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Albacore - Northern Pacific
Marine Resource  Fact Sheet
Stock status report 2018
Albacore - Northern Pacific
Fact Sheet Citation  
Owned byInter-American Tropical Tuna Commission (IATTC) – More
Related observationsLocate in inventorydisplay tree map
 
Species:
FAO Names: en - Albacore, fr - Germon, es - Atún blanco, ru - Тунец длинноперый
Geographic extent of Albacore - Northern 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
Aq Res State Trend
Exploitation stateModerately 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
 

Data provided by the relevant Members on catches of albacore, by gear and area (north and south of the equator), are shown in (Table A-6). Albacore catches for the entire EPO are shown in (Table A-2a). A portion of the albacore catch is taken by troll vessels, included under “Other gears” (OTR) in Table A-2a.

There are two stocks of albacore in the Pacific Ocean, one in the northern hemisphere and the other in the southern hemisphere. Albacore are caught by longline gear in most of the North and South Pacific, but not often between about 10°N and 5°S, by trolling gear in the eastern and central North and South Pacific, and by pole-and-line gear in the western North Pacific. In the North Pacific about 57% of the fish are taken in pole-and-line and troll fisheries that catch smaller, younger albacore, whereas about 95% of the albacore caught in the South Pacific are taken by longline. The total annual catches of South Pacific albacore ranged from about 25,000 to 50,000 t during the 1980s and 1990s, but increased after that, to between about 68,000 and 88,000 t during 2012-2016, averaging about 81,000 t, of which 29% was taken in the eastern Pacific Ocean (EPO) (Figure F-1a)
Figure F-1a: Retained catches of South Pacific albacore. The catches from the EPO are broken down by gear.

The total annual catches of North Pacific albacore peaked in 1976 at about 125,000 t, declined to about 38,000 t in 1991, and then increased to about 122,000 t in 1999 (Figure F-1b).




Figure F-1b: Retained catches of North Pacific albacore. The catches from the EPO are broken down by gear.

They declined again in the early 2000s, then recovered but during 2012-2016 they declined from about 92,000 to 58,200 t, averaging about 78,000 t, of which 27% was taken in the EPO.

Juvenile and adult albacore are caught mostly in the Kuroshio Current, the North Pacific Transition Zone, and the California Current in the North Pacific and in the Subtropical Convergence Zone in the South Pacific, but spawning occurs in tropical and subtropical waters, centering around 20ºN and 20ºS latitudes. North Pacific albacore are believed to spawn between March and July in the western and central Pacific.

The movements of North Pacific albacore are strongly influenced by oceanic conditions, and migrating albacore tend to concentrate along oceanic fronts in the North Pacific Transition Zone. Most of the catches are made in water temperatures between about 15º and 19.5ºC. Details of the migration remain unclear, but juvenile fish (2- to 5-year-olds) are believed to move into the eastern Pacific Ocean (EPO) in the spring and early summer, and return to the western and central Pacific, perhaps annually, in the late fall and winter, where they tend to remain as they mature. This pattern may be complicated by sex-related movements of large adult fish (fork length >125 cm), which are predominately male, to areas south of 20°N. The significance of such movements for the demographic dynamics of this stock are uncertain at present.

Less is known about the movements of albacore in the South Pacific Ocean. The juveniles move southward from the tropics when they are about 35 cm long, and then eastward along the Subtropical Convergence Zone to about 130°W. When the fish approach maturity they return to tropical waters, where they spawn. Recoveries of tagged fish released in areas east of 155°W were usually made at locations to the east and north of the release site, whereas those of fish released west of 155°W were usually made at locations to the west and north of the release site.

The most recent published stock assessments for the South and North Pacific stocks of albacore are from 2015 and 2017, respectively. The assessments indicate that it is not likely that either stock is overfished or that overfishing is taking place.

See also fishery fact sheet:EPO Tunas and billfishes fishery
Retained catches of South Pacific albacore. The catches from the EPO are broken down by gear.
Assessment
 
Overall Assessment Results

IATTC resolution C-05-02 on North Pacific albacore, supplemented by Resolution C-13-03, requires that the total level of fishing effort for North Pacific albacore tuna in the EPO not be increased beyond the levels that were in effect at the time. During 2014-2016 the total effort was 31,604 vessel-days (95% of the 2002-2004 reference level), and the average number of vessels operating was 753 (83% of the 2002-2004 level).

An assessment of North Pacific albacore, using fisheries data through 2015, was conducted in April 2017 at a workshop of the Albacore Working Group (ALBWG) of the International Scientific Committee for Tuna and Tuna-like Species in the North Pacific Ocean (ISC). The stock was assessed using an age- and sex-structured Stock Synthesis (SS version 3.24AB) model fitted to time series of standardized CPUE and size-composition data. Three major changes were made to the base case model from the previous assessment in 2014:

  1. Most importantly, a new procedure was used to standardize the index (1996-2015) based on Japanese longline data used to indicate trends in adult albacore abundance, and the results represented a substantial improvement relative to previous assessments. This new index had good contrast and, based on Age-Structured Production Model (ASPM) diagnostic analyses, was informative on both population trend and scale.
  2. The start year of the base case model was changed from 1966 to 1993. This eliminated both the influence of poorly-fitting Japanese longline size-composition data for 1975-1992, and the conflict between these data and the primary adult abundance indices.
  3. In previous assessments, the instantaneous rate of natural mortality (M) was assumed to be 0.3 yr-1 for both sexes at all ages. The basis for this assumption was reviewed, and found to be poorly supported. Sex-specific M-at-age vectors were developed from a meta-analysis, with a combined-sex M that scaled with size for ages 0-2, and sex-specific M fixed at 0.39 and 0.48 yr-1 for age-3+ males and females, respectively.


