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Pacific bluefin tuna - Eastern Pacific (EPO)
Marine Resource  Fact Sheet
Stock status report 2015
Pacific bluefin tuna - Eastern Pacific (EPO)
Fact Sheet Citation  
Owned byInter-American Tropical Tuna Commission (IATTC) – More
Related observationsLocate in inventorydisplay tree map
 
Species:
FAO Names: en - Pacific bluefin tuna, fr - Thon bleu du Pacifique, es - Atún aleta azul del Pacífico, ar - تونة أجنحة زرقاء للمحيط الهادئ, zh - 太平洋蓝鳍金枪鱼
Geographic extent of Pacific bluefin tuna - Eastern Pacific (EPO)
Main Descriptors
Considered a single stock: No        Spatial Scale: Regional
Management unit: Yes        Reference year: 2014
 
 
Biological State and Trend
State & Trend Descriptors
PartnerFIRMS
Exploitation rateHigh fishing mortalityHigh fishing mortality
Abundance levelLow abundanceLow abundance
FAO
Exploitation stateOverexploited
Habitat and Biology
Bottom type: Unspecified.   Depth zone: Abyssal ( >1000m).   Horizontal distribution: Oceanic.   Vertical distribution: Pelagic.  

Geographical Distribution
Jurisdictional distribution: Highly migratory

Water Area Overview
Spatial Scale: Regional

Geo References
Resource Structure
Considered a single stock: No


Tagging studies have shown that there is exchange of Pacific bluefin between the eastern and western Pacific Ocean. Larval, postlarval, and early juvenile bluefin have been caught in the western Pacific Ocean (WPO), but not in the eastern Pacific Ocean (EPO), so it is likely that there is a single stock of bluefin in the Pacific Ocean (or possibly two stocks in the Pacific Ocean, one spawning in the vicinity of Taiwan and the Philippines and the other spawning in the Sea of Japan).
Exploitation
 

The catches of Pacific bluefin in the EPO during 1985-2014, by gear, are shown in Table A-2a. Purse-seine and pole-and-line vessels accounted for over 94% of the total EPO retained catch during 1999-2013. During this period the annual retained catch of bluefin in the EPO by purse-seine vessels averaged 4.6 thousand t (range 1.2 to 9.9 thousand t). The preliminary estimate of the retained purse-seine catch of bluefin in 2014, 4.9 thousand t, is slightly greater than the average for 1999-2013 (Table A-2a), (Table A-2a (cont.)), (Table A-2a (cont.)).

The catches of Pacific Bluefin in the entire Pacific Ocean, by flag and gear, are shown in (Table A-5a). The data, which were obtained from the International Scientific Committee for Tuna and Tuna-like Species in the North Pacific Ocean (ISC), are reported by fishing nation or entity, regardless of the area of the Pacific Ocean in which the fish were caught.

Catches of Pacific bluefin by recreational gear in the EPO are reported in numbers of individual tuna caught, whereas all other gears report catch in weight (metric tons). These numbers are then converted to metric tons for inclusion in the EPO catch totals for all gears. The original catch data for 1985-2014, in numbers of fish, are presented in (Table A-5b).

Most of the commercial catches of bluefin in the EPO are taken by purse seiners. Nearly all of the purse-seine catches have been made west of Baja California and California, within about 100 nautical miles of the coast, between about 23°N and 35°N. Ninety percent of the catch is estimated to have been between about 60 and 100 cm in length, representing mostly fish 1 to 3 years of age. Aquaculture facilities for bluefin were established in Mexico in 1999, and some Mexican purse seiners began to direct their effort toward bluefin during that year. During recent years, most of the catches have been transported to holding pens, where the fish are held for fattening and later sale to sashimi markets. Lesser amounts of bluefin are caught by recreational, gillnet, and longline gear. Bluefin have been caught during every month of the year, but most of the fish are taken during May through October.

Bluefin are exploited by various gears in the WPO from Taiwan to Hokkaido. Age-0 fish about 15 to 30 cm in length are caught by trolling during July-October south of Shikoku Island and south of Shizuoka Prefecture. During November-April, age-0 fish about 35 to 60 cm in length are taken by trolling south and west of Kyushu Island. Age-1 and older fish are caught by purse seining, mostly during May-September, between about 30°-42°N and 140°-152°E. Bluefin of various sizes are also caught by traps, gillnets, and other gear, especially in the Sea of Japan. Small amounts of bluefin are caught near the southeastern coast of Japan by longlining. The Chinese Taipei small-scale longline fishery, which has expanded since 1996, takes bluefin tuna more than 180 cm in length from late April to June, when they are aggregated for spawning in the waters east of the northern Philippines and Taiwan.

The high-seas longline fisheries are directed mainly at tropical tunas, albacore, and billfishes, but small amounts of Pacific bluefin are caught by these fisheries. Small amounts of bluefin are also caught by Japanese pole-and-line vessels on the high seas.

