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We investigated the succession process of intestinal bacteria during seed production in full-cycle aquaculture of Pacific bluefin tuna (Thunnus orientalis). During the seed production, eggs, healthy fish, rearing water, and feeds from three experimental rounds in 2012 and 2013 were collected before transferring to offshore net cages and subjected to a fragment analysis of the bacterial community structure. We identified a clear succession of intestinal bacteria in bluefin tuna during seed production. While community structures of intestinal bacteria in the early stage of larvae were relatively similar to those of rearing water and feed, the bacterial community structures seen 17 days after hatching were different. Moreover, although intestinal bacteria in the late stage of larvae were less diverse than those in the early stage of larvae, the specific bacteria were predominant, suggesting that the developed intestinal environment of the host puts selection pressure on the bacteria in the late stage. The specific bacteria in the late stage of larvae, which likely composed 'core microbiota', were also found on the egg surface. The present study highlights that proper management of the seed production process, including the preparation of rearing water, feeds, and fish eggs, is important for the aquaculture of healthy fish. [ABSTRACT FROM AUTHOR]

Controversies remain regarding the periodicity, or seasonality, of otolith growth band formation, which directly influences a correct age determination of Atlantic bluefin tuna using this structure. The aim of this work was to apply marginal increment analysis and marginal edge analysis to determine the timing of band deposition. The index of completion was analyzed using general additive models to evaluate the importance of variables, such as month, age/size, and reader. Results indicate that the opaque band formation begins in June and is completed by the end of November. From the end of the year to the beginning of the following year, there is minimal marginal edge growth as the translucent band begins to form. The translucent zone then reaches a maximum development in May. The results obtained in this study provide evidence that the annulus formation in the otoliths of Atlantic bluefin tuna are completed later in the calendar year than previously thought. This would mean it is necessary to delay the date of the current July 1st adjustment criterion to November 30. [ABSTRACT FROM AUTHOR]

In this work, a comparison is made between the aquaculture activity of bluefin tuna in Baja California and the production of maquiladoras on land and its relationship with the fourth transformation in Mexico, through a bibliographic and documentary review during the years 2002 to 2022. The ranches tuna fishermen maintain a social and economic activity, although they will have to emphasize the application of their own research and venture into a new model within the fourth transformation. [ABSTRACT FROM AUTHOR]

The North Sea is one of the busiest and most exploited marine areas on Earth and is home to many highly migratory and economically important species. At the northern boundary, a 300‐km corridor between Norway and Shetland forms a major egress point from the North Sea to the Norwegian Sea and broader Atlantic Ocean, which is known to be used by many focal species including Atlantic salmon, European eel, European sturgeon, Atlantic bluefin tuna, basking shark, Atlantic mackerel, spiny dogfish, among others. We argue that this relatively shallow 300‐km corridor is a critical area for ecological and oceanographic research in the North Sea to understand species distribution, migratory patterns, responses to climate, fisheries, and more. Instrumentation of the Bergen‐Shetland Corridor with a line of oceanographic and biological tracking infrastructure would help capture the spatiotemporal dynamics of the ocean and its major fauna between the North Sea and Norwegian Sea, a boundary between management areas from ICES and OSPAR. [ABSTRACT FROM AUTHOR]

Western Atlantic bluefin tuna (ABT) undertake long-distance migrations from rich feeding grounds in the North Atlantic to spawn in oligotrophic waters of the Gulf of Mexico (GoM). Stock recruitment is strongly affected by interannual variability in the physical features associated with ABT larvae, but the nutrient sources and food-web structure of preferred habitat, the edges of anticyclonic loop eddies, are unknown. Here, we describe the goals, physical context, design and major findings of an end-to-end process study conducted during peak ABT spawning in May 2017 and 2018. Mesoscale features in the oceanic GoM were surveyed for larvae, and five multi-day Lagrangian experiments measured hydrography and nutrients; plankton biomass and composition from bacteria to zooplankton and fish larvae; phytoplankton nutrient uptake, productivity and taxon-specific growth rates; micro- and mesozooplankton grazing; particle export; and ABT larval feeding and growth rates. We provide a general introduction to the BLOOFINZ-GoM project (Bluefin tuna Larvae in Oligotrophic Ocean Foodwebs, Investigation of Nitrogen to Zooplankton) and highlight the finding, based on backtracking of experimental waters to their positions weeks earlier, that lateral transport from the continental slope region may be more of a key determinant of available habitat utilized by larvae than eddy edges per se. [ABSTRACT FROM AUTHOR]

Larval abundances of Atlantic bluefin tuna (ABT) in the Gulf of Mexico are currently utilized to inform future recruitment by providing a proxy for the spawning potential of western ABT stock. Inclusion of interannual variations in larval growth is a key advance needed to translate larval abundance to recruitment success. However, little is known about the drivers of growth variations during the first weeks of life. We sampled patches of western ABT larvae in 3–4 day Lagrangian experiments in May 2017 and 2018, and assessed age and growth rates from sagittal otoliths relative to size categories of zooplankton biomass and larval feeding behaviors from stomach contents. Growth rates were similar, on average, between patches (0.37 versus 0.39 mm d−1) but differed significantly through ontogeny and were correlated with a food limitation index, highlighting the importance of prey availability. Otolith increment widths were larger for postflexion stages in 2018, coincident with high feeding on preferred prey (mainly cladocerans) and presumably higher biomass of more favorable prey type. Faster growth reflected in the otolith microstructures may improve survival during the highly vulnerable larval stages of ABT, with direct implications for recruitment processes. [ABSTRACT FROM AUTHOR]

