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Yellowfin tuna - Eastern Pacific
Marine Resource  Fact Sheet
Stock status report 2019
Yellowfin tuna - Eastern Pacific
Fact Sheet Citation  
Yellow fin, Eastern Pacific Ocean (EPO)
Owned byInter-American Tropical Tuna Commission (IATTC) – More
Related observationsLocate in inventorydisplay tree map
 
Species:
FAO Names: en - Yellowfin tuna, fr - Albacore, es - Rabil, ru - Тунец желтоперый
Geographic extent of Yellowfin tuna - Eastern Pacific
Main Descriptors
Considered a single stock: Yes        Spatial Scale: Regional
Reference year: 2018
 
 
Biological State and Trend
State & Trend Descriptors
PartnerFIRMS
Exploitation rateModerate fishing mortality, close to that corresponding to MSYModerate fishing mortalityGreen
Abundance levelIntermediate abundanceIntermediate abundance
FAO Categories
Exploitation stateFully exploited
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: Yes
Exploitation
 

The annual catches of yellowfin during 1989-2018 are shown in (Table A-1).

and,
Figure B-1: Total catches (retained catches plus discards) for the purse-seine fisheries, by set type (DEL, NOA, OBJ), and retained catches for the longline (LL) and other (OTR) fisheries, of yellowfin tuna in the eastern Pacific Ocean, 1975-2018. The purse-seine catches are adjusted to the species composition estimate obtained from sampling the catches. The 2018 data are preliminary.



The 2018 EPO catch of 239 thousand t is less than the average for the previous 5-year period (244 thousand t). In the WCPO, the catches of yellowfin reached a record high of 676 thousand t in 2017.

The annual retained catches of yellowfin in the EPO, by gear, during 1989-2018 are shown in Table A-2a. During 2003-2017 the annual retained purse-seine and pole-and-line catch averaged 233 thousand t (range: 167 to 384 thousand t). The preliminary estimate of the retained catch in 2018, 237 thousand t, is 13% greater than that of 2017, and 2% greater than the 2003-2017 average. On average, about 0.6% (range: 0.1 to 1.5%) of the total purse-seine catch of yellowfin was discarded at sea during 2003-2017 (Table A-2a). During 1990-2003, annual longline catches in the EPO averaged about 23 thousand t (range: 12 to 35 thousand t), or about 8% of the total retained catches of yellowfin. They then declined sharply, to an annual average of 10 thousand t (range: 8 to 13 thousand t), or about 4% of the total retained catches, during 2005-2017. Catches by other fisheries (recreational, gillnet, troll, artisanal, etc.), whether incidental or targeted, are shown in Table A-2a, under “Other gears” (OTR); during 2003-2017 they averaged about 2 thousand t.

See also fishery fact sheet:EPO Tunas and billfishes fishery
Total catches (retained catches plus discards) for the purse-seine fisheries, by set type (DEL, NOA, OBJ), and retained catches for the longline (LL) and other (OTR) fisheries, of yellowfin tuna in the eastern Pacific Ocean, 1975-2018. The purse-seine catches are adjusted to the species composition estimate obtained from sampling the catches. The 2018 data are preliminary.
Assessment
 
Assessment Model
Type:  Age-structured
An integrated statistical age-structured stock assessment model, Stock Synthesis

The model used for the current update assessment of yellowfin in the EPO (SAC-10-07) was unable to reconcile data that apparently carry contradictory signals about the status of the stock (SAC-10 INF-F). This needs to be resolved before the model can be used as a basis for management advice, and a workplan has been developed in preparation for the scheduled benchmark assessment in 2020. In the meantime, the staff developed data-based indicators to monitor the relative status of the stock (SAC-10-08).

For the full version of this analysis, see document SAC-10-08.


