Purse seine fishing vessels catch nearly 65% of the 4.4 million tons of tuna caught globally every year. Globally it is estimated that 1,664 purse seine vessels are authorized to fish for tuna, however only 678 are considered large-scale tropical tuna purse seiners with the ability to hold about 637,000 tons of fish . In 2010, these vessels caught roughly 2.8 million tons of tropical tunas.
A purse seine is a net set vertically in the water. When a school of tuna is sighted, the purse seine vessel encircles the school and traps them in the net by linking back up with a smaller vessel. Purse Seine is an extremely consistent and efficient method, enabling fishers to catch and freeze large quantities of tuna. These vessels can fish either by spotting free-swimming schools of tuna or by utilizing floating objects that attract fish, either natural or manmade objects like FADs. All floating objects – that’s any inanimate object, including vessels and large dead animals – attract mixed aggregations of fish and improve a vessel’s chances of catch.
When fishing on free-swimming schools of tuna, purse seine fishing has an average bycatch rate that is less than 1%. The bycatch rate for purse seiners that use FADs ranges from around 2% in the western and central Pacific Ocean to nearly 8% in the Atlantic Ocean.
According to a study commissioned by ISSF, purse seine vessels consume 368 liters of fuel in order to land 1 ton of tuna.