Fisheries and Resources Monitoring System

EspañolFrançais
Bigeye tuna - Eastern Pacific (EPO)
Marine Resource  Fact Sheet
Stock status report 2018
Bigeye tuna - Eastern Pacific (EPO)
Fact Sheet Citation  
Owned byInter-American Tropical Tuna Commission (IATTC) – More
Related observationsLocate in inventorydisplay tree map
 
Species:
FAO Names: en - Bigeye tuna, fr - Thon obèse(=Patudo), es - Patudo, ru - Тунец большеглазый
Geographic extent of Bigeye tuna - Eastern Pacific (EPO)
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 rateFishing mortality rate close to that for MSYModerate fishing mortalityGreen
Abundance levelSpawning biomass close to that for MSYIntermediate 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 bigeye during 1988-2017 are shown in (Table A-1). Overall, the catches in both the EPO and WCPO have increased, but with considerable fluctuations. In the EPO, the average catch for the period was 104 thousand t, with a low of 73 thousand t in 1989 and a high of 149 thousand t in 2000. In the WCPO the catches of bigeye increased to more than 77 thousand t during the late 1970s, decreased during the early 1980s, and then increased steadily to 113 thousand t in 1996. In 1997 the total jumped to 158 thousand t, and reached a high of 180 thousand t in 2004. Since 2004 the catch has fluctuated between 132 and 158 thousand t.

The annual retained catches of bigeye in the EPO by purse-seine and pole-and-line vessels during 1988-2017 are shown in Table A-2a. The number of fish-aggregating devices (FADs), placed in the water by fishermen to attract tunas, increased from 550 in 1992 to over 2,700 by 1995. This led to a sudden and dramatic increase in the purse-seine catches. Prior to the increase in number of FADs, the annual retained purse-seine catch of bigeye in the EPO was about 5 thousand t (Table A-2a). ; by 1994 it was 35 thousand t, and in 1996 was over 60 thousand t. Since then, it has fluctuated between 44 and 95 thousand t. The preliminary estimate of the retained catch in the EPO in 2017 is 66 thousand t.

During 2000-2016 the percentage of the purse-seine catch of bigeye discarded at sea has steadily decreased, from 5% in 2000 to less than 1% in 2014, for an average discard rate of about 1.9%. No bigeye catch has been reported by pole-and-line vessels in recent years.

From 1985 to 1993, before the expansion of the FAD fishery, longliners caught an average of 95% of the bigeye in the EPO (average 86 thousand t; range; 66 to 104 thousand t). During 2002-2016 this average dropped to 38%, with a low of 25% in 2008 (average: 39 thousand t; range: 26 to 74 thousand t). The preliminary estimate of the longline catch in the EPO in 2017 is 31 thousand t as shown in Table A-2a.

Small amounts of bigeye are caught in the EPO by other gears, as shown in Table A-2a.

See also fishery fact sheet:EPO Tunas and billfishes fishery
Total catches (retained catches plus discards) of bigeye tuna by the purse-seine fisheries, and retained catches for the longline fisheries, in the eastern Pacific Ocean, 1975-2017 The purse-seine catches are adjusted to the species composition estimate obtained from sampling the catches. The 2017 catch data are preliminary.
Assessment
 
Assessment Model
Type:  Age-structured
An integrated statistical age-structured stock assessment model, Stock Synthesis

The results of the update stock assessment of bigeye tuna (Thunnus obesus) in the eastern Pacific Ocean (EPO) conducted in 2018 using the same methodology as in previous years, revealed several uncertainties which led the staff to question its use as a basis for management advice. The staff has therefore developed a suite of stock status indicators for bigeye, as an alternative basis for management advice and for monitoring the stock and the fishery until the uncertainties in the stock assessment have been resolved.
Assumption

There have been substantial changes in the bigeye tuna fishery in the EPO over recent decades (Figure D-1).
Total catches (retained catches plus discards) of bigeye tuna by the purse-seine fisheries, and retained catches for the longline fisheries, in the eastern Pacific Ocean, 1975-2017 The purse-seine catches are adjusted to the species composition estimate obtained from sampling the catches. The 2017 catch data are preliminary.

