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Context: In pursuit of protecting 30% of the ocean by 2030, large scale marine protected areas (LSMPAs) are rapidly increasing, especially in small island developing states (SIDS). Many SIDS have limited offshore research expertise or capacity to evaluate the efficacy of LSMPAs. The offshore Palau National Marine Sanctuary (PNMS) necessitated the Republic of Palau to develop its offshore research ability aimed at supporting science-based management. Owing to Palau's important tuna fishery, investigating tuna reproductive biology in the PNMS was prioritized as a first step in evaluating the protective significance of the PNMS for tuna. Aims: The aim of this study was to develop a useful and practical platform to conduct large scale ocean research within the context of SIDS. Methods: A platform to conduct offshore research was developed. Reproductive histology and the presence and abundance of larvae were used to investigate tuna reproductive biology in the PNMS. Key results: Most tunas sampled were mature, with 3 of the 59 sampled fish actively spawning. Twenty-two tuna larvae were collected across five offshore sites, and modeling results suggest larvae originated from these sites. Conclusions: Findings suggest tuna spawn, to some extent, within the PNMS, and the PNMS provides local protection to tuna populations during this time. A research platform with five steps for developing, undertaking and understanding offshore research in SIDS was developed. Challenges and tips experienced are also detailed. Implications: This platform can support the ever-increasing demand for offshore research in small island, large ocean states with limited resources and expertise. Conducting research in large offshore areas usually require large research vessels, significant funding and specific expertise, most of which are not readily available in small island developing states. Even with limited funding, facilities and expertise, we were able to answer a key research question for the fully offshore Palau National Marine Sanctuary. Furthermore, by doing so developed a research platform with five key steps to develop and implement offshore research with limited resources and expertise. [ABSTRACT FROM AUTHOR]

ABSTRACT To reduce catches of juvenile bigeye and yellowfin tuna, while maintaining skipjack catches under drifting fish aggregating devices (dFAD), we analyzed spatiotemporal distributions of dFAD catches by European purse seiners in the Eastern Atlantic Ocean during 1996–2019. To detect hotspots of juvenile dFAD catches, we: identified periods of maximum abundance using a seasonal sub‐series diagram; normalized monthly FAD catches per unit effort; and used emerging hotspots analysis on spatiotemporal density. Two main spatiotemporal strata were identified in the Guinean Gulf, which could be used to establish moratoria on dFAD fishing. These spatiotemporal strata differed from the existing ICCAT moratorium, which spanned a larger part of the African coast. Our findings also indicated that time‐area closures of dFAD‐fishing lasting 3–4 months in smaller areas could be more effective than the current dFAD moratorium to reduce unwanted bycatch in the Eastern Atlantic region. The two metrics we developed for comparison provided clear and measurable evidence that demonstrated how strategic and data‐informed moratoriums can lead to substantial improvements in conservation. [ABSTRACT FROM AUTHOR]

ABSTRACT Bigeye tuna (Thunnus obesus; BET) and yellowfin tuna (Thunnus albacares; YFT) are commercially and ecologically important Atlantic Ocean species. Numerous studies have examined interacting species with clearly synchronous or asynchronous dynamics, but few have investigated interactions among tuna species. This study investigated the effects of climate indices on the standardized catch per unit effort (CPUE) and habitat preferences of BET and YFT in the Atlantic Ocean. The indicators for both tuna species were found to be influenced by the Atlantic Multidecadal Oscillation (AMO) and Tropical North Atlantic index. The AMO had the strongest effect on standardized CPUE for the two species, and habitat suitability also reflected AMO trends. We compared CPUE trends in overlapping suitable habitat areas and estimated variations in primary prey abundance for between BET and YFT to evaluate their species' competition for limited prey and habitat area resources. The standardized CPUE, habitat suitability index (HSI), and primary prey levels (squid and crustaceans) of BET all increased following the change to the positive AMO phase after the 1990s. Although the HSI value for YFT also increased in an area of habitat overlap, the corresponding standardized CPUE decreased. We suggest that this pattern of a decreasing‐standardized CPUE for YFT may have been caused by competition for limited prey and habitat area resources in the overlap area. [ABSTRACT FROM AUTHOR]

Tuna are economically important as food resources in food markets. However, because tuna is often processed into steaks or fillets, the meat can be difficult to identify through morphological features. For effective fishery management and to protect the rights of consumers, it is necessary to develop a molecular method to accurately identify the species used in tuna products. Herein, we discovered five single-nucleotide polymorphism (SNP) sites via 2b-RAD sequencing and developed five SNP-based real-time polymerase chain reaction assays for the rapid identification of five highly priced tuna species. Three species-specific TaqMan systems were designed to identify albacore tuna (Thunnus alalunga), bigeye tuna (T. obesus), and southern bluefin tuna (T. maccoyii) and two cycling systems were designed to identify yellowfin tuna (T. albacares) and Atlantic bluefin tuna (T. thynnus). The systems showed good specificity and sensitivity (sensitivity of 0.0002 ng μL−1 for albacore tuna, bigeye tuna, and southern bluefin tuna and 0.002 ng μL−1 for yellowfin tuna and Atlantic bluefin tuna). Both systems were able to distinguish the target species from other species in a specific, sensitive, and accurate manner. Thus, these methods can be employed for the identification of species used in tuna products, protecting consumers and producers from economic fraud. [ABSTRACT FROM AUTHOR]

Managing populations of wild harvested species requires the ability to regularly provide accurate abundance assessments. For most marine species, changes in abundance can only be monitored indirectly, using methods reliant on harvest-based indices, with significant inherent limitations surrounding the estimation and standardization of harvest effort. Tropical tunas are some of the most exploited marine species in the world and are among several species in critical need of alternative methods for estimating abundance. Addressing this concern, we developed the Associative Behaviour-Based abundance Index (ABBI), designed to provide direct abundance estimates for animals, which exhibit an associative behaviour with aggregation sites. Its implementation in the western Indian Ocean on skipjack tuna (Katsuwonus pelamis), yellowfin tuna (Thunnus albacares) and bigeye tuna (Thunnus obesus), revealed similar trajectories in their relative abundance. The ABBI stands as a potentially promising alternative to enhance traditional tropical tuna stock assessments methods, as well as a new opportunity to assess the abundance of other wild species that display an associative behaviour with physical structures found in their natural environment. [ABSTRACT FROM AUTHOR]

