Fishing nets are, in general, divided into two types, bottom gill nets and drift nets. The type of nets the fisherman are choosing depends on what kind of fish he wants to catch.
Bottom Gill nets are used to catch fish that live near the sea bed, e.g., cod and flatfish like plaices, soles, turbot's or similar. Those nets are placed on the bottom at fixed with anchors.
Drift nets are floating in, or close to the surface, and the nets are hanging vertically in the water like a curtain. Drift nets are designed to catch fish that are living near to the surface, e.g., herring, trouts, mackerel, etc.
Bottom gill nets are designed to be placed on the bottom of the sea, and this is managed by tying a number of nets together to a long row. This row is anchored to the bottom in both ends to keep these in the correct position. Bottom gill nets have a negative buoyancy that makes it possible for the nets to sink to the bottom and catch the fish. This kind of net can be used on almost every sea-bottom.
Drift nets are a type of nets that are floating in or near the surface, and you need to mark them properly thus, other vessels can pass the nets without they are causing difficulties. Drift nets are often equipped with buoy lights as well as radar reflectors.