The International Seafood Sustainability Foundation (ISSF) -- a coalition of scientists, the tuna industry and World Wildlife Fund for Nature -- says there has been a 3% increase in the number of purse seine vessels worldwide since 2017. 

ISSF has issued a 'snapshot' of the world's tuna purse seine fleet, which shows there were at least 1,871 purse seiners fishing for tuna worldwide as of June 2018, up from 1,815 in 2017.

"Having an accurate estimate of active vessels is critical for managing tuna fishing capacity regionally as well as globally -- and preventing overfishing," said ISSF, adding that purse seine vessels account for over 60% of the world’s tuna catch. 

Around 673 (down from 685 last year) are defined as large-scale vessels targeting tropical tunas, with a combined fishing capacity of over 860,000 cubic meters. 507 of those large-scale vessels are registered on the ISSF ProActive Vessel Register (PVR), which represent 75% in number and 82% in fish hold volume.

About 25% of the 673 large-scale vessels are authorized to fish in more than one region governed by a regional fisheries management organization (RFMO).

The number of vessels with registered International Maritime Organization (IMO) numbers has also grown steadily and is now 60% overall for all gears combined; nearly 100% of the purse seine vessels listed on the ISSF PVR have IMO numbers. ISSF has long recommended in its RFMO advocacy positions and in conservation measures 4.1 and 4.2 that vessels obtain IMO numbers, identifiers that do not change even if the vessel ownership, national registration, or name changes. Unique vessel identifiers like IMO numbers are an important tool to combat illegal, unreported and unregulated fishing, it said. 

To provide an annual updated best estimate, ISSF combs through and aggregates information from the five tuna RFMOs and other sources. "Although purse seine vessels account for over 60% of the world’s tuna catch, the exact number of authorized purse seine vessels is only known by searching multiple databases," said ISSF