Scallop, Queen, scallops

Aequipecten opercularis

Method of production — Caught at sea
Capture method — Dredge
Capture area — North East Atlantic (FAO 27)
Stock area — Wales
Stock detail — All Areas
Picture of Scallop, Queen, scallops

Sustainability rating three info

Sustainability overview

The main issue in the Welsh scallop fishery are the large data gaps, particularly on scallop distribution, abundance and population dynamics. This prevents effective and suitable management. Liverpool Bay fishery shows stable population trends. Scallop fisheries in Wales are more strictly regulated than anywhere else in the UK e.g. temporal closure; spatial closure within 1nm of the Welsh coastline; a minimum landing size and compulsory Vessel Monitoring Systems (VMS). Generally, queen scallop fishing causes less disturbance than king scallop dredging as they generally use otter trawls or skid dredges. Additionally, to mitigate the impact on the seabed, there are limits on permits, dredges, and prohibitions from fishing in certain areas.


Queenies are a fast growing species with a maximum lifespan that rarely exceeds five years. Queen scallops are simultaneous hermaphrodites (i.e. an individual has both male and female reproductive organs) and become sexually mature at 1-2 years at approximately 40mm shell height. Although smaller than King scallops they can grow up to about 90mm. Queen scallops are broadcast spawners (i.e. they release eggs and sperms into the sea) and can spawn in both spring and summer. When one individual spawns, pheromones contained in the eggs and sperms released into the water column, signal to neighbouring scallops to release their own eggs and sperms ensuring synchronous spawning. Thus, in order for spawning (and subsequently recruitment) to successfully occur Queen scallops need to be present at relatively high densities. In low density populations there is a risk that the spawning stock may not be present at high enough densities to successfully reproduce (i.e. there are too few individuals around to come into contact for fertilisation), a phenomenon known as the Allee effect. They are usually found at depths down to about 100m on sand or gravel. It feeds on plankton and other organic material by filter feeding. They reach market size of 55mm (minimum landing size in Isle of Man; 40mm for rest of the Irish Sea) within 2-3 years depending on the available micro-algae feed from the water column.

Stock information

Criterion score: 0.5 info

Stock Area


Stock information

Queen scallop abundance is highest in Liverpool Bay with very low densities in the Llyn Peninsula and Cardigan Bay.

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 of scallops, researchers need longer term data-series and improvements in sampling methods. Current sampling methods have limitations: dredges do not effectively measure very small scallops, some areas cannot be dredged (leaving large areas un-surveyed) and once an area has been dredged it reduces the catch potential in that area. The camera tows and photo methods can be impractical because it is difficult to see and estimate scallop populations in soft and disturbed sediments.

To determine the stock status for scallops, researchers need to define the level where the stock is sustainable and/or where the stock population is at risk. These levels are called reference points. In the absence of reference points, it is difficult to determine how healthy a population is, however conclusions can still be made to evaluate the health of the stock. For example, the surveys shown 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. The total mortality is highest in the open area of the Special Area of Conservation (SAC), which is much larger than the natural mortality. The closed area in Cardigan Bay SAC has higher densities of scallops than open, fished areas. Cardigan Bay stock appears to be a self-recruiting fishery and there is a risk of overfishing.

There are no reference points and it is difficult to determine the population of scallops because they aggregate and they are difficult to detect through survey methods.


Criterion score: 0.5 info

There is no harvest strategy for scallops though scallop fisheries in Wales are more strictly regulated than anywhere else in the UK. Cardigan Bay is a designated Special Area of Conservation (SAC) - this means that dredging is banned in parts of the bay, deemed ‘closed’ areas. Management includes 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, compulsory vessel monitoring systems and permits. However, the effectiveness of management is unknown as the stock status has not been evaluated. The Welsh government are currently considering further management measures.

The MPA protection existing in Wales has been in place since 2010 and Wales has been reasonably effective in protecting its key MPAs and inshore waters from scallop dredging. These include seven marine SACs, covering over 15,000km square (30% of Welsh seas out to 12nm). Six of these SACs ban scallop dredging. In addition, scallop dredging is banned from within 1nm of the entire Welsh coast. However, a significant area of Cardigan Bay is open to scallop dredging which is that is highly controversial. This controversy is due to the lack of evidence provided to prove that there hasn’t been an impact on associated fish, mobile mammals (particularly dolphins) and other parts of the ecosystem that are typical features of the site. Dolphins may be particularly impacted by the re-introduction of scallop dredging due to the disturbance of the seabed and degrading the habitat that dolphin prey depend on (flatfish; demersal fish groundfish etc).