Atlantic bluefin tuna (ABT) (Thunnus thynnus) travel long distances to spawn in oligotrophic regions of the Gulf of Mexico (GoM) which suggests these regions offer some unique benefit to offspring survival. To better understand how larval survival varies within the GoM a spatially explicit, Lagrangian, individual-based model was developed that simulates dispersal and mortality of ABT early life stages within realistic predator and prey fields during the spawning periods from 1993 to 2012. The model estimates that starvation is the largest cumulative source of mortality associated with an early critical period. However, elevated predation on older larvae is identified as the main factor limiting survival to late postflexion. As a result, first-feeding larvae have higher survival on the shelf where food is abundant, whereas older larvae have higher survival in the open ocean with fewer predators, making the shelf break an optimal spawning area. The modeling framework developed in this study explicitly simulates both physical and biological factors that impact larval survival and hence could be used to support ecosystem based management efforts for ABT under current and future climate conditions. [ABSTRACT FROM AUTHOR]

We used linear inverse ecosystem modeling techniques to assimilate data from extensive Lagrangian field experiments into a mass-balance constrained food web for the Gulf of Mexico open-ocean ecosystem. This region is highly oligotrophic, yet Atlantic bluefin tuna (ABT) travel long distances from feeding grounds in the North Atlantic to spawn there. Our results show extensive nutrient regeneration fueling primary productivity (mostly by cyanobacteria and other picophytoplankton) in the upper euphotic zone. The food web is dominated by the microbial loop (>70% of net primary productivity is respired by heterotrophic bacteria and protists that feed on them). By contrast, herbivorous food web pathways from phytoplankton to metazoan zooplankton process <10% of the net primary production in the mixed layer. Nevertheless, ABT larvae feed preferentially on podonid cladocerans and other suspension-feeding zooplankton, which in turn derive much of their nutrition from nano- and micro-phytoplankton (mixotrophic flagellates, and to a lesser extent, diatoms). This allows ABT larvae to maintain a comparatively low trophic level (~4.2 for preflexion and postflexion larvae), which increases trophic transfer from phytoplankton to larval fish. [ABSTRACT FROM AUTHOR]

Phytoplankton growth and microzooplankton grazing rates were measured in repeated profiles of dilution experiments incubated in situ on a drift array in order to assess microbial production and food web characteristics in the oligotrophic bluefin tuna spawning habitat of the Gulf of Mexico (May peak spawning seasons, 2017–2018). Grazing often exceeded growth with the processes more balanced overall in the surface mixed layer, but biomass accumulated in the mid-euphotic zone. Community production estimates (260–500 mg C m−2 day−1) were low compared to similar open-ocean studies in the Pacific Ocean. Prochlorococcus was a consistent major contributor (113–204 mg C m−2 day−1) to productivity, while diatoms and dinoflagellates (2–10 and 4–13 mg C m−2 day−1, respectively) were consistently low. Prymnesiophytes, the most dynamic component (34–134 mg C m−2 day−1), co-dominated in 2017 experiments. Unexpected imbalances in grazing relative to production were observed for all picoplankton populations (Prochlorococcus , Synechococcus and heterotrophic bacteria), suggesting a trophic cascade in the absence of mesozooplankton predation on large microzooplankton. Study sites with abundant larval tuna had the shallowest deep chlorophyll maxima and significant net positive phytoplankton growth below the mixed layer. [ABSTRACT FROM AUTHOR]

Bluefin tuna spawn in restricted areas of subtropical oligotrophic seas. Here, we investigate the zooplankton prey and feeding selectivity of early larval stages of Atlantic bluefin tuna (ABT, Thunnus thynnus) in larval rearing habitat of the Gulf of Mexico. Larvae and zooplankton were collected during two multi-day Lagrangian experiments during peak spawning in May 2017 and 2018. Larvae were categorized by flexion stage and standard length. We identified, enumerated and sized zooplankton from larval gut contents and in the ambient community. Ciliates were quantitatively important (up to 9%) in carbon-based diets of early larvae. As larvae grew, diet composition and prey selection shifted from small copepod nauplii and calanoid copepodites to larger podonid cladocerans, which accounted for up to 70% of ingested carbon. Even when cladoceran abundances were <0.2 m−3, they comprised 23% of postflexion stage diet. Feeding behaviors of larvae at different development stages were more specialized, and prey selection narrowed to appendicularians and primarily cladocerans when these taxa were more abundant. Our findings suggest that ABT larvae have the capacity to switch from passive selection, regulated by physical factors, to active selection of presumably energetically optimal prey. [ABSTRACT FROM AUTHOR]

We investigated size-fractioned biomass, isotopes and grazing of mesozooplankton communities in the larval habitat of Atlantic bluefin tuna (ABT) in the oceanic Gulf of Mexico (GoM) during the peak spawning month of May. Euphotic-zone biomass ranged from 101 to 513 mg C m−2 during the day and 216 to 798 mg C m−2 at night. Grazing varied from 0.1 to 1.0 mg Chl a m−2 d−1, averaging 1–3% of phytoplankton Chl a consumed d−1. Carnivorous taxa dominated the biomass of > 1-mm zooplankton (78% day; 60% night), while only 13% of smaller zooplankton were carnivores. δ15N enrichment between small and large sizes indicates a 0.5–0.6 trophic-step difference. Although characteristics of GoM zooplankton are generally similar to those of remote oligotrophic subtropical regions, zooplankton stocks in the ABT larval habitat are disproportionately high relative to primary production, compared with HOT and BATS averages. Growth-grazing balances for phytoplankton were resolved with a statistically insignificant residual, and trophic fluxes from local productivity were sufficient to satisfy C demand of suspension feeding mesozooplankton. While carnivore C demand was met by local processes in the central GoM, experiments closer to the coastal margin suggest the need for a lateral subsidy of zooplankton biomass to the oceanic region. [ABSTRACT FROM AUTHOR]