Age-reading protocols for tuna species using annual growth zones in thin-cut transverse otolith sections have produced greater age estimates than previous methods. Lifespan estimates for yellowfin (YFT) and bigeye (BET) tuna (Thunnus albacares and T. obesus) were validated up to 16–18 years in the western North Atlantic Ocean using bomb 14C dating and the current study extends the approach to YFT and BET of the western and central Pacific Ocean (WCPO). Archived otoliths from young-of-the-year (YOY) tuna caught in the WCPO were analysed for 14C to establish a reference chronology covering 30 years (1989–2019). This YOY 14C time series exhibited strong concordance with existing coral-otolith 14C references for the tropical-subtropical Pacific Ocean and was combined as a single chronology. Otolith cores from YFT aged 1–14 years and BET aged 1–13 years from presumed annual counts were analysed for 14C. These measurements aligned with the reference chronology for the calculated hatch years for both species. These findings provide strong evidence that growth zones in thin-sectioned otoliths are deposited annually for YFT and BET of the WCPO and that age interpretation is correct using the current age reading protocol with little to no bias. [ABSTRACT FROM AUTHOR]

Tropical tuna fisheries support some of the largest artisanal and industrial fisheries worldwide. Approximately 37% of the tropical tuna catch by industrial purse seiners is obtained from tuna associated with drifting fish aggregating devices (DFADs), where three tuna species coexist: skipjack (Katsuwonus pelamis) , bigeye (Thunnus obesus), and yellowfin tuna (Thunnus albacares) , with stocks subject to different health status. Purse seine fishers heavily rely on acoustic technology to detect and assess the quantity of tuna at DFADs. Yet, accurately distinguishing between species using solely acoustic methods is limited by insufficient knowledge about each species' acoustic response across frequencies. This study was carried out on six swimbladdered individuals belonging to two sets with mean lengths of 51.9 ± 9.5 and 52.9 ± 2 cm. It focuses on the frequency response obtained from ex situ measurements of yellowfin tuna recorded at 38, 70, 120, and 200 kHz, which revealed a flat response across frequencies, with b20 values of −72.4 ± 9, −73.2 ± 8, -72.3 ± 8, and −72.3 ± 9 dB, respectively. These results, contrast with previous findings on bigeye and skipjack, demonstrating the discrimination potential of acoustics in these three species. To harness this potential, a discrimination algorithm was developed. [ABSTRACT FROM AUTHOR]

Several odontocete species depredate catch and bait from fishing gear, resulting in their bycatch and causing substantial economic costs. There are no known mitigation methods for odontocete depredation in pelagic longline fisheries that are effective, do not harm odontocetes and are commercially viable. Understanding odontocetes' depredation strategies can contribute to mitigating this human-wildlife conflict. Using observer data from the Hawaii-based tuna longline fishery, this study summarized teleost and elasmobranch species-specific mean posterior odontocete depredation rates using a simple Bayesian binomial likelihood estimator with a Bayes-Laplace prior. Depredation rates of species with sufficient sample sizes ranged from a high of 1.2% (1.1 to 1.3 95% highest posterior density interval or HDI) for shortbill spearfish to a low of 0.002% (0.001 to 0.003 95% HDI) for blue shark. Depredation of catch is a rare event in this fishery, occurring in about 6% of sets. When depredation did occur, most frequently odontocetes depredated a small proportion of the catch, however, there was large variability in depredation rates between teleost species. For example, bigeye tuna was two times more likely to be depredated than yellowfin tuna (odds ratio = 2.03, 95% CI: 1.8–2.3, P<0.0001). For sets with depredation, 10% and 2% of sets had depredation of over half of the captured bigeye tuna and combined teleosts, respectively. All elasmobranch species had relatively low depredation rates, where only 7 of almost 0.5M captured elasmobranchs were depredated. Odontocetes selectively depredate a subset of the teleost species captured within sets, possibly based on net energy value, chemical, visual, acoustic and textural characteristics and body size, but not median length, which was found to be unrelated to depredation rate (Pearson's r = 0.14, 95% CI: -0.26 to 0.50, p = 0.49). Study findings provide evidence to support the identification and innovation of effective and commercially viable methods to mitigate odontocete depredation and bycatch. [ABSTRACT FROM AUTHOR]

Oxygen minimum zones in the open ocean are predicted to significantly increase in volume over the coming decades as a result of anthropogenic climatic warming. The resulting reduction in dissolved oxygen (DO) in the pelagic realm is likely to have detrimental impacts on water-breathing organisms, particularly those with higher metabolic rates, such as billfish, tunas, and sharks. However, little is known about how free-living fish respond to low DO environments, and therefore, the effect increasing OMZs will have cannot be predicted reliably. Here, we compare the responses of two active predators (bigeye tuna Thunnus obesus and yellowfin tuna Thunnus albacares) to DO at depth throughout the eastern Pacific Ocean. Using time-series data from 267 tagged tunas (59,910 days) and 3D maps of modelled DO, we find that yellowfin tuna respond to low DO at depth by spending more time in shallower, more oxygenated waters. By contrast, bigeye tuna, which forage at deeper depths well below the thermocline, show fewer changes in their use of the water column. However, we find that bigeye tuna increased the frequency of brief upward vertical excursions they performed by four times when DO at depth was lower, but with no concomitant significant difference in temperature, suggesting that this behaviour is driven in part by the need to re-oxygenate following time spent in hypoxic waters. These findings suggest that increasing OMZs will impact the behaviour of these commercially important species, and it is therefore likely that other water-breathing predators with higher metabolic rates will face similar pressures. A more comprehensive understanding of the effect of shoaling OMZs on pelagic fish vertical habitat use, which may increase their vulnerability to surface fisheries, will be important to obtain if these effects are to be mitigated by future management actions. [ABSTRACT FROM AUTHOR]

The management of fish aggregating devices (FAD) creates heated debates in tuna fishery management organizations striving to reduce the number of deployed floating objects. Through several econometric models and a machine learning approach, we evaluate the consequences of three management scenarios on the catch and profit of the French purse‐seine fleet operating in the Indian Ocean: (1) a half reduction in the number of authorized buoys per vessel, (2) a 72‐day closure of FAD fishing with and (3) without re‐allocation of effort on free schools. The results show a significant decrease of fleet profits by 7%, 10% and 18% respectively. We hypothesize an "economic trap" of FAD fishing caused by the far greater efficiency of this harvesting technique for larger vessels searching for economies of scale, and by the overfished status and catch limitation of yellowfin (Thunnus albacares) and bigeye (Thunnus obesus) tunas in the Indian Ocean. The results are compared with other studies looking at the impact of FAD management measures in other oceans. [ABSTRACT FROM AUTHOR]

Bigeye tuna (BET) and yellowfin tuna (YFT) are economically important target species of pelagic fisheries worldwide, especially for tropical Pacific nations whose economies and food sources are heavily affected by commercial and sustenance tuna fishing. The El Niño‐Southern Oscillation (ENSO) has a strong effect on the oceanographic conditions in the equatorial Pacific, including BET and YFT equatorial habitat and fishing grounds. For optimal fisheries management, the effects of environmental variability such as ENSO on the stocks and on the performance of fisheries must be known and predictable. However, besides some model predictions, the effects of ENSO on these two tuna species are not well understood. In this study, I investigate the statistical relationships between past ENSO conditions and equatorial fisheries using the Multivariate ENSO Index, sea surface temperature (SST), and catch and effort records from the longline fisheries in the region. Results of this study indicate that El Niño events have both delayed and concurrent positive effects on BET and YFT catch per unit effort (CPUE). The delayed positive ENSO effect on CPUE is hypothesized to be the result of enhanced recruitment acting via different mechanisms in the west than in the east. The concurrent positive effects on CPUE could be due to catchability, abundance, and/or vertical distribution of BET and YFT relative to fishing gear and require further investigation. Further exploration of the mechanisms that may underlie the results presented here could lead to predictability of CPUE of these two tuna species. [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.

The Tongan fisheries targeting the species of albacore (Thunnus alalunga), bigeye (Thunnus obesus), skipjack (Katsuwonus pelamis), and yellowfin tuna (Thunnus albacares), comprising the main tuna catch landed, within the EEZ of Tonga is critical to the economy of Tonga. Thus, it is crucial to study the spatiotemporal pattern of their catch and the influence of environmental and physical variables, in addition to the month and year of the catch. To this end, sets of eight generalized additive models were applied to model the distribution of these four species. Selection among competing models was carried out based on k-fold cross-validation, using RMSPE prediction error as a measure of model predictive performance. The following sets of predictors were considered; sea surface temperature, sea surface chlorophyll, bottom depth, month, and year. In addition, to assess the influence of fronts, gradients in SST and Chl-a were computed and used as predictors. Catch year was the most important variable for all, except Albacore tuna, for which month was the important variable. The third most important variable was SST for albacore and bigeye tuna, whereas bottom depth was the most important variable for skipjack and yellowfin tuna. A standardized index of CPUE indicates mostly inter-annual variation in CPUE for albacore and bigeye tuna, whereas a it indicates a general increase in CPUE for skipjack and yellowfin tuna. Hotspots of albacore tuna catches are around the northern and southern edges of the exclusive economic zone and typically during the months of June to August. The bigeye tuna hotspots were concentrated on the eastern side of the islands, in waters overlying trenches; this was most obvious during the months of January to June. Skipjack tuna hotspots were near the edges of the exclusive economic zone, although it is caught in smaller amounts to the three tuna species considered and higher catch rates were observed only after 2014. For yellowfin tuna, the highest catch rates were concentrated around the islands and descending towards the southern edge of the EEZ. As part of the initiative of this study to support national optimal resource management, this study generated standardized CPUE (indices of abundance), an important input in stock assessment, and also looked into the potential influence of environmental and physical variables on the CPUE of these valuable tuna stocks within the EEZ of Tonga. [ABSTRACT FROM AUTHOR]

The potential impacts of climate change on the distribution of tuna in Pacific Island countries' exclusive economic zones have yet to be investigated rigorously and so their persistence and abundance in these areas remain uncertain. Here, we estimate optimal fisheries areas for four tuna species: albacore (Thunnus alalunga), bigeye (Thunnus obesus), skipjack (Katsuwonus pelamis), and yellowfin (Thunnus albacares). We consider different climate change scenarios, RCP 2.6, RCP 4.5, RCP 6.0, and RCP 8.5, within a set of tuna catch records in the exclusive economic zone of Tonga. Using environmental and CPUE datasets, species distribution modelling estimated and predicted these fisheries areas in the current and future climatic scenarios. Our projections indicate an expansion in area and a shift of productive areas to the southern part of this exclusive economic zone of Tonga. This is an indication that future climatic scenarios might be suitable for the species under study; however, changes in trophic layers, ocean currents, and ocean chemistry might alter this finding. The information provided here will be relevant in planning future national actions towards the proper management of these species. [ABSTRACT FROM AUTHOR]

The genus Thunnus (family Scombridae) comprises eight species of tunas of which all but one are targeted by industrialized fisheries. Although intact individuals of these species can be distinguished by morphological characteristics, researchers and managers often rely on dressed, frozen, juvenile or larval fish samples, which often necessitates the identification of molecular species. Here the authors investigate short amplicon (SA) and unlabelled probe high‐resolution melting analysis (UP‐HRMA) as a low‐cost, high‐throughput molecular genotyping assay capable of distinguishing between albacore tuna (Thunnus alalunga), blackfin tuna (Thunnus atlanticus), bigeye tuna (Thunnus obesus), Atlantic bluefin tuna (Thunnus thynnus) and yellowfin tuna (Thunnus albacares) in the Gulf of Mexico. Although SA‐HRMA of variable regions in the NADH dehydrogenase subunit 4 (ND4) and subunit 5 (ND5), and subunit 6 (ND6) of the mtDNA genome did yield some species‐specific diagnostic melting curves (e.g., ND4 assay can reliably distinguish Atlantic bluefin tuna), genotype masking produced excessive variation in melting curves for reliable multi‐species identification. To minimize the genotyping masking of SA‐HRMA a 26 base pair long UP containing four SNPs was developed within a 133 bp segment of ND4. The UP‐HRMA is able to reliably distinguish Gulf of Mexico species T. thynnus, T. obesus, T. albacares and T. atlanticus by UP melting temperature at 67, 62, 59 and 57°C, respectively. The developed UP‐HRMA assay is a lower‐cost, higher‐throughput, alternative to previously published molecular assays for tuna identification that can be easily automated for large data sets, including ichthyological larval surveys, fisheries specimens lacking distinguishing morphological characteristics or detection of fraudulent trading of tuna species. [ABSTRACT FROM AUTHOR]

Bioaccumulation is the process by which living organisms accumulate substances, such as pesticides, heavy metals, and other pollutants, from their environment. These substances can accumulate in the organism's tissues over time, leading to potential health risks. Bioaccumulation can occur in both aquatic and terrestrial ecosystems, and can have a significant impact on the health of both humans and wildlife. The objective of this study is to find out if the concentrations of metals in the tuna species of the Canary Islands are suitable for human consumption and if they pose a health risk. Fifteen samples of Acanthocybium solandri, Katsuwonus pelamis, Thunnus albacares, Thunnus obesus and Thunnus thynnus present in canaries were analyzed. Ten grams of muscle were taken from each specimen and the metals Al, Cd, Cr, Cu, Fe, Li, Ni, Pb and Zn were determined by Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES). The tuna species that presented more metals with a higher concentration compared to the others was T. thynnus, reaching up to 100 times more than the other studied species in Fe content with 137.8 ± 100.9 mg/Kg, which may be due to the fact that it is the largest species that reaches ages of more than fifteen years. The species Thunnus thynnus should not be suitable for commercialization according to the current legislation on the concentrations of Cd in blue fish, since 75% of the specimens studied exceeded the concentration legislated for Cd. A total of 40% of the studied specimens of this this species exceeded the legislated values for the concentration of Pb in oily fish meat, so this species must be monitored to ensure that it does not pose a risk to human health. [ABSTRACT FROM AUTHOR]

Oceanic temperature fluctuations are one of the leading factors affecting marine fish populations. Indian Ocean Dipole (IOD), characterized as the sea surface temperature (SST) anomaly change, is an ocean–atmosphere interactive process causing interannual climate variability in the Indian Ocean. Influences of the IOD on the tuna catch rates are supported by previous research. Yet, there remains limited information about the impacts on the abundance of tuna stocks. In this study, we used the standardized Catch Per Unit Effort (CPUE) index to present the stock abundance and compared the effects of the IOD on the bigeye tuna (Thunnus obesus) and yellowfin tuna (Thunnus albacares) among different management areas of the Indian Ocean Tuna Commission (IOTC). Results show significant correlations between IOD events on both species' abundance in the tropical western Indian Ocean. However, in the tropical eastern Indian Ocean and the southern Indian Ocean, neither bigeye nor yellowfin tuna abundances were significantly correlated by the IOD. For the whole Indian Ocean, IOD was significantly correlated uniquely with the yellowfin tuna abundance. Our results emphasized the importance of evaluating the climate variability effects over fisheries abundance species by species and per fishing areas analyses. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate changes in the thermoregulatory mechanisms of juvenile yellowfin tuna, Thunnus albacares, with increasing body size by using archival tag data from 28 fish released in Japanese waters (fork length [FL] 35–92 cm). Fish with a body size of 35 cm FL remaining within the surface waters had lower thermal excess (0.4 °C), and fish with a body size of 40–60 cm FL undertaking brief diving at depths > 100 m had higher thermal excess (0.5–1.0 °C). However, the thermal excess did not consistently increase with body size, as has been reported for bigeye tuna. Heat budget models indicated inconsistent trends of decreased or increased heat production with body size. Yellowfin tuna regulate body temperatures by controlling the whole-body heat-transfer coefficient (λ) by 1.2–2.0 fold during descents and ascents, independent of body size, restricting λ for thermo-conservation during descent and increasing λ to absorb ambient heat during ascent. Compared with bigeye tuna, the vertical distributions of juvenile yellowfin tuna were limited to surface waters because of less efficient physiological thermoregulatory mechanisms. However, deep dives exceeding 1000 m, probably for predator avoidance, accompanied by rest in surface waters to recover from unusually higher behavioral activity, and vertical behavior similar to bigeye tuna “characteristic behavior” were observed. Compared to the thermoregulatory mechanisms of other tunas, those of juvenile yellowfin tuna are considered to be adaptive to tropical and subtropical shallower waters. [ABSTRACT FROM AUTHOR]

