King scallop

Stock Status Score: 0.5

There is no dedicated assessment of the Shetland scallop fishery beyond 6nm. Instead, the Scottish Marine Directorate periodically assesses a combined Shetland stock covering the 0-6nm and 6-12nm zones. The latest assessment indicates some concern regarding fishing pressure, but not biomass.

Route 2 (data-limited) scoring has been applied due to uncertainty around fishing pressure and stock biomass reference points. King scallops are considered highly resilient to fishing pressure.

The Scottish Marine Directorate periodically assesses king scallop stocks around Scotland, including the Shetland region encompassing both the SSMO-managed inshore fishery (0-6nm) and the adjacent 6-12nm zone. The most recent assessment, using data up to 2023, reported a substantial increase in recruitment and stock size since 2017. Catches have also increased over this period, while fishing pressure has remained relatively stable. This is consistent with trends observed in the UHI Shetland inshore assessment, where LPUE has increased despite relatively stable fishing effort.

The Marine Directorate assessment estimated spawning stock biomass at 19,818 tonnes in 2022, substantially above the precautionary biomass reference point of 5,197 tonnes. Together with the increasing LPUE observed in the inshore fishery, this suggests that biomass is currently at a healthy level and there is no concern regarding stock size.

Fishing mortality was estimated at 0.136 in 2022, slightly above the FMSY proxy of 0.13. The assessment also notes that fishing mortality may be underestimated, which increases uncertainty around the estimate. While the exceedance is small, it suggests some concern regarding fishing pressure and indicates that exploitation may be above the threshold for maximum sustainable yield.

Overall, the Marine Directorate assessment indicates no concern regarding biomass but some concern regarding fishing pressure. However, given the positive recruitment trends, increasing stock size and uncertainty surrounding the assessment estimates, this concern may be resolved by future assessments. Confidence remains limited by the lack of annual assessments, which may delay detection of changes in stock status and the timely implementation of responsive management.

Management of the Target Stock Score: 0.75

Alignment with Scientific Advice Score: 0.75

Monitoring, Control and Surveillance Score: 0

Few appropriate management measures are in place for the Shetland scallop fishery beyond 6nm. There are no catch limits or harvest control rules, and limited stock-specific information is available to inform management decisions. As a result, fishing pressure is not adjusted in response to changes in stock status, increasing the risk of overexploitation. However, the fishery operates within a comprehensive monitoring, control and surveillance framework, with mandatory Remote Electronic Monitoring (REM) providing a high level of oversight and compliance monitoring.

The Shetland Shellfish Management Organisation (SSMO) manages and regulates shellfish fisheries within 0-6 nautical miles of Shetland. Beyond 6 nautical miles, scallop dredging is managed under national Scottish legislation, principally the Regulation of Scallop Fishing (Scotland) Order 2017 and subsequent amendments.

Unlike the inshore SSMO fishery, where annual stock assessments are used to support management decisions, the 6-12nm fishery is assessed only periodically through broader Scottish Marine Directorate assessments of the Shetland stock. As a result, management of the 6-12nm fishery relies largely on technical measures rather than regular, stock-specific monitoring. In addition, there is no total allowable catch (TAC) for king scallops in Scottish waters and no harvest control rule linking fishing opportunities or effort to changes in stock abundance. Consequently, management cannot respond directly to annual changes in stock status, and there is limited evidence that fishing mortality is routinely adjusted to maintain stocks at sustainable levels.

Scallop dredge fisheries in Scottish waters, including the 6-12nm zone around Shetland, are managed through a range of technical and spatial measures:

• A minimum landing size (MLS) of 105 mm applies to king scallops. This MLS protects juvenile scallops, which mature at around 80 mm. However, the Scottish MLS is lower than the 110 mm MLS applied elsewhere in the UK and may not fully protect spawning biomass, as reproductive output increases disproportionately with scallop size.
• The number of dredges that may be deployed is restricted to 16 within 12 nautical miles of the coast and 28 beyond 12 nautical miles. Some vessels with qualifying historic track records are permitted to operate with up to 20 dredges in the 6-12nm zone.
• Additional gear restrictions apply, including limits on towbar length and the number of towbars deployed.
• Several areas are permanently or seasonally closed to scallop dredging to protect vulnerable seabed habitats and species. In addition to reducing habitat impacts, closures that overlap with scallop grounds may support stock stability by providing refuges from fishing and protecting a proportion of the spawning stock.