Tagging studies, conducted with conventional and archival tags, have revealed a great deal of information about the life history of bluefin. Some fish apparently remain their entire lives in the WPO, while others migrate to the EPO. These migrations begin mostly during the first and second years of life. The first- and second-year migrants are exposed to various fisheries before beginning their journey to the EPO. The migrants, after crossing the ocean, are exposed to commercial and recreational fisheries off California and Baja California. Eventually, the survivors return to the WPO.

Bluefin more than about 50 cm in length are most often found in waters where the sea-surface temperatures (SSTs) are between 17° and 23°C. Fish 15 to 31 cm in length are found in the WPO in waters where the SSTs are between 24° and 29°C. The survival of larval and early juvenile bluefin is undoubtedly strongly influenced by the environment. Conditions in the WPO probably influence the portions of the juvenile fish there that migrate to the EPO, and also the timing of these migrations. Likewise, conditions in the EPO probably influence the timing of the return of the juvenile fish to the WPO.

See also fishery fact sheet:EPO Tunas and billfishes fishery
Retained catches of Pacific bluefin tuna.
Assessment
 
Overall Assessment Results

A full stock assessment was carried out by the Pacific Bluefin Working Group of the International Scientific Committee for Tuna and Tuna-like Species in the North Pacific Ocean (ISC) in 2012. The assessment was conducted with Stock Synthesis 3, an integrated statistical age-structured stock assessment model. Uncertainties were found in the assessment, and these were characterized through a series of 20 models, each with alternative data weightings and structural assumptions. While no single model scenario provided a good fit to all sources of data deemed reliable, long-term fluctuations in spawning stock biomass (SSB) occurred throughout the assessment period (1952-2011), and the SSB has been declining for more than a decade; however, there is no evidence of reduced recruitment. Age-specific fishing mortality has increased 8-41% in the recent period (2007-2009) relative to the baseline period (2002-2004) used in recent WCPFC and IATTC conservation measures.

A model configuration was chosen as the representative model to determine stock status and provide management advice, acknowledging that while it represents the general conclusions above, the model was unable to reconcile all key data sources. According to this model, estimated age-specific fishing mortalities for the stock in the recent period (2007-2009) relative to 2002-2004 (the base period for the current WCPFC conservation measures) show increases of 4, 17, 8, 41 and 10% for ages 0, 1, 2, 3 and 4+, respectively. Although no target or limit reference points have been established for the Pacific bluefin stock, the current F (2007-2009 average) is above all target and limit biological reference points commonly used for management. The current (2010) Pacific bluefin SSB level is near historic low levels, and the ratio of SSB in 2010 relative to unfished SSB is low.

Stock projections of spawning biomass and catches of Pacific bluefin tuna from 2011 to 2030 were conducted assuming alternative harvest scenarios. Recent WCPFC and IATTC conservation and management measures that entered into force in 2011 and 2012, respectively, combined with additional Japanese domestic regulations aimed at reducing mortality, if properly implemented and enforced, are expected to contribute to improvements in the stock status of Pacific bluefin tuna.

The ISC stock assessment was updated in 2014 using data up to and including 2013. The results of the updated assessment generally followed those of the previous assessment. The IATTC staff conducted an alternative analysis of the data outside the stock assesment model (document SAC-05-10a). This analysis confirmed the results of the ISC update assessment. The average recruitment for the last five years was estimated to be below the historical average. Estimated age-specific fishing mortalities on the stock during 2009-2011 relative to 2002-2004 increased for ages 0-6 and decreased for ages 7+. Although no target or limit reference points have been established for the Pacific bluefin stock under the auspices of the IATTC, the average fishing mortality during 2009-2011 exceeds all target and limit biological reference points (BRPs) commonly used by fisheries managers except one, and the depletion ratio (ratio of SSB in 2012 relative to unfished SSB ) is less than 6%. In summary, based on reference point ratios, overfishing is occurring and the stock is overfished. Based on projection results, the recently-adopted conservation measures, if continued in to the future, are expected to increase the SSB even if the recent low recruitment continues. A full stock assessment of bluefin tuna will be carried out by the ISC in March 2016.

The total catches of bluefin have fluctuated considerably during the last 50 years (Figure E-1).
Figure E-1: Retained catches of Pacific bluefin tuna.

The consecutive years of above-average catches (mid-1950s to mid-1960s) and below-average catches (early 1980s to early 1990s) could be due to consecutive years of above-average and below-average recruitments.

The IATTC has adopted resolutions to restrict the catch of bluefin tuna in the EPO. Resolutions C-12-09, C-13-02, and C-14-06 limit the commercial catches in the IATTC Convention Area by all CPCs to 10,000 metric tons during 2012-2013, 5,000 metric tons in 2014, and 6,600 during 2015-2016, respectively.
Management
Management unit: Yes
Source of information
 
Inter-American Tropical Tuna Commission (IATTC). “"Tunas and billfishes in the eastern Pacific Ocean in 2014. Inter-American Tropical Tuna Commission." Fishery Status Report. IATTC 2015.” Click to openhttp://www.iattc.org/PDFFiles2/FisheryStatusReports/FisheryStatusReport13.pdf
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