Scallop Fisheries

Tab One


Scallop Habitat & Stock Status Survey
Mini Sled Surveys
Skid trials
The Red Bag Scheme
Brown Crabs: Do you catch Berried Hens?

Fishing intensity trial - Cardigan Bay

We are proposing to run an experiment in the Cardigan Bay SAC, as part of their EFF project. The work aims at quantifying the effect of scallop fishing on the seabed in order to advise the Welsh Government on possible sustainable options for the scallop fishery in an ecosystem approach framework.

The experiment will consist of 14 corridors fished by scallop dredgers across a gradient of fishing intensities. The effect of dredging on the benthic ecosystem will be assessed by sampling the seabed before and directly after scallop dredging with the RV Prince Madog. At least one more scientific survey will be conducted after a few months to monitor recovery. To read more about this follow the link below to the full experimental design document.

Fishing intensity trial – Experimental design.

Our request to undertake this Cardigan Bay scallop fishing intensity study has been submitted to the Welsh Government and NRW and the appropriate assessment is under way.

The tender document to select the vessels which will take part in the experiment is now available here:

Advertisement of tender

INVITATION TO TENDER - Experimental investigation to determine the effects of different levels of scallop fishing intensity on seabed organisms and habitat in the Cardigan Bay Special Area of Conservation (SAC).  



Experimental area and proposed design. The key refers to the number of times the area is to be swept, with 0.25 referring to a quarter of an area being swept, 1 an area being fully swept once and 8 an area being fully swept 8 times.

Scallop Habitat & Stock Status Survey

The first scallop stock status and habitat monitoring surveys were successfully carried out using the RV Prince Madog in 2012. The first survey was conducted in June 2012 to gather baseline information on scallop distribution, abundance and population dynamics. We looked at several areas from Liverpool Bay down to Cardigan Bay, in four commercially fished scallop areas.  The second survey was conducted in October 2012 to gather information on habitats using a drop down camera system.

The 2013 stock status and habitat surveys have now been successfully completed and the report is available below:

Mini Sled Surveys

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Image: Hilmar Hinz - Camera sled

The first trial of deploying our underwater camera system from a fishing vessel has been carried out.

The system is a light steel sled with a small GoPro underwater video camera attached. The sled is simple to use and has been designed to be deployed from fishing vessels to gather habitat data. Thanks to Cardigan Bay scallop fisher, Len Walters the first trials have been completed. A total of 16 sites have already been surveyed by him and the data successfully gathered. It is in the process of being analysed with clips from the videos available in video & images.

Register your details to get involved in carrying out your own habitat surveys from your scallop boat.

Skid trials

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Image: Harriet Salomonsen - Skids on scallop dredges

Scallop dredges can cause damage to the sea floor as the heavy chain bags that hold the catch drag along the seabed. This is also likely to put more strain on gear and increase fuel consumption of fishing vessels. Dr. Hilmar Hinz with SEACAMS has been developing a solution. By attaching sets of steel skids to the underside of the bag it is lifted clear of the ground, reducing damaging effects.

To test out the new system trials were conducted on the beach. Hard boiled eggs were laid out on the sand to replicate marine life and the sled was towed through the eggy obstacle course. Far fewer eggs were crushed under the gear with skids, giving the first results that this could be a success.

The first sea trials have now been carried out thanks to Mark Roberts, Len Walters and their crew.  All the data was collected successfully. This included data from tension loggers which recorded the load from the gear to compare skids versus no skids.      

The Red Bag Scheme

This Scheme was established by Cefas to assess scallop stocks. It is a simple method that we are using to collect information on the status of scallop stocks in Welsh waters. A sample of at least 120 scallops above MLS is kept in a red bag that we will give you. A sample sheet needs filling in with details of the number of undersized scallops that are discarded. The bag is then landed as usual to the processor. The processed flat shells are returned to the bag and collected by Bangor University for age determination.  

The first bag has been returned to us, thanks fisher Mark Roberts and processor AM seafoods.

Register your details to get involved in the Red Bag Scheme or contact:

Brown Crabs: Do you catch Berried Hens?

Image: Berried Brown crab - Jodie Haig

We are interested in collecting samples of berried Brown crab.

