How is tuna caught with surrounding nets?

Pelagic species like tuna gather together in dense shoals, which has led to the creation of different fishing nets designed to catch these schools of fish. One of the most important systems is the surrounding net – a method of fishing where the shoal swimming close to the surface is encircled. It is a large, very long rectangular wall of netting, with a large number of floats along the top line to stop it from sinking in the sea.

The bottom of the net has a lead line to help to keep the net vertical in the water. The purse line is a very strong line that passes through rings placed on the bottom of the surrounding net with the purpose of closing the net once the fish have been encircled. Once a school of tuna has been detected, the boat, with the help of a dinghy or skiff, circles the school of fish. When the school has been encircled, the net is closed at the bottom by pulling the purse line, forming a cone and thus trapping the tuna.

The cone is gradually closed, and drawn slowly towards the side of the vessel. The tuna are then lifted onto the boat with a crane and a brailer, and are frozen immediately to keep their properties intact. The environmental impact of the purse seine is very low, as bycatch is released during the process. Atunlo has been awarded APR sustainability certification, the requirements of which include the duty to maximise the survival of aquatic bycatch while ensuring the safety of the crew.

These techniques to release associated species shall apply, as a minimum, to sharks, whale sharks, broadnose sevengill sharks, sea turtles, manta rays and rays. Atunlo is also ISSF registered. One of the main action points of this non-profit organisation is avoiding bycatch. For this purpose, the ISSF collects data annually from purse seiners in order to monitor, report and minimise bycatch.

Atunlo requests written guarantees from its suppliers of good practices on-board, avoiding transactions with operators that do not comply with:

– policies prohibiting the removal of shark fins,
– policies implementing the use of non-entangling FADs,
– good practice policies for the protection of sharks and sea turtles.