Within Cardigan Bay SAC, there is only one area open for scallop dredging (for a limited time each year). However, these measures were based on limited evidence available at the time (2010). A recent 2 year Scallop Fishing Intensity Experiment research programme conducted by Bangor University supports a controlled fishery in the area of the SAC which is currently closed to fishing. Cardigan Bay in Wales and adjacent waters are important for marine wildlife and include various marine special areas of conservation (SACs) that are intended to protect a number of species and habitats.

Further studies will aim to determine the catch per unit effort (CPUE) using VMS and logbook data (from the MMO). However, using CPUE to determine the stock status is problematic because the time-series is short as no fishery dependent data (i.e. size and age data) have ever been collected in Wales. Therefore, a mixture between fishery-independent and fishery-dependent data is required to determine the stock status.

In regards to how effective the research and monitoring is in the fishery, there are no reference points and time-series are short which significantly limits the understanding of the stock. To determine the stock status of scallops, researchers need longer term data-series and improvements in sampling methods.

Scallop surveys are conducted using three methods: still images, video and dredge estimates due to the limitations of survey methods: dredges do not effectively measure very small scallops, some areas cannot be dredged, leaving large areas un-surveyed and once an area has been dredged, the population is instantly reduced. The camera tows and photo methods can be impractical because it is difficult to see and estimate scallop populations in soft and disturbed sediments. These methods show strong similarities however, some variance remains due to: habitat types affect the ability to see scallops when buried in soft sediments; the patchiness of scallop beds (where dredge and video tows were not able to be conducted in the same area); dredges are size selective (not detecting scallops <4 years very well) and variance between the types of dredges. These methods are used to detect changes in size and age structure, growth rates, weight and reproductive status and more recently mortality rates.

Data are collected on landings, effort, fleet composition and potentially for catch rate indicators. Catches from non-Welsh fleets are significant but recorded.

Welsh vessels that dredge in Welsh waters are required to use VMS. This allows for cheaper monitoring and surveillance. Very few scallop dredges have been prosecuted though illegal fishing is known to occur.

Recently, further Welsh Fishery Independent surveys have started including three further years of annual surveys. These data will be used to create a stock assessment model. The model will use age-structure, spatial differences, surplus production and delay-difference. To manage the fishery effectively, the advice will have to determine how much dredging can occur and provide thresholds to suit both the seabed and the benthic communities. Additionally, VMS data and habitat data will be used to determine scallop distribution. Industry-led surveys in the future might be a better platform to collect data. Attempts to improve camera design for survey methods are underway to ensure this is the pure method to determine abundance.

MCS recommends that protected areas should be strategically located and designed to offer multiple benefits wherever possible and that they are well monitored and enforced. Fishing mortality needs to be sufficient to account for the species. Additionally, the stock dynamics must be catered for in management.

Capture Information

Criterion score: 0.5 info

Scallop dredging is a significantly more damaging method of fishing compared to manual harvesting by divers. This can lead to damage to important habitats and reduced biodiversity.

In bycatch studies, bycatch levels were observed to be higher in queen dredges than king dredges, because of the size of their belly rings. Bycatch in queen dredges in Liverpool Bay was around three times higher than in Llyn Peninsula and four times that in Cardigan Bay. Liverpool Bay bycatch was comprised of higher diversity and rich fauna with many fragile species (e.g. purple sea urchin Spatangus purpureus), suggesting that the area has not been highly impacted by fishing in recent years.

Brown crabs are particularly sensitive to scallop dredges as they are found in the same habitat as scallops. 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).

Queen dredgers are generally less damaging to the seabed than dredges used to catch king scallops. 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 substantially reduces biodiversity, seabed stability, local nursery areas and therefore commercial fisheries. Mixed sand and mud habitats generally have diverse benthic communities with a high biomass. Conversely, 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. Soft sediments are generally much less sensitive to disturbance, depending on their sediment structure, morphology and presence of vulnerable features.

In a Welsh and Manx study, dredging Modiolus reefs reduced biodiversity of the associated community by 59-90%. Therefore, protecting biogenic reefs is extremely important to protect substrates, ecosystem function and to support commercial fisheries.

Welsh SAC habitats contain vulnerable features such as colonies of dead man’s fingers Alcyonium digitatum and rich communities of hard substrata species are found between 1.5 and 3nm.

These effects 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.

Measures to protect the seabed include permit limits, number of dredge limits, and prohibitions from fishing in certain areas e.g. fishing within 1nm from Welsh coasts. The gear mesh or ring size should be as selective as possible to allow juveniles to escape. 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.


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