Simple Summary: We investigated the influence of the lunar cycle on bluefin tuna prey composition in the Strait of Messina by stomach content analysis. We tested if the lunar phases could determine changes in mesopelagic prey composition and abundance. Moreover, we considered two potential impacts of the lunar cycle: the lunar irradiance and the strength of currents. These factors could affect availability of mesopelagic prey in upper waters of the study area. Mesopelagic fish and cephalopod prey were 60.7% of overall diet by number. In summary, the Strait of Messina has highly specific hydrodynamic and biological features which strongly depend on upwelling currents, which in turn are influenced by the lunar cycle (new and full moon with strong currents, quarters with fewer currents). Upwelling causes water mixing, bringing to the surface a large amount of mesopelagic fauna which become more readily available to tuna. Lunar irradiance contributes to the variation of prey composition, increasing the success of visual predation on mesopelagic resources at high light in the water column. The influence of the lunar cycle on bluefin tuna foraging in the upwelling area of the Strait of Messina was investigated by exploring trophic interaction with mesopelagic fish and cephalopod prey. To focus on how the lunar cycle could affect availability of mesopelagic prey for this predator, we tested potential differences in the diet related to each lunar phase. Moreover, we considered two potential impacts of the lunar cycle: the lunar irradiance and the strength of currents. Overall, 2672 prey items were mesopelagic fish and cephalopods, representing 60.7% of overall diet by number. The main mesopelagic fish prey items were lanternfishes and dragonfishes, while Onychoteuthis banksii was the most important cephalopod prey. In summary, the Strait of Messina has highly specific hydrodynamic and biological features which strongly depend on upwelling currents, which in turn are influenced by the lunar cycle (new and full moon with strong currents, quarters with fewer currents). Upwelling causes water mixing, bringing to the surface a large amount of mesopelagic fauna which become more readily available to tuna. Lunar irradiance contributes to the variation of prey composition, increasing the success of visual predation on mesopelagic resources at high light in the water column. [ABSTRACT FROM AUTHOR]

Accounting for spatial and temporal variation in targeting is a concern in many catch per unit effort (CPUE) standardization exercises. In this study we standardized southern bluefin tuna (Thunnus maccoyii, SBT) CPUE from the Korean tuna longline fishery (1996-2018) using generalized linear models (GLMs) with operational set by set data. Data were first explored to investigate the operational characteristics of Korean tuna longline vessels fishing for SBT, such as the spatial and temporal distributions of effort, and changes in the nominal catch rates among major species and species composition. Then we estimated SBT CPUE by area used for the stock assessment in the CCSBT (Commission for the Conservation of Southern Bluefin Tuna) and identified two separate areas in which Korean tuna longline vessels have targeted SBT and albacore tuna (T. alalunga), with targeting patterns varying spatially, seasonally and longer term. We applied two approaches, data selection and cluster analysis of species composition, and compared their ability to address concerns about the changing patterns of targeting through time. Explanatory variables for the GLM analyses were year, month, vessel identifier, fishing location (5° cell), number of hooks, moon phase, and cluster. GLM results for each area suggested that location, year, targeting, and month effects were the principal factors affecting the nominal CPUE. The standardized CPUEs for both areas decreased until the mid-2000s and have shown an increasing trend since that time. [ABSTRACT FROM AUTHOR]

Tuna muscle is known to contain high levels of mercury, necessitating the monitoring of mercury concentrations in farmed fish at production sites. There is currently no straightforward in on-site method for testing whether the mercury levels in farmed tuna exceed regulatory limits. This study investigated the potential application of liquid asymmetric-electrode plasma optical emission spectroscopy (LAEP-OES) to estimate mercury concentrations in the tissues of cultured Pacific bluefin tuna at aquaculture farms. No significant differences in mercury concentrations were observed between the ventricle tissue and biopsied tissue from tuna bleeding site (TTBS), which can be harvested without reducing the market value of farmed tuna (Hg concentration of the ventricle tissue and the TTBS, median: 0.41 and 0.40 mg/kg, respectively). In addition, the relationship between mercury concentrations in the ventricle tissue and in the edible portions of three tuna fish was examined. The findings showed that total mercury level in the edible tissues varied, with the ratio of the mercury level in edible tissues to that in the ventricle ranging from 0.39 to 1.08. A positive correlation was observed between the average total mercury levels in edible tissues and ventricle tissue. These results suggest that determining the total mercury level in the ventricle, which is typically discarded at processing sites, may serve as a convenient proxy for quality control and monitoring purposes using the LAEP-OES method. However, larger sample sizes are needed to validate the proposed approach more robustly. • Bluefin tuna muscle contains high levels of mercury. • A method for on-site mercury testing for bluefin tuna was developed. • A ventricle-based mercury test was proposed to enhance food safety. [ABSTRACT FROM AUTHOR]

In this study, the purpose was to screen novel angiotensin converting enzyme inhibitory peptides (ACEIPs) from tuna muscle taking two-steps enzymatic hydrolysis (Neutrase and Alkaline). Following isolation and purification by ultrafiltration, the Sephadex G-15 gel chromatography and reversed-phase high-performance liquid chromatography based on active-guide, the amino acid sequence was identified using Q-Orbitrap-MS/MS. Five peptides were chose synthesized based on the in silico screening methods. Among these, the two novel ACEIPs LTGCP and YPKP showed better inhibitory ability, and their corresponding IC 50 values were 64.3 μM and 139.6 μM. Subsequently, the interaction mechanism of the best active peptide (LTGCP) against ACE was investigated by inhibitory pattern, molecular docking and molecular dynamic simulation. The result displayed that LTGCP was a mix-type inhibitor against ACE from the Lineweaver-Burk plots. LTGCP formed seven hydrogen bonds based on the molecular docking and the binding energy was −7.29 kcal/mol. LTGCP formed a stability complex with ACE based on the molecular dynamic simulation. Besides, LTGCP exhibited good stability in various temperature, pH and gastrointestinal digestion. Finally, the 0.125 mM ∼ 1.0 mM LTGCP exhibited no-toxic for Caco-2 cell. In summary, these findings showed that tuna was a good material to prepare ACEIPs and LTGCP may be the good potential antihypertensive drug or nutraceuticals. [Display omitted] [ABSTRACT FROM AUTHOR]

