General life history
Pacific bluefin tuna can live for more than 20 years and mature at about 3 years (~40 in or 100 cm) (http://isc.ac.affrc.go.jp/working_groups/pacific_bluefin_tuna.html
Pacific bluefin tuna occur widely throughout the North Pacific Ocean and in the Southern Hemisphere in limited amounts.
Pacific bluefin tuna spawn to the south of Japan
from April to June and the larvae are carried first by the Kuroshio Current
north during the summer through winter of the first year. Ages 0-1 fish tend to
migrate north along the Japanese and Korean coasts in the summer and south in
the winter. Some juvenile fish are carried east along the North Pacific Gyre and
at 10-14 months these fish arrive off Baja California. After two to six years,
these fish return to the western North Pacific Ocean to spawn (Bayliff, 1980; Kitagawa et al., 2002; and others).
Historical catch of Pacific bluefin tuna has ranged from about 9,000 to 40,000 mt. The catch in 2010 was ~18,000 mt (recent 5-year average: 22,000 mt, historical average: 23,000 mt). Japan usually catches more than half the total catch. Until the early 1980s the US had a substantial catch ranging from 2,000-11,000 mt, mostly from purse-seines. In the last ten years, the US catch has ranged from about 60-700 mt,
with the majority of catch
attributed to recreational fishing. Starting around 2000, the Mexico and Korea catches increased.
The purse-seine catch
accounts more than half the total catch and since the early 1990s, the catch of
age-0 Pacific bluefin tuna has increased significantly
Figure 2. Historical annual catch of Pacific bluefin tuna by country, 1952-2011 (data in calendar year 1952 and 2010 are incomplete). From 2012 ISC Pacific Bluefin Tuna Stock Assessment Summary.
The International Committee for Tuna and Tuna-Like Species in the North Pacific Ocean (ISC) conducted a full assessment of the Pacific bluefin tuna stock in 2012 with data from 1952-2010 and concluded that the stock was experiencing overfishing and in an overfished condition. However, specific reference points have not been adopted for this stock.
- While the PBFWG did not agree on a single model for best determining the values of fishing intensity (F), the WG did find that F for 2007-09 (F2007-09) is above all calculated target and limit biological reference points (FMAX, FMED, F20%) in all models. FMSY is approximately equal to F20%. The average F for the 2007-09 fishing years (F2007-09) exceeded FMAX by 112% in what the PBFWG refered to as the “representative model run”.
- The 2010 spawning stock biomass (SSB2010 = 22,606 mt) was estimated to be about 3.6% of unfished SSB, or if there had been no fishing. Unfished SSB = 633,468 mt. The SSB2010 is also far below the SSB associated with maximum sustainable yield (SSBMSY = 124,498 mt). SSB has been declining for over a decade; however, there is no evidence of reduced recruitment. The PBFWG did not determine the ratio of SSB relative to other reference points.
NOAA Fisheries determined the stock to be experiencing overfishing in 2010.
Table 1. Computed F-based biological reference points (BRPs; Fmax, Fmed, and F20%) for Pacific bluefin tuna relative to F2002-2004 and F2007-2009, estimated depletion ratio (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 (e.g., the computed F-based BRP value of 0.54 for Run 1 Fmax (F2002-2004) implies that the average 2002-2004 levels of F exceed Fmax by 85% ((1÷0.54)*100)).
2012 ISC Conservation Advice
(from the 2012 Intercessional ISC Plenary Meeting)
The current (2010) PBF biomass level is near historically low biomass levels and experiencing high exploitation levels above all potential biological reference points (BRPs). 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 the recovery of the stock. 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.
Pacific bluefin tuna (Thunnus orientalis) is managed under the respective highly migratory species fisheries management plans for both the Pacific Fishery Management Council and the Western Pacific Fishery Management Council. Because the stock occurs Pacific-wide, stock assessments are conducted by the International Scientific Committee for Tuna and Tuna-like Species in the North Pacific Ocean (lSC) . The Western and Central Pacific Fishery Commission (WCPFC) is responsible for international management of the population.
Current conservation and management measures
In December 2012, the Western and Central Pacific Fishery Commission adopted a conservation and management measure (CMM) applicable to 2013 that was similar to a 2010 CMM. The 2012 CMM specifies that “total fishing effort by their vessels fishing for Pacific bluefin tuna in the area north of the 20 degrees north shall stay below the 2002-2004 levels for 2013, except for artisanal fisheries. Such measures shall include those to reduce catches of juveniles (age 0-3) below the 2002-2004 levels, except for Korea. Korea shall take necessary measures to regulate the catches of juveniles (age 0-3) by managing Korean fishery in accordance with this CMM. CCMs shall cooperate for this purpose.” For full text see; http://www.wcpfc.int/system/files/documents/meetings/northern-committee/8th-regular-session/delegation-proposals-and-papers/NC8-DP-01-%5BEXPLANATION-AND-IMPLEMENTATION-CMM-2010-04%5D.pdf
The WCPFC 2010 conservation and management measure (CMM 2010-04) specifies that “total fishing effort by their vessels fishing for Pacific bluefin tuna in the area north of the 20 degrees north shall stay below the 2002-2004 levels for 2011 and 2012, except for artisanal fisheries. Such measures shall include those to reduce catches of juveniles (age 0-3) below the 2002-2004 levels, except for Korea. Korea shall take necessary measures to regulate the catches of juveniles (age 0-3) by managing Korean fisheries in accordance with this CMM. CCMs shall cooperate for this purpose.” For full text see: http://www.wcpfc.int/system/files/documents/conservation-and-management-measures-and- resolutions/conservation-and-management-measures-/CMM%202010-04%20%5BPacific%20Bluefin%20Tuna%5D%2004112011.pdf
The 2012 Inter-American Tropical Tuna Commission (IATTC) Resolution (Resolution C-12-09) specifies that “1. In the IATTC Convention Area, the commercial catches of bluefin tuna by all the CPCs during the two-year period of 2012-2013 shall not exceed 10,000 metric tons; 2. The commercial catch of bluefin tuna in the commercial fishery in the Convention Area shall not exceed 5,600 metric tons during the year 2012; 3. Notwithstanding paragraphs 1 and 2, any CPC with a historical record of Eastern Pacific bluefin catches may take a commercial catch of up to 500 metric tons of Eastern Pacific bluefin tuna annually.” For full text see: http://www.iattc.org/PDFFiles2/Resolutions/C-12-09-Conservation-of-bluefin-tuna.pdf
Bayliff, W.H. 1980. Synopsis of biological data on the northern bluefin tuna, Thunnus thynnus (Linnaeus, 1758), in the Pacific Ocean. Spec. Rep. Inter-American Tropical Tuna Commission (2):261–93.
Kitagawa, T., H. Nakata, S. Kimura, T. Sugimoto and H. Yamada. 2002. Differences in vertical distribution and movement of Pacific bluefin tuna (Thunnus thynnus orientalis) among areas: the East China Sea, the Seaof Japan and the western North Pacific. Mar. Fresh. Res. 53:245-252.