Scallop Biology

Scallops belong to the family Pectenidae. There are two common species of scallops in British waters; the king or great scallop (Pecten maximus) and the queen scallop (Aequipecten opercularis). The main target species in the D&S IFCA’s District is the king scallop.

The king scallop is a bivalve mollusc. The lower right valve of the scallop is convex and off-white in colour and the upper left valve is flat and reddish-brown. Both ae marked with up to 17 distinct radiating ribs. Sessile invertebrates, such as barnacles and tube worms often grow on the shells. Maximum shell size varies with most being <150mm at the widest part of the shell. They reach reproductive maturity at a minimum size of 60mm and are fully mature at 3-5 years, living up to 20 years.

The king scallop is a filter feeder, pumping water through a filter in the gill chamber to remove particulate organic matter and phytoplankton. The scallop recesses into the sediment and orientates to the water current which is thought to help them feed more efficiently and imposes rhythms of feeding and digestion, phased with the tidal cycle. The scallop has a number of eyes around the shell margin, each of which can process images. It has several predators including large crabs, cephalopods, and a range of starfish.

The distribution range for king scallops is from Norway to the Atlantic coast of Spain, at depths of up to 200m. Settlement is on sediment, usually made up of fine sand or gravel and sometimes mud. The distribution within scallop beds has been described as patchy, with densities rarely found at one scallop per m² and are more typically 0.1-0.01 scallops per m² on good fishing grounds.

Scallop Fisheries

King scallops are an important national marine resource to the United Kingdom. Scallops are the third most valuable species landed by UK vessels, worth £74.1 million in first sale value in 2016, £74.5 million in 2017 and £71.3 million in 2018.

The main method of capture of the king scallop in the UK is by dredge. This is normally a “Newhaven” type dredge, fitted with a spring-loaded tooth bar. The teeth can flex backwards, allowing them to pass over harder ground without snagging and breaking, and improving catch efficiency. There are usually between 2 and 22 dredges attached per side to a towing bar with rubber wheels on each end designed to roll along the seabed. The number of dredges towed by UK vessels depends on local regulations and vessel size. In the D&S IFCA’s District this is restricted to a total of 12 dredges. King scallops are also targeted by mechanical dredge and can be dive caught, though these make up less than 5% of total landings. There is also scallop cultivation on a small scale.  

There are no catch limits for king scallops in UK waters. Fisheries administrations manage king scallop fishing by setting minimum landing sizes, restrictions on number of dredges, gear specifications, area closures and effort controls, and in some cases, such as in the D&S IFCA’s District, there are seasonal closures and time restrictions. The scallop fishery in the D&S IFCA’s District is managed via the Mobile Fishing Permit Byelaw. The permit conditions can be read in detail here:

Scallop Stock Assessment Methodology Study

Stock assessments are an important aspect of successful fisheries management; however, little is currently known about the state of the UK scallop stocks. The traditional method of carrying out king scallop stock assessments is by dredge; however, this has been reported as having low efficiency and can be destructive. With sensitive and closed areas, and possible enhancement areas, there is a need for non-destructive methods of surveying with an increased efficiency. A Masters student undertook a research thesis, in collaboration with D&S IFCA, with the aim to investigate the suitability of different non-destructive methods of surveying within the inshore waters of Devon.

A pyramid frame camera system based on Dr Stokesbury’s SMAST sampling pyramid (Stokesbury et al, 2004), which is used in America, was compared with a towed Flying Array camera system and dive surveys. The results indicated that the most appropriate method for king scallop stock assessments is the towed Flying Array camera system, which was designed by Plymouth University to undertake habitat mapping (Sheehan et al, 2010). This method can cover a large area in a short time period at different depths, and king scallop are more detectable with the oblique angle of the camera.

Since this project was carried out in 2017 and 2018, further scallop stock assessments have been carried out by Cefas (Centre for Environment, Fisheries and Aquaculture Science) in some stock areas. This will continue as an ongoing programme of work. Cefas has further developed the use of cameras as a method for undertaking stock assessments. As part of this work, Cefas worked with D&S IFCA to trial the use of the Flying Array as a stock assessment methodology, onboard the RV Endeavour in the English Channel. This trial was very successful.  Some of the additional work Cefas undertook including tagging scallops to get further information about growth and movement.

Salcombe Estuary Scallop Fishery

There is a small-scale highly regulated king scallop fishery operating in Salcombe Estuary in the D&S IFCA’s District. The fishery is managed under the D&S IFCA Mobile Fishing Permit Byelaw Category 2 (estuary) Permit Conditions. The fishery is restricted to a three-month period and is open from 15th December to 15th March. Under the permit conditions, dredging is spatially restricted to an area within Salcombe Estuary between a line drawn across the estuary from Snapes Point to Scoble Point and a line drawn across the estuary from Woodville Rocks to Ager Point, avoiding the seagrass beds.  Vessels involved in the fishery must not exceed seven metres in length.  Fishers can only use non-toothed dredges, no wider than one metre, and a maximum of two dredges can be used at any one time. Dredges must be hand hauled, and fishing can only take place between 0900hrs and 1600hrs on weekdays, but not during public holidays. All scallops landed must be above the Minimum Conservation Reference Size of 100mm. Landings data must also be sent back to D&S IFCA at the end of the season.

A small-scale scallop stock assessment was undertaken to look at the abundance and sizes of scallops pre- and post-fishing for the 2011-12 and 2012-13 seasons. Several tows with the dredges were carried out over a one-day period, before and after the fishery opened and closed, with each scallop being measured.

The results showed little variation between stock levels and size distributions of scallops across the surveys.

The report can be read here.

In 2020 a full comprehensive review of the data collected since 2007 will be carried out for this fishery.

Main page reviewed on 3rd July 2020 with a minor update made on 23rd December 2020 (scallop statistics/values).


Sheehan E.V., Stevens T.F., Attrill M.J. (2010) A Quantitative, Non-Destructive Methodology for Habitat Characterisation and Benthic Monitoring at Offshore Renewable Energy Developments. PLoS ONE 5(12): e14461.

Stokesbury, K. D. E., Harris, B. P., Marino II, M. C., and Nogueira, J. I. (2004) Estimation of sea scallop abundance using a video survey in off-shore US waters. Journal of Shellfish Research, 23(1):33-40