Scallop, King, scallops

Pecten maximus

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

Non-territorial waters (outside 12nm)

Picture of Scallop, King, scallops

Sustainability rating five info

Sustainability overview

There has been increasing concerns for the King Scallop stock in recent years. Landings-per-unit-effort has decreased with concurrent increases in landings and effort. Productivity has also decreased recently. A full stock assessment is due shortly. Using the data-limited matrix, produces a score of 1 for stock status. Management is lacking in the Irish sea stock and a Pan-Irish Sea Management Board is required to improve it. Scallop dredging is one of the most destructive bottom-towed year methods. Bycatch generally include a large amount of benthic species e.g. crabs and some vulnerable elasmobranch species. There are a lack of management measures to protect both sensitive species and sensitive habitats outside Manx waters.


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: 1 info

Stock Area

Isle of Man

Stock information

In recent seasons, the number of vessels and effort has increased in the fishery, concurrent with declining landings-per-unit-effort (LPUE), prompting concerns within the fishing industry. Productivity has also decreased recently. Effort levels are considered to be too high to sustainably maintain the fishery. The Isle of Man’s Department for Environment, Food and Agriculture believe that the fishery is fished at an unsustainable level.There has been increasing concerns for the King Scallop stock in recent years. A full stock assessment is due shortly. There are currently no reference points, however, there is increased concern for stock biomass and fishing mortality.


Criterion score: 0.75 info

The average size of vessels used to operate ring-nets in the district has steadily increased over the last twenty years. They now range from an overall length of 9.99 metres to 14.95 metres.

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 dredging and of other towed gears on the seabed however is largely determined by how exposed the seabed is to natural disturbance i.e. wave action. Consequently, less exposed areas such as those found in inshore waters are more vulnerable to the effects of dredging. These effects can however be mitigated by a combination of technical conservation and spatial protection measures such as permanent and rotational closures.

A typical or standard scallop dredge, known as a Newhaven dredge, comprises a heavy steel frame, with a mesh net top and belly rings of interlocked steel forming the cod end. At the front of the dredge a toothed bar is present which penetrates the seabed, removing the recessed scallop and flipping it into the body of the dredge. Dredges are used in series, connected to a rigid wheeled bar and may have up to 20 dredges per bar.

Non-target species, such as echinoderms (starfish, urchins etc.), crabs and undersized scallops are often taken as bycatch or damaged in situ. When undamaged, undersize scallops can be returned live to the sea.

Also of concern is the effect of the elevated level of exploitation of dredging on queen scallop beds near Manx waters. Queen scallops in Manx waters are well managed, but have a poor stock status. Some Queen scallop beds are protected from queen scallop fishing yet, king scallop dredges can prosecute these fisheries and degrade stocks further. Therefore, greater management between queen and king scallop fleets is required.


Marine Management Organisation. 2017. Minimum Conservation Reference Sizes (MCRS) in UK waters. Available at: Accessed on 15.09.2017

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

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.

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.

Seafish. 2017. Seafish Economic Analysis: UK king scallop dredging sector 2008-2016. Edinburgh, UK. Available at: