A fishing dredge, also known as a scallop dredge or oyster dredge, is a kind of dredge which is towed along the bottom of the sea by a fishing boat in order to collect a targeted edible bottom-dwelling species. The gear is used to fish for scallops,

oyster Oyster is the common name for a number of different families of salt-water bivalve molluscs that live in marine or brackish habitats. In some species, the valves are highly calcified, and many are somewhat irregular in shape. Many, but no ...

s and other species of clams, crabs, and

sea cucumber Sea cucumbers are echinoderms from the class (biology), class Holothuroidea ( ). They are benthic marine animals found on the sea floor worldwide, and the number of known holothuroid species worldwide is about 1,786, with the greatest number be ...

.Moore G., Jennings S. & Croxall J. (2000
''Commercial Fishing: The Wider Ecological Impacts.''
British Ecological Society. . Page 14 The dredge is then

winch A winch is a mechanical device that is used to pull in (wind up) or let out (wind out) or otherwise adjust the tension (physics), tension of a rope or wire rope (also called "cable" or "wire cable"). In its simplest form, it consists of a Bobb ...

ed up into the boat and emptied. Dredges are also used in connection with the work of the naturalist in

marine biology Marine biology is the scientific study of the biology of marine life, organisms that inhabit the sea. Given that in biology many scientific classification, phyla, family (biology), families and genera have some species that live in the sea and ...

, notably on the Challenger Expedition.

Construction

The dredge is usually constructed from a heavy steel frame in the form of a scoop. The frame is covered with chain mesh which is open on the front, which is towed. The chain mesh functions as a net. Dredges may or may not have teeth along the bottom bar of the frame. In Europe, early dredges had teeth, called tynes, at the bottom. These teeth raked or ploughed the sand and mud, digging up buried clams. This design was improved by using spring-loaded teeth that reduced bottom snagging, and so could be used over rough ground. The

New Bedford New Bedford is a city in Bristol County, Massachusetts, United States. It is located on the Acushnet River in what is known as the South Coast (Massachusetts), South Coast region. At the 2020 United States census, 2020 census, New Bedford had a ...

(USA) dredge does not have teeth. Dredge nets have a coarse mesh in order to let organisms smaller than the target species through. The net catches the larger organisms: in the case of scallop dredging that includes the scallops' predators, such as whelks,

starfish Starfish or sea stars are Star polygon, star-shaped echinoderms belonging to the class (biology), class Asteroidea (). Common usage frequently finds these names being also applied to brittle star, ophiuroids, which are correctly referred to ...

and octopus. In some cases, several dredges are attached to a wheeled rigid axle in groups of three or four. A number of these dredges can be towed from a heavy spreading bar, usually one from each side of the vessel. The length of the bar and number of dredges towed depends on the power of the vessel and the room on the side deck for working the dredges. The number might be three on each side of a small boat up to 20 on each side for a vessel with 1500 hp. The great weight and strength of the gear can disturb the ground it is towed over, overturning rocks and dislodging and crushing organisms in its path. Like a better mouse trap, there is still a challenge for inventors to produce a kinder and more gentle scallop dredge. MIT (2007
''Kinder, gentler scallop dredge invented.''
Retrieved April 13, 2008.

Types of dredgers

File:Mussel dredgers at Carlingford harbour - geograph.org.uk - 174327.jpg,

Mussel Mussel () is the common name used for members of several families of bivalve molluscs, from saltwater and Freshwater bivalve, freshwater habitats. These groups have in common a shell whose outline is elongated and asymmetrical compared with other ...

dredgers File:N.58, Pascin - Nieuwpoort.jpg, Fishing vessel equipped with a

benthic The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from the Ancient Greek word (), meaning "the depths". ...

dredge, leaving the port of Nieuwpoort File:Oyster boats, Carrick Roads - geograph.org.uk - 625045.jpg, Oyster boats of the Truro oyster fleet. This fishery is the last in the world to work by sail alone

Dredging history

File:FMIB 34138 Scallop dredge.jpeg, Scallop dredge, 1889 File:PSM V06 D022 Vessels dredging for oysters.jpg, Vessels dredging for oysters, c. 1875 File:Oyster dredging boat, Ballina NSW (Northern Star (Lismore), 29 Sep 1926, p 13).jpg, Rare photograph of an oyster dredging boat, used in Australian estuaries ( Ballina, NSW, 1926)

Dredging art

File:Twachtman John Oyster Boats North River.jpg, ''Oyster Boats North River,'' by John Henry Twachtman (1853–1902) File:Oyster Sloop, Cos Cob c1902 Childe Hassam.jpg, ''Oyster Sloop, Cos Cob,'' by

Childe Hassam Frederick Childe Hassam (; October 17, 1859 – August 27, 1935) was an American Impressionist painter, noted for his urban and coastal scenes. Along with Mary Cassatt and John Henry Twachtman, Hassam was instrumental in promulgating Impressionis ...

(c.1902) File:Oysterdredging1.jpg, ''Dredging For Oysters'', by Alexander Rummler. WPA mural. File:Hemy Ch N@Einheimische in Falmouth.JPG, Oyster dredging, by Charles Napier Hemy (1841–1917)

Notes

References

* National Research Council (US) (2002
''Effects of Trawling and Dredging on Seafloor Habitat.''
Committee on Ecosystem Effects of Fishing. * Hall-Spencer & Moore PG (2000) Scallop dredging has profound, long-term impacts on maerl beds. ICES Journal of Marine Science. 57, 1407-1415.

External links

photo of scallop dredge

drawing of scallop dredge

{{DEFAULTSORT:Fishing Dredge Fishing industry Nautical terminology