Search

The management and conservation of tuna and other transboundary marine species have to date been limited by an incomplete understanding of the oceanographic, ecological and socioeconomic factors mediating fishery overlap and interactions, and how these factors vary across expansive, open ocean habitats. Despite advances in fisheries monitoring and biologging technology, few attempts have been made to conduct integrated ecological analyses at basin scales relevant to pelagic fisheries and the highly migratory species they target. Here, we use vessel tracking data, archival tags, observer records, and machine learning to examine inter- and intra-annual variability in fisheries overlap (2013–2020) of five pelagic longline fishing fleets with North Pacific albacore tuna (Thunnus alalunga, Scombridae). Although progressive declines in catch and biomass have been observed over the past several decades, the North Pacific albacore is one of the only Pacific tuna stocks primarily targeted by pelagic longlines not currently listed as overfished or experiencing overfishing. We find that fishery overlap varies significantly across time and space as mediated by (1) differences in habitat preferences between juvenile and adult albacore; (2) variation of oceanographic features known to aggregate pelagic biomass; and (3) the different spatial niches targeted by shallow-set and deep-set longline fishing gear. These findings may have significant implications for stock assessment in this and other transboundary fishery systems, particularly the reliance on fishery-dependent data to index abundance. Indeed, we argue that additional consideration of how overlap, catchability, and size selectivity parameters vary over time and space may be required to ensure the development of robust, equitable, and climate-resilient harvest control rules.

Introduction: Evaluating the thermal tolerance of commercially valuable tuna species and their behavioral responses to the limits of this tolerance is essential for evaluating the effects of changes in water temperature driven by global climate change on their distribution and fisheries. We aimed to identify the lower thermal tolerance (Tmin) of juvenile albacore tuna (ALB) and evaluate their behavioral response to Tmin by focusing on wild behavior in the northern distributional limit. Additionally, we investigated how vertical behavior is linked to the vulnerability of ALB to Japanese longline (LL) and pole-and-line (PL) fisheries. Methods: We explored the swimming depths and water temperatures of four previously reported tagged individuals migrating from subtropical to temperate areas and identified Tmin and its depths in the water column as unfavorable depths (DTmin). To investigate the spatial patterns of ALB fishery grounds for LL and PL fisheries, we analyzed hotspots specific to each type of gear using the historical Japanese fishery logbook for both fisheries. Results: Comparisons of the fishery grounds between the two fisheries revealed that PL hotspots appeared in the northern areas, while LL hotspots were in the southern regions. We also discovered that the vertical distribution of ALB became shallow in high-latitude areas, which were strongly affected by DTmin shallowing at high latitudes. Discussion: These results provide evidence of a behavioral response among juvenile ALB that avoids Tmin by remaining at the surface. We discuss the implications of the results for latitudinal changes in the vulnerability of ALB to fisheries in terms of the overlapping depth between ALB vertical habitats and the gear-setting depth for each fishery. [ABSTRACT FROM AUTHOR]

The lifestyle and culture of South Pacific Island countries have been long intertwined with oceanic resources. These countries are heavily dependent on tuna resources for their economies and socioeconomic livelihoods. Despite their importance, the mechanisms behind tuna stock trajectory patterns need to be better understood. With changing climatic and environmental conditions, it has become vital to understand the impact of these changes on tuna resources and if possible include them in long-term tuna harvest and management plans. A significant portion of the stock dynamics of yellowfin tuna (Thunnus albacares), albacore tuna (Th. alalunga) and bigeye tuna (Th. obesus) in the South Pacific Region may possibly be explained only by the environmental factors of sea surface temperature (SST) and Atlantic Multidecadal Oscillation AMO. The relationship of monthly SST and AMO was investigated with time series stock patterns of Th. albacares, Th. alalunga and Th. obesus in the Eastern and Western Pacific Ocean for the years 1972 to 2019. Monthly variables that exhibited significant correlation with CPUE variables were used in the Generalised Linear Model and Generalized Additive Model to reproduce the CPUE trajectory of the three tuna species from 1972 to 2019. Results showed that a significant portion of stock dynamics of Th. albacares, Th. alalunga and Th. obesus can be explained well by two environmental conditions of SST and AMO. This shows that a large portion of tuna variation in the Eastern and Southern Pacific is related to environmental conditions. Models with single variables are evidence of the significant individual effect of SST and AMO on stock time series of each tuna species. Models with two variables had a better fit in comparison to models with a single variable for all tuna stocks. Possibilities of two significantly different patterns in the trajectory of the three tuna species and environmental conditions used in the models were also observed. The trajectory patterns seemed to change around the 1990s and had significantly different means, indicating possible regime shifts. Environmental conditions play a highly significant role in structuring tuna stock trajectory in the South Pacific and need to be included in tuna management / harvest plans to ensure sustainability of this important resource. The importance of regime shifts should be recognised and further investigated for possible inclusion in tuna sustainability plans due to their influence on long-term tuna trajectory patterns.

