Purse-seine Fishing
Purse-Sein Fishing © John Surrick, Chesapeake Bay Foundation, Marine Photobank.

Seine nets are large vertically floating nets with monofilament plastic which boats use to surround shoals of fish they have identified on fishing sonar technology. The nets can extend from one mile to several miles long. Once fish are in the base of the net, the base is drawn together creating a “purse”, catching a high volume of fish. Commercially important species such as tuna, herring and mackerel are usually targeted with this type of gear. There are two different methods of purse seining, the one boat and two boat system. Purse seining with a single boat is now considered more economical, even though shooting a purse seine with two boats is more time efficient and a larger type of gear can also be operated. There a number of different steps in purse seine fishing:

1. Finding the fish – fish shoals can be detected from the surface using observational techniques (e.g. seabirds aggregating over a certain area) and also by using sonar and fish finding technology.

2. Setting the net – the fishing vessel moves ahead, drops the net with buoys attached and moves in a circular path setting the net, this can take as little as five minutes.

3. Purse – The extremities of the net are drawn back into the boat, each end of the purse are pulled in together, starting the pursing of the bottom of the net, the pursing then proceeds to be gradually drawn in tight.

4.The fish are gathered together at the end of the net, it is brought closer to the boats side this is when the fish can then be brailed or pumped onboard into storage.

Purse seining is associated with high levels bycatch of non-target fish and other marine life and the accidental catch and discarding of juvenile commercial fish species. Tuna purse seine fisheries probably apply the most intensive direct human impact on the epipelagic ecosystems in all oceans, mainly due to the worldwide scale of purse-seine fisheries and their associated bycatch of non-target vulnerable species such as sharks and marine mammals such as turtles and dolphins. The amount of bycatch from this type of gear ranges from 60% of the catch, as in some temperate ground fisheries, to over 10 times the amount of catch in some tropical shrimp fisheries. Many species of shark are caught as bycatch during this method of fishing including Blue (Pironace glauca), Silky (Charcharhinus falciformis), Blacktip (Charcharhinus limbatus), hammerhead species (Family – Sphyrnidae) as well as Oceanic Whitetip Sharks (Carcharhinus longimanus).