fishing and fisheries

A sardine fisherman casting a net in the Sea of Cortez, Mexico. This is a traditional mthod of catching fish, superseded in many parts of the world by ships trawling with much larger nets.

Octopus being prepared for sale at the Tokyo fish market.

The king mackerel, often referred to as the kingfish, is found mainly in the warm waters of the Indian Ocean. It usually reaches up to 2 m/6.6 ft in length and 45 kg/100 lb in weight. The king mackerel can be caught using live bait such as other fish, usually elf or mullet, or by an artificial lure.

Industrial fishing, especially tuna fishing and canning, is an increasingly significant factor in the economy of the Seychelles. Earnings from licence fees, paid by foreign trawlers to fish Seychelles territorial waters, are growing every year.

A lobster fisherman in the town of Le Guilvinec-Lechiagat in Brittany, northeast France. Lobsters are traditionally caught by means of baited traps. Modern traps are made with plastic-coated steel rods and braided nylon net, as opposed to the more traditional baskets. Typical baits include mackerel and crab bodies.

Pollack, Pollachius pollachius, are members of the cod family. Widely distributed in waters from the northern Mediterranean to the Atlantic as far north as Iceland, they are still plentiful in the English Channel off the coasts of Devon and Cornwall, where the traditional method of handline fishing is often used to catch them.

The Brixham sailing trawler was a type of wooden fishing vessel built in the town of Brixham between the 1880s and 1920s. More than three hundred were built and sailed out of Brixham, a fishing port on the south Devon coast. Brixham was once home to one of the largest wooden trawler fleets in the world. Today, only a few of the original boats remain.

Fishermen from Chile. Chilean waters are the primary area for fishing in South America, and one of the most important fisheries in the world. The main types of fish caught are mackerel, sardines, and anchovies.

Mussel farming in Chile. Mussel farming is an increasingly popular and profitable form of aquaculture. Fishermen collect the mussels from lines to which dense clusters have attached themselves. The most commonly farmed mussel is the blue mussel, Mytilus edulis.

Mussel farming in Chile. Chile is one of the most important fisheries in the world, and in addition to line- and-net caught fish such as mackerel and anchovy, fish farming is now increasingly practised. Large clusters of mussels attach themselves to lines, from which the fish farmers collect them.

Fishing boats with mussels and fish, Chile. Chile is the most important fishery in South America, and one of the world's leading exporters of fish. With a very long marine coastline and excellent water quality, Chile's waters are home to an abundance of fish and crustaceans, which form an important part of the country's economy.

The harvesting of fish and shellfish from the sea or from freshwater; for example, cod from the North Sea and carp from the lakes of China and India. Fish are an excellent source of protein for humans, and fish products such as oils and bones are used in industry to produce livestock feed, fertilizers, glues, and drugs. Most of the world's catch comes from the oceans. The world's total fish catch is about 100 million tonnes a year (1995).

The world fish catch increased by an average of 7% each year 1950–70. Refrigerated factory ships allowed filleting and processing to be done at sea, and Japan evolved new techniques for locating shoals (by sonar and radar) and catching them (for example, with electrical charges and chemical baits). By the 1970s, overfishing had led to serious depletion of stocks, and heated confrontations between countries using the same fishing grounds. A partial solution was the extension of fishing limits to 320 km/200 mi. The North Sea countries have experimented with the artificial breeding of fish eggs and release of small fry into the sea. In 1988, overfishing of the northeastern Atlantic led to hundreds of thousands of seals starving on the north coast of Norway. A United Nations (UN) resolution was passed in 1989 to end drift-net fishing (an indiscriminate method) by June 1992. Marine pollution is blamed for the increasing number (up to 30%) of diseased fish in the North Sea.

Stocks of several deep-water fish have been decreasing since the 1970s because of the global boom in deep-water fishing. As traditional fisheries in shallow water became depleted, there was a growth in commercial interest in deep-water fisheries, but deep-water fish are slow-growing and do not reproduce rapidly enough. For example, stocks of New Zealand's orange roughy, one of the first deep-water fish to be exploited, fell by 90% in the 1970s, and there are no signs of recovery. This may have a permanent effect on deep-water ecosystems, with the disappearance of slow-growing species in favour of faster-reproducing fish.

