Mediterranean Bluefin Research Articles

The Mediterranean Storm-petrel, Bluefin Tuna fish-farms and the storm Gloria: the ‘perfect storm’

In 2021 we published a six-year study (2015–2020) of the occurrence of the Mediterranean Storm-petrel Hydrobates pelagicus spp. melitensis around a Mediterranean Bluefin Tuna Thun- nus thynnus fish-farm, where high concentrations took place during spring and summer. Great abundances of storm-petrels were recorded in 2020, with more than 100 individuals registered throughout April–August, whereas in previous years only a few individuals had been detected in June–July. These figures suggest either an increasing trend of storm-petrel occurrence in the area (i.e. by learning) or an exceptional episode, probably related to storm Gloria in January 2020. Here, we present the results of censuses undertaken in 2021–2022 whose numbers were lower than those registered in 2020 in May–July. This supports the idea that the events occurring in southern Catalonia after storm Gloria created the ‘perfect storm’ for storm-petrels in this area.

The Northeast Atlantic and Mediterranean bluefin tuna fishery: Back from the brink

At the turn of the century, the Northeast Atlantic and Mediterranean bluefin tuna stock (BFT-E) appeared to be heading towards collapse. In 2006, a recovery plan was introduced with the purpose of restoring the stock. Stock size is now increasing. In fact, the stock is now believed to be sustainably harvested. The fishery is managed by ICCAT, a Regional Fisheries Management Organisation (RFMO). Several authors question the effectiveness of RFMOs. This paper analyses how cooperation has been achieved as well as the stability of the current cooperative management regime. A main conclusion of the analysis is that RFMO management of BFT-E is very successful. This brings hope for the management of high seas fisheries worldwide.

Exploitation shifted trophic ecology and habitat preferences of Mediterranean and Black Sea bluefin tuna over centuries

AbstractDuring recent decades, the health of ocean ecosystems and fish populations has been threatened by overexploitation, pollution and anthropogenic‐driven climate change. Due to a lack of long‐term ecological data, we have a poor grasp of the true impact on the diet and habitat use of fishes. This information is vital if we are to recover depleted fish populations and predict their future dynamics. Here, we trace the long‐term diet and habitat use of Atlantic bluefin tuna (BFT), Thunnus thynnus, a species that has had one of the longest and most intense exploitation histories, owing to its tremendous cultural and economic importance. Using carbon, nitrogen and sulphur stable isotope analyses of modern and ancient BFT including 98 archaeological and archival bones from 11 Mediterranean locations ca. 1st century to 1941 CE, we infer a shift to increased pelagic foraging around the 16th century in Mediterranean BFT. This likely reflects the early anthropogenic exploitation of inshore coastal ecosystems, as attested by historical literature sources. Further, we reveal that BFT which migrated to the Black Sea–and that disappeared during a period of intense exploitation and ecosystem changes in the 1980s–represented a unique component, isotopically distinct from BFT of NE Atlantic and Mediterranean locations. These data suggest that anthropogenic activities had the ability to alter the diet and habitat use of fishes in conditions prior to those of recent decades. Consequently, long‐term data provide novel perspectives on when marine ecosystem modification began and the responses of marine populations, with which to guide conservation policy.

Vertebrae reveal industrial-era increases in Atlantic bluefin tuna catch-at-size and juvenile growth

Abstract Climate change and size-selective overexploitation can alter fish size and growth, yet our understanding of how and to what extent is limited due to a lack of long-term biological data from wild populations. This precludes our ability to effectively forecast population dynamics and support sustainable fisheries management. Using modern, archived, and archaeological vertebrae dimensions and growth rings of one of the most intensely exploited populations, the eastern Atlantic and Mediterranean bluefin tuna (Thunnus thynnus, BFT), we estimated catch-at-size and early-life growth patterns from the 3rd century bce to the 21st century ce to understand responses to changes in its environment. We provide novel evidence that BFT juvenile growth increased between the 16th–18th, 20th, and 21st centuries, and is correlated with a warming climate and likely a decrease in stock biomass. We found it equally plausible that fisheries-induced evolution has acted to increase juvenile BFT growth, driving earlier maturation as a result of size-selective exploitation. Coincidently, we found limited evidence to suggest a long history of large ( >200 cm FL) BFT capture. Instead, we found that the catch-at-size of archaeological BFT was relatively small in comparison with more intensive, 20th and 21st century tuna trap fisheries which operated further from shore. This complex issue would benefit from studies using fine-scale biochronological analyses of otoliths and adaptation genomics, throughout the last century especially, to determine evolutionary responses to exploitation, and further disentangle the influence of temperature and biomass on fish growth.