The Atlantic bluefin tuna (ABFT) population ranges throughout the Atlantic Ocean and Mediterranean Sea, and consists of multiple contingents that use diverse habitats and show different movement patterns over the life cycle. Based on body size, elemental and isotopic data of C and N in muscle and liver, we analysed eastern-stock ABFT by comparing mid-sized individuals caught by hook-and-line gears with larger individuals harvested from traps in the Strait of Gibraltar (SoG). Our results show that trophic-related chemical markers have potential for separating temporarily sympatric contingents throughout the ABFT population range, reflecting size-dependent spatial distribution and differential patterns of residency and migration. We present evidence of long-term residency of ABFT in the SoG that persists until the estimated age of ∼5 years (size of ∼140 cm in straight fork length). This age apparently marks a turning point in the life history, where there occurs an ontogenetic switch in the migratory behaviour and distributional pattern. This study contributes new insight into our knowledge about size structure and residency-movement patterns in eastern ABFT. It shows distinct size-dependent migratory and spatial dynamics. The present results encourage further investigation on poorly studied ABFT contingents for a better understanding of the population dynamics towards more comprehensive management plans. [Display omitted] • Trophic chemical markers allow separation of different sympatric ABFT contingents. • ABFT long-term residents and long-distance migrants temporarily occur at the SoG. • Size-dependent spatial distribution and differential patterns of residency and migration. • Ontogenetic switch in migratory and distributional patterns takes place at age 5 yr. [ABSTRACT FROM AUTHOR]

We fit a biphasic Lester Model to back-calculated size-at-age data for Atlantic bluefin tuna (Thunnus thynnus) captured in the western Atlantic management area that had been genetically assigned to either the western (Gulf of Mexico) or eastern (Mediterranean) spawning stocks. We tested the hypothesis that spawning-stock variation exists in age-at-maturity for this species using a Bayesian approach to incorporate and compare the support for different growth models and maturity scenarios considered for the western spawning stock. The biphasic Lester Model out-performed the uniphasic von Bertalanffy model and showed good fits for describing individual growth variability in Atlantic bluefin tuna. The Lester Model provided estimates of individual age-at-maturity and spawning, from which spawning ogives were generated and compared to two reproductive scenarios currently considered for the western spawning stock; either an early (age at 50 % maturity at 4 years) or late maturity scenario (age at 50 % maturity at 10). The results derived from the Lester Model demonstrate a lack of stock-specific variation in reproductive dynamics for Atlantic bluefin tuna, and provide support for an early maturity scenario for the western spawning stock. • We fit a biphasic model to back-calculated growth data for Atlantic bluefin tuna (Thunnus thynnus). • No overall difference was found in growth or maturity between tuna from genetically distinct stocks. • Estimates for western bluefin provide a spawning ogive that is similar to that of the eastern stock. [ABSTRACT FROM AUTHOR]

Temperature is the most important abiotic factor controlling the very early life of fish. Data on development, hatching, and survival responses of fertilized fish eggs to varying temperatures are essential to understand fitness of Atlantic bluefin tuna (ABFT) and Atlantic bonito (AB). In this study, we investigated i) the effect of temperature on viable hatching rate and ii) the relationship between temperature and the timing necessary to reach different developmental stages. Our findings show that the thermal range for viable egg hatching is colder in AB than in ABFT. ABFT eggs hatch from 18 to 33 ºC, highest around 26–27 ºC; below 21 ºC or above 30 ºC at least 50 % of the hatched larvae were abnormal, while below 19 ºC and above 32 ºC the larvae had no chance to survive, having highest survival chance at around 26 ºC. In AB, eggs hatched from 16 ºC to 28 ºC, being optimal around 21–22 ºC, the incidence of abnormal larvae was very high above 27 ºC and at 16.5 ºC, and larvae had no chance to survive above 28 ºC and had the highest survival chance at around 21 ºC. ABFT eggs required longer times to hatch than other tuna species. The results obtained in this study are an important tool for aquaculture; here, we describe the best temperature conditions for successful and viable hatching in ABFT and AB, which may help to improve modelling tools and to develop better indices of annual recruitment and the possible impact of future global temperature changes. • We examined the effect of temperature on early developmental stages of Atlantic bluefin tuna and Atlantic bonito eggs. • The time to reach the different egg developmental stages and hatching decreased as temperature increased. • The time to reach the different egg developmental stages and hatching was higher in Atlantic bonito. • Bluefin tuna eggs hatch at 18.5–33.5 ºC; bonito eggs hatch at 16.5–28 ºC. • Higher or lower temperatures increased mortality and the incidence of abnormal larvae. [ABSTRACT FROM AUTHOR]

This study addresses existing gaps in our understanding of the ecology of killer whales by investigating their habitat use dynamics in the Atlantic coastal waters of North Africa, the Iberian Peninsula, and the Gulf of Biscay. Despite previous research on their distribution during the Atlantic Bluefin tuna migration in the Strait of Gibraltar and adjacent waters, substantial knowledge gaps persist, particularly regarding their movement patterns beyond these regions and seasonal variations in habitat use. Utilizing killer whale occurrence records from 2020 to 2023 and considering environmental factors influencing prey presence, we employed seasonal spatial distribution models. MaxEnt models exhibited robust predictive performance, emphasizing distance to shore, depth, and sea surface temperature as key factors influencing killer whale habitat suitability. Spatial distribution patterns reveal a peak in coastal waters of the southern Iberian Peninsula and North Africa during winter and spring, with a significant shift northward and expansion during summer and autumn towards the Gulf of Biscay. This expansion suggests a broader distribution of killer whales in the Northeast Atlantic during warmer months, encompassing a diverse range of habitats. The research underscores a substantial interaction (47%) between killer whales and recreational vessels, posing concerns for both the killer whales and maritime safety. This study provides valuable insights on killer whale habitat use in the Atlantic waters from North Africa to the Gulf of Biscay, thereby supporting conservation and management efforts in the region. • Killer whales show dynamic habitat changes along the Atlantic coast. • Distance to shore, depth, and temperature shape habitat suitability. • Killer whale habitat suitability linked to tuna migration dynamics. • 47% of killer whale records involve interactions with recreational vessels. [ABSTRACT FROM AUTHOR]

