It has been well recognized for many years that control of fishing capacity is essential for the management of tuna resources (fishing capacity here does not refer to fish carrying capacity but to the fleet potential to harvest tuna in relation to the current stock level). It was more than a decade ago, when FAO adopted the International Plan of Action for fishing capacity. Since then, distant water longline fishery has cut down fleet size substantially. On the contrary, the size of purse seine fleet has kept expanding.
These trends reflect the economy of each fleet. The longliners are now operating at the margins of economic breakpoint, due to the reduction of abundance of large tuna, as a result of other fisheries’ preceding catch of juveniles.
Therefore the only choice left for the longliners was the reduction of fleet size. Distant-water longline operators in the world established an organization, OPRT, in order to eliminate IUU fishing vessels, and reduce the fishing fleet size. The major actions taken were the establishment of a world registration of active vessels, and buy-back and scrap policy at the cost of vessel-owners which remained active. This fleet reduction has made adoption of regulatory measures for the longliners easier and improved the fishing economy of longliners.
Unfortunately, this reduction of longline fleet was offset by an expansion of purse seiners. We should understand that the fishing capacity of a fleet increases constantly with an improvement in fishing technology, even if the fish-carrying capacity or number of vessels stays constant. The annual rate of increase in fishing efficiency of purse seiners is far more than that of longliners, while longliners’ efficiency has been even reduced by various restrictions set on them for the mitigation of by-catches.
In the Eastern Pacific Ocean, the so-called vessel registry system, which intended to cap the total volume of the purse seine fish hold has been in effect. Scientists estimated that current fishing capacity of the purse seiners is at least in excess by 30% of the appropriate level to harvest tuna sustainably in that area. Besides, this registry system is experiencing many difficulties in maintaining the volume of the fish hold. The consequences were the increase of fishing capacity, which makes the adoption of proper fish regulations harder, and in turn has an adverse effect on the catch rate and profit of fishers.
The control of purse seine fishing capacity is an urgent global task for the world tuna management. (This is an extract of the portion of purse seine capacity from an article covering fishing capacity.)