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Yellowfin tuna - Eastern Pacific
Marine Resource  Fact Sheet
Stock status report 2020
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: 2019
 
 
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 1990-2019 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, 1975-2019. The purse-seine catches are adjusted to the species composition estimate obtained from sampling the catches. The 2019 data are preliminary.



The 2019 EPO catch of 228 thousand t is 8% less than the average of 248 thousand t for the previous 5-year period (2014-2018). In the WCPO, the catches of yellowfin reached a record high of 692 thousand t in 2017..

The annual retained catches of yellowfin in the EPO, by gear, during 1990-2019 are shown in Table A-2a. Over the most recent 15-year period (2004-2018), the annual retained purse-seine and pole-and-line catches have fluctuated around an average of 224 thousand t (range: 167 to 274 thousand t). The preliminary estimate of the retained catch in 2019, 228 thousand t, is 5% less than that of 2018, but 2% greater than the 2004-2018 average. On average, about 0.5% (range: 0.1 to 1.1%) of the total purse-seine catch of yellowfin was discarded at sea during 2004-2018 (Table A-2a). During 1990-2004, 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 2005-2018. Catches by other fisheries (recreational, gillnet, troll, artisanal, etc.), whether incidental or targeted, are shown in Table A-2a, under “Other gears” (OTR); during 2005-2018 they averaged about 2 thousand t.

See also fishery fact sheet:EPO Tunas and billfishes fishery
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, 1975-2019. The purse-seine catches are adjusted to the species composition estimate obtained from sampling the catches. The 2019 data are preliminary.
Assessment
 
Assessment Model
Type:  Age-structured
An integrated statistical age-structured stock assessment model, Stock Synthesis

A workplan to improve the stock assessments for tropical tunas was completed taking into consideration the results of the external review of yellowfin. The yellowfin review panel did not single out a particular model configuration as a replacement for the current base case model, but suggested a variety of alternatives for the staff to consider.

To encompass as many scenarios as possible, the staff developed a pragmatic risk assessment framework to apply for both species, which included the development of hypothesis, the implementation and weighting of models, and the construction of risk tables based on the combined result (SAC-11-08, SAC-11-INF-F,SAC-11-INF-J).

To solve the inconsistencies, spatiotemporal models were used to produce new purse-seine and longline indices and associated length frequencies, but the inconsistencies were not resolved (Figure B-4).
Figure B-4: Top - Relative abundance indices derived from catch per unit of effort of purse-seine and longline fisheries standardized using spatiotemporal models. Bottom – Spatial domain of the purse-seine and longline derived indices.

The mismatch was most apparent in 2001-2003, when a peak occurred earlier in the longline index and later in the purse-seine index (opposite to what was expected given the growth and selectivity assumptions of the model). By incorporating length classes in the standardization, it became clear that the differences were due mainly to the 1998 cohort (of an important El Niño year) being prominent in the longline index, while not showing in in purse-seine index, and the opposite occurring with the 1999 cohort (an equally important La Niña year). Spatial heterogeneity was considered as the most plausible explanation for the unresolved inconsistencies.

Three overarching hypotheses related to the degree of spatial mixing of the yellowfin tuna stock in the EPO where developed (SAC-11-INF-J). Of those, the high-mixing hypothesis was assumed for the benchmark assessment, with the purse-seine index assumed the most representative of the core of the exploited population (SAC-11-07). A series of lower hierarchical level hypotheses were developed regarding other major uncertainties in the previous assessment.

From those, 12 reference models were developed, which combine components that address changes in selectivity and catchability, growth, asymptotic selectivity, and density-dependence in the index catchability as shown in (Table B-1).
Table B-1: Model configurations (hypotheses) used for yellowfin tuna in the EPO (from SAC-11-08 Table A)

Each reference model was run with four steepness of the stock-recruitment relationship assumptions (0.7, 0.8, 0.9, and 1.0). A total of 48 models composed the benchmark assessment for yellowfin tuna (SAC-11-07). In addition, new fishery definitions were implemented, and spline selectivity functions were adopted for most fisheries. All EPO catches were added to the models, which were fit to a standardized purse-seine index of abundance for the EPO north of 5°N and to the length-composition data from the purse-seine fisheries that operate north of 5°N, in order to avoid contamination of the signal with that of a possible southern population. The models were diagnosed for model misspecification, lack of fit, retrospective bias, among others (SAC-11-07). Rather than choosing a base-case model, all models where used to produce management advice by combining them using relative weights determined based on several criteria, including performance on model diagnostics (SAC-11-INF-J).
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 (t) of yellowfin, skipjack, and bigeye tunas, by all types of gear combined, in the Pacific Ocean. The EPO totals for 1993-2019 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
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 1,386,639 148,557 137,201 285,758 665,899 1,854,293 2,520,192
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 261,871 559,734 821,605 153,092 1,688,958 1,842,050 95,408 132,507 227,915 510,371 2,381,199 2,891,570
2011 216,720 520,937 737,657 283,509 1,534,944 1,818,453 89,460 154,391 243,851 589,689 2,210,272 2,799,961
2012 213,310 602,975 816,285 273,519 1,758,388 2,031,907 102,687 155,702 258,389 589,516 2,517,065 3,106,581
2013 231,170 548,776 779,946 284,043 1,835,068 2,119,111 86,029 143,156 229,185 601,242 2,527,000 3,128,242
2014 246,789 590,102 836,891 265,490 2,006,092 2,271,582 96,045 154,976 251,021 608,324 2,751,170 3,359,494
2015 260,293 573,947 834,240 334,051 1,793,193 2,127,244 104,737 136,280 241,017 699,081 2,503,420 3,202,501
2016 255,196 634,165 889,361 342,579 1,795,389 2,137,968 92,829 144,409 237,238 690,604 2,573,963 3,264,567
2017 224,556 691,839 916,395 327,571 1,626,818 1,954,389 102,577 123,309 225,886 654,704 2,441,966 3,096,670
2018 252,976 686,445 939,421 291,276 1,840,609 2,131,885 93,458 141,792 235,250 637,710 2,668,846 3,306,556
2019 228,288 * 228,288 349,965 * 349,965 95,192 * 95,192 673,445 * 673,445



), (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, 2014-2018. 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, 2019. 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, 1975-2019. The purse-seine catches are adjusted to the species composition estimate obtained from sampling the catches. The 2019 data are preliminary.

In 2020, stock status indicators (SSIs) were developed for yellowfin using the data collected in the EPO as a whole (SAC-11-05).

Most floating-object fishery SSIs suggest that the yellowfin stock has potentially been subject to increased fishing mortality, mainly due to the increase in the number of sets in the floating-object fishery since 2005. and corresponding increase in catch for yellowfin, associated with decline in catch-per-set and reduction in the average length of the fish in the catch for the floating-object fishery as shown in (Figure B-2) and (Figure B-3).
Figure B-2:

Description: Indicators of total effort in the EPO, based on purse-seine data closure-adjusted capacity, 2000-2019; annual total number of sets, by type, 1987-2019) and based on longline data for 2000-2018 (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.
Figure B-3: Indicators (catch (t and numbers); CPUE (t/day fished); average length (cm)) for the yellowfin tuna stock in the eastern Pacific Ocean, from purse-seine fisheries; relative catch and relative average length, obtained from standardized length composition using spatiotemporal model, from longline fisheries.

This coincided with a declining trend in the yellowfin longline CPUE index based on spatio-temporal modelling which remained at low historic levels since 2005 (Figure B-4).
Figure B-4:

Description: Indicators (catch (t and numbers); CPUE (t/day fished); average length (cm)) for the yellowfin tuna stock in the eastern Pacific Ocean, from purse-seine fisheries; relative catch and relative average length, obtained from standardized length composition using spatiotemporal model, from longline fisheries


Data

Trends in some of the other SSIs do not support the interpretation that increased fishing mortality is occurring as a result of an increase in the numbers of floating-object sets, such as trends in catch-per-set for other set types mean length of yellowfin in the other set types and the longline SSIs. The SSI based on spatio-temporal modelling of CPDF for the purse-seine fishery associated with dolphins shows a period of low values starting in 2015 which coincides with a period of increased yellowfin catches in floating-objects set as shown in Figure B-3 and Figure B-4.



