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Yellowfin tuna - Eastern Pacific
Marine Resource  Fact Sheet
Stock status report 2016
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: 2015
 
 
Biological State and Trend
State & Trend Descriptors
PartnerFIRMS
Exploitation rateModerate fishing mortality, close to that corresponding to MSYModerate fishing mortalityGreen
Abundance levelIntermediate abundanceIntermediate abundance
Aq Res State Trend
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 1986-2015 are shown in (Table A-1). The EPO totals for 1993-2015 include discards from purse-seine vessels with carrying capacities greater than 363 t. The El Niño event of 1982-1983 led to a reduction in the catches in those years, whereas the catches in the WCPO were apparently not affected. Although the El Niño episode of 1997-1998 was greater in scope, it did not have the same effect on the yellowfin catches in the EPO. In the EPO, catches increased steadily to a high of 443 thousand t in 2002; they decreased substantially in 2004, reaching their lowest level during 2006-2008, at only 44% of the highest catches of the 2001-2003 period. The 2015 catch of 246 thousand t is greater than the average for the previous 5-year period (234 thousand t). In the WCPO, the catches of yellowfin reached a new high of 611 thousand t in 2014, surpassing the previous record of 600 thousand t in 2008.

The annual retained catches of yellowfin in the EPO by purse-seine and pole-and-line vessels during 1986-2015 are shown in (Table A-2a), (Table A-2a (cont.)), (Table A-2a (cont.)). The average annual retained catch during 2000-2014 was 257 thousand t (range: 167 to 413 thousand t). The preliminary estimate of the retained catch in 2015, 245 thousand t, was 5% larger than that of 2014, but 5% less than the average for 2000-2014. The average amount of yellowfin discarded at sea during 2000-2014 was about 1% of the total purse-seine catch (retained catch plus discards) of yellowfin (range: 0.1 to 2.4%) (Table A-2a).

The annual retained catches of yellowfin in the EPO by longliners during 1986-2015 are shown in Table A-2a. During 1990-2003 catches averaged about 23 thousand t (range: 12 to 35 thousand t), or about 8% of the total retained catches of yellowfin. Longline catches declined sharply beginning in 2005, averaging 10 thousand t per year (range: 8 to 13 thousand t), or about 4% of the total retained catches, through 2014. Yellowfin are also caught by recreational vessels, as incidental catch in gillnets, and by artisanal fisheries. Estimates of these catches are shown in Table A-2a, under “Other gears” (OTR); during 2000-2014 they averaged about 1 thousand t.

See also fishery fact sheet:EPO Tunas and billfishes fishery
Total catches (retained catches plus discards) for the purse-seine fisheries, and retained catches for the pole-and-line and longline fisheries, of yellowfin tuna in the eastern Pacific Ocean, 1975-2015. The purse-seine catches are adjusted to the species composition estimate obtained from sampling the catches. The 2015 catch data are preliminary.
Assessment
 
Assessment Model
Type:  Age-structured
An integrated statistical age-structured stock assessment model, Stock Synthesis

The most current stock assessment of yellowfin tuna (Thunnus albacares) in the eastern Pacific Ocean (EPO). An integrated statistical age-structured stock assessment model (Stock Synthesis Version 3.23b) was used in the assessment, which is based on the assumption that there is a single stock of yellowfin in the EPO.
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 of yellowfin are relatively low in the vicinity of the western boundary of the EPO at 150ºW (Figure A-1a and A-1b).
Average annual distributions of the purse-seine catches of yellowfin, by set type, 2010-2014. The sizes of the circles are proportional to the amounts of yellowfin caught in those 5° by 5° areas.
Annual distributions of the purse-seine catches of yellowfin, by set type, 2015. 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 EPO is taken in purse-seine sets on yellowfin associated with dolphins and in unassociated schools (Figure B-1).
Figure B-1: Total catches (retained catches plus discards) for the purse-seine fisheries, and retained catches for the pole-and-line and longline fisheries, of yellowfin tuna in the eastern Pacific Ocean, 1975-2015. The purse-seine catches are adjusted to the species composition estimate obtained from sampling the catches. The 2015 catch data are preliminary.

