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Single helix earth anchors Guyed mast anchor. An earth anchor is a device designed to support structures, most commonly used in geotechnical and construction applications. Also known as a ground anchor, percussion driven earth anchor or mechanical anchor, it may be impact driven into the ground or run in spirally, depending on its design and intended force-resistance characteristics.
Nylon fishing net with float line attached to small plastic floats. A fishing net is a net used for fishing. Some fishing nets are also called fish traps, for example fyke nets. Fishing nets are usually meshes formed by knotting a relatively thin thread. Early nets were woven from grasses, flaxes and other fibrous plant material. Later cotton ...
The technique, in its most simple iteration, consists in setting up net barriers to trap the tuna when they migrate into the Mediterranean Sea from the Atlantic Ocean (February to July), on their way to spawn and until recently, on their return journey, ("al revés"); the bycatch contains, among others, bullet tuna (auxis rochei), little tunny ...
Midwater trawling catches pelagic fish such as anchovies and mackerel, whereas bottom trawling targets both bottom-living fish and semi-pelagic species such as cod, squid, shrimp, and rockfish. Trawling is done by a trawler, which can be a small open boat with only 30 hp (22 kW) or a large factory trawler with 10,000 hp (7,500 kW).
In fish trawls, the grid is mounted so the smallest organisms (juvenile fish, shrimp) pass through the grid and enter the sea again. In shrimp trawls, the grid pushes the largest organisms (fish) through a hole in the roof of the net, reducing by-catch of fish. The latter type of grid is mandatory in Norway and has been in use for 20 years. [11]
Fishing traps – A fish trap is a trap used for fishing. Fish wheel – A fish wheel is a device for catching fish which operates much as a water-powered mill wheel. Fishing weir – A fishing weir, or fish weir, is an obstruction placed in tidal waters or wholly or partially across a river, which is designed to hinder the passage of fish.
V-shaped structures in rivers could be as long as 60 metres and worked by directing fish towards fish traps or nets. Such fish traps were evidently controversial in medieval England. Magna Carta includes a clause requiring that they be removed: "All fish-weirs shall be removed from the Thames, the Medway, and throughout the whole of England ...
The anchor (chain) of the mooring can also be seen. Traps are often moored at a specific depth in the water column (usually below the euphotic zone or mixed layer) in a particular location, but some are so-called Lagrangian traps that drift with the surrounding ocean currents (though they may remain at a fixed depth). These latter traps travel ...