How the purse seine method works
Purse seine is the term that indicates both the tool and the fishing technique used to fish species that come back to life on the bench (from the smaller ones of sardines and anchovies to the larger ones like those of mackerel and tuna).
The nets are used to completely enclose, in a circular shape, a part of the sea in which a large quantity of fish has been concentrated.
Usually the fish school is attracted to the night hours in a certain stretch of sea by one or more small boats equipped with very powerful light sources called Lampara.
The bench is expected to be very compact in order to spread around it a rectangular net with floating corks in the upper part and a line of weights in the lower part; when the school is surrounded the net closes at the bottom and is slowly withdrawn until the fish are concentrated in a space small enough to be retrieved with a tile.
How it's done?
There are several types of networks based on the species you intend to fish: the most common, mostly used to catch small school fish (blue fish) is called purse seine or saccoleva, but there are others like the flying trap, used above all in the Adriatic for the capture of tuna (which has much greater dimensions and strength than purse seines, does not use light sources and is lowered very quickly on the shoal once the shoal has been sighted).
The shape is always that of a great man bed sheet: the upper part is equipped with floats that keep it on the surface, while in the lower part there are weights that help to maintain the vertical descent. In the latter, at regular intervals, there are also iron rings in which the steel cable used to close the net is passed: at the end of the drop the cable is recovered to transform the cylinder formed by the net into a bag , in order to prevent the escape of fish.
The most delicate phase of the process is the initial one, in which the captain begins the control operations to identify the size of the shoals of blue fish in the sea area that is being crossed; it is essential to carry out this check carefully, because the net is only recovered once per trip!
Regarding the environmental impact, purse seine fishing is generally considered sustainable, because does not damage the seabed and fishing alone schools of fish of approved species; it is not considered as such when used in combination with Fad.
THE Fad (Fish Aggregate Device) are floating rafts equipped with GPS that are left to drift and then recovered: a floating object in an immense expanse of water is usually of great interest to animals so, within a few days, large quantities of fish of all kinds (and, consequently, also the large predators sought by fishermen).
When the ships then return to retrieve the devices, they lower the purse seine and fish for everything that has gathered there, including unsaleable and sometimes protected species.
Lately fishing with FADs has been banned, but given the difficulty of controlling fishermen on the high seas, it is always advisable to rely on certified sustainable products.