Potential toxic elements (PTEs) in wild and farmed Atlantic bluefin tuna (Thunnus thynnus) from Mediterranean Sea: Risks and benefits for human consumption

Being on the top of the food chain, tunas are subjected to significative phenomena of bioaccumulation of conservative contaminants such as Potential Toxic Elements (PTEs). In this study, Cd, Pb and Fe levels in muscle of Mediterranean bluefin tuna (Thunnus thynnus) were determined by atomic absorption spectroscopy (GFAAS), both in wild and farmed groups, to investigate the safety and the quality of this fish as seafood. A total of 68 samples were collected, wild samples (n = 30) from Sardinia island (Italy) and farmed samples (n = 38) from an aquaculture fish farm in Malta. Mean values, expressed as mg kg−1 wet weight, were found as 0.014 (wild) and 0.02 (farmed) for Cd; 0.11 (wild) and 0.03 (farmed) for Pb and 13 (wild) and 7 (farmed) for Fe. Relationships between metal concentrations and biometric parameters were evaluated and a comparison between the levels of metals of wild and farmed groups has also been conducted. No statistically significant difference between the two groups was found for Cd, with 99% of samples below the EU limit. The difference for Pb levels were statistically significant, with wild samples showing concentrations more than four times higher than the farmed ones, but with 98% of samples below the EU limit. The levels of Fe were significantly lower in the farmed group with respect to wild specimens, although samples of both groups could be considered good products for the intake of this element. On the base of the recommended tolerable weekly intakes, samples of this study can be considered a safe seafood.

Singularities of surface mixing activity in the Western Mediterranean influence bluefin tuna larval habitats

Understanding how the surface dynamics of the ocean influence the spawning and larval ecology of many large pelagic species, in particular tuna species, is a major challenge. For temperate tunas, the selection of geographically restricted spawning grounds is influenced by environmental conditions, but the influence of surface mixing properties on the early life stages of these species remains poorly understood. Here, based on ichthyoplankton samples collected over 4 yr and satellite-derived finite size Lyapunov exponents (FSLEs), we examined how horizontal mixing activity drives the probability of presence of Atlantic bluefin tuna Thunnus thynnus larvae. We further analyzed the spatial and temporal scales of the FSLE variability at which the relationship between larval presence and mesoscale activity is maximized. We found that moderate mixing activity strongly favors the spatial-temporal distribution of larval habitats, evidencing an optimal environmental window of bluefin tuna spawning and early life development within the mesoscale dynamics. During the spawning season, the Balearic Sea presents a unique spatial and temporal hydrodynamic scenario within the Western Mediterranean. These results can be used for developing oceanographic indicators and improving larval abundance indices that are currently used in Atlantic bluefin tuna stock assessments.

The dynamics of Italian competitive positioning in the Mediterranean Bluefin tuna industry

The bluefin tuna or Thunnus thynnus is one of the widely recognised fish species since ancient times. Italy is the most important players in the international arena, however, the introduction of a system of total allowable catches and other measures established by the International Commission for the Conservation of Atlantic Tunas, has deeply changed the competitive positioning of Italy. The aim of this study is to perform an analysis of the comparative advantage of Italy by using the relative trade advantage index. Findings reveal that Italy has gained a competitive advantage in the Maltese market and has suffered a loss of the historical competitive advantage in the Japanese one. Results suggest to policymakers, managers, and stakeholders should put in place strategies addressed to retain a major part of the added value of the bluefin tuna, without setting aside all the aspect related to the sustainability of the fishing catch.

The dynamics of Italian competitive positioning in the Mediterranean Bluefin tuna industry

The bluefin tuna or Thunnus thynnus is one of the widely recognised fish species since ancient times. Italy is the most important players in the international arena, however, the introduction of a system of total allowable catches and other measures established by the International Commission for the Conservation of Atlantic Tunas, has deeply changed the competitive positioning of Italy. The aim of this study is to perform an analysis of the comparative advantage of Italy by using the relative trade advantage index. Findings reveal that Italy has gained a competitive advantage in the Maltese market and has suffered a loss of the historical competitive advantage in the Japanese one. Results suggest to policymakers, managers, and stakeholders should put in place strategies addressed to retain a major part of the added value of the bluefin tuna, without setting aside all the aspect related to the sustainability of the fishing catch.

PCBs and PCDD/Fs in Bluefin Tuna: Occurrence and Dietary Intake.

Polychlorinated biphenyls (PCBs) and polychlorinated dibenzo-furans (PCDD/Fs) were measured in Mediterranean bluefin tuna (Thunnus thynnus) to verify the compliance with the EU regulations for food commercialization. The estimated intakes were also evaluated. The analyses were performed by gas chromatography-ion trap tandem mass spectrometry (GC-MS-MS). The PCBs were dominant (1132.0 ng g−1 l.w.), followed by PCDFs (23.2 pg g−1 l.w.) and PCDDs (8.5 pg g−1 l.w.). The pollutant levels (dl-PCBs: 0.7 pg TEQ/g w.w.; PCDD/Fs: 1.9 pg TEQ/g w.w.) and their sum expressed as TEQ values (2.6 pg TEQ/g w.w.) remained below the limits for human consumption proposed by the European Union. On the contrary, the sum of the six indicator non-dioxin-like PCBs (84.2 ng g−1 w.w.) was slightly above the maximum level fixed by the in-force legislation. The estimated dietary intakes for PCDD/Fs plus dl-PCBs were below the toxicological reference values (TRVs) set by various international bodies, while non-cancer and cancer risk assessment revealed a safety concern. Additionally, the estimated intake of ndl-PCBs exceeded the maximum levels set by different European countries. These findings suggest caution in tuna consumption together with an active and frequent surveillance of the chemical quality of its flesh.

Seasonal differences in parasite infection of skipjack tuna in Madeira archipelago

Seasonal differences in parasite infection of skipjack tuna in Madeira archipelago

Evolutionary constraints limiting the variation of Expressed Sequence Tag-linked microsatellite loci, prevent the detection of local adaptation in Mediterranean Bluefin tuna

The Atlantic Bluefin tuna (BFT, Thunnus thynnus), one of the largest top-predator fish inhabiting the pelagic ecosystems of the North Atlantic Ocean and Mediterranean Sea, has been extensively overexploited in recent decades. However, in the Mediterranean Sea, the mixing rates between the eastern, central and western basins have not yet been fully and finally resolved. To date electronic tagging, otolith and genetic markers cannot still disentangle the pattern of tuna movements and population structuring in the basin, essential background for a proper management of BFT fisheries. Here, we used Expressed Sequence Tag-linked (EST-linked) microsatellites to explore population dynamics and adaptive evolution of Mediterranean T. thynnus. For this purpose, 16 EST-linked microsatellites were genotyped in 177 tuna individuals from the Mediterranean Sea and several methods were used to explore population genetic structuring and estimate/detect signals of local adaptation. Bayesian clustering results indicated the presence of a single cluster, corroborated also by the Correspondence Analysis and pairwise FSTs. Similarly, the two methods used for the detection of outlier loci (LOSITAN and BayeScan), did not reveal any pattern suggesting the presence of selective pressure on the EST Simple Sequence Repeat (SSR) used. Our results suggest that the low level of polymorphism detected in this study could be ascribed to the presence of relatively conserved regions flanking these microsatellites. These genomic regions are probably not involved in physiological responses to local adaptation.