A recent Atlantic-wide tag-recapture experiment run by the International Commission for the Conservation of Atlantic Tunas was an opportunity to directly validate otolith increment deposition rates for bigeye tuna (Thunnus obesus) and yellowfin tuna (T. albacares) in the region. Age and time at liberty were estimated by using annual and daily increment counts for sectioned otoliths from sampled fish previously injected with oxytetracycline and later recaptured. The use of annual increment counts resulted in greater age estimates than those from daily increment counts for fish >55 cm straight fork length (SFL). Use of daily increment counts led to underestimation of time at liberty for fish >55 cm SFL at recovery, compared with known times at liberty. In contrast, predictions based on annual increment counts are accurate across the entire size range of sampled fish, validating the notion that increments are deposited annually. We therefore recommend that counting annual increments be the preferred method for aging yellowfin and bigeye tuna from the Atlantic Ocean and that the use of daily increments for aging be limited to young of the year. Aging fish accurately is important for stock assessments in which data on age and growth play an increasingly essential role in examining population dynamics. It is crucial that otolith reading practices and analyses based on age data reflect the most up-to-date recommendations for age estimation. [ABSTRACT FROM AUTHOR]

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This study analyses the mercury (Hg) concentration in the meat of Thunnus albacares and Thunnus obesus caught from the western equatorial Atlantic Ocean. The objective was to estimate the Hg intake via tuna ingestion and presents the possible health risk assessment. For T. albacares and T. obesus, the median concentration was 212 ng·g-1 and 475.1 ng·g-1 wet weight, respectively. The Hg concentrations were below the maximum tolerable limit established by international and Brazilian regulations for fishery products. The consumption would pose a risk for human populations that ingest more than 80 g·day-1. Regular monitoring of both human consumption rates and Hg levels in fish are recommended. [ABSTRACT FROM AUTHOR]

The influence of bait type and leader material on target and bycatch species was assessed through fishing experiments in the Portuguese shallow pelagic longline fishery in the Atlantic Ocean. Wire leaders were found to decrease catch rates of commercially valuable species such as bigeye tuna and yellowfin tuna, while increasing catch rates of elasmobranchs, including the blue shark and shortfin mako. The odds ratios of capture swordfish and tunas also decrease when using wire leaders, while elasmobranchs have higher odds ratios of capture and at-haulback mortality when using wire leaders. Squid bait led to higher catches of targeted tuna species, however it also resulted in higher catches of marine turtles. For most of the taxa caught at-haulback mortality risk was found to be higher on squid bait, which may be related with increased deep-hooking events. While bait type and leader material did not significantly affect size selectivity for most species, wire leaders were found to retain larger blue sharks and fish bait attracted smaller-sized swordfish. This study showed that banning wire leaders on pelagic longline fisheries is an effective measure for reducing the retention of pelagic shark species, particularly of large size blue sharks. • Wire leaders led to reduced catch rates of tuna species. The odds of capturing swordfish were also lower with wire leaders. • Wire leaders increased catch rates of elasmobranchs, including the blue shark and shortfin mako. • This study supports the exclusion of wire leaders in pelagic longline fisheries to reduce retention of pelagic shark species. • Squid bait increased tuna catches but resulted in higher marine turtle catches and higher risk of at-haulback mortality. [ABSTRACT FROM AUTHOR]

Food fraud is common in the tuna industry because of the economic benefits involved. Ensuring the authenticity of tuna species is crucial for protecting both consumers and tuna stocks. In this study, GC-Q-TOF and UPLC-Q/Orbitrap mass spectrometry-based metabolomics were used to investigate the metabolite profiles of three commercial tuna species (skipjack tuna, bigeye tuna and yellowfin tuna). A total of 22 and 77 metabolites were identified with high confidence using GC-Q-TOF and UPLC-Q/Orbitrap mass spectrometry, respectively. Further screening via chemometrics revealed that 38 metabolites could potentially serve as potential biomarkers. Hierarchical cluster analysis showed that the screened metabolite biomarkers successfully distinguished the three tested tuna species. Furthermore, a total of 27 metabolic pathways were identified through enrichment analysis based on the Kyoto Encyclopaedia of Genes and Genomes (KEGG) pathways. [ABSTRACT FROM AUTHOR]

Cookiecutter sharks are pelagic ectoparasites that feed on pieces of flesh from large marine animals. Knowledge on these sharks is still rather scant, with the few existing works successfully using bites found on prey to reveal ecological patterns. This study aims to identify cookiecutter shark bite patterns on pelagic fishes in aggregated schools to gain an understanding of the ecology of these sharks. Data were collected by accompanying landings and onboard in tuna fishing vessels in the western equatorial Atlantic Ocean off Brazil. A total of 138 bite wounds were found on the bigeye tuna (Thunnus obesus), common dolphinfish (Coryphaena hippurus), skipjack tuna (Katsuwonus pelamis), and yellowfin tuna (Thunnus albacares). The most bitten species were the bigeye and yellowfin tuna, together accounting for 85% of all bites. Our findings offer novel insights into ectoparasitic ecology between cookiecutter sharks and pelagic fishes, identifying three major patterns: (i) preference of the sharks for the ventral surface of pelagic fishes; (ii) plasticity in biting tactics, with both bottom-up and lateral attacks; and (iii) habitat-dependent bite incidence (larger sharks commonly bite the skipjack tuna in epipelagic zones, whereas smaller sharks predominantly bite the bigeye tuna in mesopelagic zones). These results contribute to narrowing the gaps in knowledge on the ecology of the elusive, dwarf cookiecutter sharks. Further studies are needed for a better understanding of how shark-pelagic fish interactions are affected by the fishing of aggregated schools. [ABSTRACT FROM AUTHOR]

This study investigated the interannual variability of yellowfin tuna (Thunnus albacares) and bigeye tuna (Thunnus obesus) catches in the southwestern tropical Indian Ocean (SWTIO) over 25 years and its relationship to climate variability. The results indicate that the catch amount in the northern SWTIO exhibits a significant relationship with the temperature, salinity, and current variability in the upper ocean (< 400 m), associated with a significant subsurface upwelling variability, which is prominent only in the northern region. An increase of the tuna catches in the northern region is associated with the deepening of the thermocline depth and 20°C isotherm depth of the Seychelles–Chagos Thermocline Ridge, indicating suppression of the subsurface upwelling. Further analysis reveals that the catch amounts in the SWTIO tend to increase during the positive phase of the Indian Ocean Dipole. However, the catch variability in the northern SWTIO is more closely related to the El Niño–Southern Oscillation than the Indian Ocean Dipole. Favorable conditions for catches seem to develop in the northern region during El Niño years and continue throughout the following years. This relationship suggests the potential predictability of catch amounts in the northern SWTIO, an energetic region with strong subsurface upwelling variability.

Oceanic temperature fluctuations are one of the leading factors affecting marine fish populations. Indian Ocean Dipole (IOD), characterized as the sea surface temperature (SST) anomaly change, is an ocean–atmosphere interactive process causing interannual climate variability in the Indian Ocean. Influences of the IOD on the tuna catch rates are supported by previous research. Yet, there remains limited information about the impacts on the abundance of tuna stocks. In this study, we used the standardized Catch Per Unit Effort (CPUE) index to present the stock abundance and compared the effects of the IOD on the bigeye tuna (Thunnus obesus) and yellowfin tuna (Thunnus albacares) among different management areas of the Indian Ocean Tuna Commission (IOTC). Results show significant correlations between IOD events on both species’ abundance in the tropical western Indian Ocean. However, in the tropical eastern Indian Ocean and the southern Indian Ocean, neither bigeye nor yellowfin tuna abundances were significantly correlated by the IOD. For the whole Indian Ocean, IOD was significantly correlated uniquely with the yellowfin tuna abundance. Our results emphasized the importance of evaluating the climate variability effects over fisheries abundance species by species and per fishing areas analyses.

Authentication of anglerfish species (Lophius spp.) by means of polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) and forensically informative nucleotide sequencing (FINS) methodologies. We thus examined the sequences corresponding to those albacore-labelled tuna products (MW557512, MW557513, MW557514) claimed to be mislabelled bluefin tuna due to a best BLAST hit with sequence EU562888, belonging to I T. thynnus i according to GenBank. Accurate genetic based seafood product traceability requires developing approaches that unequivocally discriminate between species, for which it is essential to understand intra-specific variability as well as each species' evolutionary context. As shown above, questioning our understanding of the evolutionary history of the species under investigation is essential for seafood fraud studies and could avoid errors such as the one made by Blanco-Fernandez et al. when they report mislabeling of albacore products. [Extracted from the article]

We investigated the associative behavior of skipjack (Katsuwonus pelamis), yellowfin (Thunnus albacares), and bigeye (T. obsesus) tuna within multi‐species aggregations associated with drifting fish aggregating devices (dFADs) in two different regions of the western Indian Ocean: the Mozambique Channel and the Seychelles, using acoustic telemetry. We documented the residence and absence times of tunas at two temporal scales (coarse and fine scale) and made comparisons between regions. A total of 56 tunas were tagged and released at 7 different dFADs (4 in the Mozambique Channel and 3 in the Seychelles) during four research cruises. We recorded the first observations of skipjack tuna making excursions of more than 24 hours away from dFADs before returning and confirmed findings of other studies showing that yellowfin tuna can make long excursions (4.07 days) before returning to their home dFADs. Combining both studied regions, average residence times were 7.59 days (min 0.03; max 16.49), 6.64 days (min 0.01; max 26.72), and 4.58 days (min 0.09; max 18.33) for bigeye, yellowfin, and skipjack tuna, respectively. Exponential models best fitted the residence times for all three tuna species, indicating time‐independent probabilities of departure from dFADs. For yellowfin tuna, at a coarse temporal scale, no regional differences were observed in the residence times. However, at a fine temporal scale, regional differences were apparent in both residence and absence times. This study provides new information on the associative behavior of tunas at dFADs in the Indian Ocean which is key to improving the science‐based management of dFADs. [ABSTRACT FROM AUTHOR]

The dynamic of marine environmental parameters affects the distribution of commercial tuna in the sea of the maritime continent. Hence, the objectives of this study are to develop spatial distribution models for the four main tuna species in the Maritime continent's sea with reasonable accuracy, identify their correlation with marine environmental parameters, and investigate areas of interaction between those tuna species. The study develops the distribution models for albacore (Thunnus alalunga), bigeye (Thunnus obesus), yellowfin (Thunnus albacares), and skipjack (Katsuwonus pelamis) tuna species, utilizing multi-sensor satellite remote sensing and maximum entropy. The results show models have good performance, focusing on environmental factors such as sea surface temperature (SST), chlorophyll-a (CHL), and sea surface height anomalies (SSHA), combined with eddy kinetic energy (EKE). Seasonal variations in potential tuna habitats are revealed, emphasizing the influence of those marine environmental conditions. From December to May, the four commercial tuna species were distributed in conditions characterized by SST of 26–31.5 °C, CHL levels of 0–3 mg/l, SSHA of −0.3 to 0.2 m, and EKE of 0–1 m2/s2, while from June to November, they experienced SST of 23–31 °C, CHL levels of 0–4 mg/l, SSHA of −0.5 to 0.3 m, and EKE of 0–1.1 m2/s2. The spatial persistence of the four tuna species emerged mainly around the south sea of Java, with skipjack being the most common species found in the sea of the maritime continent. With sufficient and evenly distributed tuna presence records, the results indicate the potential for extrapolation beyond the training data to estimate habitat suitability for the four commercial tuna distributions. The results also suggest potential competition between tuna species sharing ecological niches and highlight possible overlapping areas where different tuna species interact with the same fishing gear. • The species distribution models for the four tuna species, which performed well, were developed. • Environmental factors affecting tuna distribution in the sea of the Maritime Continent: SST, CHL, SSHA, and EKE. • Seasonal variations for the distribution of the four tuna species were revealed with skipjack being the most common species. • Tuna species distributed mainly persisted in the southern Java Sea. • This study also reveals overlapping areas of tuna habitats and their interactions with the same fishing gear. [ABSTRACT FROM AUTHOR]

Quantifying vertical distributions of pelagic predators elucidates pelagic ecosystem structure and informs fisheries management. In the tropical South Atlantic Ocean, the recently designated large-scale marine protected area around Ascension Island hosts diverse pelagic predators for which basin-specific vertical habitat information is minimal or absent. We used pop-up satellite archival tags to analyse vertical habitat use in 12 species (bigeye tuna Thunnus obesus , blue marlin Makaira nigricans , blue shark Prionace glauca , dolphinfish Coryphaena hippurus , Galapagos shark Carcharhinus galapagensis , oceanic whitetip Carcharhinus longimanus , sailfish Istiophorus albicans , silky shark Carcharhinus falciformis , swordfish Xiphias gladius , tiger shark Galeocerdo cuvier , wahoo Acanthocybium solandri , and yellowfin tuna Thunnus albacares) and quantify parameters (temperature, dissolved oxygen, diel cycles, lunar phase) known to constrain vertical movements. Predator depth distributions varied widely, and classification trees grouped predators into four clades: (i) primarily epipelagic; (ii) partial thermocline use; (iii) oscillatory diving with thermocline/sub-thermocline use; and (iv) extensive use of sub-thermocline waters. Vertical habitat differences were linked to thermal physiology and foraging ecology, and species-specific physical constraints from other ocean basins were largely conserved in the South Atlantic. Water column features defined species-specific depth distributions, which can inform fisheries practices and bycatch risk assessments and population estimates. [ABSTRACT FROM AUTHOR]

This report presents information on the Grenada tuna fisheries, the components and results of the pre-assessment itself, and recommendations to improve the fisheries' status in relation to the Marine Stewardship Council Fisheries Standard. Grenada's yellowfin and bigeye tuna fisheries were assessed against the MSC standard for sustainable fisheries. This standard encompasses three distinct principles: Principle 1 -sustainability of the stocks; Principle 2 - ecosystem impacts; and Principle 3 - effective management. Each Principle in turn comprises a set of performance indicators (PI), of which there are 28 in total. The fishery was assigned a score for each performance indicator, where 60 is the minimum acceptable performance, 80 is global best practice, and 100 is near perfect performance. A pre-assessment is an optional preliminary review to inform whether a fishery is ready to enter full assessment. Alternatively, it may also be used to identify knowledge gaps and key areas for improvement at the initial stages of a fishery improvement project. Overall, the pre-assessment identified a significant number of shortcomings that would currently preclude the fishery from achieving conformity with the MSC Fisheries Standard. Fundamental issues hindering the sustainability of Grenada's tuna fisheries include inadequate management of yellowfin and bigeye tuna stocks by the International Commission for the Conservation of Atlantic Tunas (ICCAT); lack of national fisheries monitoring, which precludes an adequate assessment of fishery ecosystem impacts, including on retained and discarded bycatch, and protected species; and a failure of the country's fisheries legal framework to establish well defined long-term sustainability objectives for the national fisheries. [ABSTRACT FROM AUTHOR]

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Numerous pelagic species are known to associate with floating objects (FOBs), including tropical tunas. Purse seiners use this behaviour to facilitate the capture of tropical tunas by deploying artificial drifting fish aggregating devices (dFADs). One major recent change has been the integration of echosounders in satellite-tracked GPS buoys attached to FOBs, allowing fishers to remotely estimate fishable biomass. Understanding the effects of this new technology on catch of the three main tuna species (yellowfin tuna, Thunnus albacares ; bigeye tuna, Thunnus obesus ; and skipjack tuna, Katsuwonus pelamis) is important to accurately correct for this change in catch-per-unit-effort (CPUE) indices used for stock assessments. We analysed catch data from the French purse seine fleet for the period 2010–2017 in the Indian Ocean to assess the impact of this fleet's switch to echosounder buoys around 2012. Results indicate that echosounders do not increase the probability a set will be succesful, but they have a positive effect on catch per set, with catches on average increasing by ≈ 2 − 2.5 tonnes per set (⁠ ≈ 10 % ⁠) when made on the vessel's own dFADs equipped with an echosounder buoy. Increases were due to a decrease in sets below ≈ 25 tonnes and an increase in those greater than ≈ 25 tonnes, with a non-linear transition around this threshold. This increase explains the considerable investment of purse seiners in echosounder buoys, but also raises concerns about bias in stock size estimates based on CPUE if we do not correct for this fishing efficiency increase. [ABSTRACT FROM AUTHOR]

Skipjack (Katsuwonus pelamis), yellowfin (Thunnus albacares) and bigeye (Thunnus obesus) tuna are the target species of tropical tuna fisheries in the Indian Ocean, with high commercial value in the international market. High fishing pressure over the past three decades has raised concerns about their sustainability. Understanding life history strategies and stock structure is essential to determine species resilience and how they might respond to exploitation. Here we provide a comprehensive review of available knowledge on the biology, ecology, and stock structure of tropical tuna species in the Indian Ocean. We describe the characteristics of Indian Ocean tropical tuna fisheries and synthesize skipjack, yellowfin, and bigeye tuna key life history attributes such as biogeography, trophic ecology, growth, and reproductive biology. In addition, we evaluate the available literature about their stock structure using different approaches such as analysis of fisheries data, genetic markers, otolith microchemistry and tagging, among others. Based on this review, we conclude that there is a clear lack of ocean basin-scale studies on skipjack, yellowfin and bigeye tuna life history, and that regional stock structure studies indicate that the panmictic population assumption of these stocks should be investigated further. Finally, we identify specific knowledge gaps that should be addressed with priority to ensure a sustainable and effective management of these species. [ABSTRACT FROM AUTHOR]