Assumption

Yellowfin are distributed across the Pacific Ocean, but the bulk of the catch is made in the eastern and western regions. Purse-seine catches in the vicinity of the western boundary of the EPO at 150oW are relatively low, but have been increasing, mainly in sets on floating objects (
Table A-1 Annual catches of yellowfin, skipjack, and bigeye tunas, by all types of gear combined, in the Pacific Ocean. The EPO totals for 1993-2018 include discards from purse-seine vessels with carrying capacities greater than 363 t.
  YFT SKJ BET Total
  EPO WCPO Total EPO WCPO Total EPO WCPO Total EPO WCPO Total
1989 299,436 348,104 647,540 98,921 787,708 886,629 72,994 98,489 171,483 471,351 1,234,301 1,705,652
1990 301,522 390,428 691,950 77,107 857,067 934,174 104,851 116,370 221,221 483,480 1,363,865 1,847,345
1991 265,970 416,609 682,579 65,890 1,077,398 1,143,288 109,121 99,354 208,475 440,981 1,593,361 2,034,342
1992 252,514 424,965 677,479 87,294 971,558 1,058,852 92,000 119,335 211,335 431,808 1,515,858 1,947,666
1993 256,199 365,631 621,830 100,434 926,617 1,027,051 82,843 103,733 186,576 439,476 1,395,981 1,835,457
1994 248,071 405,421 653,492 84,661 990,437 1,075,098 109,331 117,497 226,828 442,063 1,513,355 1,955,418
1995 244,639 409,174 653,813 150,661 1,020,852 1,171,513 108,210 100,642 208,852 503,510 1,530,668 2,034,178
1996 266,928 411,433 678,361 132,335 1,011,907 1,144,242 114,706 112,724 227,430 513,969 1,536,064 2,050,033
1997 277,575 493,038 770,613 188,285 906,376 1,094,661 122,274 158,380 280,654 588,134 1,557,794 2,145,928
1998 280,606 598,998 879,604 165,489 1,169,422 1,334,911 93,954 168,127 262,081 540,049 1,936,547 2,476,596
1999 304,638 512,991 817,629 291,249 1,047,417 1,338,666 93,078 150,842 243,920 688,965 1,711,250 2,400,215
2000 286,863 560,932 847,795 230,479 1,156,160 1,386,639 148,557 137,201 285,758 665,901 1,854,293 2,520,194
2001 425,008 527,859 952,867 157,676 1,080,053 1,237,729 130,546 137,859 268,405 713,230 1,745,771 2,459,001
2002 443,458 482,664 926,122 167,048 1,258,988 1,426,036 132,806 158,153 290,959 743,312 1,899,805 2,643,117
2003 415,933 540,331 956,264 300,470 1,252,996 1,553,466 115,175 128,596 243,771 831,578 1,921,923 2,753,501
2004 296,847 578,045 874,892 217,249 1,348,940 1,566,189 110,722 180,393 291,115 624,818 2,107,378 2,732,196
2005 286,492 547,082 833,574 283,453 1,397,441 1,680,894 110,514 143,482 253,996 680,459 2,088,005 2,768,464
2006 180,519 481,285 661,804 309,090 1,494,070 1,803,160 117,328 152,574 269,902 606,937 2,127,929 2,734,866
2007 182,141 512,270 694,411 216,324 1,647,760 1,864,084 94,260 138,656 232,916 492,725 2,298,686 2,791,411
2008 197,328 606,650 803,978 307,699 1,619,329 1,927,028 103,350 149,059 252,409 608,377 2,375,038 2,983,415
2009 250,413 540,660 791,073 239,408 1,784,286 2,023,694 109,255 147,666 256,921 599,076 2,472,612 3,071,688
2010 261,871 559,625 821,496 153,092 1,688,957 1,842,049 95,408 132,293 227,701 510,371 2,380,876 2,891,247
2011 216,720 520,937 737,657 283,509 1,534,944 1,818,453 89,460 154,391 243,851 589,689 2,210,270 2,799,959
2012 213,310 602,975 816,285 273,519 1,758,388 2,031,907 102,687 155,702 258,389 589,516 2,517,061 3,106,577
2013 231,170 548,716 779,886 284,043 1,835,068 2,119,111 86,029 143,156 229,185 601,909 2,526,993 3,128,902
2014 246,781 589,434 836,215 265,490 2,006,087 2,271,577 96,045 153,876 249,921 608,047 2,749,389 3,357,436
2015 260,433 573,292 833,725 334,066 1,793,172 2,127,238 104,737 135,457 240,194 685,201 2,502,807 3,188,008
2016 255,196 634,187 889,383 342,579 1,795,283 2,137,862 92,829 144,407 237,236 690,142 2,571,609 3,261,751
2017 224,551 676,183 900,734 327,624 1,626,589 1,954,213 102,550 122,630 225,180 637,397 2,425,402 3,062,799
2018 238,778 * 238,778 288,636 * 288,636 86,102 * 86,102 613,516 * 613,516



