Fisheries

I

Introduction

Fisheries, name applied both to the commercial enterprises that gather fish and shellfish, and to the waters where such fishing takes place. Fisheries are mostly marine but also exist on large lakes and rivers. The most productive fisheries extend outwards from coastlines as far as the continental shelf, an average of about 80 km (50 mi) from the shore. They are less than 200 m (650 ft) deep but, owing to favourable currents and temperatures, and abundant plant life, they hold most of the oceans' fish. Fisheries are particularly productive in areas of upwelling, where cold, deep, and nutrient-rich waters are carried to the surface. The gathering of whales, molluscs, crustaceans, and kelp is also considered part of the fishery industry.

II

Major Fisheries

Rich fisheries are found in the North Sea, along the west coast of Great Britain, over the continental shelf of Iceland, on the Grand Banks off eastern Canada, on the Georges Banks off New England, off the south-western United States and Peru, in the Bering Sea, in the Gulf of Alaska, and off the coasts of Japan.

III

Types of Fish Caught

Two kinds of finned fish are taken from salt-water fisheries: pelagic and demersal. Pelagic fishes frequent near-surface water, usually migrate seasonally, and travel in schools. They include tuna, salmon, anchovies, sardines, and herring. Demersal fishes, or groundfishes, frequent ocean bottoms and are less gregarious. They include cod, halibut, sole, haddock, and flounders. Invertebrates are abundant animal species in the ocean, but make up only a small per cent by weight of the catch. They are taken mostly in shallow waters; oysters, clams, scallops, lobsters, crabs, shrimps, and squid are of greatest commercial importance.

IV

Methods of Fishing

In commercial fishing, nets are either pulled close to the surface or trawled along the bottom. The most effective surface net is the purse seine, a long, curtain-like net that hangs into the water from floats. It is towed in a circle around a school of fish and then drawn shut at the bottom, like a purse, with a rope. The gill net is made with mesh size just large enough for the head of the fish to pass through and the gills to catch in the mesh. Gill nets are most often left to drift on the surface for pelagic fish, but are also anchored on the bottom for groundfish. The otter trawl dredges demersal fish such as cod and is the most important net for commercial fishing in deep water. It is towed by two long cables. Near the mouth of its sock-shaped net, holding it open, are two boards that are forced sideways and downwards by their movement through the water.

Longlines, which are used to catch both surface fish (such as tuna) and groundfish (such as halibut) are long, heavy ropes to which are attached auxiliary lines with baited hooks. They can extend for several kilometres and are attached to moored buoys or trolled from vessels. The laden lines are hauled in by winches.

Deep-water shellfish, especially scallops and sea clams, are gathered by power dredges. Closer to shore, oysters are also collected with dredges or long-handled tongs. Intertidal clams are dug at low tide with long-tined rakes. Crabs are dredged or caught in wire traps. Lobsters are caught in traps made of wood or wire.