The SSI based on spatio-temporal modelling of CPUE for the longline fishery do not coincide with the purse-seine one as shown in Figure B-4. Identifying the causes of differences in the SSIs is difficult, even when SSIs are considered in aggregate. The inconsistencies among SSIs for yellowfin may be due to an interaction between potential stock structure and differences in the spatial distribution of effort in the different set types. In addition, catch-per-set may not be a reliable indicator of abundance, particularly for the target species (i.e. yellowfin in the dolphin-associated fishery). Nonetheless, the fact that most SSIs based on the floating-object fishery are consistent with an increase in fishing mortality in that fishery means that precautionary management measures should be considered to prevent further increases.


Results
Assessment Indicator
Type: Recruitment

The 48 models of the benchmark assessment estimate similar relative recruitment trends, regardless of the steepness assumed (Figure B-5).
Figure B-5: Annual relative recruitment of yellowfin tuna to the fisheries of the EPO estimated by the 48 models and weighted average (black dashed line). The lines and dots indicate the maximum likelihood estimates of recruitment, and the shaded areas the approximate 95% confidence intervals around the estimates. The estimates are scaled so that the average recruitment is equal to 1.0 (dashed horizontal line). See model descriptions in Table B-1. The weighted average is computed using the weights assigned to each model in SAC-11-INF-J.

All biomass trajectories have declining trends, but they vary in the magnitude of the declines (Figure B-6). All models indicate the highest F for fish aged 21+ quarters (5.25+ years), followed by fish aged 11-20 quarters (2.75-5 years) (Figure B-7).
Figure B-7: Average annual fishing mortality (F) of yellowfin tuna in the EPO, by age group (in quarters), for all gears, estimated by the 48 models and weighted average. See model descriptions in Table B-1. The weighted average was computed using the weights assigned to each model in SAC-11-INF-J.





All models estimate similar impacts of the different types of fisheries (Figure B-8).
Figure B-8: Impact of fishing, 1985-2019: trajectory of the spawning biomass (a fecundity index, see text for details) of a simulated population of yellowfin tuna that was never exploited (dashed line) and that predicted by each model, with a steepness of 1.0 (solid line). The shaded areas between the two lines show the portions of the impact attributed to each fishing method.



The longline and the sorted discard fisheries have the smallest impact, while the purse-seine fisheries associated with dolphins have the greatest impact during most of the assessment period (1984-2019). In 1990s the impact of the floating-object fisheries started to be noteworthy, and surpassed that of the unassociated fisheries around 2008 and that of the purse-seine fisheries associated with dolphins in 2018.

The results from the reference models are combined in a risk analysis to provide management advice (SAC-11-08). The probabilities of exceeding the reference points where computed using each model result and its associated weight, the final estimates are in (

Table B-3); (Figure B-9 and Figure B-10)
Figure B-9:

Description: Kobe (phase) plot of the time series of estimates of spawning stock size (S) and fishing mortality (F) of yellowfin tuna relative to their MSY reference points. The colored panels are separated by the target reference points (SMSY and FMSY). Limit reference points (dashed lines), which correspond to a 50% reduction in recruitment from its average unexploited level, based on a conservative steepness (h) of 0.75 for the Beverton-Holt stock-recruitment relationship, are merely indicative, since they vary by model and are based on all models combined. The center point for each model indicates the current stock status, based on the average fishing mortality (F) over the last three years; The solid black circle represents all models combined; to be consistent with the probabilistic nature of the risk analysis and the HCR, it is based on P(Scur/SLIMIT<x) = 0.5 and P(Fcur/FMSY>x) = 0.5. The lines around each estimate represent its approximate 95% confidence interval.
Figure B-10: Yellowfin probability density functions for Fcur/FMSY, Fcur/FLIMIT and Scur/SLIMIT broken down into different components for models developed to address: a) combined; b) issues with the index of abundance; c) misfit to the composition data for the fishery with asymptotic selectivity; and d) different assumptions on steepness (h).