Albacore tuna (Thunnus alalunga) is one of the target species of tuna longline fishing, and waters near the Cook Islands are a vital albacore tuna fishing ground. Marine environmental data are usually presented with different spatial resolutions, which leads to different results in tuna fishery prediction. Study on the impact of different spatial resolutions on the prediction accuracy of albacore tuna fishery to select the best spatial resolution can contribute to better management of albacore tuna resources. The nominal catch per unit effort (CPUE) of albacore tuna is calculated according to vessel monitor system (VMS) data collected from Chinese distant-water fishery enterprises from January 1, 2017 to May 31, 2021. A total of 26 spatiotemporal and environmental factors, including temperature, salinity, dissolved oxygen of 0–300 m water layer, chlorophyll-a concentration in the sea surface, sea surface height, month, longitude, and latitude, were selected as variables. The temporal resolution of the variables was daily and the spatial resolutions were set to be 0.5° × 0.5°, 1° × 1°, 2° × 2°, and 5° × 5°. The relationship between the nominal CPUE and each individual factor was analyzed to remove the factors irrelavant to the nominal CPUE, together with a multicollinearity diagnosis on the factors to remove factors highly related to the other factors within the four spatial resolutions. The relationship models between CPUE and spatiotemporal and environmental factors by four spatial resolutions were established based on the long short-term memory (LSTM) neural network model. The mean absolute error (MAE) and root mean square error (RMSE) were used to analyze the fitness and accuracy of the models, and to determine the effects of different spatial resolutions on the prediction accuracy of the albacore tuna fishing ground. The results show the resolution of 1 ° × 1° can lead to the best prediction accuracy, with the MAE and RMSE being 0.0268 and 0.0452 respectively, followed by 0.5° × 0.5°, 2° × 2° and 5° × 5° with declining prediction accuracy. The results suggested that 1) albacore tuna fishing ground can be predicted by LSTM; 2) the VMS records the data in detail and can be used scientifically to calculate the CPUE; 3) correlation analysis, and multicollinearity diagnosis are necessary to improve the prediction accuracy of the model; 4) the spatial resolution should be 1 ° × 1 ° in the forecast of albacore tuna fishing ground in waters near the Cook Islands. [ABSTRACT FROM AUTHOR]

Marine fisheries around the globe are increasingly exposed to external drivers of social and ecological change. Though diversification and flexibility have historically helped marine resource users negotiate risk and adversity, much of modern fisheries management treats fishermen as specialists using specific gear types to target specific species. Here, we describe the evolution of harvest portfolios amongst Pacific Northwest fishermen over 35+ years with explicit attention to changes in the structure and function of the albacore (Thunnus alalunga, Scombridae) troll and pole-and-line fishery. Our analysis indicates that recent social–ecological changes have had heterogenous impacts upon the livelihood strategies favoured by different segments of regional fishing fleets. As ecological change and regulatory reform have restricted access to a number of fisheries, many of the regional small (60 ft) targeting albacore are more specialized now than previously observed, even as participation in multiple fisheries has become increasingly common for this size class. In describing divergent trajectories associated with the albacore fishery, one of the US West Coast's last open-access fisheries, we highlight the diverse strategies and mechanisms utilized to sustain fisheries livelihoods in the modern era while arguing that alternative approaches to management and licensing may be required to maintain the viability of small-scale fishing operations worldwide moving forward.

The present study utilised a geometric mean model in which sea surface temperature, oxygen, and sea surface salinity were used to predict the effects of climate change on the habitats of mature albacore tuna in the Indian Ocean under multiple representative concentration pathway (RCP) scenarios. Data pertaining to the albacore tuna fishing conducted by Taiwanese longline fisheries during the October–March period in 1998–2016 were analysed. The fishery data comprised fishing location (latitude and longitude), fishing effort (number of hooks used), number of catches, fishing time (month and year), and fish weight. Nominal catch per unit effort data were standardised to mitigate the potential effects of temporal and spatial factors in causing bias and overestimation. The Habitat Suitability Index (HSI) scores of potential habitats for mature albacore in the Indian Ocean are predicted to change considerably in response to varying levels of predicted climate change. Under projected warm climate conditions (RCP 8.5), the stratification of water is predicted to cause low HSI areas to expand and potential habitats for mature albacore to shift southward by 2100. The findings derived from these mature albacore habitat forecasts can contribute to the evaluation of potential hazards and feasible adaptation measures for albacore fishery resources in the context of climate change. The distribution trends pertaining to potential habitats for mature albacore should be used with caution and can provide resource stakeholders with guidance for decision-making. [ABSTRACT FROM AUTHOR]

To maintain sustainable fisheries, albacore tuna is one of the commercial fish species whose management is regulated globally by the Regional Fisheries Management Organizations. Generally, sea surface temperature (SST) and chlorophyll-a (SSC) are used to determine fish suitability based on the catch data. In this research, we attempt to identify optimal habitats for albacore tuna in the southeastern Indian Ocean by analyzing in situ data based on onboard observers on tuna long line vessels from 2006–2019 and optimum interpolation sea surface temperature from NOAA-Advanced Very High-Resolution Radiometer and sea surface chlorophyll-a from Aqua MODIS satellites. The albacore tuna’s habitat suitability index was examined using the generalized additive model. The results suggested that albacore tuna inhabited waters with an SST range of 15–26 °C and SSC concentration of 0.075–0.125 mg/m3. In the Indian Ocean, most albacore tunas were captured at higher latitudes of 20°-30° S.