The Thunnini, or tuna, comprise many species with very different commercial values. The principal raw tuna product on the market is sashimi, for which the species used is difficult to identify through conventional morphological analysis. The present study amplified the cytochrome b gene (Cytb) of 4 major tuna species used for preparing sashimi—yellowfin tuna (Thunnus albacares), southern bluefin tuna (Thunnus maccoyii), bigeye tuna (Thunnus obesus), and Atlantic bluefin tuna (Thunnus thynnus)—and 4 species commonly mislabeled as components of tuna sashimi—albacore tuna (Thunnus alalunga), skipjack tuna (Katsuwonus pelamis), striped marlin (Tetrapturus audax), and swordfish (Xiphias gladius). Polymerase chain reaction (PCR) amplicons were digested with 5 restriction enzymes—Eco147 I, Hinf I, Mbo I, Xag I, and Hind II—to obtain characteristic restriction maps of the above‐mentioned raw tuna species and the commonly mislabeled species. An identification method using PCR restriction fragment length polymorphism (PCR‐RFLP) was established and validated using 39 commercial tuna sashimi samples, which verified that this method provides results consistent with those obtained by classical sequencing. PCR‐RFLP has several advantages over classical sequencing, such as simplicity, speed and accuracy. This technique could support species identification for raw tuna and sashimi. [ABSTRACT FROM AUTHOR]

Estimates of age and growth of yellowfin (Thunnus albacares) and bigeye (Thunnus obesus) tuna remain problematic because validation of growth zone deposition (opaque and translucent) has not been properly evaluated. Otolith growth structure (zone clarity) can be poorly defined for tropical tunas, but the use of bomb radiocarbon dating has validated age estimates to 16–18 years for yellowfin and bigeye tuna. Use of the radiocarbon decline period — defined by regional coral and otoliths — provided valid ages through ontogeny. Yellowfin tuna aged 2–18 years (n = 34, 1029–1810 mm FL) and bigeye tuna aged 3–17 years (n = 12, 1280–1750 mm FL) led to birth years that were coincident with the bomb radiocarbon decline. The results indicate there was no age reading bias for yellowfin tuna and that age estimates of previous studies were likely underestimated for both species. [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]

The true tunas (Scombridae, Scombrinae, I Thunnus i spp.) are oceanodromous species with wide geographical distributions. Since tunas are highly targeted by both commercial and recreational fishers in the Mediterranean, it is unlikely that Yellowfin Tuna would have remained unnoticed if they occurred regularly in this sea. Computer generated distribution maps for Thunnus albacares (Yellowfin tuna), with modelled year 2050 native range map based on IPCC RCP8.5 emissions scenario, version 10/2019. [Extracted from the article]

Biological reference point (BRP) is one of the essential components in the management strategy evaluation that is used to determine the status of fishery stock and set management regulations. However, as BRPs can be derived from different models and many different BRPs are available, the effectiveness and consistency of different BRPs should be evaluated before being applied to fisheries management. In this study, we used a computation-intensive approach to identify optimal BRPs. We systematically evaluated 1500 combinations of alternative BRPs in managing the bigeye tuna (Thunnus obesus) and yellowfin tuna (Thunnus albacares) fisheries in the Indian Ocean. The effectiveness and consistency of these BRPs were evaluated using four performance measures related to fisheries landing performance and biomass conservation. Monte Carlo simulation was used to evaluate various uncertainties. The results suggest that the proposed computation-intensive approach can be effective in identifying optimal BRPs with respect to a set of defined performance measures. We found that the current maximum sustainable yield (MSY)-based BRP combinations are effective target BRPs to manage the bigeye and yellowfin tuna fisheries with the “linear” harvest control rule (HCR). However, using the “knife-edge” HCR, better BRPs could be found for both the bigeye and yellowfin tuna fisheries management with improved fisheries and conservation performance. The framework developed in this study can be used to identify suitable BRPs based on a set of defined performance measures for other fisheries.

The movements, and hence stock structures, of bigeye tuna, Thunnus obesus , and yellowfin tuna, Thunnus albacares , remain poorly defined despite their importance to food security, livelihoods and government revenue in many nations. We examined the parasite fauna of juvenile bigeye tuna and juvenile yellowfin tuna from areas within and outside Indonesia to determine how far they may have moved since metamorphosis and acquisition of a piscivorous diet. Patterns in parasite data between collection areas were consistent between the two tuna species. Fish from two outlier areas, Maldives and the Solomon Islands, harboured a distinct parasite fauna from those from adjacent Indonesian areas, although occasionally showed similarity with those from within the Indonesian archipelago. Within Indonesia, the parasite data indicated that few juvenile fish moved west from the Pacific Ocean into the archipelago and few moved west from the archipelago into the eastern Indian Ocean. While sampling of adult fish is required to fully resolve the stock structure of both tuna species, the results provide a necessary first-step in examining structuring of the two tuna species in Indonesia and indicate that juveniles of both species may have more restricted movement than is recognized in current management arrangements. [ABSTRACT FROM AUTHOR]

Summary: The present study aims to characterize and compare the diet of bigeye and yellowfin tunas caught on aggregated schools in the western equatorial Atlantic Ocean. The samples were collected from January 2011 to June 2016. The tunas were measured on board and the stomachs were removed after evisceration. The stomachs were analyzed regarding their Index of Fullness and the importance of each prey in the diet was estimated by the Index of Relative Importance (IRI). The diet overlap was assessed by the Morisita‐Horn's Index, Non‐Metric Multidimensional Scale (NMDS), and Analysis of Similarity (ANOSIM). The feeding strategy was determined by the Costello's Diagram. The 195 bigeye and 212 yellowfin tunas ranged in fork length from 51 to 137 cm and 43 to 174 cm, respectively. The diet of bigeye tuna was composed of 10 families of fish, three cephalopod families, and four crustacean orders. The diet of yellowfin tuna was composed of 11 families of fish, three cephalopod families, and three crustacean orders. The yellowfin tuna seems to feed upon more abundant prey species near the surface like flying fish, which have the concentration enhanced by the light attractors on the boat, and occasionally on other prey from deeper habitats like lanternfish, squids, and pomfret. Bigeye tuna feed mainly at prey that commonly occurs in deeper habitats like squids, drift fish, lanternfish, and pomfret. [ABSTRACT FROM AUTHOR]