However, these measures primarily control fishing effort rather than fishing mortality. Although the Shetland stock is periodically assessed by the Scottish Marine Directorate, there is no TAC or harvest control rule linking fishing opportunities or effort to changes in stock status. As a result, management cannot demonstrate that exploitation rates are adjusted in response to changing biomass or fishing mortality. This reduces confidence that fishing pressure will remain sustainable over time and indicates that management requires considerable improvement.

Monitoring, control and surveillance of UK fisheries are delivered through licensing, vessel tracking, statutory reporting, observer coverage, inspections and other monitoring systems. All commercial fishing vessels must hold a valid UK fishing licence to operate in UK waters, although exemptions may apply to some unpowered vessels under 10 metres. Depending on the area, target species and activity, additional permits or authorisations may also be required.

Vessel tracking requirements vary by vessel size, area and administration through Vessel Monitoring Systems (VMS) and, where applicable, inshore VMS (iVMS).

• Vessels 12 m and over must report their position every two hours via VMS.

• Vessels under 12 m report their position continuously where iVMS applies, or may operate full VMS where required by licence conditions or when fishing offshore.

Reporting of fishing activity, catches, landings, discards and port movements is mandatory, with logbooks supporting traceability:

• Vessels 12 m and over submit electronic logbooks under Council Regulation 1224/2009.

• Vessels 10–12 m (and under 10 m Producer Organisation vessels) use paper logbooks, updated daily and submitted within 48 hours of landing.

• Non-PO vessels under 10 m are generally exempt unless required by licence conditions.

UK vessels must also carry fishery observers when directed, providing independent verification of activity and catch. Remote Electronic Monitoring (REM), using cameras, sensors and positional data, is being increasingly deployed to improve data quality and support enforcement. Its rollout is supported by the Fisheries Act 2020 and the Joint Fisheries Statement. In Scotland, REM has been mandatory for scallop dredge vessels since June 2024, strengthening the ability of regulators to verify fishing activity and compliance with gear and spatial restrictions.

Despite these monitoring measures, there have been occasional reports of scallop dredge vessels entering Marine Protected Areas (MPAs) in Scottish waters. Five incursions were reported between July and December 2025. However, none occurred within MPAs around Shetland, with incidents instead recorded in the South Arran MPA, Scapa Flow and Loch Alsh MPA. There is currently no evidence that such infringements are widespread, although commercial buyers are encouraged to verify catch locations where possible.

Together, vessel licensing, statutory catch reporting, vessel monitoring systems, REM, fishery observers and compliance inspections provide a comprehensive framework for monitoring fishing activity and deterring illegal, unreported and unregulated (IUU) fishing. Enforcement measures include financial penalties, prosecution, licence suspension and other sanctions where infringements are identified. The UK has also committed to tackling IUU fishing internationally and maintains mechanisms to identify and restrict vessels involved in such activities. Overall, there is a high degree of confidence that the fishery operates within the UK's monitoring, control and surveillance framework.

The Marine Conservation Society views Remote Electronic Monitoring (REM) with cameras is one of the most cost-effective tools for providing reliable fisheries data and aiding informed management decisions. Fully monitored fisheries enhance collaboration, data accuracy, stock recovery, and reduce impacts on marine wildlife and habitats. However, the full potential of REM may only be achieved when it tracks fishing location and documents catch and bycatch, particularly where vulnerable species and habitats are at risk.

The Fisheries Act (2020) requires the development of Fisheries Management Plans (FMPs) (replacing EU Multi-Annual Plans) in the UK. 43 FMPs have been proposed and are at various stages of development and implementation, these should all be published by the end of 2028. FMPs have the potential to be very important tools for managing UK fisheries, although data limitations may delay them for some stocks. It is also essential the UK governments define and adopt a standardised approach or model across the four nations to a universally defined FMP design, to ensure the consistence, quality and coherence of all the proposal FMPs. 

The Marine Conservation Society is keen to see publicly available Fishery Management Plans for all commercially exploited stocks, especially where stocks are depleted, that include: 

• An overview of the fishery including current stock status, spatial coverage, current fishing methods and impacts 

• Targets for fishing pressure and biomass, and additional management when those targets are not being met, based on the best scientific evidence 

• Timeframes for stock recovery 

• Improved data collection, transparency, and accountability, supported by technologies such as Remote Electronic Monitoring (REM) 

• Consideration of wider environmental impacts of the fishery, including habitat impacts and minimising bycatch 
• Stakeholder engagement 

Capture Method Score: 0.75

Habitat Impacts: 0.75

Bycatch Impacts: 0.5

Vulnerable and ETP Species: 0.5

Ecosystems and Trophic Webs: 0.5

King scallops are predominantly caught using dredges that physically penetrate and disturb the seabed. Although available evidence suggests that impacts on the main bycatch species are minimal, uncertainty remains regarding unquantified mortality of some non-target species which remain on the seabed. There is also potential for interactions with ETP species in the area, and current information is insufficient to conclude with confidence that the fishery is not hindering the recovery of vulnerable populations. While the direct ecosystem effects of scallop removal are considered limited, dredging-related impacts, including bycatch and habitat disturbance, may contribute to cumulative pressures on already altered ecosystems and food webs in the region.

