Fishing with gill net tools is the type of fishing that requires the most experience, with regard to the behaviour of the species that can be fished in the different seasons. This fishing is performed by fishermen who have a profound "culture" of the sea. The quantity of catches made depends on this culture of theirs. The encircling gill net is a normal fixed net (gill net) that, instead of being lowered into the sea in a straight line, are lowered in a circle or semicircle. This fishing system is generally used close to the shore, with small fishing vessels, to catch fish that are found amassed in a fairly restricted space. Once the circle is closed, the boat is placed inside it and it starts making noises to frighten the fish and direct them towards the walls of the net. The catch is made by gillnetting, enmeshing or entanglement in the net itself and the fish remain trapped there.
In an attempt to pass through the net, the fish puts its head through one of the spaces in the mesh as far as its gill cover (1). Here, the thread of the mesh tightens around it, so that it cannot turn back nor go forward (2), since the circumference of its body is larger than the size of the space in the mesh, until it becomes trapped (3).
The fish squeezes into the mesh and is able to go beyond its gill cover, but it becomes trapped in the area of its first dorsal fin, since the circumference at that point of its body is larger than that of the mesh, thus preventing the fish from moving forward.
The fish is too large for the size of the mesh to permit either of the two capture methods described above, but it has several particular protuberances (antennae, bodily unevenness, spines) which, by getting entangled in the netting, make it possible to capture it. The movements of the prey, as it tries to free itself, end up facilitating its entanglement in the netting, where it becomes trapped.