Tuna is a crucial economic fish species in the ocean, and the research on predicting the location of tuna fishing grounds has always been a key issue in deep-sea fisheries. Tuna, being a highly active fish that moves vertically in the ocean, is extremely sensitive to changes in marine environmental factors. This study aimed to investigate the impact of environmental factors and water depth changes on the accuracy of tuna fishing ground prediction. To achieve this, convolutional neural networks (CNNs) were utilized to train datasets using four key environmental factors - concentration of chlorophyll-a (CHLa), seawater temperature (ST), concentration of dissolved molecular oxygen (Oxy), and seawater salinity (SS) - at various depths ranging from 0 to 300 meters. A binary classification fishing ground prediction model for high and low yield areas of albacore and yellowfin tuna in the Western and Central Pacific Ocean was constructed. The goal was to identify the optimal fishing ground prediction model trained under these conditions and to explore the potential impact of environmental factors and water depth on the prediction accuracy of the model. The data used in this study included information from the Western and Central Pacific Ocean albacore and yellowfin tuna fisheries from 2003 to 2016, along with corresponding environmental data, which were used as the training and validation sets. The fishing data and environmental data from 2017 were then utilized as the test set to develop fishing ground prediction models for the two fish species. The results indicate that using convolutional neural networks to construct fishing ground prediction models is indeed feasible, and spatio-temporal information plays a significant role in optimizing predicting models for tuna fishing ground. Among the models developed for the same fish species using the four marine environmental factors at different depths, the model based on CHLa at each depth was found to be the most effective, while the model constructed using Oxy at the same depth performed the worst. Furthermore, the albacore fishing ground prediction model demonstrated significantly higher efficacy compared to the yellowfin tuna fishing ground prediction model when using the same marine environmental factors. It was also observed that the accuracy of fishing ground prediction models for the same species varied depending on water depth, even when based on the same marine environmental factors. These findings highlight the importance of considering both environmental factors and water depth in predicting tuna fishing grounds accurately. • Deep learning was used to analyze depth-varied marine environments to predict albacore and yellowfin tuna fishing grounds. • Chlorophyll-a-based models excelled in depth-based fishing ground forecasts; oxygen-based models underperformed. • Predictive models favored albacore over yellowfin tuna for the same environmental conditions. • The accuracy of the fishery forecasting models varied for the same species depending on the water depth. [ABSTRACT FROM AUTHOR]

The present study utilised a geometric mean model in which sea surface temperature, oxygen, and sea surface salinity were used to predict the effects of climate change on the habitats of mature albacore tuna in the Indian Ocean under multiple representative concentration pathway (RCP) scenarios. Data pertaining to the albacore tuna fishing conducted by Taiwanese longline fisheries during the October–March period in 1998–2016 were analysed. The fishery data comprised fishing location (latitude and longitude), fishing effort (number of hooks used), number of catches, fishing time (month and year), and fish weight. Nominal catch per unit effort data were standardised to mitigate the potential effects of temporal and spatial factors in causing bias and overestimation. The Habitat Suitability Index (HSI) scores of potential habitats for mature albacore in the Indian Ocean are predicted to change considerably in response to varying levels of predicted climate change. Under projected warm climate conditions (RCP 8.5), the stratification of water is predicted to cause low HSI areas to expand and potential habitats for mature albacore to shift southward by 2100. The findings derived from these mature albacore habitat forecasts can contribute to the evaluation of potential hazards and feasible adaptation measures for albacore fishery resources in the context of climate change. The distribution trends pertaining to potential habitats for mature albacore should be used with caution and can provide resource stakeholders with guidance for decision-making.

Albacore tuna (Thunnus alalunga) exhibit patchy concentrations associated with biological process at a wide range of spatial scales, resulting in variations in their catchability by fishing gears. Here, we investigated the association of catch variation for pelagic longlines in the South Pacific Ocean with oceanographic mesoscale structures (in horizontal dimension) and ambient conditions (in vertical dimension). The distribution of albacore tuna as indicated by catch per unit effort (CPUE) of longlines was significantly related to the presence of mesoscale structures, with higher CPUE found at locations closer to thermal fronts and with greater gradient magnitudes, as well as areas marked by peripheral contour line of the anticyclone indicated by Sea Surface Height Anomalies ~0.05 m. Surface mesoscale current velocity had the negative effect on the catch, probably as a result of decreased catchability by shoaling the hook depth. Vertical distribution of albacore in the survey region of South Pacific Ocean was hardly restricted by ambient temperature and oxygen concentration, though effect of ambient temperature was relevant and showed a negatively linear correlation with CPUE at the range of 20–24°C. On the contrary, albacore distribution was evidently dominated by the water depth and showed strong preference on water depth of 200 m, which was likely a representative feeding layer. The presence of prey resources and their accessibility by albacore revealed by mesoscale structures in the biological and physical processes, and catchability determined by the location of the baited hooks comprehensively contribute to the variability of catch. [ABSTRACT FROM AUTHOR]

Considerable uncertainty remains over how increasing atmospheric CO2 and anthropogenic climate changes are affecting open‐ocean marine ecosystems from phytoplankton to top predators. Biological time series data are thus urgently needed for the world's oceans. Here, we use the carbon stable isotope composition of tuna to provide a first insight into the existence of global trends in complex ecosystem dynamics and changes in the oceanic carbon cycle. From 2000 to 2015, considerable declines in δ13C values of 0.8‰–2.5‰ were observed across three tuna species sampled globally, with more substantial changes in the Pacific Ocean compared to the Atlantic and Indian Oceans. Tuna recorded not only the Suess effect, that is, fossil fuel‐derived and isotopically light carbon being incorporated into marine ecosystems, but also recorded profound changes at the base of marine food webs. We suggest a global shift in phytoplankton community structure, for example, a reduction in 13C‐rich phytoplankton such as diatoms, and/or a change in phytoplankton physiology during this period, although this does not rule out other concomitant changes at higher levels in the food webs. Our study establishes tuna δ13C values as a candidate essential ocean variable to assess complex ecosystem responses to climate change at regional to global scales and over decadal timescales. Finally, this time series will be invaluable in calibrating and validating global earth system models to project changes in marine biota.Anthropogenic climate change is expected to alter open‐ocean marine ecosystems from phytoplankton to top predators. Our study revealed that changes in the marine carbon cycle can be traced in the tissues of marine top predators. We detected a worldwide decrease in tuna δ13C values over the 2000–2015 period. Our analysis suggests a widespread shift in marine phytoplankton community structure or a change in phytoplankton physiology, while this does not exclude other factors that may act in synergy (Suess effect, productivity, trophic fractionation factor). [ABSTRACT FROM AUTHOR]

In the current study, remotely sensed sea surface ocean temperature (SST) and sea surface chlorophyll (SSC), an indicator of tuna abundance, were used to determine the optimal feeding habitat zone of the southern Indian Ocean (SIO) albacore using a habitat suitability model applied to the 2000–2016 Taiwanese longline fishery data. The analysis showed a stronger correlation between the 2-month lag SSC and standardized catch per unit effort (CPUE) than 0-, 1-, 3-, and 4-month lag SSC. SST also exhibited a stronger correlation with standardized CPUE. Therefore, SST and SSC_2 were selected as final variables for model construction. An arithmetic mean model with SST and SSC_2 was deemed suitable to predict the albacore feeding habitat zone in the SIO. The preferred ranges of SSC_2 and SST for the feeding habitat of immature albacore were 0.07–0.09 mg m−3 and 16.5–18.5 °C, respectively, and mainly centralized at 17.5 °C SST and 0.08 mg m−3 SSC_2. The selected habitat suitability index model displayed a high correlation (R2 = 0.8276) with standardized CPUE. Overall, temperature and ocean chlorophyll were found to be essential for albacore habitat formation in the SIO, consistent with previous studies. The results of this study can contribute to ecosystem-based fisheries management in the SIO by providing insights into the habitat preference of immature albacore tuna in the SIO.

Anionic trypsin from albacore tuna spleen was purified by chromatographic separations on Q-Sepharose, Superdex 75 and Arginine Sepharose 4B. The trypsin migrated as single bands in both SDS-PAGE and native-PAGE. The molecular weight of purified trypsin was estimated to be 30 kDa using SDS-PAGE. The enzyme exhibited maximal activity at pH 9.0 and 55 °C for hydrolysis of Boc-Val-Pro-Arg-MCA. pH and temperature stabilities of the trypsin were well maintained in the pH range of 6–11 and over a temperature range from 20 up to 50 °C. The enzyme was effectively inhibited by soybean trypsin inhibitor, N ‑tosyl‑ l ‑phenyl‑alanine chloromethyl ketone (TLCK) and Pefabloc SC. The N -terminal amino acid sequence of 20 residues of the purified enzyme was IVGGYECQAHSQPHQVSLNA, which is highly homologous to other fish trypsins. The k cat / K m of the enzyme for Boc-Val-Pro-Arg-MCA was 2.60 ± 0.07 s−1 mM−1. Purified trypsin also hydrolysed fish muscle proteins, suggesting its effectiveness in degradation of food proteins. Unlabelled Image • A 30 kDa albacore tuna spleen anionic trypsin was purified and characterized. • The purified enzyme showed high activity over a wide pH and temperature range. • The enzyme was also stable at high salt concentration. • The purified trypsin was able to hydrolyze fish muscle proteins effectively. [ABSTRACT FROM AUTHOR]

Abstract South Pacific albacore is a species of primary importance in the longline fishery of a number of Small Island Developing States in the Western and Central Pacific Ocean. Despite the fact that the stock is assessed as not being subject to overfishing and not overfished, economic returns have declined significantly over the past decade. This has led to calls for management intervention. Given stated biological and economic objectives for the fishery, members of the Pacific Islands Forum Fisheries Agency proposed an interim stock target reference point to the Western and Central Pacific Fisheries Commission that would imply a larger stock size, higher catch rates and a more profitable fishery (FFA Members, 2015). The purpose of this study is to examine the biological and economic consequences along the trajectories of two distinct longline effort reduction regimes that achieve the proposed target reference point within 20 years and review the trade-offs in terms of forgone catch or effort and forgone revenue. The two effort regimes examined are a one-off reduction implemented immediately, and a phased reduction under which effort is reduced by a fixed percent each year. The results are discussed in the light of wider Pacific Island objectives for fishery production and fleet profitability and highlights the importance of moving beyond a purely biological stock-based focus when providing management advice. Highlights • The South Pacific albacore stock is biologically healthy but fishery unprofitable. • Different effort reduction regimes yield different economic consequences. • Fast sharp effort reduction shown to generate higher rents than gradual cuts. • Management effort cut decision may consider wider objectives other than rents. [ABSTRACT FROM AUTHOR]

Decision strategies in fisheries management are often directed by the geographic distribution and habitat preferences of target species. This study used remote sensing data to identify the optimal feeding habitat of albacore tuna in the Southern Atlantic Ocean (SAO) using an empirical habitat suitability model applying longline fisheries data during 2009–2015. An arithmetic mean model with sea surface temperature (SST) and sea surface chlorophyll-a concentration (SSC) was determined to be suitable for defining the albacore habitat in the SAO. The optimal ranges of SST and SSC for the habitat were approximately 16.5 °C–19.5 °C and 0.11–0.33 mg/m3, respectively. The study revealed a considerable positive trend between the suitable habitat area and standardized catch per unit effort (r = 0.97; p < 0.05); due to the west-to-east and northward development of the suitable habitat, albacore schools moved to the northeast of the SAO, thus increasing catch probability in April to August in that region. Overall, the frontal structure of SST and SSC plays an essential role in the formation of potential albacore habitats in the SAO. Our findings could contribute to the establishment of regional ecosystem-based fisheries management in the SAO.

Aim: We examined potential environmental drivers of broad‐scale spatial patterns in the trophic structure of marine ecosystems as represented by nitrogen stable isotopes in globally distributed marine predators. Additionally, we assessed the effects of spatial scale on the predictive capabilities of environmental variables. Location: Global oceans. Time period: 2000 to 2015. Major taxa studied: Tunas: Thunnus albacares, Thunnus obesus, Thunnus alalunga. Methods: We undertook a global compilation and meta‐analysis of the bulk nitrogen stable isotope ratios (δ15N values) of three tuna species (n = 4,281). After adjusting for regional variations in baseline δ15N values using a global ocean biogeochemistry model, generalized additive mixed models were employed to infer global‐scale oceanographic controls of trophic structure, using cosmopolitan tuna species as a model. Results: For the three tuna species, variation in trophic position estimated using bulk δ15N values was largely explained by geographical location and the corresponding oxygen minimum layer depth. Tuna trophic positions declined in areas with reduced oxygen at depth. Food‐chain length, as captured by maximum trophic position, was longer in areas of the western Pacific Ocean and shorter in the northern Atlantic and eastern Pacific Oceans. Trophic adaptability of the tuna predators, as indicated by intraspecific variability, was highest in the western and central Pacific Ocean and lowest in the northern Atlantic Ocean. Our analysis demonstrated that while tunas share similar functional trophic roles, deeper‐foraging tuna species had higher trophic positions globally. The predictive capacity of environmental variables decreased at finer (regional) spatial scales. Main conclusions: Our work suggests that habitat compression resulting from the predicted global expansion of oxygen minimum zones with ocean warming will impact the trophic structure of marine food webs and the corresponding foraging habits of marine predators. Spatial scale analyses highlighted the importance of representing differences in regional ecological dynamics in global‐scale trophic and ecosystem models. [ABSTRACT FROM AUTHOR]

For management purposes, albacore tuna ( Thunnus alalunga, Bonnaterre 1788) in the North Atlantic are considered to be from one homogenous stock. However, multiple lines of evidence suggest that there is some degree of stock complexity. In this study, the stock structure of North Atlantic albacore tuna is investigated using otolith shape analysis. Juvenile albacore tunas were collected from the commercial fishery in the Bay of Biscay region over a three-year period (2012–2014). Catches were concentrated in two main areas: within the Bay of Biscay (East) and off the western shelf edge (West). Otolith shape was defined using Elliptical Fourier analysis and was compared between albacore from these two catch locations using generalised canonical discriminant analysis. The results show significant differences in otolith shape between albacore from the Eastern and Western locations using Elliptical Fourier descriptors. The discriminant analysis and jack-knifed cross-validation classification correctly classified East and West samples with a success rate of 72% and 75% respectively. The results suggest that two components with distinct environmental life histories contribute to the fishery in the Northeast Atlantic. It also implies that albacore juveniles display some degree of fidelity to their feeding areas. [ABSTRACT FROM AUTHOR]

The waters surrounding the Balearic archipelago are considered to be prime spawning habitats of the bluefin tuna (Thunnus thynnus) and other tuna species such as albacore (T. alalunga) in the Mediterranean. During the 2003 bluefin and albacore spawning season, a tuna larval survey (TUNIBAL 0703) was carried out to assess the distribution of bluefin larvae in relation to hydrographic mesoscale features. Tuna larvae were collected by means of surface plankton tows with a bongo gear with a quadrangular mouth measuring 1 m diagonally. The otolith microstructure of 157 and 71 field-captured larvae of Mediterranean bluefin and albacore, respectively, were analyzed to estimate the daily growth pattern. Furthermore, biochemical analysis to estimate DNA, RNA and protein content was done on another batch of 114 bluefin and 132 albacore larvae. The size range included pre-flexion to post-flexion larvae, from 2.8 to 8.6 mm in body length. bluefin and albacore larvae grew linearly in standard length (0.35 and 0.33 mm/day, respectively) and potentially with respect to dry weight. No significant differences between species were observed in the size-weight relationship, or in the allometric relationship of body size and weight to otolith radius. However, the relationship of DNA and RNA to body size and weight showed a significant difference between species. Bluefin tuna larvae showed a greater nucleic acid content than albacore larvae. Protein content showed no significant differences with respect to body length.

Albacore tuna are widespread in the North Pacific Ocean and the basis of an important commercial fishery. These fish live mainly within a fairly narrow thermal niche range defined by sea surface temperature ( SST) isotherms between 14 and 19°C. Because the fish's thermal range coincides with strong latitudinal temperature gradients off the northwest coast of North America, there is a great deal of seasonal and interannual variability in the distribution of these fish, and a significant potential for a new habitat in this region with anthropogenic climate change. We use historical catch and effort data from the Canadian troll fleet to define the fish's thermal niche, and document observed shifts in distribution associated with interannual climate variability. We then use an ensemble of climate model simulations from the Coupled Model Intercomparison Project to estimate northward extension of the potential habitat under anthropogenic warming scenarios. A potential new habitat is about half a million square kilometres even under a moderate mitigation scenario. Estimates are smaller for some months of the year in which the fishery is conducted, but as well as opening up new regions, the length of season in which the fishery is active may be extended in the northern part of the range. However, much of the potential new habitat will be in oceanic waters with relatively low productivity. Our estimated area of potential habitat is based on the fish's thermal niche and assumes that other biologically important factors such as food will not be limiting. [ABSTRACT FROM AUTHOR]

The south Pacific albacore tuna ( Thunnus alalunga ) stock is predicted to remain above the adopted limit reference point under recent increased catch levels. However, vessel catch rates are predicted fall and economic conditions worsen, which is of particular concern for those smaller-scale fleets within Pacific island countries and territories that rely on this stock for income and employment. We examine candidate target reference points that might achieve wider management objectives integrating across multiple plausible states of nature using a deterministic bio-economic model, and potential implications of those targets for the stock and fisheries through stochastic stock projections. Maximum sustainable yield (MSY), the ‘default’ reference point within the Western and Central Pacific Fisheries Commission, implied a relatively low stock size and more than a 1-in-3 chance of the stock falling below the limit reference point. Minimum target levels, defined by the permissible level of risk (5–20%) of falling below the limit reference point, implied larger stock sizes than at MSY, but a halving in longline catch rates that would lead to increased social and economic hardship. These results suggest that economic, rather than biological, requirements will provide the standards for an albacore target reference point. However, achieving maximum economic yield (MEY) implied severe reductions in effort, likely incompatible with objectives for employment within the local fishery sector or the level of vessel licensing revenue. Sub-optimal but improved economic performance levels examined, such as a 10% revenue margin over economic costs, or revenues equal to the economic costs, could be obtained with less severe reductions in effort. Identifying an acceptable target reference point compatible with fishery objectives, and ways to transition from recent fishing levels to those targets, is urgently needed to ensure fleets remain viable. [ABSTRACT FROM AUTHOR]

Signature fatty acids were used to explore trophic variations in albacore and skipjack tuna sampled from the southwestern Pacific Ocean. There were clear spatial differences in fatty acid profiles between albacore sampled in the Coral (tropical zone centered at ~20°S) and Tasman (temperate zone centered at ~42°S) Seas; however, few differences were observed in fatty acid profiles of albacore sampled off Tasmania and New Zealand. Fatty acid signatures of the Tasman Sea samples reflected a food web based more on diatoms and included: 20:5ω3 (EPA), 18:1ω7, 22:1ω11, 18:2ω6, 18:4ω3, 18:3ω3, and 20:4ω3. In contrast, albacore from the Coral Sea had a distinct fatty acid signature which included 20:4ω6, 22:5ω6, 17:0, 22:4ω6, 24:0, and 17:1. Multivariate analyses revealed the importance of 22:6ω3 (DHA) in Coral Sea-caught albacore which also had a DHA/EPA ratio more than twice that in all other groups suggesting a greater dinoflagellate contribution and/or a higher trophic position. Fatty acid markers indicative of krill consumption were significantly higher in temperate-caught albacore although skipjack were closest in fatty acid composition to krill. These results were likely due to differences at the base of the food web in these two seas suggesting that signature fatty acids can be used as indicators of ecosystem change: in this case the gradual ‘tropicalization’ of the eastern seaboard of Australia through the southward extension of the East Australian Current. Our findings also indicate comparatively lower concentrations of healthful ω3 long-chain polyunsaturated fatty acids, in particular the content of DHA and EPA, in the tropical samples. This suggests that tropicalization could adversely affect the dietary intake of albacore and other marine predators in the region. Such changes are readily detectable by fatty acid analysis. [ABSTRACT FROM AUTHOR]

Fatty acids are a valuable tool in ecological studies because of the large number of unique structures synthesized. They provide versatile signatures that are being increasingly employed to delineate the transfer of dietary material through marine and terrestrial food webs. The standard procedure for determining fatty acids generally involves lipid extraction followed by methanolysis to produce methyl esters for analysis by gas chromatography. By directly transmethylating ~50 mg wet samples and adding an internal standard it was possible to greatly simplify the analytical methodology to enable rapid throughput of 20-40 fish tissue fatty acid analyses a day including instrumental analysis. This method was verified against the more traditional lipid methods using albacore tuna and great white shark muscle and liver samples, and it was shown to provide an estimate of sample dry mass, total lipid content, and a condition index. When large fatty acid data sets are generated in this way, multidimensional scaling, analysis of similarities, and similarity of percentages analysis can be used to define trophic connections among samples and to quantify them. These routines were used on albacore and skipjack tuna fatty acid data obtained by direct methylation coupled with literature values for krill. There were clear differences in fatty acid profiles among the species as well as spatial differences among albacore tuna sampled from different locations. [ABSTRACT FROM AUTHOR]

Highlights: [•] Issues regarding the accuracy and precision of CPUE standardizations prevail. [•] Standardization using normal and finite mixture models is compared. [•] Residual diagnostics in the finite mixture model are markedly improved. [•] Precision of estimates is increased. [•] Fish abundance and fleet behavior are more accurately reflected. [Copyright &y& Elsevier]

• Isotope variability of three tuna species is mainly affected by the spatial component. • δ15N spatial predictions suggest three regions with highest values. • Fish size affects δ13C values in albacore and bigeye tuna. Stable isotope (δ13C and δ15N) analysis is an ecological tracer technique that reveals information on links between trophic levels, migratory species movement patterns, or geographic variations due to the different oceanic processes affecting them. Tuna species are ecologically important and can be used as proxies to generate information on how different variables –spatio-temporal, environmental and biological– can affect ecological tracers such as stable isotopes at the basin level. Thus, the main objective of this study is to examine how spatiotemporal, biological, baseline isotopic values and environmental drivers impact stable isotope distribution in three tuna species –albacore (Thunnus alalunga), bigeye (T. obesus) and yellowfin (T. albacares) in the Pacific Ocean (obtained from the Global data set for nitrogen and carbon stable isotopes of tunas) using Generalized Additive Modeling (GAM). The results suggest that the three species δ15N and δ13C values are mainly affected by the spatial and size or spatial and physical (depth) predictors. The highest isotopic values in the three species were found to be associated with hydrological and oceanographic conditions (Island Mass Effect), generating more productive areas and serves as a feeding ground for various commercially and ecologically important species. Spatial predictions (best-fitted GAM) of δ15N suggest three regions with the highest values: 1) Western Central Pacific (Solomon Island, 160-190°E); 2) Central Pacific (French Polynesia, 200-230°E); 3) Eastern Pacific (Southern California Current; 240°E, 20°N). For δ13C, the same three regions were observed with some differences in centroids –southwestward, northward, and southeastward, respectively. This knowledge can be used to infer ecosystem productivity, using isotope signatures at an ocean basin scale. [ABSTRACT FROM AUTHOR]

Abstract: Length frequency data are essential to the stock assessments of albacore (Thunnus alalunga) which has been either fully- or over-exploited in many regions of the world. To obtain ‘visible’ and verifiable length data, a photo-based length measurement approach was previously developed in which fishers take photos of fish adjacent to a plastic calibration board with colored squares using ordinary digital camera technology. Here we assess the feasibility of implementing the photo-based approach using direct comparisons with measured lengths from observer programs. Data from the Taiwanese longline albacore fishery are used to assess the utility of the photo approach in terms of accuracy (with considerations of on-board photographing and at-land length estimation) and cost (comparing with port-sampling and observer programs). Results indicate potentially significant cost savings compared with the other two programs, with acceptable levels of estimation error. [ABSTRACT FROM AUTHOR]

Abstract: Pepsinogen (PG) from the stomach of albacore tuna (Thunnus alalunga) was purified to homogeneity by using a series of chromatographies involving Sephacryl S-200HR, Sephadex G-50 and DEAE-cellulose with a 658-fold increase in purity. Based on the native-PAGE and zymography, PG showed a single band with pepsin activity. Molecular weights (MW) of PG and active pepsin were estimated to be 39.9 and 32.7kDa as determined by SDS–PAGE, respectively. PG was converted to the corresponding pepsin through an intermediate form (MW≈36.8kDa) and the complete activation was observed after 30–60min. The N-terminal amino acid sequence of the first 15 amino acids of activation segment of pepsinogen was FHKLPLIKGKTAREE. The optimal pH and temperature for pepsin activity were 2.0 and 50°C, respectively. The activity was stable in the pH range of 2–5. Residual activity more than 85% was found after heating at temperatures up to 50°C for 30min. Pepsin activity was strongly inhibited by pepstatin A, whilst E-64, ethylenediaminetetraacetic acid (EDTA) and soybean trypsin inhibitor exhibited the negligible effect. SDS and cysteine also showed inhibitory effects, whilst ATP, molybdate, NaCl and CaCl2 had no impact on pepsin activity. [Copyright &y& Elsevier]

The South Equatorial Counter Current (SECC) strongly influences the American Samoa Exclusive Economic Zone (EEZ) and changes strength on a seasonal and ENSO cycle. A strong SECC is associated with a predominantly anticyclonic eddy field as well as increased micronekton biomass and catch-per-unit-effort (CPUE) for albacore tuna, the economically important target species of the local longline fishery. A strong SECC carries chlorophyll a-rich waters from upwelling regions at the north coast of New Guinea towards the EEZ, most likely resulting in the observed increase in micronekton biomass, forage for albacore. Relatively stable anticyclonic eddies show a further increase in micronekton biomass, apparently advected from neighboring SECC waters. The presence of forage presumably concentrates albacore, thus resulting in the observed increase in CPUE. High shear regions of neither anticyclonic nor cyclonic eddies correlate with increased micronekton biomass. Areas characterized by South Equatorial Current (SEC) waters correspond to areas with the lowest micronekton biomass and the highest number of aggregative structures, which are most likely small pelagic fish shoals. Micronekton composition in SEC waters differs from that in the SECC. During El Niños, the seasonal signals at the north shore of New Guinea and in the SECC are exceptionally strong and correspond to higher albacore CPUE in the EEZ. My results suggest that the strength of upwelling and the resulting increase in chlorophyll a at New Guinea, as well as the Southern Oscillation Index, could be used to predict the performance of the local longline fishery for albacore tuna in the American Samoa EEZ. [ABSTRACT FROM AUTHOR]

Changes in the fatty acid composition of 13 bled and blast-frozen U.S. West Coast albacore tuna (Thunnus alalunga) were determined following custom-canning and 5 weeks of canned storage. In accordance with typical custom-canning procedures, no additional packing materials were used, and the product did not undergo a precooking step. Raw albacore tuna was found to be rich in n-3 polyunsaturated fatty acids (PUFA5), with an average of 9.1% (% wt of total fatty acids) EPA and 33.8% DHA. Canning and short-term storage did not cause major fluctuations in the fatty acid profiles of the albacore tuna, with no significant changes in the total fractions of saturated fatty acids (30-31%), monounsaturated fatty acids (19%), PUFAs (50%), or n-3 PUFAs (46-47%). On a tissue weight basis, U.S. West Coast albacore tuna was found to contain high levels of total n-3 PUFAs, with 3.3 g/100 g tissue in raw tuna and 4.0-4.1 g/100 g tissue in products that were canned and stored for 5 weeks. [ABSTRACT FROM AUTHOR]

The American Samoa fishing ground is a dynamic region with strong mesoscale eddy activity and temporal variability on scales of <1 week. Seasonal and interannual variability in eddy activity, induced by baroclinic instability that is fueled by horizontal shear between the eastward-flowing South Equatorial Counter Current (SECC) and the westward-flowing South Equatorial Current (SEC), seems to play an important role in the performance of the longline fishery for albacore. Mesoscale eddy variability in the American Samoa Exclusive Economic Zone (EEZ) peaks from March to April, when the kinetic energy of the SECC is at its strongest. Longline albacore catch tends to be highest at the eddy edges, while albacore catch per effort (CPUE) shows intra-annual variability with high CPUE that lags the periods of peak eddy activity by about 2 months. When CPUE is highest, the values are distributed toward the northern half of the EEZ, the region affected most by the SECC. Further indication of the possible importance of the SECC for longline performance is the significant drop in eddy variability in 2004 when compared with that observed in 2003 – resulting from a weak SECC – which was accompanied by a substantial drop in albacore CPUE rates and a lack of northward intensification of CPUE. From an ecosystem perspective, evidence to support higher micronekton biomass in the upper 200 m at eddy boundaries is inconclusive. Albacore's vertical distribution seems to be governed by the presence of prey. Albacore spend most of their time between 150 and 250 m, away from the deep daytime and shallow nighttime sonic scattering layers, at depths coinciding with those of small local maxima in micronekton biomass whose backscattering properties are consistent with those of albacore's preferred prey. Settling depths of longline sets during periods of decreased eddy activity correspond to those most occupied by albacore, possibly contributing to the lower CPUE by reducing catchability through rendering bait less attractive to albacore in the presence of prey. [ABSTRACT FROM AUTHOR]

Abstract: In this study, results from an observer programme on a drift net fishery in the eastern North Atlantic are presented. Observers recorded all fish, marine mammals, seabirds and turtles caught and discarded and coverage ranged from 47.8% of the fleet (n =7 vessels) in 1996, to 2.2% (n =21 vessels) in 1998. A minimum of seven fish species were caught and landed during the fishing period; albacore tuna (Thunnus alalunga) comprised approximately 99% of the total landings (by number) in both years. Eleven fish species were discarded, of which blue shark (Prionace glauca) was the most frequently recorded representing 68% of all fish discarded by number. At least four species of seabird (Northern Gannet Morus basanus, Northern Fulmar Fulmarus glacialis, Manx shearwater Puffinus puffinus, Atlantic Puffin Fratercula arctica) and two species of turtle, including the leatherback turtle (Dermochelys coriacea), were also entangled. Eight species of Cetacea were recorded as bycatch during these fishing operations, including common dolphins Delphinus delphis and striped dolphins Stenella coeruleoalba. Length–frequency distributions for both these dolphin species suggest that age segregation occurs. Using landings of albacore tuna as an indicator of effort, the extrapolated decadal scale data from Irish and other driftnet fleets operating in this area suggest that during the period 1990–2000, a minimum (95% confidence intervals) of 778,452 (622,520–934,384) blue sharks were caught, with a substantial proportion discarded. An estimated 24,358 dolphins were killed during these years by these fleets, of which 11,723 (7670–15,776) were common dolphins and 12,635 (10,009–15,261) were striped dolphins. Although this type of fishing was effective at catching the target species, it removed a large biomass of megafauna and likely accelerated the decline of blue sharks in this area. [Copyright &y& Elsevier]

Abstract: Fifty-six cans containing meat from either the dorsal loin or the ventral flap of 10 troll-caught albacore tuna were tested for total mercury concentration prior to and after canning and retort cooking. The albacore tuna were harvested off the US Pacific Coast during the 2004 season and weighed between 5.4 and 10.2kg. Tuna meat was packed in cans raw or in water or olive oil, and cans were drained before post-canning analysis. The average concentrations of total mercury were: 0.17ppm (range 0.09–0.24ppm) in the pre-canned samples and 0.21ppm (range 0.10–0.33ppm) in the post-canned samples. Although the mercury concentration per gram of tissue was significantly higher following canning, the overall amount of mercury in the samples did not change significantly. [Copyright &y& Elsevier]

Abstract: Minced albacore muscle was treated with high-hydrostatic pressure at 275 and 310 MPa for 2, 4, and 6 min and their effects on shelf life at 4 and −20 °C were studied. Physical (texture, color), chemical (moisture and lipid content, pH, lipid oxidation, electrophoresis), and microbiological analyses were carried out. Pressure increased pH, protected from lipid oxidation, maintained low microorganisms levels, changed the color of the muscle, and induced the formation of high molecular weight polypeptides most likely through disulfide bonding promoting texture improvement of samples. Pressure improved the shelf life of minced albacore muscle for >22 days at 4 °C and >93 days at −20 °C. [Copyright &y& Elsevier]

Ninety-one albacore tuna (Thunnus, alalunga) captured during the 2003 commercial fishing season were tested for total mercury content in muscle tissue. The fish were harvested between 32.72°N (off Southern California) and 48.30°N (off the northern tip of Washington) between July and November. Fish weighed from 3.14 to 11.62 kg and were 50.8-86.4 cm long. Total mercury content in the albacore muscle tissue ranged from 0.027 ppm (µg/g) to 0.26 ppm. The average total mercury content was 0.14± 0.05 ppm. which is below the U.S. Food and Drug Administration action level and Canadian standards (1.0 ppm methylmercury and 0.50 ppm total mercury. respectively). Total mercury concentrations showed positive correlations with length and weight of albacore (R² = 0.40 and 0.38. respectively). but there was no correlation with date of capture or lipid content. Results indicate that Pacific troll-caught albacore have low levels of total mercury in the edible flesh and are well within international safety standards for mercury levels in fish. [ABSTRACT FROM AUTHOR]

A reverse dot-blot DNA/DNA hybridization method coupled with a non-radioactive nucleic acid detection system was evaluated for the direct detection of the emerging pathogen Stenotrophomonas maltophilia in albacore tuna, a fish species of high commercial value in Europe and the US. Probes consisting of total genomic DNA of S. maltophilia, when used in dot-blot hybridization assays, differed in a sufficient way with respect to Morganella morganii, Enterobacter aerogenes Enterobacter agglomerans, Klebsiella planticola, Acinetobacter baumani and other bacteria frequently isolated from spoiled tuna fish species, as to allow its specific detection in extracts of albacore tuna. The introduction of an enrichment step prior to DNA isolation and labelling allowed the successful detection of 102 viable cells of S. maltophilia in 1 ml of artificially-contaminated albacore muscle extracts with no cross-hybridization with other Gram-negative competing microflora being observed. The detection strategy described in this work may be useful for the detection and control of S. maltophilia in tuna fish species and seafood products. [Copyright &y& Elsevier]