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Stock structure is one of the fundamental assumptions for assessing and managing fisheries resources. Investigation of stock structure should be conducted holistically, involving reviews of as much information as possible, because suggested conclusions from different studies are often contradictory. Here, all available information related to the stock structure of Pacific bluefin tuna (Thunnus orientalis), whose stock status is of concern, was reviewed to consider an appropriate stock structure hypothesis for management purposes. Although current stock assessment of this species assumes that it is a single-stock resource, it has two, or possibly three, known spawning grounds and exhibits complex migration behavior. Nevertheless, to date there is no documentation of its stock structure per se, and it thus warrants a thorough review. After analyzing a variety of studies regarding Pacific bluefin tuna, no information exclusively pointing to the existence of multiple stocks was identified. Instead, many studies support the conclusion that Pacific bluefin tuna from the two spawning grounds mix as the tuna grows. Therefore, it is considered appropriate to manage Pacific bluefin tuna as a single stock. This is an important conclusion for its management, particularly for the pending management strategy evaluation for this stock, which should account for all major sources of uncertainty including plausible stock structure hypotheses. [ABSTRACT FROM AUTHOR]

The age of sexual maturity of the Atlantic bluefin tuna (Thunnus thynnus; ABFT) is a reference point for stock assessment and management. The International Commission for the Conservation of Atlantic Tunas (ICCAT) recognizes a western and an eastern Atlantic ABFT stock, based on the assumptions of separate, exclusive spawning grounds, i.e., the northern Gulf of Mexico and the Mediterranean Sea, with different ages of sexual maturity, 8–12 years vs 3–5 years, respectively. Multiple line of evidences indicate that spawning is not restricted to the Gulf of Mexico and the Mediterranean Sea, and reconsideration of historical documents, as well as results from recent studies, indicate that sexual maturation schedules of the two proposed stocks are similar (3–5 years). The present review of classical and recent literature suggests that ABFT have more complex reproductive behavior than previously considered: on eastern spawning grounds 50% of ABFT females reproduce at 3 years of age and 100% are sexually mature at 5 years of age. In the western management area, younger adults (age ≥ 5 years) and some larger adults apparently spawn in the northwest Atlantic Ocean across the Slope and Caribbean Seas, whereas the Gulf of Mexico spawners are mostly large adults (age ≥ 8 years). [ABSTRACT FROM AUTHOR]

Ectoparasitic flatworms of Nasicola (Monogenoidea: Capsalidae), which infect nasal epithelium of true tunas (Thunnus spp.), are not well studied, nor have their impacts on the host's olfactory organ been evaluated. Infections of Nasicola hogansi on Atlantic bluefin tuna, Thunnus thynnus, were investigated with emphasis on the relationship between infection prevalence, abundance and mean intensity with bluefin tuna size, sex, body condition and capture month, as well as histopathological effects. Commercially caught Atlantic bluefin tuna (n = 161, 185–305 cm curved fork length) from the Gulf of Maine were sampled during June through August 2009 for infections by N. hogansi. A total of 247 specimens of N. hogansi were collected, with a prevalence of 45.3%, mean abundance of 1.57 (CI: 1.21–2.03) and mean intensity of 3.45 (CI: 2.91–4.22). Neither fish sex nor landing month had a significant effect on parasite parameters. Larger and better‐conditioned Atlantic bluefin tuna had a higher mean intensity of infection. Pathology associated with infection by N. hogansi included extensive necrosis, sloughing of the nasal epithelium and associated inflammation of underlying connective tissues. Further epidemiological and pathological study of this host–parasite system is warranted since impaired olfaction, if present, could adversely affect spawning and migration of this top ocean predator. [ABSTRACT FROM AUTHOR]

The fishing and aquaculture industries generate a huge amount of waste during processing and preservation operations, especially those of tuna. Recovering these by-products is a major economic and environmental challenge for manufacturers seeking to produce new active biomolecules of interest. A new hyaluronic acid was extracted from bluefin tuna's vitreous humour to assess its antioxidant and pharmacological activities. The characterization by infrared spectroscopy (FT-IR), nuclear magnetic resonance ((1D 1H) and 2D (1H COSY, 1H/13C HSQC)) and size exclusion chromatography (SEC/MALS/DRI/VD) revealed that the extracted polysaccharide was a hyaluronic acid with high uronic acid content (55.8 %) and a weight average molecular weight of 888 kDa. This polymer possesses significant anti-radical activity and ferrous chelating capacity. In addition, pharmacological evaluation of its anti-inflammatory and analgesic potential, using preclinical models, in comparison with reference drugs (Dexamethasone, diclofenac, and acetylsalicylate of lysine), revealed promising anti-inflammatory activity as well as interesting peripheral and central antinociceptive activity. Therefore, our new hyaluronic acid compound may therefore serve as a potential drug candidate for the treatment of pain sensation and inflammation of various pathological origins. [Display omitted] • A novel hyaluronic acid was extracted from the vitreous humour of bluefin tuna. • The physicochemical properties of the isolated hyaluronic acid were studied. • The isolated hyaluronic acid demonstrated significant pharmacological properties. • The hyaluronic acid demonstrated promising potential as an anti-inflammatory agent. [ABSTRACT FROM AUTHOR]