Tagging studies of yellowfin throughout the Pacific indicate that the fish tend to stay within 1800 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. This is consistent with the fact that longline catch-per-unit-of-effort (CPUE) trends differ among areas in the EPO. However, movement rates between these putative stocks, as well as across the 150°W meridian, cannot be estimated with currently-available tagging data.
Data

The assessment of yellowfin tuna in the eastern Pacific Ocean in 2015 is similar to the previous assessment, except that separate series of length-frequency data for Japanese longline commercial and training vessels are now available, and both were used in the assessment.

As noted in IATTC Stock Assessment Report 16 and previous assessments, these interpretations are uncertain, and highly sensitive to the assumptions made about the steepness parameter (h) of the stock-recruitment relationship, the average size of the older fish (L2), and the assumed levels of natural mortality (M). The results are more pessimistic if a stock-recruitment relationship is assumed, if a higher value is assumed for L2, and if lower rates of M are assumed for adult yellowfin. A likelihood profile on the virgin recruitment (R0) parameter showed that data components diverge on their information about abundance levels.

Sensitivity analyses indicated that the results are more pessimistic if the weighting assigned to length-frequency data is changed, using recommended data weighting methods, and more optimistic if the model is fitted closely to the index of relative abundance based on the catch per unit of effort (CPUE) of the northern dolphin-associated purse-seine fishery rather than of the southern longline fishery.
Results
Assessment Indicator
Type: Recruitment

There is uncertainty about recent and future levels of recruitment and biomass (Figure B-2).
Figure B-2: Estimated annual recruitment at age zero of yellowfin tuna to the fisheries of the EPO. The estimates are scaled so that the average recruitment is equal to 1.0 (dashed horizontal line). The solid line illustrates the maximum likelihood estimates of recruitment, and the shaded area indicates the approximate 95% confidence intervals around those estimates.

There have been two, and possibly three, different productivity regimes since 1975, and the levels of maximum sustainable yield (MSY) and the biomasses corresponding to the MSY may differ among the regimes. The population may have switched in the last ten years from a high to an intermediate productivity regime (Figure B-5).
Figure B-5: Spawning biomass ratios (SBRs) for yellowfin tuna in the EPO, including projections for 2016-2026 based on average fishing mortality rates during 2013-2015, from the base case (top) and the sensitivity analysis that assumes a stock-recruitment relationship (h = 0.75, bottom). The dashed horizontal line (at 0.21 and 0.30, respectively) identifies the SBR at MSY. The solid curve illustrates the maximum likelihood estimates, and the estimates after 2016 (the large dot) indicate the SBR predicted to occur if fishing mortality rates continue at the average of that observed during 2013-2015, and average environmental conditions occur during the next 10 years. The shaded area indicates the approximate 95% confidence intervals around those estimates.




Results
Assessment Indicator
Type: Fishing mortality

The highest fishing mortality (F) has been on fish aged 11-20 quarters (2.75-5 years). (Figure B-3).
Figure B-3: Average annual fishing mortality (F) by age groups, by all gears, of yellowfin tuna recruited to the fisheries of the EPO. The age groups are defined by age in quarters.

The average annual F has been increasing for all age classes since 2009, but in 2015 it showed a slight decline for the 11-20 quarter age group.

Historically, the dolphin-associated and unassociated purse-seine fisheries have the greatest impact on the spawning biomass of yellowfin, followed by the floating-object fisheries. (Figure B-4).
Figure B-4: Biomass trajectory of a simulated population of yellowfin tuna that was never exploited (dashed line) and that predicted by the stock assessment model (solid line). The shaded areas between the two lines show the portions of the fishery impact attributed to each fishing method.

In more recent years, the impact of the floating-object fisheries has been greater than that of the unassociated fisheries. The impacts of the longline and purse-seine discard fisheries are much less, and have decreased in recent years. Increasing the average weight of the yellowfin caught could increase the MSY.


Results
Assessment Indicator
Type: SSB

The spawning biomass ratio (SBR) has been below average since 2006, with the exception of 2008-2010, which resulted from a high recruitment in 2006. The recent fishing mortality rates (F) are slightly below the MSY level (Fmult = 1.02), and the recent levels of spawning biomass (S) are estimated to be below that level (Srecent/SMSY = 0.95) (Figure B-6).



and (Table B-1).
Source of information
 
Inter-American Tropical Tuna Commission (IATTC).  “"Tunas and billfishes in the eastern Pacific Ocean in 2015. Inter-American Tropical Tuna Commission." Fishery Status Report. IATTC 2016.” Click to openhttp://www.iattc.org/PDFFiles2/FisheryStatusReports/FisheryStatusReport14.pdf
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