A cast net is a fishing net which is designed to be thrown out into shallow water and then hauled back in with a payload of fish. People have been using cast nets for thousands of years, as mosaics from Ancient Greece, Rome, and China indicate, and they continue to be popular for recreational fishing. Cast nets are not widely used in the commercial fishing industry, because they are so labor intensive, but they are often on display in fishing museums and the headquarters of fishing companies as they are of historical interest.
A basic cast net is a giant circle of netting with weighted edges. The net is attached to a line so that it can be retrieved, and another line is attached to a drawstring which can be used to pull the net closed, trapping fish inside. As a general rule, a cast net is designed to be thrown by hand, but it is also possible to use a net thrower or net launcher, especially for big nets, which can be hard to handle.
These nets are designed for use in water which is shallow and free of obstructions such as reeds, rocks, or submerged logs. To use a cast net, the fisherman throws the lightweight net out onto the water, where it spreads out and then begins to settle very rapidly, thanks to the weighted edges. As the net approaches bottom, it is pulled closed and reeled back in with a load of fish.
Learning to handle a cast net can take time. These nets are prone to tangling if they are not handled and stored carefully, and big nets can be tough to work with. Cast nets also have to be checked regularly for holes requiring repair, as otherwise fish could slip out, and one needs to be fairly strong to pull the net in, since the net can get very heavy with a full load of fish. Cast nets are also subject to a bycatch of unwanted fish, since there is no way to control which species wind up in the net.
Some people enjoy learning to use a cast net because they have an interest in old-fashioned fishing techniques, and it can be pleasant to work with a cast net once one gets the hand of it. One also sees cast nets on television stories about survivors cast ashore on remote islands, and in books about the same topic. Incidentally, should you find yourself in such a situation, you may want to be aware that cast nets are most effective in water which is as deep as the diameter of the net.