Scallop, King, scallops

Pecten maximus

Method of production — Caught at sea
Capture method — Dredge
Capture area — North East Atlantic (FAO 27)
Stock area — Irish Sea
Stock detail — 7a: Isle of Man (Non-territorial waters outside 12nm)
Certification — FIP Stage 2. Click [here for info on FIP](
Picture of Scallop, King, scallops

Sustainability rating four to five info

Sustainability overview

Updated: November 2019.

Isle of Man king scallops are a data limited stock, but abundance is decreasing and fishing pressure is high. 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 includes a large amount of benthic species e.g. crabs and some vulnerable elasmobranch species. There is a lack of management measures to protect sensitive species and habitats outside Manx waters.

Through a Fishery Improvement Project, efforts are being made to improve understanding of the stock, implement harvest control rules and mitigate impacts of dredging.


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

Irish Sea

Stock information

Stock assessments of scallops with Isle of Man territorial waters (0-12nm) are regularly undertaken, but the stock structure of king scallops outside of this area, i.e. in the Irish Sea, is not so well understood. This means there is a potential mismatch between fisheries management within Isle of Man territorial waters and the actual stock area. The assessment of scallops within Isle of Man territorial waters indicates that there is concern for both the biomass and fishing pressure. King scallops have a low-to-moderate vulnerability to fishing (scoring 26 out of 100).

While there are no reference points to indicate whether stock size is at a sustainable level or not, the survey abundance index of Isle of Man king scallops has been declining since 2015, with a significant decline from 2016 to 2017 (46%). The 2018 scallop survey showed evidence of recruitment impairment and a high fishing mortality. Landings per unit effort are continuing to decrease. However, the April 2019 Isle of Man scallop survey showed some increases in abundance, and a number of pre-recruits (scallops that are currently too small to be fished) in some areas. This could indicate a positive trajectory for the stock in future years, but for now the scientific advice still recommends reductions in fishing pressure.


Criterion score: 0.75 info

Management is lacking in the Irish Sea stock and a Pan-Irish Sea Management Board is required to improve it. There are a lack of measures to protect the stock and the habitat. However, the minimum landing size (110 mm) is slightly higher in this region than most EU minimum landing sizes which are normally at 100 mm.

Capture Information

Criterion score: 0.75 info

Scallop dredging is a significantly more damaging method of fishing than 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.


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MMO. 2017. Evidence requirement R046: Impact of external pressures on fisheries in Western Waters (area 7). Available at:

Ondes, Fikret & Kaiser, Michel & Murray, Lee. (2017). Fish and invertebrate by-catch in the crab pot fishery in the Isle of Man, Irish Sea. Journal of the Marine Biological Association of the United Kingdom. 1-13. doi: 10.1017/S0025315417001643. Available from: [accessed Sep 20, 2017].

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UK Scallop Management Conference, 2019. Report of first UK Scallop Management Conference, 4-5 February 2019, London, UK. Available at [Accessed on 07.11.2019].