview

The status of the stock in Cardigan Bay is unknown. More data and improved survey methods are required to determine the status of the stock. Cardigan Bay is a designated Special Area of Conservation (SAC) - this means that dredging is banned in parts of the bay, deemed ‘closed’ areas.

Scallop fisheries in Wales are more strictly regulated than anywhere else in the UK e.g. temporal closure between 1 May to 31 October; a spatial closure within 1nm of the Welsh coastline and areas prohibited dredging areas, a minimum landing size of 110 mm and regulations on gear size and compulsory vessel monitoring systems. However, the effectiveness of management is unknown as the stock status has not been evaluated.

The Cardigan Bay SAC is an important area for supporting species such as bottlenose dolphins, grey seals and seabed features and are protected under EU legislation. Therefore scallop dredging must be managed sufficiently to support the ecosystem. However, there is much debate and uncertainty on how much scallop dredging negatively impacts the seafloor and the species which depend on it. Of concern is the use of bottom towed fishing gear in Marine Protected Areas (MPAs), especially sites to protect seabed features or where an appropriate impact or risk assessment has not been undertaken to demonstrate that the activity has no significant effect to the site.

Avoid eating scallops below their legal minimum landing size and during their breeding season (April to September).


King scallops are bivalve molluscs found in a range of depths from shallow waters in sea lochs to over 100m. They inhabit sandy-gravel and gravel seabeds. They have 2 shells or valves, the upper being flat, and the under or right valve, cup shaped. They are hermaphrodites (i.e. both male and female) and become fully mature at about 3 years old (80 to 90mm in length). Spawning occurs in the warmer months, from April to September. The species can grow to more than 20cm in length and live for more than 20 years, although average sizes are in the range of 10-16cm.

Stock information

Criterion score: 0.5 info

Stock Area


Stock information

The scallop industry employs 75 fishers in Wales and scallops are the most valuable landed species in Wales. King scallop dominates the scallop catch in Cardigan Bay.

The main issue in the Welsh scallop fishery are the large data gaps, particularly on scallop distribution, abundance and population dynamics. Three years of surveys have been conducted on scallops in three locations throughout Wales (Liverpool Bay, North Western Llyn Peninsula and Cardigan Bay), however, there has been no conclusion on the status of the stock. To determine the stock status, researchers need to define the level where the stock is sustainable. This levels is called a reference point. This is not available for the scallop fishery, however surveys have been conducted allowing some conclusions on the health of the stock.

The surveys showed that scallops populations vary vastly depending on the location. Liverpool Bay (one of the three areas sampled) has been shown to have stable scallop densities and a stable age and size structure over the past 3 years.

In Cardigan Bay studies, recruitment was very variable and is dependent upon weather, climate, habitat suitability, level of fishing intensity. This variable recruitment must be considered in management. The open area is experiencing poor recruitment potentially threatening the long-term economic viability of the fishery. Cardigan Bay stock appears to be a self-recruiting fishery and there is a risk of overfishing. Scallop densities were three to six times higher in the closed areas of Cardigan Bay SAC compared to the open area. Surveys within Cardigan Bay showed that total mortality is about four times higher in the open area compared to the closed area. The exploitation rate of the open area is deemed as very high, where 75% of mortality was due to fishing. Further studies are required to understand if this is sustainable.


Criterion score: 0.5 info

Capture Information

Criterion score: 0.75 info

Scallop dredging is a significantly more damaging method of fishing compared to manual harvesting by divers. Dredging can cause considerable disturbance of the seabed leading to damage to important habitats and reduced biodiversity.

The impact of the dredge depends on how much mortality is caused by the fishing method and the recovery rate of the biota effected. Hydraulic dredges have been found to cause the most depletion among bottom trawling methods, removing 41% of biota and penetrating on average 16.1 cm, into the seabed.

The impact of dredging on the seabed vary with different seabed types and how exposed the seabed is to natural disturbance i.e. wave action. Typically, less exposed seabed areas such as inshore waters and vulnerable habitats are more vulnerable to the effects of dredging. Destroying maerl beds in Wales is expected to substantially reduce biodiversity (50-90%) and seabed stability, local nursery areas and therefore commercial fisheries. Soft sediments are generally much less sensitive to disturbance, depending on their sediment structure, morphology and vulnerable features. More naturally stable seabed environments are generally more sensitive to ecological disturbance. Therefore, seabeds and ecosystems naturally adapted to disturbance by currents and storms e.g. in soft mud / sand sediments are less likely to incur long-term damage.

The open area of the Cardigan Bay SAC hosts sandy habitats interspersed with underlying cobble and boulder habitat covered by highly mobile sand. However, some areas of the SAC contain slow richer communities of hard substrata species (e.g. within 1.5 and 3nm).

Of concern is the use of bottom towed fishing gear in Marine Protected Areas (MPAs), especially sites to protect seabed features or where an appropriate impact or risk assessment has not been undertaken to demonstrate that the activity has no significant effect to the site.

Dredging impacts can however be mitigated by a combination of technical conservation and spatial protection measures such as permanent and rotational closures. It is argued that permanent fishery closures may not necessarily provide detectable increases in target species and their associated communities and that closures incur limited conservation benefits based on the natural disturbance of marine environments.

The main legislation to protect scallops and the habitats and ecosystem in which they live is the Habitats Directive. This Directive is the primary basis for protecting cetaceans both at a European level and within the Member States of the European Union by ensuring biodiversity through the conservation of natural habitats and of wild fauna and flora in the European territory of the Member States”. The Habitats Directive also requires that the UK manages SAC’s effectively through conservation measures suitable for the ecological requirements of the habitats and species present on the sites. The Bottlenose dolphin is a primary feature of the site since 2001. More recent designated features include sandbanks; reefs; sea caves; grey seal (Halichoerus grypus); sea lamprey (Petromyzon marinus); and the river lamprey (Lampetra fluviatilis).

Bycatch species and abundance varies significantly between locations but in Cardigan Bay bycatch is very low mainly including spider crabs and brown crabs. In a recent study survival rates of brown crabs were low (45% of crabs were dead/ severely damaged; 24% had missing limbs) and they require a lot of energy to repair themselves (which is vital for their growth and the moulting process).


Lambert, G.I., Murray L.G., Kaiser M.J., Salomonsen H., Cambie, G. 2013. - Welsh waters scallop survey - Cardigan Bay to Liverpool Bay July-August 2013. Bangor University, Fisheries and Conservation Report No. 30. pp 44.

ICES. 2016. Report of the ICES Scallop Assessment Working Group (WGScallop), 3-7 October 2016,Aberdeen, UK.ICES CM 2016/ACOM: 24. 39 pp.

Welsh Government. 2016. Proposed new management measures for the scallop fishery in Cardigan Bay. Available at: [Accessed on 01.07.2017]

Project Inshore. 2016. Project Inshore MSC Pre-Assessment Database: Scallop, Liverpool bay, Scallop Dredge Details. Available at: . [Accessed on 02.07.17]

Ondes, F., Kaiser, M. and Murray, L. 2016. Quantification of the indirect effects of scallop dredge fisheries on a brown crab fishery. Marine Environmental Research, 119, pp.136-143.

Howarth, L. M. & Stewart, B. D. 2014. The dredge fishery for scallops in the United Kingdom (UK): effects on marine ecosystems and proposals for future management. Report to the Sustainable Inshore Fisheries Trust. Marine Ecosystem Management Report no. 5, University of York, 54 pp.

Lambert, G.I., Murray L.G., Hinz H., Kaiser M.J. 2014. - Status of scallop populations in Welsh waters. Bangor University, Fisheries and Conservation Report No. 41. pp 61

Sea Fisheries Wales. The Scallop Fishing (Wales) (No.2) Order 2010.269.

Sciberras, M., Hinz, H., Bennell, J., Jenkins, S., Hawkins, S. and Kaiser, M. (2013). Benthic community response to a scallop dredging closure within a dynamic seabed habitat. Marine Ecology Progress Series, 480, pp.83-98.

Simmonds, M.P., Green, M., James, V., Eisfeld, S., Lott, R. 2012. Towards evaluating the effectiveness of MPAs for cetacean conservation in Wales. Paper SC/64/E6 presented to the IWC Scientific Committee, June 2012, Panama City, Panama. 22 pp.

Countryside Council for Wales. 2009. Cardigan Bay European Marine Site: Advice provided by the countryside council for wales in fulfilment of Regulation 33 of the conservation (natural habitats) Regulations 1994. Available at:

Pen Ll?n a r Sarnau. 2012. Available at: [Accessed on 30.06.2017]

JNCC. 2017. The Habitats Directive: selection of Special Areas of Conservation in the UK. Available at: [Accessed on 02.07.2017]

Western Telegraph. 2017. Illegal Cardigan Bay scallop dredgers face fine of up to 1m in biggest case ever brought by Welsh Government. [online] Available at: [Accessed 4 Jul. 2017].

Lambert, G.I.2013. Science Update: WP2 Habitat mapping: December 2013. Bangor University, Fisheries and Conservation Science Update. Available at: