|Albacore - Northern Pacific|
|Marine Resource Fact Sheet|
|Albacore - Northern Pacific|
|FAO Names: en - Albacore, fr - Germon, es - Atún blanco, ru - Тунец длинноперый|
|Considered a single stock: Yes Spatial Scale: Regional|
Management unit: Yes Reference year: 2015
Biological State and Trend
Habitat and Biology
Bottom type: Unspecified. Depth zone: Abyssal ( >1000m). Horizontal distribution: Oceanic. Vertical distribution: Pelagic.
Jurisdictional distribution: Highly migratory
Considered a single stock: Yes
The catches of albacore in the entire Pacific Ocean, by gear and area (north and south of the equator) are shown in (Table A-6
). The catches of albacore in the EPO, by gear, are shown in (Table A-2a
), (Table A-2a (cont.)
), (Table A-2a (cont.)
). A significant portion of the albacore catch is taken by troll gear, included under “Other gears” (OTR) in Table A-2a.
There are two stocks of albacore in the Pacific Ocean, one occurring 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 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-1a)
|Figure F-1a: Retained catches of North Pacific albacore. |
Following a second decline in the early 2000s, catches have recovered slightly, and have fluctuated between about 69,000 and 95,000 t in recent years (2006-2013). During 2010-2014 the average annual catch was about 84,000 t. 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, ranging from about 59,000 to 88,000 t during 2003-2013. (Figure F-1b).
|Figure F-1b: Retained catches of South Pacific albacore. |
During 2010-2014 the average annual catch was about 82,000 t.
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 stock assessments for the South and North Pacific stocks of albacore were presented in 2012 and 2014, respectively.
See also fishery fact sheet:EPO Tunas and billfishes fishery
| Retained catches of North Pacific albacore. |
Overall Assessment Results
An assessment of North Pacific albacore using fisheries data through 2012 was conducted at a workshop of the Albacore Working Group of the International Scientific Committee for Tuna and Tuna-like Species in the North Pacific Ocean (ISC), held in April 2014. The stock was assessed using an age- and sex-structured Stock Synthesis (SS Version 3.24f) model fitted to time series of standardized CPUE and size-composition data over a 1966 to 2012 time frame. The base-case model was fitted to the Japanese pole-and-line (PL) and longline (LL) indices, which were considered by the Working Group to be the most representative indices of abundance trends for juveniles and adults, respectively. All available fishery data from the Pacific Ocean north of the equator were used for the stock assessment, which assumed a single well-mixed stock. Sex-specific growth curves were used because there is evidence of sexually dimorphic growth, with male albacore attaining greater sizes and ages than females. The assumed value of the steepness parameter (h
) in the Beverton-Holt stock-recruitment relationship was 0.9, based on two separate external estimates of this parameter. The assessment model was fitted to the abundance indices and size-composition data in a likelihood-based statistical framework. Maximum likelihood estimates of model parameters, derived outputs, and their variances were used to characterize stock status. Several sensitivity analyses were conducted to evaluate both changes in model performance and the range of uncertainty resulting from changes in model parameters, including some of the data series used in the analyses, growth curve parameters, natural mortality, stock-recruitment steepness, initial year, selectivity estimation, and weighting of size-composition data. The conclusions reached at that workshop were presented to the eleventh plenary meeting of the ISC, held in August 2014. Among these were the following:
- The base-case model estimates that the spawning stock biomass (SSB) has likely fluctuated between 98,000 and 204,000 t between 1966 and 2012 (Figure F-2), and that recruitment has averaged about 43 million fish annually during this period. There are periods of above- and below-average recruitment at the beginning of the assessment time frame, followed by fluctuations around the average since the 1990s. Female SSB was estimated to be approximately 110,101 t in the terminal year of the assessment (2012), and stock depletion is estimated to be 35.8% of unfished SSB.
|Figure F-2: Spawning stock biomass of North Pacific albacore tuna, from the North Pacific Albacore Workshop analysis of 2012. |
- The estimated spawners per recruit (SPR) relative to the unfished population in the terminal year of the assessment is 0.41, which corresponds to a relatively low exploitation level (i.e., 1-SPR = 0.59). While the base case model’s estimate of current F-at-age on juvenile fish is lower than in 2002-2004, and current F on adult fish (50% of age-5 fish, and all fish age 6 and older) is higher, on average, than during 2002-2004.
- 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 in an overfished condition at present, as there is little evidence from the assessment that fishing has reduced SSB below reasonable candidate biomass-based reference points. (Figure F-3)
|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 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 (1966). |
- Under the base-case model, the point estimate (± SD) of maximum sustainable yield (MSY) is 105,571 ± 14,759 t, and the point estimate of spawning biomass to produce MSY (SSBMSY, adult female biomass) is 49,680 ± 6,739 t. The ratio of F2010-2012/FMSY is estimated to be 0.52, and the ratio of F2002-2004/FMSY (2002-2004 are the reference years for IATTC conservation and management measures for north Pacific albacore) is estimated to be 0.76.
- Stochastic stock projections were conducted externally to the base case model to evaluate the impact of various levels of fishing intensity on future female SSB for north Pacific albacore. Future recruitment was based on random resampling of historical recruitment for three periods: (1) low recruitment (about 29 million recruits), 1983-1989, (2) average recruitment (about 43 million), 1966-2010, and high recruitment (about 55 million recruits), 1966-1975. These calculations incorporate the structure of the assessment model (e.g., multi-fleet, multi-season, size- and age-selectivity) to produce results consistent with the assessment model. Projections started in 2011 and continued through 2041 under two levels of fishing mortality (constant F2010-2012, constant F2002-2004) and constant catch averaged for 2010-2012, and three levels of recruitment (low, average, and high, as defined above). Based on these projections, the stock performs better under the constant F2010-2012 harvest scenario than the constant F2002-2004 harvest scenario. Assuming average historical recruitment and fishing at a constant current F, median female SSB is expected to remain relatively stable between the 25th and median historical percentiles over both the short and long term. In contrast, if a low-recruitment scenario is assumed, then median female SSB declines under both harvest scenarios. The high-recruitment scenario is more optimistic, with median SSB increasing above the historical median SSB.
- The Working Group concluded that the north Pacific albacore stock is not experiencing overfishing and is probably not in an overfished condition. The current exploitation level (F2010-2012) is estimated to be below that of F2002-2004, which had led previously to the implementation of conservation and management measures for the stock in the eastern Pacific (IATTC Resolution C-05-02, supplemented by Resolution C-13-03) and the western and central Pacific Ocean (WCPFC CMM 2005-03). The Working Group noted that there is no evidence that fishing has reduced SSB below thresholds associated with the majority of biomass-based reference points that might be chosen and that 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 exploitation levels, assuming average historical recruitment in both the short and long term.
- The Working Group noted that the lack of sex-specific size data, the absence of updated estimates of important life history parameters (natural mortality, maturity), and the simplified treatment of the spatial structure of north Pacific albacore population dynamics are important sources of uncertainty in the assessment.
In 2013 the IATTC adopted resolution C-13-03
on North Pacific albacore, which
. By 1 December 2013, all CPCs were required to report catch, by gear and effort directed at northern albacore, in the Convention Area during 2007-2012, as well as the average effort for 2002-2004. The effort in vessel-days during 2007-2012 was only 2% higher than during 2002-2004, and the average number of vessels operating during 2007-2012 was about 7% lower than during 2002-2004.
Currently the Working Group is developing a work plan to implement a Management Strategy Evaluation for the North Pacific albacore stock.
Management unit: Yes
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.” http://www.iattc.org/PDFFiles2/FisheryStatusReports/FisheryStatusReport14.pdf