Marine fishing Most of the world's catch comes from the oceans, and marine fishing accounts for around 20% of the world's animal-based protein. A wide range of species is included in the landings of the world's marine fishing nations, but the majority belong to the herring and cod groups. The majority of the crustaceans landed are shrimps, and squid and bivalves, such as oysters, are dominant among the molluscs.

Almost all marine fishing takes place on or above the continental shelf, in the photic zone, the relatively thin surface layer (50 m/165 ft) of water that can be penetrated by light, allowing photosynthesis by plant plankton to take place. Pelagic fishing exploits not only large fish such as tuna, which live near the surface in the open sea and are caught in purse-seine nets, with an annual catch of over 30 million tonnes, but also small, shoaling and plankton-feeding fish that live in the main body of the water.

Examples are herring, sardines, anchovies, and mackerel, which are caught with drift nets, purse seines, and pelagic trawls. The fish are often used for fish meal rather than for direct human consumption. Demersal fishes, such as haddock, halibut, plaice, and cod, live primarily on or near the ocean floor, and feed on various invertebrate marine animals. Over 20 million tonnes of them are caught each year by trawling.

Freshwater fishing Such species as salmon and eels, which migrate to and from fresh and salt water for spawning, may be fished in either system. About a third of the total freshwater catch comes from fish farming methods, which are better developed in freshwater than in marine systems. There is large demand for trout, carp, eel, bass, pike, perch, and catfish. These are caught in ponds, lakes, rivers, or swamps. In Africa, although marine fishing is generally more important, certain areas have significant freshwater fisheries; Lake Victoria annually yields a catch of 100,000 tonnes, which is four times the total catch from the whole eastern African seaboard. In Western Europe there is very little food production from fresh water; instead the fish are usually exploited for recreational purposes or sport (see angling).

Methods The gear and methods used to catch fish are very varied and show much geographical and historical variation. The method chosen for a particular situation will depend on the species being hunted and the nature of the habitat (for example, the speed of the current, the depth of water, and the roughness of the sea bed). It is often useful to divide gear types into active (for example trawls, seines, harpoons, dredges) and passive (drift nets, traps, hooks and lines). Passive gear relies on the fish's own movements to bring them into contact with it, and may involve some method of artificial attraction such as baits or lights. Most fishing gear is operated from boats, ranging from one-person canoes to trawlers about 100 m/330 ft long.

Trawling Much of the world's fish catch is caught by trawls. These may be used on the sea bed (demersal) or in midwater (pelagic), but in all cases the equipment consists essentially of a tapered bag of netting which is towed through the water. The mouth of the net is kept open in the vertical plane by having floats on the headline and weights on the footrope. On bottom trawls these weights are usually hollow iron spheres that roll over the sea bed. In addition there may be tickler chains which help to dislodge or disturb fish from the sea bed in advance of the trawl so that they are more likely to be caught. There are three methods of keeping the net open in the horizontal plane: (1) pair trawling, in which the two trawl warps are towed by separate vessels; (2) beam trawling, in which the net is supported on a rigid frame consisting of a horizontal wooden or metal beam with a shoe at either end; and (3) otter trawling, in which an otter board (a weighted board with lines and baited hooks attached) is incorporated into each warp and acts as a hydroplane to push the warp out sideways. Most modern trawlers are otter trawlers, and many haul the net up over the stern rather than the side. The main problem with pelagic trawls is to control the depth of fishing and to relate this to the concentrations of fish. The most effective means of tracking fish for this purpose is by using an echo sounder.