Pacific bluefin tuna, Thunnus orientalis, migrates from spawning grounds in the western Pacific Ocean to foraging grounds in the California Current System (CCS), where they are thought to specialize on high energy, surface schooling prey. However, there has been substantial variability in estimates of forage availability in the CCS over the past two decades. To examine the foraging ecology of juvenile T. orientalis in the face this variability, we quantified the diet and prey energetics of 963 individuals collected in the Southern California Bight (SCB) from 2008 to 2016. Using classification and regression tree analysis, we observed three sampling periods characterized by distinct prey. In 2008, T. orientalis diet was dominated by midwater lanternfishes and enoploteuthid squids. During 2009–2014, T. orientalis consumed diverse fishes, cephalopods, and crustaceans. Only in 2015–2016 did T. orientalis specialize on relatively high energy, surface schooling prey (e.g. anchovy, pelagic red crab). Despite containing the smallest prey, stomachs collected in 2009–2014 had the highest number of prey and similar total energetic contents to stomachs collected in 2015–2016. We demonstrate that T. orientalis is an opportunistic predator that can exhibit distinct foraging behaviors to exploit diverse forage. Expanding our understanding of T. orientalis foraging ecology will improve our ability to predict its responses to changes in resource availability as well as potential impacts on the fisheries it supports. [ABSTRACT FROM AUTHOR]

An important trait of Pacific bluefin tuna (PBT) is their ability to maintain their body temperature above the ambient temperature, which allows them to occupy a wider ecological niche. However, the size at which this ability in nature develops is unclear. Therefore, this study aimed to clarify this point by monitoring the body temperature and the surrounding ambient temperature as the fish grew. PBT with fork lengths (FLs) ranging from 19.5 to 28.0 cm were implanted with archival electronic tags and released into the ocean. Data from 41 fish were obtained (recorded body and water temperatures, light level, and swimming depth (pressure) at 30-s intervals) and analyzed to elucidate the development of the ability of PBT to maintain a high body temperature. Body temperature of a PBT (< FL of ca. 40 cm) decreased in response to a vertical movement down to cooler depths, but higher body temperatures were maintained as the fish grew. The body temperature was then continuously maintained above ambient temperatures and fluctuated independently when fish attained more than 40 cm FL. Estimation of the whole-body heat-transfer coefficient and heat-production rate indicated that the latter decreased slowly with growth, while the former decreased by one order of magnitude when tuna reached 52 cm FL. Additionally, in the daytime, the whole-body heat-transfer coefficient was significantly higher than that at nighttime. Unlike other fishes including other Thunnus species, inhabiting tropical/subtropical waters, PBT rapidly acquire higher thermo-conservation ability when young, allowing capture of high-quality prey abundant in temperate waters to support high growth rates during early life. [ABSTRACT FROM AUTHOR]

Accurate understanding of changing population dynamics associated with climate change is critical for managing highly migratory fish species. However, long-term data on population dynamics and the resulting recruitment variability is still lacking for many species, making it difficult to predict and integrate the effects of ocean warming into management schemes. In this study, high-resolution stable oxygen isotope (δ18O) analysis was performed on the otoliths of adult Pacific bluefin tuna Thunnus orientalis using secondary ion mass spectrometry (SIMS) to determine the natal origin of an individual fish. The core δ18Ootolith corresponding to the larval stage greatly varied among the individuals, indicating that the larvae experienced a wide range of thermal environments. The non-hierarchical cluster analysis performed on the core δ18Ootolith grouped fish into those with higher δ18Ootolith (lower temperature) and those with lower δ18Ootolith (higher temperature), most likely representing relative temperature difference experienced between fish born in the Sea of Japan and in the Nansei Islands area. The Nansei Islands area cluster showed more variability in the early otolith growth indicating a longer spawning season, which is consistent with the observed longer spawning duration in this area. The absolute temperature estimates based on the SIMS-measured core δ18Ootolith were significantly higher than those expected from sea surface temperature data, suggesting the effects of matrix-related bias on the temperature offsets. The relative temperature difference, however, matched well with the known spawning temperature range of the two spawning grounds. The recruitment contribution from each spawning ground (all year-classes pooled, n = 51) was 45% in the Sea of Japan and 55% in the Nansei Islands area. Overall, this study demonstrated the effectiveness of SIMS δ18Ootolith analysis for investigating the natal origin of fish and its potential application in fish population dynamics studies. [ABSTRACT FROM AUTHOR]

The recent return of Atlantic bluefin tuna to northern Europe following the recovery of the east Atlantic stock has sparked substantial public and scientific interest. This is particularly true for recreational anglers in Denmark, who often consider Atlantic bluefin tuna to be the catch of a lifetime. This attitude has previously sustained a substantial recreational fishery for bluefin tuna with annual tournaments in Denmark, which peaked in the 1950s before the subsequent collapse of the stock during the 1960s. Several scientific tagging programs have recruited recreational anglers in recent years to help catch and release tagged bluefin tuna. The anglers' investment of time and money in the scientific tagging projects indicate that the recreational fishery could recover in the future. However, the economic aspects of a potential future recreational bluefin tuna fishery remain unknown. We surveyed anglers participating in a scientific catch and release bluefin tuna fishery in Denmark across three years (2018–2020) and calculated the total annual expenditures associated with the activities. Additionally, we estimated the magnitude of the negative impact (i.e., incidental mortalities) on the bluefin tuna stock. Our results show that total annual expenditures by the recreational anglers approached 1,439,540€, totaling 4,318,620€ between 2018 and 2020. We found that recreational bluefin tuna anglers had mean annual expenditures directly related to the bluefin tuna fishing between 7,047€ and 2,176€ with an associated mortality impact on the stock of less than 1 tonne annually. By comparing the mortality impact to the expenditures, we estimate that each dead Atlantic bluefin tuna during the three study years generated 398,163€ in mean annual expenditures, equivalent to approximately 1636€ kg-1. Our study demonstrates significant economic expenditures among recreational anglers who target Atlantic bluefin tuna. This provides a clear example of how a recovery of marine natural capital and related ecosystem services can support development in the blue economy. [ABSTRACT FROM AUTHOR]

