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Is skipjack resource in the Western and Central Pacific sustainable?

–Fisheries Research Agency’s report on the Status of International Resources in FY2012″—

Japan’s Fisheries Research Agency (FRA) recently published its fiscal 2012 (April 2012-March 2013) report on “the Status of International Resources,” in which it summarized the latest stock level, trend and management measures concerning 41 fishery resources including tunas which require international management. Our interest goes to tuna species in the Western and Central Pacific Ocean (WCPO). Will the skipjack, which has shown a rapid increase of catch volume in recent years, be able to sustain under the ever increasing fishing pressures? What will happen to the state of bigeye tuna, for which overfishing is taking place? In what follows, we present an excerpt of the portions of the report pertaining to those tuna species, together with bluefin and southern bluefin tunas–the two species whose stock levels were assessed as being at low levels.

WCPO skipjack
The overall catch of skipjack in the WCPO in 2011 stood at 1,557,000 tons, accounting for 87% of the total catch in the entire Pacific at 1.87 million tons. By type of fishing method, the catch by purse-seine fishing accounted for 77% (preliminary figures), with that of pole-and-line fishery standing at about 13% and that of the remaining fisheries at 10%.
The catch volume in the WCPO, which had stayed at around 400,000 tons by the 1970s, increased to nearly one million tons in the 1990s, further rising to 1.2 million tons in 2002 and reaching 1.8 million tons in 2009. In 2011, though, the catch receded to 1.56 million tons. At present, the stock is being caught at a medium level, with fishing mortality rate staying at a sustainable level. However, high-level catch of skipjack in the tropical area is causing contraction in the distribution of its stock.
Amid drastic changes in the fishing mortality rates and stock indexes related to maximum sustainable yield (MSY) in recent years, the increasing trend in fishing effort should be closely monitored. Further increase in the purse-seine fishing efforts will allow only minimal increase in the catch from the long-term viewpoint but will also cause increase in the fishing mortality of bigeye and yellowfin. This aspect should be duly considered in the management of overall fishing efforts in the WCPO.

WCPO bigeye tuna
The catch of bigeye in the Pacific increased at a gradual pace from around 120,000 tons in early 1980s, with the catch staying at around 250,000 tons since 2000. The catch of the Pacific bigeye in 2011 was 235,266 tons, the lowest level in the past decade. Of this amount, the catch in the WCPO accounted for 159,479 tons (or about 68% of the catch in the entire Pacific). The MSY of bigeye in the WCPO is estimated at 74,993 tons, while the catch in recent years largely exceeded that level.
It should be concluded that, even assuming that the recruitment has been high in recent years, the recent catch level cannot be sustained for a long period of time. The Western and Central Pacific Fisheries Commission (WCPFC) decided to develop within 2013 a plan to dissolve overfishing and recover the stock in the five year period from 2013 to 2017.

Pacific bluefin tuna
The catch of this species in the recent five years stayed between about 18,000 tons and 25,000 tons. The stock is on a declining trend. The parent biomass in 2010 is close to the lowest level vis-a-vis the 1952-2010 biomass. There is expectation that the stock will increase in a medium- and long-term range if the management measures of relevant regional fisheries management organizations–WCPFC and the Inter-American Tropical Tuna Commission (IATTC)– are strictly implemented.

Western Atlantic bluefin tuna
The world’s catch of this species in recent years stands between 1,600 tons and 2,000 tons. The stock trend indicates that the parent biomass is at a low level but tends to increase. The number of recruitment has been stable at a low level. If the International Commission for the Conservation of Atlantic Tunas (ICCAT) maintains the quota of 1,750 tons, which it adopted at its 2012 annual meeting, the 2003 excellent year class will support the parent biomass, providing a prospect for the increase of the stock in the future.

Southern bluefin tuna
The world’s catch of this species in recent years stands between 9,296 tons and 11,395 tons. The parent biomass remained unchanged in recent years. The number of immature fish is increasing and the possibility for future increase of parent biomass is high.