), (Table A-2a); (Figure A-1a and A-1b)


Figure A-1a: Average annual distributions of the purse-seine catches of yellowfin, by set type, 2013-2017. The sizes of the circles are proportional to the amounts of yellowfin caught in those 5° by 5° areas.
Figure A-1b: Annual distributions of the purse-seine catches of yellowfin, by set type, 2018. The sizes of the circles are proportional to the amounts of yellowfin caught in those 5° by 5° areas.

The majority of the catch in the eastern Pacific Ocean (EPO) is taken in purse-seine sets associated with dolphins and floating objects (Figure B-1).
Figure B-1: Total catches (retained catches plus discards) for the purse-seine fisheries, by set type (DEL, NOA, OBJ), and retained catches for the longline (LL) and other (OTR) fisheries, of yellowfin tuna in the eastern Pacific Ocean, 1975-2018. The purse-seine catches are adjusted to the species composition estimate obtained from sampling the catches. The 2018 data are preliminary.

Tagging studies of yellowfin throughout the Pacific indicate that they tend to stay within 1,800 km of their release positions. This regional fidelity, along with the geographic variation in phenotypic and genotypic characteristics of yellowfin shown in some studies, suggests that there might be multiple stocks of yellowfin in the EPO and throughout the Pacific Ocean. However, movement rates between these putative stocks, as well as across the 150°W meridian, cannot be estimated with currently-available tagging data.
Data

Both the number of floating-object sets and the number of days fished in such sets generally increased during the entire period, and in 2018 were at and above, respectively, the upper reference level (Figures B-2 and B-3).
Figure B-2: Indicators of total effort in the EPO, based on purse-seine data (closure-adjusted capacity, 2000-2018; annual total number of sets, by type, 1987-2018) and based on longline data for 1975-2017 (effort reported by all fleets, in total numbers of hooks; proportion of the effort corresponding to Japan). The dashed horizontal lines are the 5th and 95th percentiles, the solid horizontal line is the median.

The reported longline effort peaked twice, around 1990 and in the early 2000s, and has increased again since 2010; it is currently above the median as shown in Figure B-2.

Prior to 2000, the Japanese fleet, whose index of abundance and length-frequency data are used to represent all the longline fleets, exerted 50% or more of the total longline effort in the EPO, but this proportion has declined continuously since then, and in 2017 was 14%.

Because the Japanese proportion of the total longline effort has been declining, the representativeness of the standardized CPUE and average length for the Japanese fleet, used to represent all the longline fisheries for yellowfin in the EPO, needs to be further investigated (see also WSBET-02 Meeting)


Figure B-3: Indicators (catch (t); effort (days fished); CPUE (t/day fished); average length (cm)) for the yellowfin tuna stock in the eastern Pacific Ocean, from purse-seine fisheries on floating objects (OBJ).

The indicators for three of the purse-seine fisheries on floating objects (OBJ-S, OBJ-C, and OBJ-N) as shown in Figure B-3 are very similar, with catch, effort, and mean length increasing in the 1990s as the floating-object fishery expanded. The catch and effort of these fisheries are currently at or above the upper reference value, except for the OBJ-N effort, which fell substantially in 2018.

The catches of the unassociated (NOA) purse-seine fisheries have been between the lower reference level and the median since 2008, and are at the lower reference level in 2018 for NOA-N and slightly below the median for NOA-S as shown in Figure B-4.
Figure B-4: Indicators (catch (t); effort (days fished); CPUE (t/day fished); average length (cm)) for the yellowfin tuna stock in the eastern Pacific Ocean, from the unassociated (NOA) and dolphin-associated (DEL) fisheries.

The lower catches in recent years coincide with the lower effort for NOA-N, but not for NOA-S, where the effort has been around the median.

