Biological State and Trend
Habitat and Biology
Bottom type: Unspecified. Depth zone: Abyssal ( >1000m). Horizontal distribution: Oceanic. Vertical distribution: Pelagic.
Jurisdictional distribution: Highly migratory
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, 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 EPO during 1986-2015, 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 2000-2014. During this period the annual retained catch of bluefin in the EPO by purse-seine vessels averaged 4.7 thousand t (range 1.2 to 9.9 thousand t). The preliminary estimate of the retained purse-seine catch of bluefin in 2015, 3.2 thousand t, is less than the average for 2000-2014 (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 1986-2015, 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 off Baja California and California, within about 100 nautical miles of the coast, between about 23°N and 35°N. Ninety percent of the fish in the catch are 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 with SSTs 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
| Retained catches of Pacific bluefin tuna. |
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 2016. The assessment, conducted with Stock Synthesis 3, an integrated statistical age-structured stock assessment model, was a substantial improvement over the previous assessments. Long-term fluctuations in spawning stock biomass (SSB) occurred throughout the assessment period (1952-2014), and the SSB has been declining for more than a decade, with a leveling off in recent years; however, there is no evidence of reduced recruitment. Age-specific fishing mortality has increased by up to 96% (age 2) in the recent period (2011-2013) relative to the baseline period (2002-2004) used in recent WCPFC and IATTC conservation measures.
Estimated age-specific fishing mortalities for the stock in the recent period (2011-2013) relative to 2002-2004 (the base period for the current WCPFC conservation measures) show increases of 96, 4, 86, and 43% for ages 2, 3, 4 and 5, respectively, and decreases of 28 and 1% for ages 0 and 1. Although no target or limit reference points have been established for the Pacific bluefin stock, the current F (2011-2013 average) is above all target and limit biological reference points commonly used for management. The current (2014) Pacific bluefin SSB level is near historic low levels, and the ratio of SSB in 2014 relative to unfished SSB is low.
Stock projections of spawning biomass and catches of Pacific bluefin tuna from 2015 to 2034 were conducted assuming alternative harvest scenarios. Recent WCPFC and IATTC conservation and management measures, 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 IATTC staff conducted an alternative analysis to investigate the robustness of the assessment (document SAC-07-05d
). This analysis confirmed the results of the ISC update assessment
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 finding that the north Pacific bluefin stock is at very low levels and the fishing mortality is higher than any reasonable reference point is robust to model assumptions, and support previous findings. The stock is projected to rebuild under current management actions (ISC 2016, Executive summary). However, due to uncertainty in how recruitment is related to the spawning stock size and when recruitment might be impacted by the low spawning abundance level, there is concern over the low abundance of spawners. This is exacerbated by the limited number of cohorts that comprise the spawning biomass
The IATTC has adopted resolutions to restrict the catch of bluefin tuna in the EPO. Resolutions C-12-09
, and C-14-06
limit the commercial catches in the IATTC Convention Area by all CPCs to a total 10,000 metric tons during 2012-2013 fishing years , 5,000 metric tons in 2014, and a combined total of 6,600 metric tons during 2015-2016, respectively.