Accurate ultra‐short‐term wind speed prediction is extremely important for the power control of wind farms, the safe dispatch of power systems, and the stable operation of power grids. At present, most wind farms mainly rely on supervisory control and data acquisition systems to obtain operation and maintenance data which includes operating characteristics of wind turbines. In the ultra‐short‐term wind speed prediction, a long short‐term memory network is one of the commonly used deep learning methods. To address the problem that improper selection of long short‐term memory network's hyperparameters may affect the prediction results, In the present study, a hybrid prediction model based on the long short‐term memory and the modified tuna swarm optimization algorithm was established, and was used to predict after the wind speed sample data had been decomposed by successive variational mode decomposition method. The experimental results reveal that the proposed model effectively improved the accuracy of wind speed prediction for wind farms compared with the support vector regression, deep belief networks, and long short‐term memory models optimized by particle swarm optimization algorithm. [ABSTRACT FROM AUTHOR]

The effects of different freezing temperatures on the water-holding capacity and physicochemical properties of bluefin tuna were studied. The naked body, big belly and middle belly parts of bluefin tuna were stored at −18 °C and −55 °C for 180 days. The tuna was evaluated by determining the water-holding capacity, color difference, malondialdehyde (MDA), salt-soluble protein content, free amino acid (FAA), endogenous fluorescent proteins and water distribution and migration. The salt-soluble protein content was measured by the Bradford method. The color difference was measured by a CR-400 color difference meter. The water distribution and migration were analyzed by the low-field nuclear magnetic resonance (LF-NMR). The results showed little quality change during short-term frozen storage, but the frozen storage temperature of −55 °C significantly improved the quality of tuna compared with the frozen storage temperature of −18 °C. There were great differences in the salt-soluble protein content, water-holding capacity and water content the different parts of the tuna. The water-holding capacity and the protein content were the highest, and the water distribution of the naked body part was the most uniform of the three different parts. Because of the high fat content in the big belly and the middle belly, the MDA content and the odor of amino acid increased rapidly and the quality seriously decreased during the frozen storage. [ABSTRACT FROM AUTHOR]

Atlantic bluefin tuna (Thunnus thynnus; ABFT) is one of the most iconic fish species in the world. Recently, after being very rare for more than half a century, large bluefin tunas have returned to Nordic waters in late summer and autumn, marking the return of the largest predatory fish in Nordic waters. By tagging 18 bluefin tunas with electronic tags (pop-up satellite archival tags), we show that bluefin tuna observed in Nordic waters undertake different migration routes, with individuals migrating into the western Atlantic Ocean, while others stay exclusively in the eastern Atlantic and enter the Mediterranean Sea to spawn. We additionally present evidence of possible skipped spawning inferred from behavioural analyses. In Nordic waters, ABFT are primarily using the upper water column, likely reflecting feeding activity. The results support the hypothesis that ABFT migrating to Nordic waters return to the same general feeding area within the region on an annual basis. These observations may have important implications for management because (1) tunas that come into Nordic waters might represent only a few year classes (as evidenced by a narrow size range), and thus may be particularly vulnerable to area-specific exploitation, and (2) challenge the assumption of consecutive spawning in adult Atlantic bluefin tuna, as used in current stock assessment models. Without careful management and limited exploitation of this part of the ABFT population, the species' return to Nordic waters could be short-lived. [ABSTRACT FROM AUTHOR]

Keywords: Dead end; Pacific bluefin tuna; Primordial germ cell; Sterile; Thunnus orientalis EN Dead end Pacific bluefin tuna Primordial germ cell Sterile Thunnus orientalis 3872 3876 5 06/14/22 20220701 NES 220701 The I dead-end i ( I dnd i ) gene was first identified in zebrafish, I Danio rerio i , as a germ plasm component encoding an RNA-binding protein (Weidinger et al., 2003). To examine germ cell deficiency in addition to observations by GFP labeling, we conducted whole-mount immunostaining using anti-germ cell marker Vasa antibodies, as described previously (Hayashida, Higuchi, Hashimoto, et al., 2021), and histological analysis. In fact, inhibiting I dnd i expression causes faulty migration and ablation of zebrafish PGCs, resulting in germ cell deficiency (Weidinger et al., 2003). The zebrafish Dnd protein binds to 3' untranslated regions (3'UTR) of germline RNAs, such as I nanos i mRNAs, thereby protecting them against microRNA-mediated degradation, so they can contribute to the migration and survival of primordial germ cells (PGCs) (Kedde et al., 2007; Weidinger et al., 2003). [Extracted from the article]

Every spring a 600 lb Atlantic bluefin tuna travels over 3000 miles from Newfoundland to its spawning grounds in the Gulf of Mexico. That it does so on a meal of a couple of bluefish is nothing short of remarkable. Humans will likely never engineer such an efficient swimming machine. Of course, that has not stopped us from trying. We have achieved remarkable progress by following a strategy of inspiration by nature. At the same time, our fish-like robots often fall short of matching fish performance by a considerable margin. Despite our advances, we are still left asking the question: How do fish swim so well? In this Primer, James C. Liao discusses a diversity of mechanisms underlying swimming efficiency in fishes, focusing on the structure of the body, swimming movements, flow exploitation, and sensory feedback. [ABSTRACT FROM AUTHOR]

