Cod in a trawl net People have been catching fish from the sea, rivers and lakes for thousands of years. Fishing is still a source of food, and an important industry for many people living near the sea. Most fish are now caught by fleets using modern equipment. This is called commercial fishing. Japan, China and Russia are the largest commercial fishing nations. There are about 30,000 kinds of fish, but only a few hundred are caught commercially. The world’s major fishing grounds are the areas of relatively shallow waters that lie above the continental shelf—those parts of the Earth’s landmasses that are submerged by ocean waters.
Most sea fish are caught by fishermen working on trawlers. Trawlers are equipped with a large net that is trawled (dragged) along or just above the seabed. Distant-water trawlers, the most numerous type, can stay at sea for several months. Many of them have freezers so the fish can be gutted and frozen on board. Middle-water trawlers go out for two or three weeks, and near-water trawlers for only a few days at a time.
Trawling nets each have a mouth, a body through which the fish are guided inwards and a narrower "cod-end" where they collect. With bottom trawling, the mouth of the net is held open by a beam attached to metal plates that slide over the seabed. Smaller vessels use these kinds of trawling nets for catching flatfish or shrimp (prawns) close to shore. Some nets are fitted with rubber wheels that let the net crawl over the rocky sea bottom.
Hauling in trawl netsTrawlers also catch demersal fish, those kinds that live just above the seabed. North Atlantic trawlers catch cod in the cold waters off Canada, Greenland and Scandinavia. Japanese and American fleets catch tuna in the deep waters of the Pacific Ocean.
Fishing and fish farming provide employment for around 500 million people around the world.
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