Drive-in and lift nets
- Related Topics:
- aquaculture
- bycatch
- fishing
- hunting
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Another class of fishing methods involves driving the fish into a net or gear. A drive-in net may be one of those already mentioned or may be specially made, such as the dustpan-shaped stationary gear used in some fisheries in South Asia.
A further fishing method employs lift nets, which are submerged, then raised or hauled upward out of the water to catch the fish or crustaceans above them, often attracted by light or natural bait. This group includes small hand-operated lift nets, such as hoop and blanket nets, as well as large, mechanically and pneumatically operated lift nets. Some of these employ levers, or gallows, and are installed on the beach or on a vessel. The fish wheels used on the Tiber, Rhône, and Columbia rivers can be considered as mechanized lift nets. The most important examples of this fishing method are the stick-held dip nets of the Japanese. In contrast to the lift nets are falling gear, which can be wooden baskets, cover pots, or a variety of nets designed to be cast on fish and crustaceans from above.
Gill and entangling nets
Gill nets, which catch the fish in their meshes, are mostly used in long rows. As setnets they are anchored or fixed by stakes; as drift nets they drift freely or with a fishing craft. Before the invention of mid-water trawls, drift nets, with surrounding nets, were the principal gear for fishing pelagic fishes.
Sometimes gill nets do not catch by meshing but by entangling the fish, especially those too large for the mesh size or provided with spines or hard fins. Single-walled tangle nets are widely used to catch sturgeon, salmon, and shellfish, such as the king crab. Some tangle nets are double walled; most are triple walled, such as the trammel nets used especially for flatfish.
Machines
Harvesting machines include comparatively new types of gear that may separate the fish or shellfish from the water by pumps (pump fishing) or by mechanized dredges, as well as floating machines that dig out mollusks by means of underwater jets and transport them out of the water with the help of conveyor belts.
Vessels
Until the mid-20th century, fishing boats were largely of local design, with different types found even in adjacent ports. As fishermen started to roam farther afield for their catches, the vessels grew, and with this growth in size came an element of standardization in design. Today, fishing boat design and construction is an international industry, with the different vessel types dictated more by the fishing methods for which they are designed rather than by their port or country of origin.
The establishment of 200-mile fishing limits (see above History of commercial fishing) has altered fishing patterns and, with them, the types of vessels used by many countries. In the United States and Canada, fishing vessels have grown with the introduction of processing or factory trawlers, while the huge fleets of this type of vessel operated by Soviet-bloc countries and Japan have shrunk. In western Europe, compact fishing vessels have been developed with high catching power. The advantage of these smaller vessels is their reduced capital and operating costs.
Steel is the most common construction material, being used exclusively on larger vessels (above 25 metres). Traditional wood construction is less common because of cost and a lack of suitable timber in many areas. The use of fibreglass is increasing in smaller fishing vessels, and it is now used on vessels of up to 25 metres in length. Ferrocement has been used to a certain extent; it is mainly used in the artisanal fisheries of developing countries because, while its construction is labour intensive, its raw materials are cheap.
The aim in all fishing-boat development is to improve efficiency by building vessels that have higher catching power, smaller crews, and reduced operating costs. This development must be matched against safety concerns, as commercial fishing is one of the highest risk industries in the world. Several countries have introduced regulations governing the construction and operation of fishing vessels. The International Maritime Organization, convened in 1959 under the auspices of the United Nations, is responsible for devising international regulations covering such aspects of fishing vessel design as construction, stability, safety equipment, and watertight integrity. These regulations are likely to lead to further standardization in design.
The Food and Agriculture Organization of the United Nations has introduced a classification scheme of fishing vessels based primarily on the gear used.
Trawlers
Most trawlers are single-screw vessels with powerful engines and deck machinery for dragging the trawl nets.
Side trawlers
On this traditional type of trawler, the trawl is launched and recovered from the side of the vessel. The side trawler is characterized by the wheelhouse and superstructure at the stern and a raised forecastle at the bow. The hull lines follow a traditional seaworthy form, with a pronounced deck sheer giving a high bow and stern. The working deck may be covered.
Stern trawlers
Practically all trawlers built today are stern trawlers, with the trawl launched and recovered over the stern. The vessels are generally designed with the wheelhouse and superstructure forward, often forming part of the raised forecastle. By contrast, the working deck aft is lower, and, on the larger trawlers a ramp is built into the stern up which the trawl is pulled onto the deck. On smaller stern trawlers the trawl is lifted on board by a hoist.