Scallop, Queen, scallops

Aequipecten opercularis

Method of production — Caught at sea
Capture method — Dredge
Capture area — North East Atlantic (FAO 27)
Stock area — Irish Sea
Stock detail — 7a: Wales (All areas)
Picture of Scallop, Queen, scallops

Sustainability rating three info

Sustainability overview

Updated: November 2019.

The main issue in the Welsh scallop fishery is 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. King scallop fisheries in Wales are strictly regulated, but management measures don’t apply to queen scallop fisheries. 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 and 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: 0.25 info

Stock Area

Irish Sea

Stock information

The main issues in the Welsh scallop fishery are the large data gaps, particularly on scallop distribution, abundance and population dynamics. Queen scallops have a low vulnerability to fishing (scoring 22 out of 100). Queen scallop abundance is highest in Liverpool Bay, with very low densities in the Llyn Peninsula and Cardigan Bay. There is no indication of concern for fishing pressure or biomass.

Three years of surveys have been conducted on king and queen 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 stocks. To determine the stock status, researchers need to define the level where the stock is sustainable. This is called a reference point. This is not available for the scallop fisheries, however surveys have been conducted allowing some conclusions on the health of the stocks.

The surveys showed 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.

It is difficult to determine the population of scallops because they aggregate and they are difficult to detect through survey 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 help with stock assessments, further studies will aim to determine the catch per unit effort (CPUE) using VMS and logbook data. 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 of fishery-independent and fishery-dependent data is required to determine the stock status. 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.


Criterion score: 0.5 info

There is no harvest strategy for scallops, and while the Welsh king scallop fishery is more strictly regulated than anywhere else in the UK, the queen scallop fishery has very few specific management measures. The effectiveness of management is unknown as the stock status has not been evaluated.

There are seven marine Special Areas of Conservation (SACs) in Welsh waters, covering over 15,000km square (30% of Welsh seas out to 12nm). Six of these SACs ban scallop dredging. However, a significant area of Cardigan Bay SAC is open to scallop dredging for a limited time each year, which is highly controversial. The use of bottom towed fishing gear in MPAs is of concern, especially in sites designated to protect seabed features. Cardigan Bay SAC is designated primarily for bottlenose dolphins, but seabed protection is important due to the potential disturbance and degrading of habitat that dolphin prey depend on (flatfish, demersal fish groundfish etc.). A 2-year Scallop Fishing Intensity Experiment research programme conducted by Bangor University in 2014 and 2015 supported a controlled fishery within the SAC. This in itself is controversial, as the research used a previously dredged area of seabed as a reference point, rather than pristine areas (i.e. which had never been subjected to scallop dredging), to assess long-term impacts of dredging.

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 dredgers have been prosecuted though illegal fishing is known to occur.

Capture Information

Criterion score: 0.5 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. Queen scallop dredges tend to be less impactful than king scallop dredges, as they are modified with skis or skids, which reduce the amount that the dredge penetrates the seabed.

Worryingly, mitigation of impacts of the queen scallop fishery on marine protected areas was de-prioritised in 2016 because of existing legislation to manage scallop fishing. However, that legislation relates specifically to king scallop dredging, meaning there is little in place to specifically manage and mitigate the queen scallop fishery.

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).

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. Queen dredges are generally less damaging to the seabed than dredges used to catch king scallops. The impact of dredging on the seabed varies with different seabed types and how exposed the seabed is to natural disturbance, e.g. 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. 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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