The indicators for the northern and inshore purse-seine fisheries associated with dolphins (DEL-N and DEL-I) are similar, and have generally fluctuated around the median, with low catch, effort, and CPUE in the late 1970s and early 1980s.

They are currently around the median, except for the DEL-I catch and effort, which are below the median, and the average length, which in DEL-I is at the lower reference level, but in DEL-N, where it has been high since at least 2010, it is above the upper reference level. The DEL-S fishery has much lower catch and effort, with a peak in catch in the early 2000s. The recent CPDFs (catch per days fished) have fluctuated at or above the median for NOA-N, and at or below the median level for NOA-S.

The catches of both longline fisheries (LL-N and LL-S) have shown some increase in recent years, mostly due to increased effort, from the expansion of the Chinese fleet in the EPO (
Table A-3a Catches of yellowfin tuna by purse-seine vessels in the EPO, by vessel flag. The data have been adjusted to the species composition estimate, and are preliminary.
  COL CRI ECU EU MEX NIC PAN PER SLV USA VEN VUT C + OTR1 Total
1989 - C 17,588 C 116,928 - 10,557 1,724 C 73,688 42,944 C 14,567 277,996
1990 C C 16,279 C 115,898 - 6,391 C - 50,790 47,490 22,208 4,197 263,253
1991 C - 15,011 C 115,107 - 1,731 C - 18,751 45,345 29,687 5,625 231,257
1992 C - 12,119 C 118,455 - 3,380 45 - 16,961 44,336 27,406 5,419 228,121
1993 3,863 - 18,094 C 101,792 - 5,671 - - 14,055 43,522 24,936 7,559 219,492
1994 7,533 - 18,365 C 99,618 - 3,259 - - 8,080 41,500 25,729 4,324 208,408
1995 8,829 C 17,044 C 108,749 - 1,714 - - 5,069 47,804 22,220 4,005 215,434
1996 9,855 C 17,125 C 119,878 - 3,084 - - 6,948 62,846 10,549 8,322 238,607
1997 9,402 - 18,697 C 120,761 - 4,807 - - 5,826 57,881 20,701 6,803 244,878
1998 15,592 - 36,201 5,449 106,840 - 3,330 - C 2,776 61,425 17,342 5,004 253,959
1999 13,267 - 53,683 8,322 114,545 C 5,782 - C 3,400 55,443 16,476 11,002 281,920
2000 6,138 - 35,492 10,318 101,662 C 5,796 - - 4,374 67,672 8,247 13,563 253,262
2001 12,950 - 55,347 18,448 130,087 C 9,552 - C 5,670 108,974 10,729 32,180 383,937
2002 17,574 - 32,512 16,990 152,864 C 15,719 C 7,412 7,382 123,264 7,502 31,068 412,287
2003 9,770 - 34,271 12,281 172,807 - 16,591 C C 3,601 96,914 9,334 27,710 383,279
2004 C - 40,886 13,622 91,442 C 33,563 - C C 39,094 7,371 46,577 272,555
2005 C - 40,596 11,947 110,898 4,838 33,393 - 6,470 C 28,684 C 31,276 268,102
2006 C - 26,049 8,409 69,449 4,236 22,521 - C C 13,286 C 22,679 166,629
2007 C - 19,749 2,631 65,091 3,917 26,024 - C C 20,097 C 32,507 170,016
2008 C - 18,463 3,023 84,462 4,374 26,993 C C C 17,692 C 30,050 185,057
2009 C - 18,167 7,864 99,785 6,686 35,228 C C C 25,298 C 43,729 236,757
2010 20,493 - 34,764 2,820 104,969 9,422 34,538 C C - 21,244 C 22,758 251,008
2011 18,643 - 32,946 1,072 99,812 7,781 18,607 - C C 18,712 C 9,278 206,851
2012 20,924 - 29,485 1,065 93,323 7,541 15,932 - C C 23,408 C 6,339 198,017
2013 16,476 - 27,655 511 114,706 8,261 18,301 C C - 24,896 C 7,381 218,187
2014 17,185 - 37,546 760 120,980 8,100 19,349 C C 1,105 23,025 - 6,016 234,066
2015 17,270 - 50,153 C 106,171 6,876 26,558 783 C 3,212 30,428 - 4,276 245,727
2016 19,280 - 59,280 C 93,928 11,047 23,249 1,647 C 4,578 23,812 - 5,298 242,118
2017 15,102 - 55,685 C 80,862 9,345 19,915 3,348 C 6,497 16,806 - 3,372 210,932
2018 21,772 - 57,484 C 101,511 7,698 22,419 1,466 C 3,298 18,291 - 3,368 237,307
1Includes: BLZ, BOL, CHN, GTM, HND, UNK



