Fisheries and Resources Monitoring System

Pacific bluefin tuna - Eastern Pacific (EPO)
Fact Sheet Title  Fact Sheet
Stock status report 2022
Pacific bluefin tuna - Eastern Pacific (EPO)
Fact Sheet Citation  
Owned byInter-American Tropical Tuna Commission (IATTC) – ownership
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Species List:
Species Ref: 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
ident Block Pacific bluefin tuna - Eastern Pacific (EPO)
Aq Res
Biological Stock: No         Value: Regional
Management unit: Yes        Reference year: 2021
Aq Res State Trend
Aq Res State Trend
Aq Res State Trend Aq Res State Trend
Aq Res State TrendModerate fishing mortalityModerate fishing mortalityGreen
Aq Res State TrendIntermediate abundanceIntermediate abundance
Aq Res State Trend
Aq Res State TrendRecovering
Habitat Bio
Bottom Type: Unspecified.   Depth Zone: Abyssal ( >1000m).   Horizontal Dist: Oceanic.   Vertical Dist: Pelagic.  

Geo Dist
Geo Dist: Highly migratory

Water Area Overview
Spatial Scale: Regional

Water Area Overview
Aq Res Struct
Biological Stock: No

Tagging studies have shown that there is exchange of Pacific bluefin between the eastern and western Pacific Ocean. Larval, post larval, 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).

The catches of Pacific bluefin in the entire Pacific Ocean, by gear, as reported by the vessels’ flag governments to the International Scientific Committee for Tuna and Tuna-like Species in the North Pacific Ocean (ISC), are shown in Table A-5a (Table A-5a).

The catches of Pacific bluefin in the EPO during 1992-2021, by gear, are shown in Table A-2a (Table A-2a). In recent years, purse-seine vessels account for over 91% of the annual catch. The 1992-2020 average EPO retained catch is 3.8 thousand t (range: 600 t to 9.9 thousand t); the preliminary estimate for 2021 is 3.1 thousand t (Table A-2a).

Catches of Pacific bluefin by recreational gear in the EPO are reported in numbers of individual fish caught, whereas all other gears report catches in weight; the data are therefore converted to weights for inclusion in the EPO catch totals. The original catch data for 1992-2021, in numbers of fish, are presented in Table A-5b (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 in the EPO during every month of the year, but most of the fish are taken from May through October.

Bluefin are exploited by various gears in the WPO from Taiwan to Hokkaido, Japan. Age-0 fish, about 15 to 30 cm in length, are caught by the Japanese troll fishery 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 in troll fisheries 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. Additionally, 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. Then, after crossing the ocean, they 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 recruitment, and thus the portions of the juvenile fish there that migrate to the EPO, as well as 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
EPO Tunas and billfishes fishery: Retained catches of Pacific bluefin tuna, by gear, 1952-2020. GN: gillnet; LL: longline; LX: hook and line; OTR: other; PS: purse seine.
Bio Assess

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, by gear, 1952-2020. GN: gillnet; LL: longline; LX: hook and line; OTR: other; PS: purse seine.

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 estimated impact of the fisheries on the bluefin population for the entire time period modeled (1952-2018) is substantial. The WPO fisheries have had a greater impact than the EPO fisheries, and their impact increased starting in 1980s only leveling off in 2000s (Figure E-2).
Figure E-2: Estimates of the impact on the Pacific bluefin tuna population of fisheries in the EPO and in the WPO (upper panel). The dashed line represents the estimated hypothetical unfished spawning biomass, and the solid line the estimated actual spawning biomass. The shaded areas indicate the impact attributed to each fishery. The lower panel presents the proportion of impact attributed to the EPO and WPO. (Figure from the draft Executive Summary of ISC 2022 stock assessment; subject to change and approval by the ISC Plenary.)

The WPO fisheries have had a greater impact than the EPO fisheries, and their impact increased starting in 1980s only leveling off in 2000s.

A benchmark 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 2022. The assessment was conducted with Stock Synthesis 3, an integrated statistical age-structured stock assessment model. The base-case model results show that: (1) spawning stock biomass (SSB) fluctuated throughout the assessment period (fishing years 1952-2020); (2) the SSB steadily declined from 1996 to 2010; (3) the SSB has increased since 2011 resulting in the 2020 SSB being back to the 1996 level; (4) total biomass after 2011 continued to increase with an increase in young fish, creating the 2nd highest biomass peak in the assessed history in 2020; (5) fishing mortality (F%SPR), which declined to a level producing about 1% of SPR in 2004-2009, returned to a level producing 30.7% of SPR in 2018-2020; and (6) SSB in 2020 was 10.2% of SSBF=0, an increase from the 5.6% of SSBF=0 estimated for 2018 in the 2020 assessment (2018 was the last year of the 2020 assessment). Based on the model diagnostics, the estimated biomass trend for the last 40 years is considered robust although SSB prior to the 1980s is uncertain due to data limitations. The SSB in 2020 was estimated to be around 65,464 t, which is a 30,000 t increase from 2018 according to the base-case model. An increase of young fish (0-2 years old) biomass was observed in 2016-2020, likely resulting from low fishing mortality on those fish and is expected to accelerate the recovery of SSB in the future even further. Historical recruitment estimates have fluctuated since 1952 without an apparent trend. A substantial decrease in estimated F is observed in ages 0-2 in 2018-2020 relative to the previous years (note that stricter management measures in WCPFC and IATTC have been in place since 2015).

The point estimate of the 2020 SSB was 10.2% of the SSB in the absence of fishing (10.2%SSBF=0), and the recent (2018-2020) fishing mortality (F) corresponds to F30.7%SPR. Because the harvest strategy includes catch limits, fishing mortality is expected to decline, i.e., Fx%SPR will increase as biomass increases. No biomass-based limit or target reference points have been adopted to evaluate whether Pacific bluefin is overfished. However, the stock is overfished relative to common target reference points, but does not exceed the IATTC limit reference point used for tropical tunas. Also, no fishing intensity-based limit or target reference points have been adopted to evaluate whether overfishing of Pacific bluefin is occurring.

Resolution C-18-02 states that the Commission recognizes that the management objective of the IATTC is to maintain or restore fish stocks at levels capable of producing MSY, and shall implement a provisional rebuilding plan by adopting an 1) initial (first) rebuilding target of SSBmed, 1952-2014 (the median point estimate for 1952-2014) to be achieved by 2024 with at least 60% probability and 2) a second rebuilding target of 20%SSBF=0 to be achieved within 10 years of reaching the initial rebuilding target or by 2034, whichever is earlier, with at least 60% probability. The IATTC has adopted resolutions to restrict the catch of bluefin tuna in the EPO (e.g. C-16-08, C-18-01, C-20-02, C-21-05). Resolution C-21-05 states that during 2021-2022, in the IATTC Convention Area, combined total commercial catches of Pacific bluefin tuna by all CPCs shall not exceed the catch limit of 7,295 metric tons. During 2023-2024, in the IATTC Convention Area, combined total commercial catches of Pacific bluefin tuna by all CPCs shall not exceed the catch limit of 7,990 metric tons. Resolution C-18-02 also requires that no later than the IATTC meeting in 2020, taking into account the outcomes of the Joint IATTC-WCPFC NC Working Group, the Commission shall consider and develop candidate reference points and harvest control rules. These candidate reference points and harvest control rules will be forwarded to the Joint IATTC-WCPFC NC Working Group and ISC for consideration and potential inclusion in a management strategy evaluation to be completed by the ISC. This task has still not been accomplished.

The 2020 SSB was above the initial rebuilding target but remains below the second rebuilding target adopted by the WCPFC and IATTC. However, stock recovery is occurring at a faster rate than anticipated by managers when the Harvest Strategy to foster rebuilding were implemented in 2014. Projections based on the base-case model under several harvest scenarios and time schedules as requested by the RFMOs, including the harvest strategy proposed at the Joint WCPFC NC-IATTC WG meeting. Under all examined scenarios the second rebuilding target is reached, and the risk of SSB falling below the historical lowest SSB at least once in 10 years is negligible. Some scenarios had the future impact ratios between WPO and EPO specified by the RFMOs and were tuned to achieve the second rebuilding target with 60% probability, and result in larger catch increases.
Management unit: Yes
Inter-American Tropical Tuna Commission (IATTC). “Report on tuna fishery, stocks, and ecosystem in the Eastern Pacific Ocean in 2021. Inter-American Tropical Tuna Commission. Fishery Status Report. IATTC 2022.” Click to open,-stocks,-and-ecosystem-in-the-Eastern-Pacific-Ocean-in-2021-(1).pdf
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