Dredges dominate the king scallop fishery because they are highly efficient, but they also pose significant environmental risks, particularly to sensitive seabed habitats. A standard king scallop dredge (Newhaven dredge) consists of a heavy steel frame and chainmail net, with a toothed bar that flips scallops into a net. Dredges are attached to tow bars dragged along the seabed, with up to two dredges per bar. The number of dredges used is limited by vessel engine power and regional legislation.

As they move, dredges penetrate the substrate by around six centimetres and can reduce benthic species abundance and richness by 8–12% with each pass. In naturally dynamic habitats, such as sandy sediments exposed to strong wave action, benthic communities often recover relatively quickly. However, recovery can be much slower in more stable or structurally complex habitats, including gravel beds, maerl beds and seagrass meadows, where disturbance may persist for many years or even decades. Long-lived and slow-growing species are particularly vulnerable to repeated dredging activity.

Around Shetland, king scallops are primarily associated with sand, mud and gravel substrates. The region also supports a range of sensitive benthic habitats, including maerl beds, kelp forests and horse mussel beds. Within the inshore zone (0-6nm), areas containing vulnerable habitats are protected from dredging through spatial management measures implemented by the SSMO. Beyond 6nm, habitat protection is delivered through the wider Scottish Marine Protected Area (MPA) network.

While there is no evidence of MPA incursions by scallop dredgers around Shetland, five incidents involving dredge vessels were reported elsewhere in Scotland between July and December 2025. Incursions by bottom-towed fishing gears into MPAs designated to protect seabed habitats can damage sensitive features, reducing biodiversity and habitat quality and potentially affecting ecosystem functioning and productivity. Although these incidents do not appear to be widespread, The Marine Conservation Society would encourage buyers to verify the catch locations of their scallops if there is a risk they have been illegally obtained from an MPA, as this would be a default red rating.

Bycatch is another important consideration in the king scallop fishery. While bycatch data are often limited in UK and EU fisheries, the inshore Marine Stewardship Council (MSC)-certified fishery records bycatch and can provide an indication of the species likely to be encountered in waters beyond 6nm. Reported bycatch includes queen scallops, brown crab, whelks, sea urchins and horse mussels. Evidence from stock assessments and fisheries research within the inshore (0-6nm) fishery indicates that queen scallops, brown crabs and whelks typically comprise only a small proportion of the catch, are regularly monitored, and are subject to established management measures. Consequently, there is little evidence that the scallop fishery is having a significant impact on these populations.

However, uncertainty remains regarding the full extent of bycatch mortality, particularly for organisms that are damaged by dredging but not retained in the catch. Such impacts are unlikely to be recorded, and post-capture mortality can be high. As a result, there is a risk of population-level impacts on non-target species, especially those that are not routinely monitored or represented in catch data.

Scallop dredges may incidentally catch endangered, threatened, or protected (ETP) species. In this area, the species most likely to interact with the fishery are demersal elasmobranchs, including the critically endangered common skate complex and vulnerable porbeagle shark. These species are protected and cannot be retained, so any individuals caught must be returned to the sea as quickly as possible. However, information on interactions between the 6-12nm fishery and ETP species is limited, reducing confidence that impacts are negligible and raising the possibility that the fishery could be hindering the recovery of vulnerable populations.

King scallops are low-trophic-level suspension feeders that filter plankton from the water column and form part of the diet of a range of predators, including fish, crustaceans, cephalopods and elasmobranchs. Scallops are not keystone species and current levels of biomass removal by the fishery are unlikely to result in trophic cascades or other substantial food-web effects.

Nevertheless, the wider North Sea ecosystem has undergone significant change in recent decades as a result of climate change and fishing pressure. Rising sea temperatures have altered trophic pathways through reductions in zooplankton abundance, while declines in key forage species, such as sandeels, have affected food-web structure and energy transfer. In Shetland, reductions in sandeel abundance have also been linked to declines in seabird populations that depend on them for food.

Although the removal of scallops is unlikely to drive ecosystem change directly, scallop dredging can result in bycatch mortality, seabed disturbance and the smothering of benthic habitats. These impacts may act cumulatively alongside other ecosystem pressures, meaning that the overall ecosystem impact of the fishery cannot be considered negligible.