Seine nets Seine nets operate by trapping fish within encircling gear. The Danish seine resembles a light trawl with very long side pieces, or wings, but is operated differently. The method consists of dropping a large buoy and then paying out up to 4 km/2.5 mi of warp in dogleg shape, then the net, followed by a further length of rope warp in reverse dogleg, bringing the boat back to the buoy, which is then picked up before hauling in the rope warps. As the ropes straighten on the sea bed, they channel the fish into a narrow path between them. The fish are then swept up by the net as it is hauled towards the boat. This method requires smooth sandy ground. Beach seines are similar to Danish seines but may consist simply of a wall of netting. They are set in a line or semicircle parallel to a beach and can then be hauled onto the beach, trapping the fish between the net and the shore. Salmon are often caught this way in estuaries. Purse seines, nets that close like a purse, are used to catch pelagic fish such as herring, mackerel, and tuna, which form dense shoals near the surface. Once a shoal has been located, usually by echo sounder, the net is shot around it by one vessel and later hauled in towards another. The nets are large, often as long as 30 nautical miles, and are not usually hauled aboard like trawls. Instead the fish are scooped or pumped out of the net into the ship's hold. They have caused a crisis in the South Pacific where Japan, Taiwan, and South Korea fish illegally in other countries' fishing zones.

Gill nets Gill nets passively depend on the fish entangling themselves in the meshes of the net, usually being held fast by their gill covers. An example is the drift net used for pelagic fish, but in many areas it is now superseded by purse seines and pelagic trawls. Drift nets are walls of netting suspended from floats on the surface. Those used in the East Anglian herring fishery were only 70 m/230 ft long but were set in fleets up to 4 km/2.5 mi long. Herring were caught in them as they came up to the surface at night to feed. Other types of gill net can be used near the sea bed, and one, the trammel, is still used quite commonly in inshore fisheries along the south coast of England. This typically consists of a curtain of large- and small-mesh netting into which the fish swim, forcing the small-mesh net into the large and becoming trapped in a net bag.

Traps Netting panels can be arranged to form traps into which fish are guided or attracted; those used on the northeast coast of England to catch salmon are good examples. Many crustaceans, such as lobsters and crabs, are normally taken in baited baskets set in strings of several hundred laid over suitable ground. Earthenware jars are used as octopus traps in the Mediterranean.

Lines and hooks Although a distinct method of catching fish, lines and hooks can be regarded as a special type of trap. Natural or artificial baits are used and the gear may be fished anywhere from the sea bed to the surface. Hooks and lines fished off the sea bed may be towed from moving boats, which is called trolling. The largest lines, called long lines, are those used by the Japanese to catch tuna in ocean areas. These are up to 80 km/50 mi long and the baited hooks hang well below the surface from the buoyed lines.

Dredges Dredges act like small trawls to collect molluscs and other sluggish or sessile organisms; some are hydraulic and use jets of water to dislodge the molluscs from the bottom and wash them into the dredge bag or directly onto the boat via a conveyor belt.

Other methods Molluscs may also be gathered by hand, either on foot at low water or by divers below the shoreline. Rakes may be used to dig out cockles from within the sand. Other methods include dip, lift and cast nets, harpoons, and spears.

History Until the introduction of refrigeration, fish was too perishable to be exported, and fishing met local needs only. Between 1950 and 1970, the global fish catch increased by an average of 7% each year. On refrigerated factory ships, filleting and processing can be done at sea. Japan evolved new techniques for locating shoals (by sonar and radar) and catching them (for example, with electrical charges and chemical baits).

Tensions over fishing rights in the North Atlantic heightened March 1995, after Canadian authorities captured a Spanish trawler in international waters off the Newfoundland coast, and charged its captain with violating international quotas by overfishing. The action prompted outrage within the European Union (EU) and provoked Spain to send warships to protect its fishing vessels. Canada responded by sending two of its own gunships to the area. The dispute ended April 1995 after Canada and the EU reached an agreement providing for greater enforcement of existing quotas.

Subsidization Fishing fleets receive heavy national subsidies; the global fishing industry received $54 billion (£35 billion) worth of subsidy 1992, yet made a loss of $50 billion. According to an estimate by the Food and Agriculture Organization 1993, annual spending on fishing amounts to £83 billion to catch £47 billion worth of fish.

Depletion of fishing grounds There are good economic reasons for using the most efficient methods of fishing as long as there is some control over the number of fish deaths caused. In the absence of effective control, the number of fish killed may be too high, with more fish being caught than are being replaced by new births. The maximum sustainable yield is the largest catch that can regularly be taken in the long term without reducing the stock. Exceeding this amount (overfishing) will reduce the size of the stock below a safe level and result in smaller catches per unit of fishing effort. This will have economic repercussions, which may reduce the amount of fishing effort expended in the area, thus enabling the stock to recover. This, however, is bad conservation and a wasteful way of exploiting a resource; exploitation should proceed at or below maximum sustainable yield.

