Trawling: pulling a bag- shaped net through the sea is an unselective method and can catch a wide variety of species including non-target species (by-catch). Trawling on the seabed can also cause great physical damage e.g. to coral, seaweed bed; midwater trawls have lower by-catch but can kill some non-target organisms e.g. porpoises caught in bass trawls.
Long-lining: long fishing lines reduce the by-catch of using nets but can catch other species on the hooks e.g. albatorosses, turtles and sharks.
Purse seining: a net is cast around a shoal of fish, drawn tight then pulled in. It is possible to selectively catch particular species e.g. tuna, mackerel, sardines.
Drift-netting: nets supported by floats catch species such as tuna and herring but also catch by-catch species e.g. dolphins, whales, turtles and sharks
Factory ships: these alow the processing and preservation of large quantities of fish which allows fishing fleets to operate far from their home ports. Long-distance fleets use a lot of fuel.
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