Dynamic ocean management (DOM), a new frontier in the field of operational ecology for marine resource management, is a means of protecting the dynamic features and species in the ocean by allowing management measures to move and adapt in space and time. Most DOM applications have been implemented within the jurisdictional waters of single nations, avoiding the potential issues and challenges arising from coordination in transboundary regions, which can be challenging due to the overlap of multiple and diverse jurisdictions and governance systems. This study focuses on the implementation of DOM in transboundary regions. A novel approach is presented using a geospatial information system to automatically identify relevant stakeholders from two sectors (i.e., marine traffic and marine fisheries) across multiple maritime boundaries. The objective of this study was to test the geospatial information system and examine the variability of stakeholder networks when DOM was applied in a transboundary marine region. We tested our approach in a complex geopolitical region, the Western Mediterranean Sea, building on simulated management strategies for two highly mobile species, the bluefin tuna (Thunnus thynnus) and the fin whale (Balaenoptera physalus). Substantial differences in stakeholder networks were identified depending on the focal species, highlighting the widespread responsibility among marine users for bluefin tuna compared to fin whale. Potential issues and solutions for identifying the most suitable stakeholder and governance frameworks are discussed, allowing recommendations to support the implementation of DOM in complex geopolitical contexts. [ABSTRACT FROM AUTHOR]

The first comprehensive extinction risk assessments for the 61 species of tunas, mackerels and billfishes for the IUCN Red List (Collette et al., 2011, I Science i , 333, 291-292) have recently been updated. Overall, 17 of the 61 species changed Red List category, 10 to a category of lesser extinction risk and seven to a category of greater extinction risk. One population of a species may be severely overfished while other populations of the same species may be healthy, so the species might still be assessed globally as Least Concern. [Extracted from the article]

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]

The genus Thunnus of the family Scombridae includes three species of bluefin tunas (Atlantic bluefin tuna – T. thynnus, Pacific bluefin tuna - T. orientalis and southern bluefin tuna - T. maccoyii). The bluefin tunas were first recognized as two independent species (Northern and Southern bluefin) based on subtle differences in morphological characters. Northern bluefin tunas are now recognized as morphologically, geographically and genetically separate species located in the Atlantic and Pacific oceans.The Pacific bluefin (T. orientalis) is the only species which remains unmanaged; this lack of management persists despite intensive fisheries on both sides of the Pacific. The current life history model indicates that these fish spawn in the western Pacific (Sea of Japan, Philippine Sea and East China Sea). Either late in the first year or early in the second year, a portion of the population migrates to the western coast of the United States and Mexico, a journey of over 8700 km (Bayliff et al., 1991). The young fish that have migrated into the eastern Pacific are thought to remain there for several years, feeding on sardines and anchovies in regions of intense upwelling (Bayliff et al., 1991, Bayliff, 1993). While these tuna are fished only seasonally off California and Mexico, they may be a year-round resident (Bayliff, 1991). The migrants then travel back to the western Pacific to spawn. Why some bluefin remain in the western Pacific while others migrate across the ocean basin is unresolved. How long they stay in the eastern Pacific, what habitats are most important, what triggers their return to the west is unclear.

Underwater noise has been identified as a relevant pollution affecting marine ecosystems in different ways. Despite the numerous studies performed over the last few decades regarding the adverse effect of underwater noise on marine life, a lack of knowledge and methodological procedures still exists, and results are often tentative or qualitative. A monitoring methodology for the behavioral response of bluefin tuna (Thunnus thynnus) when exposed to ship and wind turbine operational noises was implemented and tested in a fixed commercial tuna feeding cage in the Mediterranean sea. Fish behavior was continuously monitored, combining synchronized echosounder and video recording systems. Automatic information extracted from acoustical echograms was used to describe tuna reaction to noise in terms of average depth and vertical dimensions of the school and the indicators of swimming speed and tilt direction. Video recordings allowed us to detect changes in swimming patterns. Different kinds of stimuli were considered during bluefin tuna cage monitoring, such as noise generated by feeding boats, wind farm operational noise, and other synthetic signals projected in the medium using a broadband underwater projector. The monitoring system design was revealed as a successful methodological approach to record and quantify reactions to noise. The obtained results suggested that the observed reactions presented a strong relationship with insonification pressure level and time. Behavioral changes associated with noise are difficult to observe, especially in semi-free conditions; thus, the presented approach offered the opportunity to link anthropogenic activity with possible effects on a given marine species, suggesting the possibility of achieving a more realistic framework to assess the impacts of underwater noise on marine animals.

The parasitic blood flukes Cardicola forsteri and C. orientalis are an ongoing health concern for Southern Bluefin Tuna Thunnus maccoyii (SBT) ranched in Australia. In this study we compared the effect of treatment, company, and ranching year on blood fluke infections in ranched SBT. SBT were sampled during the 2018 and 2019 ranching seasons from praziquantel (PZQ) treated pontoons and untreated pontoons managed by two companies. Severity of infection was diagnosed by several criteria including adult fluke counts from hearts, egg counts from gill filaments and the use of specific quantitative polymerase chain reaction (qPCR) for detection of C. forsteri and C. orientalis ITS-2 DNA in SBT hearts and gills. PZQ treatment remains highly effective against C. forsteri infection. Prevalence and intensity of Cardicola spp. infection was lower in 2019 than 2018 for Company A in treated pontoons at week 12 and week 17 of ranching, and lower for Company A than Company B in untreated pontoons at month 5 of ranching. Results indicate re-infection may be less likely in the environment near Company A pontoons, and consistent years of treatment may have lowered the parasite load in the environment. qPCR demonstrated higher sensitivity when comparing diagnostic methods for C. forsteri in heart, and higher specificity when comparing diagnostic methods for Cardicola spp. in gills. Continuing to monitor blood fluke infections in ranched SBT can help to detect changes in drug efficacy over time and help industry to develop a best practice for treatment.