The Pacific Bluefin Tuna Working Group (PBFWG) was established since the foundation of ISC. First formal stock assessment
was conducted in May 2008. The working group is focusing the preparation of the next full stock assessment,
as ISC scheduled the next stock assessment of the stock in 2012.
Pacific Bluefin Tuna (Thunnus orientalis) --- North Pacific
◊ Biological Profile
This species is widely distributed in the North Pacific Ocean and occured in the Southern Hemisphere with limited amounts.
The juveniles have trans-Pacific migration analyzed by archival tags. Migration after spawning to the Southern Hemisphere has
been also reported by pop-up tags.
✽ Life span : More than 20 years
✽ Start of maturity : About age-3 (100cm)
✽ Spawning area and season:
North Western Pacific Ocean,
May to June, and late June to August
Distribution and spawning area
of Pacific bluefin tuna.
◊ Fisheries for Pacific Bluefin Tuna in the North Pacific Ocean
Historical catch has been fluctuated in the range of 9,000~40,000t. Catch in 2009 was 20,000t (recent 5years average: 23,000t, historical average : 23,000t). Japan usually catches more than half of total catch, while until 1980s US also caught substantial amount. After 2000, Mexico and Korea increased their catch. By gear category purse seine catch always occupies more than half of total catch.
|Main fisheries landing Pacific bluefin tuna by fishing gear and country.
Annual lanfings of Pacific bluefin tuna from ISC members in the North Pacific Ocean,
◊ Stock Status (From 2012 Intercessional Plenary Meeting)
Based on the reference point ratios, overfishing is occurring (see F-based ratios in Table 1) and the stock is heavily overfished (see depletion ratios in Table 1). Model estimates of 2010 spawning stock biomass (SSB) are at or near their lowest level and SSB has been declining for over a decade; however, there is no evidence of reduced recruitment.
Table 1. Computed F-based biological reference points (BRPs; F max, Fmed, and F20% ) for Pacific bluefin tuna relative to F2002-2004 and F2007-2009, estimated depletion rate (ratio of SSB in 2010 relative to unfished SSB), and estimated SSB (mt) in year 2010 for 20 model configurations (Runs). Run 2 is highlighted as it represents the base case model for the PBF stock assessment. F-ratio based BRP values less than 1 indicate overfishing.
◊ Conservation Advice (From 2012 Intercessional Plenary Meeting)
The current (2010) PBF biomass level is near historically low biomass levels and experiencing high exploitation levels above all biological reference points (BRPs) commonly used by fisheries managers. Based on projection results, extending the status quo (2007-2009) fishing levels is unlikely to improve the stock condition.
Recently implemented WCPFC (entered into force in 2011) and IATTC (entered into force in 2012) conservation and management measures combined with additional Japanese voluntary domestic regulations aimed at reducing mortality, if properly implemented and enforced, are expected to contribute to improvements in PBF stock status. Based on those findings, it should be noted that implementation of catch limits is particularly effective in increasing future SSB when strong recruitment occurs. It is also important to note that if recruitment is less favorable, a reduction of F could be more effective than catch limits to reduce the risk of the stock declining.
The ISC requires advice from the WCPFC regarding which reference point managers prefer so that it can provide the most useful scientific advice. Until which time a decision is rendered, the ISC will continue to provide a suite of potential biological reference points for managers to consider.
Latest Stock Assessment
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Working Group Reports and Working Papers
⇒ Honolulu, USA (2004)
⇒ Shimizu, Japan (January, 2006)
⇒ Shimizu, Japan (April, 2007)
⇒ Busan, Korea (July, 2007)
⇒ Shimizu, Japan (December, 2007)
⇒ Shimizu, Japan (May, 2008)
⇒ Ishigaki, Japan (December, 2008)
⇒ Kaohsiung, Chinese-Taipei (July, 2009)
⇒ Nanaimo, Canada (July, 2010)
⇒ Shimizu, Japan (January, 2011)
⇒ La Jolla, USA (January, 2012)
⇒ Shimizu, Japan (May, 2012)
⇒ Honolulu, USA (November, 2012)
Working Group Chair