Why are we asking scallopers?
Occasionally brown crabs are caught in scalloping dredges, whilst this doesn’t occur often; it presents an exciting opportunity to look at egg development throughout a brooding season. Whilst you can catch berried hens in pots early in the brooding season, you can’t catch them later. This typically occurs early in the season, it is then very rare that you will catch a berried hen in a pot.

What we will do with them:
We will assess fecundity: counting the eggs and looking at the relationship between body size and egg number.

  • We will assess paternity: a “who’s your daddy” study, looking at whether a single brood of eggs has been fertilised by one or more males.
  • We will assess female body condition and maternal provisioning.
  • Tissues from the adult female will also be taken for genetic studies.

What we can NOT do with the data:
This is a biology project. This data can-not be used to determine by-catch of brown crabs. This data will not be collected in a way that can infer any conclusions about by-catch. We are purely interested in the crabs for their biology.
This data can-not be used to inform brooding grounds for brown crab, we are asking for coarse geographical information only. We would like to know that date they were caught, general area and some environmental features that may influence egg development.

How can you help?
Keep and freeze the berried hen sample in a bag with a label: date, area caught, and if possible water depth and temperature. We will arrange to pick up the samples at the earliest convenience.

For details contact:
Dr Jodie Haig
01248 382606


Tab Two

King scallop (Pecten maximus) and Queen scallop (Aequipecten opercularis)

The Scallop fishery employs 75 fishermen with scallops the second most valuable species landed in Wales (£3,462,905 annually). However, there is little data on these scallop populations (e.g. distribution, abundance and population dynamics) to facilitate sustainable management decisions. 


Tab Three

The King Scallop (Pecten maximus)

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The king scallop (Pecten maximus) is a large bivalve that can grow up to 15 cm long. The right valve is highly convex and off-white, yellowish, or light brown in colour. The left valve is flat and light pink to reddish brown in colour. Both valves have 15-17 radiating ribs.

Habitat & Distribution

King scallops are usually found in shallow depressions in the seabed. They prefer clean, firm sand, fine or sandy gravel, but are occasionally found in areas of muddy sand. It is found along the European Atlantic coast from northern Norway and south to the Iberian Peninsula. It has also been reported off West Africa, the Azores, Canary Islands and Madeira. King scallops are filter feeders and eat micro-organisms in the water column.

Life Cycle

Their lifespan can be up to 20 years and they reach sexual maturity between 3 and 5 years. King scallops have both male and female reproductive organs (hermaphrodites) and fertilization takes place externally. Their larvae develop in the water column and are dispersed in the currents. After 30 days they settle to the sea floor and attach to a suitable surface using their byssal threads (strong, silky fibres). Young scallops usually remain attached by byssal threads until they are between 4 and 13 mm in length and then settle on the seabed.

It is believed that adult king scallop do not migrate and only move when disturbed. Therefore, their distribution relies heavily on larval dispersion and consequently the local environmental conditions, such as currents and temperature.

The Queen Scallop (Aequipecten opercularis)

The queen scallop, Aequipecten opercularis, is a medium-sized scallop with two convex shells of variable colour. It is often light-pink to brown, orange or yellow, and may be overgrown with encrusting sponge. This species can grow to 9 cm in diameter.

Habitat & Distribution

Queen scallops are usually found between tidemarks up to depths of 100 m. They are often found in high densities on sand and gravel substrates and lie on top of the seabed instead of becoming settled in the sediment like the king scallop. They have also been found amongst horse mussel beds. This species is found from South of Norway to the Mediterranean and the Canary Isles. Queen scallops are filter feeders and eat micro-organisms in the water column.

Life Cycle

The lifespan of the queen scallop can be from 6-10 years and they reach sexual maturity at 1 year. Queen scallops have both male and female reproductive organs (hermaphrodites) and fertilization takes place externally. Their larvae develop in the water column and are dispersed in the currentss. After 11-30 days the larvae settle from the water column and attach to suitable substrates by their byssal threads (strong, silky fibers). Young scallops remain attached by byssal threads for a period of time and then settle on the seabed.

Queen scallops are known to be quite mobile and swim readily in response to disturbances such as predators, divers, and fishing gear. They swim by rapidly opening and closing their shells which allows the scallop to rise off the seabed at a steep angle before swimming horizontally for a short distance and sinking back to the seabed.


Tab Four

Science updates




Tab Five

Tab Six