Overfishing has led to fears that the world's main fishing grounds are now depleted to, or beyond, their biological limits. As fish reserves are depleted, disputes over fishing rights increase; about 50 countries were estimated to be in dispute over fishing stocks in 1995. European governments were warned in 1990 that all their main trawling grounds were overfished by 25–40%; by 1995 all the world's fish stocks were being exploited to the limit and 75% of them were in decline. FAO estimated that 90.7 tonnes of fish were caught in 1995.

A UN-sponsored global fishing accord, intended to conserve stocks and to prevent international conflicts over fishing rights, was approved by more than 100 countries in 1995. The treaty, the first to regulate fishing practices in international waters, sought to protect straddling species – those migrating to international waters from waters surrounding individual countries – but did not cover fishing activities within territorial waters (those extending 320 km/200 mi from a nation's coastline). In addition to implementing quotas and conservation measures, signatories were to take measures to reduce wastage – although many of the world's poorest people depend on fisheries for subsistence, unintended fish catches, or by-catch, discarded by fishing fleets, were estimated to account for almost one-third of the world's total fish catch.

Extending the range of species taken would result in much higher yields of fish from the sea, particularly if these were low in the food chain. It has been estimated that a world fish catch ten times larger than now would be possible if we exploited small organisms such as krill for use as food. Because of the assumed 10% conversion efficiency factor, 1,000 tonnes of phytoplankton could support 100 tonnes of krill but only 10 tonnes of zooplankton-feeding herring and 1 tonne of the majority of our food fish, which feed on other, smaller fish. In terms of utilizing marine production it is, therefore, inefficient to exploit the large carnivorous species upon which our current fisheries are based. However, abundance is not the only factor that needs to be taken into account. Ease of capture, handling, and processing must be considered, as well as whether the look and taste will appeal to the consumer, and this explains why we are eating fish like cod and plaice instead of plankton.

Ancillary industries These include the manufacture of nets, the processing of oil and fish meal (nearly 25% of the fish caught annually are turned into meal for animal feed), pet food, glue, manure, and drugs such as insulin and other pharmaceutical products.

Preservation Once fish are caught, they usually have to be preserved to reduce spoilage and are often processed into the form required by the consumer. Most processing methods (see food technology) also have a preservative function, allowing considerable periods of time between catching and marketing or consumption. This in turn makes it possible to increase the operational range of fishing vessels, and to open up markets at a distance from the ports of landing.

An early method of preservation was to keep the fish alive for as long as possible after capture in ‘live wells’ incorporated into the boats' structure, but it is generally easier to preserve dead fish because these take up less space. The use of ice in ships' holds is an effective method, but in Britain it was complicated by the need to import the ice from Norway until the first artificially made ice was sold in 1874.

The use of crushed ice in the holds has today given way to on-board freezing in many distant-water vessels. Bacterial spoilage can also be retarded by using refrigerated sea water containing antibiotics of the tetracycline group.

Curing Drying, smoking, salting, and pickling in brine are established methods of fish preservation, and drying is particularly useful in the tropics. These methods are sometimes known as curing. The one most familiar in Britain today is the smoking of herrings (to produce kippers) and haddock. Traditionally oak chippings or sawdust are used to generate the smoke.

Fish meal About 25% of fish is reduced to fish meal to be fed to livestock. Valuable oil is produced in addition to the protein-rich meal, and a type of meal known as fish-protein concentrate can be produced which is suitable for direct addition to human diets. The process consists of cooking and pressing the fish in order to extract the liquid from which oil is separated and later purified. The solids (to which are added sludge and liquid from the oil-separating processes) are then dried and ground in order to form the meal. Pelagic, plankton-feeding fish like herring and mackerel have variable but generally high oil contents (often over 20% of total weight) and are usually taken by factories in preference to white fish. A typical sample of herring would give 2–20% oil and 18–22% of solids.