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Skipjack tuna - Eastern Pacific
Marine Resource  Fact Sheet
Stock status report 2018
Skipjack tuna - Eastern Pacific
Fact Sheet Citation  
Owned byInter-American Tropical Tuna Commission (IATTC) – More
Related observationsLocate in inventorydisplay tree map
 
Species:
FAO Names: en - Skipjack tuna, fr - Listao, es - Listado, zh - 鲣, ru - Тунец полосатый (=скипджек)
Geographic extent of Skipjack tuna - Eastern Pacific
Main Descriptors
Considered a single stock: Yes        Spatial Scale: Regional
Management unit: Yes        Reference year: 2017
 
 
Biological State and Trend
State & Trend Descriptors
PartnerFIRMS
Exploitation rateModerate fishing mortalityModerate fishing mortalityGreen
Abundance levelIntermediate abundanceIntermediate abundance
FAO Categories
Exploitation stateUncertain
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 skipjack during 1988-2017 are shown in (Table A-1). Most of the skipjack catch in the Pacific Ocean is taken in the WCPO. Prior to 1998, WCPO skipjack catches averaged about 900 thousand t. Beginning in 1998, catches increased steadily, from 1.2 million t to an all-time high of 2 million t in 2014. In the EPO, the greatest yearly catches occurred between 2003 and 2017, ranging from 153 to 343 thousand t, the record catch in 2016.

The annual retained catches of skipjack in the EPO by purse-seine and pole-and-line vessels during 1988-2017 are shown in (Table A-2a). . During 2002-2016 the annual retained catch averaged 255 thousand t (range 147 to 338 thousand t). The preliminary estimate of the retained catch in 2017, 326 thousand t, is 28% greater than the average for 2002-2016, and 3% lower than the record catch of 2016. Discards of skipjack at sea decreased each year during the period, from 8% in 2004 to a low of less than 1% in 2013. During the period about 3% of the total catch of the species was discarded at sea. Small amounts of EPO skipjack are caught with longlines and other gears are shown in Table A-2a.



See also fishery fact sheet:EPO Tunas and billfishes fishery
Total catches (retained catches plus discards) of skipjack tuna by the purse-seine fisheries on floating objects and unassociated schools, and by other fisheries combined, in the eastern Pacific Ocean, 1975-2016. The purse-seine catches are adjusted to the species composition estimate obtained from sampling the catches. The 2016 catch data are preliminary.
Average annual distributions of the purse-seine catches of skipjack, by set type, 2011-2015. The sizes of the circles are proportional to the amounts of skipjack caught in those 5° by 5° areas.
Annual distributions of the purse-seine catches of skipjack, by set type, 2017. The sizes of the circles are proportional to the amounts of skipjack caught in those 5° by 5° areas.
Assessment
 
Assessment Model
Type:  Others
Fisheries Indicators

Skipjack are distributed across the Pacific Ocean, and it is likely that there is a continuous stock throughout the Pacific Ocean, with exchange of individuals at a local level, although large-scale movements are thought to be rare. The bulk of the catches of skipjack are made in the eastern and western regions; the purse-seine catches are relatively low in the vicinity of the western boundary of the EPO at 150°W. The movements of tagged skipjack generally cover hundreds, rather than thousands, of kilometers, and exchange of fish between the eastern and western Pacific Ocean appears to be limited. Movement rates between the EPO and the western Pacific cannot be estimated with currently-available tagging data.
Data

The data- and model-based indicators have yet to detect any adverse impacts of the fishery. The average weight has declined to levels seen in the early 1980s and was below its lower reference level in 2015 and 2016, but increased slightly to above that level in 2017. This can be a consequence of overexploitation, but it can also be caused by recent recruitments being greater than past recruitments or expansion of the fishery into areas occupied by smaller skipjack. The low levels are likely due to the large recruitments in 2015 and 2016 (Figure C-1)
Figure C-1: Indicators of stock status for skipjack tuna in the eastern Pacific Ocean. OBJ: floating-object fishery; NOA: unassociated fishery; CPDF: catch per day fished. All indicators are scaled so that their average equals one.

Biomass, recruitment, and fishing mortality are estimated to be highly variable over time. However, the estimates differ among the alternative assessment methods and are uncertain because: 1) it is unknown if catch-per-day-fished for purse-seine fisheries is proportional to abundance; 2) it is possible that there is a population of large skipjack that is invulnerable to the fisheries; and 3) the structure of the EPO stock in relation to the western and central Pacific stocks is uncertain.

In addition, maximum yields are estimated to be achieved with infinite fishing mortality because the critical weight is less than the average weight at recruitment to the fishery. Although, this is uncertain because of uncertainties in the estimates of natural mortality and growth. For this reason, no traditional reference points are available for skipjack tuna in the EPO. Consequently, indicators and reference levels have been used to evaluate the status of the stock.
Results
Assessment Indicator
Type: Others

Productivity and susceptibility analysis (PSA; see IATTC Fishery Status Report 12, Figure L-4) shows that skipjack has substantially higher productivity than bigeye. Biomass (B) and the fishing mortality that corresponds to MSY (FMSY) are, respectively, negatively and positively correlated with productivity. Therefore, since skipjack and bigeye have about the same susceptibility, and susceptibility is related to fishing mortality, the status of skipjack can be inferred from the status of bigeye, but only if the fishing mortality of bigeye is below the MSY level (i.e., F<FMSY). Since the updated assessment of bigeye estimates that the fishing mortality is above that level (F>FMSY), no inferences can be made about the status of skipjack. A conventional assessment of skipjack is necessary to ascertain the status of the stock, but, as noted above, this is not possible without much more extensive tagging data. Implementing the large-scale tagging program in the EPO proposed in the Strategic Science Plan for 2019-2023 is therefore critical.


Management
Management unit: Yes
Source of information
 
Inter-American Tropical Tuna Commission (IATTC).  “"Tunas and billfishes in the eastern Pacific Ocean in 2017. Inter-American Tropical Tuna Commission." Fishery Status Report. IATTC 2018.” Click to openhttps://www.iattc.org/PDFFiles/FisheryStatusReports/_English/No-16-2018_Tunas%20billfishes%20and%20other%20pelagic%20species%20in%20the%20eastern%20Pacific%20Ocean%20in%202017.pdf
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