The stock assessment results allowed for the following conclusions:

  1. The base-case model estimates that the spawning stock biomass (SSB) declines during 1993-2000, after which it becomes relatively stable. The SSB has likely fluctuated between 70,000 and 140,000 t during the assessment period (1993-2015), although those estimates are highly uncertain (coefficient of variation ≈ 40%), and the recruitment has averaged about 204 million fish annually during this period. Female SSB was estimated to be approximately 81,000 t (95% confidence interval 16,500 -145,000) in the terminal year of the assessment (2015), and stock depletion is estimated to be about 47% of unfished SSB (Figure F-2).

Spawning stock biomass of North Pacific albacore tuna estimated from the North Pacific albacore base-case model for the 2017 stock assessment (point estimate and 95% confidence interval).

  1. The estimated current (2015) spawning potential ratio (SPR; the ratio of the expected lifetime reproductive potential of an average recruit with and without fishing) is 0.53, which corresponds to a relatively low exploitation level (i.e., 1-SPR = 0.47). Instantaneous fishing mortality at age (F-at-age) is similar for both sexes through age 5, peaking at age 4 and declining to a low at age 6, after which males experience higher F-at-age than females up to age 13. Juvenile albacore (aged 2 to 4 years) comprised, on average, 70% of the annual catch during 1993-2015, reflecting the larger impact of the surface fisheries (primarily troll and pole-and-line), which catch juvenile fish, relative to longline fisheries, which catch mainly adult fish.
  2. The Kobe plot depicts the status of the stock in relation to MSY-based and MSY proxy reference points from the base-case model. The plot is presented for illustrative purposes only, since the IATTC has not established biological reference points for north Pacific albacore. The ISC Working Group concluded that the stock is likely not overfished at present, as there is little evidence from the assessment that fishing has reduced SSB below reasonable biomass-based reference points, including the limit reference point adopted by the WCPFC (20%SSBF=0) (Figure F-3).

Kobe (phase) plot for the North Pacific albacore stock from the base-case assessment model (which assumes a steepness value of 0.9). The F proxy is computed as (1-(Spawning biomass per recruit [year] / Spawning biomass per recruit [virgin])). The limit and target reference points are those proposed by the IATTC staff and are included here for illustrative purposes. The solid lines represent the proposed target reference point.The dashed lines represent the proposed limit reference points. The limit biomass reference point corresponds to a depletion level that causes a 50% reduction in recruitment from its average unexploited level based on a conservative steepness value (h = 0.75). The limit fishing mortality reference point corresponds to the fishing mortality that will drive the population to the limit biomass reference point. The squares around the most recent estimate represent its approximate 95% confidence interval. The triangle is the first estimate (1993).

  1. Under the base-case model, the point estimate of MSY is 132,072 t, and the point estimate of the spawning biomass that will the produce MSY (SSBMSY) is 24,770 t. The ratio of current (2012-2014 average) F to F at the MSY level (FMSY) is estimated to be 0.61, indicating that overfishing is not occurring. That ratio is also below the 2002-2004 level of 0.65 used as reference for IATTC conservation and management measures for North Pacific albacore.
  2. Two projections were conducted externally to the base case model to evaluate the impact of current F (2012-2014 average) and catch (2010-2014 average = 82,432 t) levels on female SSB during 2015-2025. The projections show that current F would reduce female SSB from about 81,000 t to 63,000 t (CI: 36,000 - 91,000 t) by 2025, with a 0.2 and <0.01% probability of being below the WCPFC limit reference point by 2020 and 2025, respectively. Catch would increase in 2017 and 2018, and then decline to about 60,000 t in 2024; on average, future catches would be below the 2010-2014 average. This result is most likely due to the low estimated recruitment in 2011, which would reduce female SSB beginning in 2015, the first year of the projection period. In contrast, current catch levels would reduce female SSB from about 81,000 t to 48,000 t (CI: 5,000 - 90,000 t) by 2025, and increase the probability that female SSB will be below the WCPFC reference point to about 3.5 and 30% in 2020 and 2025, respectively. These probabilities may be higher in reality, because the future projections do not include all the uncertainties from the base case model. It should be noted that the constant catch scenario is inconsistent with the current IATTC and WCPFC management approaches for north Pacific albacore.
  3. The Working Group concluded that the north Pacific albacore stock is likely not overfished and not experiencing overfishing, based on several potential reference points. The current level of fishing mortality (F2012-2014) is estimated to be below that of F2002-2004, which had led previously to conservation and management measures for the stock (IATTC Resolutions C-05-02 and C-13-03 and WCPFC CMM 2005-03). There is no evidence that fishing has reduced SSB below the WCPFC limit reference point, and population dynamics in the north Pacific albacore stock are largely driven by recruitment, which is affected by both environmental changes and the stock-recruitment relationship. The Working Group concluded that the north Pacific albacore stock is healthy, and that current productivity is sufficient to sustain recent fishing mortality levels, assuming average historical recruitment in both the short and long term.
  4. The Working Group noted that the lack of sex-specific size data, uncertainty in the estimates of growth and natural mortality, and the simplified treatment of the spatial structure of north Pacific albacore population dynamics are important sources of uncertainty in the assessment.


The Working Group is currently undertaking a Management Strategy Evaluation (MSE) for the North Pacific albacore stock with the assistance of an analyst recently hired by the United States. An overview of the MSE work was presented during the 9th Meeting of the Scientific Advisory Committee in May 2018.
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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