All probability distributions are unimodal (Figure B-10).
Results
Assessment Indicator
Type: Average length


Results
Assessment Indicator
Type: Abundance

The degree of spatial mixing of the yellowfin tuna population in the EPO was considered the main uncertainty within the risk analysis (SAC-11-INF-J). This conclusion came from the detailed inspection of the contradictory indices of abundance. Previous assessments used five indices of abundance, one from the longline fishery and four from the purse-seine fisheries, and the length composition data from longline and purse-seine fisheries. The model was unable to reconcile indices from different fisheries and length-frequency data that apparently carried contradictory signals about the status of the stock (SAC-10 INF-F).

At the beginning of 2020, the spawning biomass (S) of yellowfin ranged from 49% to 219% of the level at dynamic MSY (S(MSY_d)); 12 models suggested that it was below that level (Figure B-9) and (Table B-2).


Figure B-9: Kobe (phase) plot of the time series of estimates of spawning stock size (S) and fishing mortality (F) of yellowfin tuna relative to their MSY reference points. The colored panels are separated by the target reference points (SMSY and FMSY). Limit reference points (dashed lines), which correspond to a 50% reduction in recruitment from its average unexploited level, based on a conservative steepness (h) of 0.75 for the Beverton-Holt stock-recruitment relationship, are merely indicative, since they vary by model and are based on all models combined. The center point for each model indicates the current stock status, based on the average fishing mortality (F) over the last three years; The solid black circle represents all models combined; to be consistent with the probabilistic nature of the risk analysis and the HCR, it is based on P(Scur/SLIMIT<x) = 0.5 and P(Fcur/FMSY>x) = 0.5. The lines around each estimate represent its approximate 95% confidence interval.
Table B-2: Management quantities for yellowfin tuna in the EPO for each reference model summarized over the four steepness values. See explanation of code in Table B-1 (from SAC-11-08 Table 1)

At the beginning of 2020, the spawning biomass (S) of yellowfin ranged from 145% to 345% of the limit reference level (S(LIMIT)); no models suggest that it was below that limit. During 2017-2019 the fishing mortality (F) of yellowfin ranged from 40% to 168% of the level at MSY (F(MSY)); 14 models suggested that it was above that level. During 2017-2019, the fishing mortality of yellowfin ranged from 22% to 65% of the limit reference level (F(LIMIT)); no models suggest that it was above that limit. Every reference model suggests that lower steepness values correspond to more pessimistic estimates of stock status: lower S and higher F relative to the reference points.

There is a low probability of Fcur being above FMSY (9%). The probability of Fcur being above FLIMIT is zero. The probability of the spawning biomass being below SMSY_d is low (12%).

The probability of the spawning biomass exceeding SLIMIT is zero. The combined expected risk of F exceeding FMSY is below 50% for six closure durations), varying from 26% (no closure) to 5% (100 days), with a low risk (9%) for the current closure (72 days). One model (Base-A) produced a pessimistic result (a risk above 50% of exceeding FMSY for all scenarios, but this model has a very low relative weight (0.01) as shown in as shown in (Table B-3); (Figure B-11)
Figure B-11: Risk curves showing the probability of exceeding the target and limit reference points (RPs) for different durations of the temporal closure for yellowfin in the EPO.



A key uncertainty not addressed in this assessment is the spatial structure of the stock of yellowfin tuna in the EPO. Future work to further improve the assessment will focus on it.


Source of information
 
Inter-American Tropical Tuna Commission (IATTC).  “"Report on tuna fishery, stocks, and ecosystem in the Eastern Pacific Ocean in 2019. Inter-American Tropical Tuna Commission." Fishery Status Report. IATTC 2020.” Click to openIATTC-95-05_The fishery and status of the stocks 2019
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