), (Table A-3b).

The standardized CPUE for LL-N has been above the median in recent years, while that for LL-S has been around the lower reference level since 2010, coinciding with a steady increase in the average length of the fish in the catches as shown in Figure B-6.
Figure B-6: Indicators for the yellowfin tuna stock in the eastern Pacific Ocean, from longline fisheries.




Results
Assessment Indicator
Type: Recruitment
Results
Assessment Indicator
Type: Average length

The indicators for the OBJ-I fishery do not show any major trends, but have wide fluctuations and are currently around the median. The average length for all fisheries is currently around the median. (Figure B-3).
Figure B-3: Indicators (catch (t); effort (days fished); CPUE (t/day fished); average length (cm)) for the yellowfin tuna stock in the eastern Pacific Ocean, from purse-seine fisheries on floating objects (OBJ).

The average length for NOA-N has been fluctuating between the lower and the upper reference levels, while NOA-S has fluctuated between the median and the upper reference level in the last ten years.The average length in the DEL-S fishery increased from almost the lower reference level to the upper reference level in during 2010-2017, with a decrease towards the median in 2018 as shown in Figure B-4.
Figure B-4: Indicators (catch (t); effort (days fished); CPUE (t/day fished); average length (cm)) for the yellowfin tuna stock in the eastern Pacific Ocean, from the unassociated (NOA) and dolphin-associated (DEL) fisheries.


Results
Assessment Indicator
Type: Abundance

In contrast to the nominal CPDF, the spatiotemporal model-derived indices of abundance for the DEL-N and DEL-I areas have been fluctuating below the median since 2006, and in 2017 reached some of their lowest values, with a slight increase in 2018 as shown in Figure B-5.
Figure B-5: Indicators for the yellowfin tuna stock in the eastern Pacific Ocean: nominal catch per days fished (CPDF) and spatiotemporal model-derived indices of abundance.

These spatiotemporal indices take into account the “patchiness” of fisheries data (fishers tend to fish where there are good catches), the area weighting, and increase in efficiency of purse-seine vessels in the recent years, but not changes in the length composition of the catches.

Indicators of relative abundance, such as the standardized CPUE for LL-S and the spatiotemporal indices for DEL-N and DEL-I, have been at low levels since 2010 (LL-S) or earlier (DEL-N, DEL-I), which might indicate a low population size for yellowfin in the EPO, and may be of concern, especially given the steady increase of the number of floating-object sets. However, a decrease in population size is not consistent with the increase in the average length of the fish in the catch observed in recent years in several fisheries (LL-S, DEL-N, NOA-S, DEL-S). This increase may indicate that older, larger fish are being caught because recent strong cohorts are being harvested (DEL-N, DEL-S); alternatively, it may indicate lower natural or fishing mortality, discarding/high-grading of catches, or changes in selectivity and/or availability, which can hinder the interpretation of CPUE indicators as indices of abundance. Because the average length increased in several fisheries simultaneously, it may be an indication that a change in the population may be happening, instead of, or in addition to, changes in selectivity and/or availability.

In conclusion, it is not clear from the indicators whether yellowfin abundance is reduced, or the fisheries are changing. Several hypotheses will be explored in preparation for the benchmark assessment in 2020 (SAC-10-01, SAC-10-INF-F.)




Source of information
 
Inter-American Tropical Tuna Commission (IATTC).  “"Tuna fishery, stocks, and ecosystem in the eastern Pacific Ocean in 2018. Inter-American Tropical Tuna Commission." Fishery Status Report. IATTC 2019.”.
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