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Scallop, King, scallops

Pecten maximus

Method of production - Caught at sea
Capture method - Dredge
Capture area - North East Atlantic (FAO 27)
Stock area - Scotland
Stock detail - Shetland
Certification - Marine Stewardship Council (MSC)
Fish type - Shellfish

Sustainability rating Click for explaination of rating

This fish, caught by the methods and in the area listed above, is a good sustainable fish to eat. Click on the rating icon above to read more and on the alternatives tab below to find similar fish to eat.

Sustainability overview

The dredge scallop fishery in Shetland is certified as an environmentally responsible fishery by the MSC and are a more sustainable choice for eating dredged scallops. 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

Stock area

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Stock information
The population estimates obtained from stock assessments indicate that although there has been a pattern of slight decline in the King scallop population since 2005, the population biomass level is stable (Leslie et al.,2010). Age structure is shown also to be stable in the period 2000-2009.


Shellfish species including scallops are often managed by what are referred to as Regulating Orders. A Regulating Order (RO) bestows upon the beneficiary the right to manage and regulate a fishery, or number of fisheries within a large area. They are granted by Scottish Ministers under the terms of the Sea Fisheries (Shellfish) Act 1967 to encourage the sustainable maintenance and management of the shellfish fishery. The Shetland Shellfish Management Organisation (SSMO) obtained a RO to manage all shellfishfisheries within 6 miles of Shetland's shoreline (approx. 600,000 hectares). Since 2000, the SSMO has introduced a restrictive licensing scheme along with other measures to conserve fish stocks, including increased minimum landing sizes, a lobster restocking programme and a maximum creel (pot) limit for fishing boats. The Order gives the SSMO powers to impose restrictions and regulations, to issue licences, and to impose tolls.The SSMO's main objectives are: to manage and regulate the fisheries for shellfish within Shetland's six mile limit, through the issue of licences and the implementation of regulations and other measures, to ensure the long-term sustainability of these fisheries; to promote the recovery of shellfish stocks through stock enhancement and other management measures; and to promote the environmental sustainability of Shetland's shellfish fisheries. Recently the SSMO obtained assistance from the NAFC Marine Centre to voluntarily develop and implement a spatial management plan that has since afforded biogenic reefs, formed by horse mussels, coralline maerl and eel grass, protection from potential disturbance. These habitats, which are listed in the EU Habitats Directive as requiring conservation, are found in a number of locations around the biologically rich waters of Shetland. This industry-science partnership initiative led to closures that were fundamental in the SSMO obtaining Marine Stewardship Council (MSC) accreditation for its King scallop fishery in 2012. 20 km square of sea area spread over 15 locations around Shetland have since been surveyed (NAFC Marine Centre, 2013) and are now statutorily closed to scallop dredging to help conserve these important features.

Capture information

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. Scallops in the Shetland area are caught using mobile gear-toothed spring-loaded dredges. The dredge consists of a triangular frame leading to a mouth opening 0.83 m wide, a tooth bar with a distance of 65 mm between teeth, length of teeth of approximately 8-10 cm long, and a bag of steel rings (75 mm internal diameter) and netting back (75 mm stretched mesh). The tooth bar rakes through the sediment lifting out scallops and the spring-loaded tooth bar swings back, allowing the dredge to clear obstacles on the seabed. The compression in the springs changes and is set up in order to work in stony grounds and to reduce incidence of stones in the dredge. The dredges are held in series on two beams, which are fished on each side of the vessel. There are a number of potential impacts of dredging activity on the wider marine ecosystem and seabed habitats. These impacts may include: bringing stones to the surface; sediment compaction and chemical changes; damage to reef and similar structures; non-catch mortalities; increased vulnerability to predation. The physical effects diminish with time, depending on the level of natural disturbance, influenced by exposure to prevailing weather conditions and tidal strength, depth and sediment type. The degree of dredge effect will be influenced by a number of factors, including: the dredge type, the width and weight, sediment type, number of dredges operated, methods of fishing and whether any form of deflector or rakes are used. The dredge trawlers used in the Shetland inshore fishery are relatively smaller, with fewer dredges and lighter gear compared with vessels more typically associated with scallop dredging on the mainland of Scotland. A project to assess new dredge types - the ecodredge - with less invasive teeth and rollers instead of belly rings will commence shortly in the Moray Firth. Management measures drafted for Special Areas of Conservation (SACs) and Marine Coastal Zones (MCZs) are likely however to recommend no demersal towed gears in areas where the seabed habitat type is a protected or sensitive feature e.g. reef. In Shetland no vessel which is used to dredge for scallops may use or carry onboard more than two tow-bars with a combined overall length, or a single tow bar with an overall length, of more than 8.80 metres, or more than a total of 10 scallop dredges. Any vessel that was using more than 10 but not more than 14 dredges, between the 1st of January 2001 and the 31st of December 2001, and for which log sheets showing the number of dredges in use were submitted to the Organisation during that period, may apply to the Organisation for a dispensation to this regulation to allow them to continue using their existing tow-bar(s) and dredges. Any dispensation granted will not be transferable to any other vessel or licensee and will lapse when the licence is surrendered. No vessel may use a scallop dredge or dredges, or may dredge, fish for or take scallops or queen scallops, before 0600 hours (local time) or after 2100 hours (local time) on any day. The minimum landing size for scallop in EU waters is 100mm, except in the northern Irish Sea (Isle of Man), Eastern English Channel and Welsh waters where it is 110 mm.

Read more about capture methods

References ;; Anon (2013) Assessment of the appropriateness of areas closed to protect priority main features from scallop dredging around Shetland. NAFC Marine Centre Report (152pp); Leslie B.,Laurenson,CH.,Shelmerdine,R.,& Winter, K.(2010). Shetland Shellfish Stock Assesments

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