All about dredging

Most of Britain’s scallops are harvested by dredging. With Rye Bay Scallop Week in full swing, we take a look at what’s involved, with a special focus on Rye Bay itself.

A scallop dredger towing eight dredges. Note the wheels for bouncing over obstacles. Picture: Seafish

Dredges are rigid structures that are towed along the seabed to target various species of shellfish. In the UK, the main dredge fishery is for king scallops, and to a lesser extent queen scallops, mussels, oyster and razor clams. Each dredge is designed specifically to suit the fishery and target species.

Scallop dredges consist of a triangular frame, about 750mm wide, with a toothed bar at the front to flip the scallops out of the seabed and into a collecting bag behind it. This bag is made of chain links forming a chain mesh on the bottom, and chain or netting on the top.

A scallop dredge: the teeth on the bar at the front flip the scallops out of the sand into the bag behind. Picture: Seafish

Several of these dredges are towed behind a heavy spreading bar, usually one bar from each side of the vessel. The length of bar and number of dredges is dictated by the power of the vessel and its length of side deck to work the dredges over. The number can vary from three or four on a small 10m boat, up to 18 to 20 on a 30m vessel with a 1500 horsepower engine.

The vessels and rigging are very similar to that of beam trawling, with the beam trawls being replaced by the steel bar with multiple dredges towed behind it. In recent years, many beam trawlers have been converted to enable them to tow scallop gear.

Although the majority of scallop vessels are registered to a few ports scattered throughout the UK, they are quite nomadic in their fishing patterns, tending to move to where there is good fishing of scallops at that particular time. They will land at any port close to the fishing grounds, and overland their catch by road to the processing factory.

Opening scallops in Brixham. Picture: Seafish

There are various other types of dredges used in the UK to target other species of shellfish. Dredges to target queen scallop tend to be larger and lighter made than dredges for king scallop, and they do not have the tooth bar to disturb the seabed. In other areas, specific styles of dredges are used to target oysters and mussels.

The size selectivity of a scallop dredge can be set by regulating on the size of the chain rings used for the bellies. Although the teeth on the bar at the front of the dredge are about 120mm long, only about 20mm of this will penetrate the seabed to flick the scallop out of the sand. There is strict legislation on the size and number of dredges used in various areas around the UK.

There is an obvious physical impact of this type of fishing gear being pulled across the seabed, and this means that the method has been criticised by many environmentalists due to the habitat destruction that occurs. The first time a scalloping vessel hauls its dredges over pristine ground it will have an undeniable impact, but fishermen argue that on soft seabeds that have already been dredged the impact is far less and the effects of tides and waves may exceed the impact of fishing activities in some areas.

Fishermen also argue that they tend to avoid areas where there are many of the features or species that Marine Conservation Zones seek to protect because scallops are generally not found there. Scallops prefer to live in less sensitive habitats such as sand and gravel, which are naturally dynamic environments due to the movement of water on the seabed from currents, tides and waves – and this is where scallop fishermen concentrate their efforts. The areas in which scallop dredges can be used are strictly controlled with fragile seabed species and habitats being protected by Special Areas of Conservation (SAC) and Marine Conservation Zones (MCZs).

An under-10m scallop dredger working Rye Bay, with three dredges hanging over the side

Scallops have long been fished in the waters of Rye Bay. Local bye-laws restricting the fishermen to harvesting their scallop catch from 1 November until the 30 April are strictly adhered to by Rye’s fleet who use the small (under 10m) RX-registered boats (pictured above). The beds are checked regularly and allowed to regenerate when necessary. There are also size restrictions on the catch, leaving the smaller scallops in the water for future years.

Checks undertaken by both DEFRA and the local fishermen ensure that stocks are healthy and sustainably maintained. The Rye Bay fishermen find that 70 to 80 feet is the minimum depth that scallops can be found in this area, which makes hand diving impractical. But with the restrictions on size, season and limited boat capacity Rye fishing industry continues to harvest annually without any noticeable reduction in stock.

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