Fish larvae are rarely a major driver of fish mortality, but tunas can produce large batches of larvae that rapidly develop the capacity to kill other fish. We combine a model for the killing potential from Atlantic bluefin tuna (BFT) larvae on larval albacore (ALB) with field observations at a major spawning ground. Both species spawn from June to August, but BFT has a narrow spawning peak at the beginning of the season that results in priority effects. Our model shows that, following a recent stock recovery, BFT larvae have increased their killing pressure, leaving areas of up to 1000 km2 with < 1% chance of ALB daily survival. Such increase in killing pressure suggests larval ALB has reduced chances to survive; yet in large areas with few BFT, other drivers of early survival prevail over BFT predation. This shows that strong predatory interactions can occur during larval stages in some fishes. [ABSTRACT FROM AUTHOR]

Steven Adolf. 2019. Tuna Wars: Powers Around the Fish We Love to Conserve. New York: Springer. Jennifer E. Telesca. 2020. Red Gold: The Managed Extinction of the Giant Bluefin Tuna. Minneapolis: University of Minnesota Press. [ABSTRACT FROM AUTHOR]

Southern Bluefin Tuna (SBT) Thunnus maccoyii (Castelnau) comprises a single, highly migratory stock that is managed internationally by the Commission for the Conservation of Southern Bluefin Tuna (CCSBT). CCSBT members are expected to provide estimates of all sources of fishing mortality within their allocation, including commercial and recreational catch and any additional mortality associated with discarded or released catch. In the absence of a national registration system for the SBT recreational fishery, which would provide a comprehensive sampling frame, an ensemble of off‐site and on‐site survey methods was used across five state jurisdictions to provide the first species‐specific national assessment of a recreational fishery in Australia. The national harvest of SBT for the 12 months from December 2018 to November 2019 by the recreational sector was 270 t (239–301 t: 95% CL). This survey has resulted in the first official recognition of a catch set aside to the recreational sector for an Australian Commonwealth managed fishery with 5% per cent of the CCSBT allocation to Australia now set aside for the sector. [ABSTRACT FROM AUTHOR]

Despite their broad distribution across the North Pacific Ocean, the only known spawning grounds for Pacific Bluefin Tuna (Thunnus orientalis) are around coastal Japan and the East China Sea. However, an increase in the prevalence of large bluefin tuna up to 10 years old in the California Current System during exceptionally warm ocean conditions has led to speculation that they may be spawning in this region. To investigate this possibility, we collected samples from 36 females (estimated 3–8 years old) between 2015 and 2019. Histological analyses revealed no signs of imminent, active, or recent spawning. Further examination of historical ichthyoplankton collections showed no records of larval bluefin tuna, but confirmed the presence of the larvae of other tuna species in waters > 24°C. Fishery-dependent records showed that bluefin tuna are rarely recorded in purse seine catches where surface temperatures exceed 23°C. Our study, therefore, provided no evidence of bluefin tuna reproduction in the CCS. However, more comprehensive sampling, in particular off southern Baja California, may be required to confirm the absence of spawning. [ABSTRACT FROM AUTHOR]

Estimated larval backward trajectories of three Tuna species, namely, Atlantic Bluefin Tuna (Thunnus thynnus, Linnaeus, 1758), Bullet Tuna (Auxis Rochei, Risso, 1801) and Albacore Tuna (Thunnus alalunga, Bonnaterre, 1788) in the central Mediterranean Sea, were used to characterize their spawning habitats, and to assess the impact of changes due to the major environmental parameters (i.e., sea surface temperature and chlorophyll-a concentration) on larval development during their advection by surface currents. We assumed that the environmental variability experienced by larvae along their paths may have influenced their development, also affecting their survival. Our results showed that the Tuna larvae underwent an accelerated growth in favorable environmental conditions, impacting on the notochord development. In addition, further updated information on spawning and larval retention habitats of Atlantic Bluefin Tuna, Bullet and Albacore Tunas in the central Mediterranean Sea were delivered. [ABSTRACT FROM AUTHOR]

Strategies used by marine vertebrates to regulate their body temperature can result in local variations, and the knowledge of these regional heterothermies is crucial for better understanding the thermophysiologies of extant and extinct organisms. In order to investigate regional heterothermies in vertebrates, we analysed the oxygen isotope composition of phosphatic skeletal elements (δ18 O p) of two endothermic fishes (Thunnus thynnus and Xiphias gladius) and three dolphins (two Delphinus delphis delphis and one Cephalorhynchus commersonii kerguelensis). We observed a consistent link between δ18 O p variations and temperature heterogeneities recorded by classical methods. Our δ18 O p data indicate that: (i) bone hydroxylapatite of the axial skeleton of dolphins mineralise at a warmer temperature than that of the appendicular one, (ii) the skull is the warmest body region in X. gladius, and (iii) T. thynnus possesses high body temperature in the skull and visceral mass region. These results demonstrate the possibility of tracking regional heterothermies in extant marine vertebrates using the δ18 O p , paving the way to direct assessment of thermophysiological specificities of both living and extinct vertebrates. From a palaeoenvironmental perspective, the significant observed δ18 O p variability questions the use of some taxa or random skeletal elements for the reconstruction of palaeoceanographic parameters such as seawater temperature and δ18 O. [ABSTRACT FROM AUTHOR]

Atlantic bluefin tuna (Thunnus thynnus; BFT) is a large (up to 3.3 m in length) pelagic predator which has been exploited throughout the eastern Atlantic and Mediterranean since prehistoric times, as attested by its archeological remains. One key insight derivable from these remains is body size, which can indicate past fishing abilities, the impact of fishing, and past migration behavior. Despite this, there exists no reliable method to estimate the size of BFT found in archeological sites. Here, 13 modern Thunnus spp. skeletons were studied to provide power regression equations that estimate body length from vertebra dimensions. In modern specimens, the majority of BFT vertebrae can be differentiated by their morphological features, and thus, individual regression equations can be applied for each rank (position in vertebral column). In an archeological context, poor preservation may limit one's ability to identify rank; hence, "types" of vertebrae were defined, which enable length estimates when rank cannot be determined. At least one vertebra dimension, height, width, or length correlated highly with body length when vertebrae were ranked (R2 > 0.97) or identified to types (R2 > 0.98). Whether using rank or type, length estimates appear accurate to approximately ±10%. Finally, the method was applied to a sample of Roman‐era BFT vertebrae to demonstrate its potential. It is acknowledged that further studies with larger sample sizes would provide more precision in BFT length estimates. [ABSTRACT FROM AUTHOR]

