Fishing with gillnets is a passive fishing method which uses a netting wall in the water. The meshes of the net are large enough for a fish to swim through with their head, but too small for its body. The fish has to turn around and is caught by its gills. The fishery with gillnets is selective because small fish can swim through and large fish cannot get their head through. Anchored gillnets are gillnets which are set on the seabed by anchors. Anchored gillnets have a vertical position in the water because there are floaters attached to the headrope and weights on the footrope of the net. By employing the net on certain places and on certain depths a fishermen can also target certain species. By changing the weights and floats gillnets can be set at different heights in the water column. Gillnets can be several kilometers long. Gillnets have a low impact on the seabed.
Driftnets are gillnets which are not anchored, but drift on the sea currents (with or whithout boat). The nets follow the dominant sea current. Target species are pelagic fish like sardines, herring, tuna and squid. These, sometimes kilometers long, nets are nicknamed ‘walls of death’ because all sorts of fish and ocean life (dolphins, sea turtles, birds and whales) get entangled in them. Driftnets are prohibited since 2002 in European waters. Driftnets do not impact the seabed. There is a lot of bycatch (which includes endangered species) and there is damage of lost gear (ghost fishing).
Encircling gillnets are gillnets which are set around a school of fish. Encircling gillnets are often used for fish that move and feed in schools like sardines, mackerel and horse mackerel. When the net is set around the schooling fish, the fishermen hit the water with paddles to get the fish into the net. This catching method has low impact on the seabed.
Trammel nets are nets consisting of 3 layers in which fish get entangled, and get stuck more when splashing. A trammel net consists of three layers of netting with a slack small mesh inner netting between two layers of large mesh netting within which fish will entangle. This fishing method has a low impact on the seabed. There is however bycatch and discarding of unwanted species (which include endangered species). The loss of nets is damaging, because they keep catching fish (ghost fishing)