Initially, most bigeye catch was taken by longline vessels. With the expansion of the fishery on fish-aggregating devices (FADs) since 1993, the purse-seine fishery has taken an increasing component of the bigeye catch. In recent years, purse-seine catches of bigeye were taken primarily between 5°N and 5°S across the equatorial Pacific as far west as the western boundary (150°W) of the EPO (Figure A-3a-b).
Figure A-3a: Average annual distributions of the purse-seine catches of bigeye, by set type, 2011-2015. The sizes of the circles are proportional to the amounts of bigeye caught in those 5° by 5° areas.
Figure A-3b: Annual distributions of the purse-seine catches of bigeye, by set type, 2017. The sizes of the circles are proportional to the amounts of bigeye caught in those 5° by 5° areas.

The longline catches of bigeye in the EPO are predominantly taken below 5°N (Figure A-4).


Figure A-4: Distributions of the average annual catches of bigeye and yellowfin tunas in the Pacific Ocean, in metric tons, by Chinese, Japanese, Korean, and Chinese Taipei longline vessels, 2012-2016. The sizes of the circles are proportional to the amounts of bigeye and yellowfin caught in those 5° by 5° areas.

There have been substantial changes in the bigeye tuna fishery in the EPO over recent decades (Figure D-1)
Figure D-1: Total catches (retained catches plus discards) of bigeye tuna by the purse-seine fisheries, and retained catches for the longline fisheries, in the eastern Pacific Ocean, 1975-2017 The purse-seine catches are adjusted to the species composition estimate obtained from sampling the catches. The 2017 catch data are preliminary.

Assessments of bigeye tuna in the EPO have been conducted as if there were a single stock of bigeye in the EPO, with minimal net movement of fish between the EPO and the western and central Pacific Ocean (WCPO).
Data

Assessment results have been consistent with the results of other analyses of bigeye tuna on a Pacific-wide basis. However, the distribution of the bigeye catches extends across the equatorial Pacific Ocean. In addition, a large amount of conventional and electronic tagging data has recently accumulated from the Pacific Tuna Tagging Program, which has focused its bigeye tagging efforts between 180° and 140°W since 2008. The tag recoveries clearly show that there is extensive longitudinal movement of bigeye across the IATTC’s management boundary at 150°W, in particular from west to east.

The IATTC staff will continue to collaborate with SPC on research into a Pacific-wide stock assessment model for bigeye. This will incorporate the new tagging data in a spatially-structured population dynamics model, which will help in the ongoing evaluation of potential biases resulting from ignoring exchange of fish across the WCPO-EPO boundary in the current approach of conducting separate assessments for the EPO and WCPO
Results
Assessment Indicator
Type: Recruitment

Because of the uncertainties identified in the update assessment of bigeye tuna conducted in 2018 (SAC-09-05 and SAC-09 INF-B), the staff used stock status indicators, similar to those used for skipjack tuna (SAC-09-07), to assess the status of the stock. The staff also investigated the relationship between the number of days fished and the number of floating-object sets, using a subset of vessels that fished mainly on floating objects.
Assessment Indicator
Type: Fishing mortality

All the indicators, except catch, show strong trends over time, indicating increasing fishing mortality and reduced abundance, and are at, or above, their reference levels (Figure D-2).
Figure D-2: Stock status indicators for bigeye tuna in the EPO, based on purse-seine data, 2000-2017. The dashed horizontal lines are the 5th and 95th percentiles, the solid horizontal line is the median. CPDF: catch per day fishing; OBJ: sets on floating objects.

The increasing number of sets and the decreasing mean weight of the fish in the catch suggests that the bigeye stock in the EPO is under increasing fishing pressure, and measures additional to the current seasonal closures, such as limits on the number of floating-object sets, are required.

It is not clear why the number of floating-object sets, per day and per vessel, is increasing, but it is probably due to the vessels’ increased efficiency in finding FADs with tuna, due in turn to both the greater number of FADs deployed and the increased use of satellite-linked buoys equipped with fish-detecting sonar, and further investigation into this phenomenon should be conducted


Assessment Indicator
Type: SSB
Projection




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
powered by FIGIS  © FAO, 2019
Powered by FIGIS
crawl