This article reports pelagic fish species recorded during the survey of cetaceans in the Finike Seamounts region and the adjacent waters in 2021. The Mediterranean flyingfish Cheilopogon heterurus (Rafinesque, 1810) and Atlantic bluefin tuna Thunnus thynnus (Linnaeus, 1758) were observed and recorded during their flight/leap movements on the water surface. The scientific sharing of these data is important in terms of emphasizing the richness of the pelagic life of the Finike Seamounts region and underlines the importance of declaring the region as a Special Environmental Protection Area (SEPA). [ABSTRACT FROM AUTHOR]

The Finike Seamounts (Anaximander) area was designated as the Special Environmental Protection Area (SEPA) in 2013 by the Turkish government to protect its unique biodiversity components such as rich benthic communities, vulnerable deep sea species and highly migratory species. As the area is not totally inside the territorial waters of Türkiye, this initiative can facilitate and be beneficial for transboundary cooperation in terms of conservation for highly mobile and vulnerable species such as sea turtles, bluefin tuna, seabirds, and cetaceans. Besides, it can be included in the Specially Protected Areas of Mediterranean Importance (SPAMI) list under the Barcelona Convention in order to promote bilateral cooperation with the neighbouring countries. Designation as one of the Ecologically or Biologically Significant Marine Areas (EBSAs) under the Convention of Biological Diversity is also another option for marine conservation in this region. Finally, the Finike Seamounts SEPA needs a long-term scientific monitoring study to understand both the benthic and pelagic components of its biodiversity. The surveys in 2021 initiated such a study and the papers published in this issue of the journal (Vol.28 No.2) as the results of 2021 surveys provide the baseline data of the Finike Seamounts SEPA to be referred and evaluated for the coming years. [ABSTRACT FROM AUTHOR]

Atlantic bluefin tuna (Thunnus thynnus) are commercially and ecologically valuable, but management is complicated by their highly migratory lifestyle. Recent collections of bluefin tuna larvae in the Slope Sea off northeastern United States have opened questions about how this region contributes to population dynamics. We analyzed larvae collected in the Slope Sea and the Gulf of Mexico in 2016 to estimate larval abundance and growth rates and used a high-resolution regional ocean circulation model to estimate spawning locations and larval transport. We did not detect a regional difference in growth rates, but found that Slope Sea larvae were larger than Gulf of Mexico larvae prior to exogenous feeding. Slope Sea larvae generally backtracked to locations north of Cape Hatteras and would have been retained within the Slope Sea until the early juvenile stage. Overall, our results provide supporting evidence that the Slope Sea is a major spawning ground that is likely to be important for population dynamics. Further study of larvae and spawning adults in the region should be prioritized to support management decisions. [ABSTRACT FROM AUTHOR]

The bluefin sea robin (Chelidonichthys spinosus), hereafter BSR, is one of the most important fish species in the South Sea of Korea. The production value of BSR in 2020 was USD 4,733,057. The production volume in Korea has shown an annual mean increase of 8.9% since 2010, but the efficiency of the fishing gear decreased due to excessive use. This has led to a decrease in the profitability of fishery operators, and as compensation, the use of fishing gear has further increased through competitive operations. Alternative measures for improving catch performance and reducing the use of fishing gear are needed. As one such measure, LED (Light-Emitting Diode) lights were attached to the pot, and the effects were determined. The field experiment results showed that the catch of BSR was higher for the experimental groups (n = 10–273) using fishing gear with LED lights (red, green, blue, and white) than for the control group (n = 2) (Kruskal–Wallis test, p < 0.05). Among the experimental groups, the pot with green light achieved the largest catch (n = 273). The use of LED lights was found to enhance the catch efficiency of pot fishing gear for BSR. [ABSTRACT FROM AUTHOR]

The purse seine fishery in the Mediterranean represents about 60% of the international catch for Atlantic Bluefin Tuna (Thunnus thynnus). Yet, tagging operations from this segment of the fisheries remain rare and despite its potential importance for management, several aspects related to the migratory behavior of Atlantic Bluefin Tuna from these areas remain unaddressed. In the present manuscript, we report the results of two tagging operations carried out on a commercial purse seiner during two consecutive years in the spawning ground around the Maltese islands in the Central Mediterranean Sea. During these operations, eight individuals were tagged and the results showed that the larger fish (> 200 cm) undertook large-scale migrations outside the Mediterranean, whereas smaller individuals did not. This study suggests that size might affect the migratory behavior of Atlantic Bluefin Tuna, and underlines the potential of large-scale tagging operations from spawning grounds to address scientific questions having significant management implications. [ABSTRACT FROM AUTHOR]

This study investigated the effects of krill and squid meal and their heat processing on the growth performance and biochemical composition of juvenile Pacific bluefin tuna (PBT) Thunnus orientalis. An experiment using a 2 × 2 factorial design examined the effects of two dietary protein sources (squid and krill meal) and heat treatment (heated and non-heated). Prey fish were provided to a reference group. Fish with an initial mean weight of 74.1 mg were fed one of the five diets. After six days of the feeding trial, the fish fed with krill meal and non-heated diets showed improved growth compared to those fed with the squid meal and heated diets. Fish fed the non-heated diets showed significantly higher whole-body crude protein and crude lipid contents than fish fed the heated diets. These results suggest that nutrient availability could be improved by using krill meal and the non-heated treatment to improve the growth performance of juvenile PBT. [ABSTRACT FROM AUTHOR]