Polychlorinated biphenyls and organochlorine pesticides as intrinsic tracer tags of foraging grounds of bluefin tuna in the northwest Atlantic Ocean

Researchers have utilized chemical fingerprints in the determination of habitat utilization and movements of the aquatic animals. In the present effort, we analyzed polychlorinated biphenyl (PCB) congeners and organochlorine pesticides in the samples of juvenile bluefin tuna caught offshore of Virginia, and in larger bluefin tuna from the Gulf of Maine and near Nova Scotia. For a given specimen, or a given location, PCB concentrations were highest, followed by DDTs, and chlordanes. Average contaminant concentrations from fish captured from the three locations were not significantly different; and PCBs, DDTs, and chlordanes correlated well with each other. Trans-nonachlor/PCB 153 ratios in bluefin tuna of eastern Atlantic (i.e., Mediterranean) origin are low compared to the corresponding ratios in fish in the western Atlantic. As the former migrate to the western Atlantic, these ratios gradually turnover due to the accumulation of biomass from forage contaminated with higher trans-nonachlor/PCB 153 ratio reflecting dissimilar use of chlordane pesticides on two sides of the Atlantic Ocean. The trans-nonachlor/PCB 153 ratio indicated that one juvenile bluefin tuna from offshore of Virginia and one large bluefin tuna from Gulf of Maine in the present study originated from foraging grounds in the Mediterranean Sea, and that they have made the trans-Atlantic migrations. The remaining individuals were determined to be either spawned in the Gulf of Mexico or the trans-nonachlor/PCB 153 ratio for the putative Mediterranean bluefin tuna was completely turned over to resemble the ratio characteristic to the western Atlantic. Based on the turnover time for trans-nonachlor/PCB 153 ratio previously determined, the residence time of juvenile bluefin tuna offshore Virginia was estimated to be at least 0.8 to 1.6years. A discriminant function analysis (DFA) plot of total PCB normalized signatures of PCB congeners showed three separate clusters, which suggested that bluefin tuna from offshore Virginia, Gulf of Maine, and Nova Scotia could have had extended residences and foraging within the areas of capture to be able to sustain the stable signatures of PCB congeners. The DFA cluster results supported the concept of metapopulation theory of spatial ecology comprising discrete aggregates of local populations of bluefin tuna where the desired prey species are likely to be abundant. Despite their highly migratory trait and endothermic advantage of foraging in broader and colder habitats, the movements and mixing across the aggregation ranges related to feeding did not appear to be extensive. Advancement in the understanding of bluefin tuna population dynamics beyond the coarse concept of trans-Atlantic migrations to the metapopulation hypothesis provides a novel exploratory tool in the stock assessment and resource management. As the chemical tracer tags are fortified naturally and document the time- and space-integrated foraging history, they promise to serve as the low-cost alternatives to the high-cost electronic data recording tags employed for addressing the migratory movements of bluefin tuna. Between the different potential chemical tracer tags, a distinct advantage of PCB/pesticide analysis over the otolith micro-constituent analysis is that the muscle tissue of a given individual bluefin tuna can be sampled repeatedly for PCB/pesticide analysis over different spatial and temporal scales in a non-lethal manner.

Trophic position of Mediterranean bluefin tuna larvae estimated by different stable isotope analysis

Trophic position of Mediterranean bluefin tuna larvae estimated by different stable isotope analysis

Dealing with Mediterranean bluefin tuna: A study in international environmental management

Bluefin tuna management is a high profile conservation issue, generating significant public interest. The species is in decline due to overfishing, with the Mediterranean population of particular concern. Japanese demand for bluefin tuna is driving overexploitation and there are no indications that this will diminish in the foreseeable future. The system of allocating catch quotas to fishing parties under the International Convention on Conservation of Atlantic Tunas (ICCAT) has been ineffective in the past. This paper argues that other avenues of international law, including via the World Trade Organisation, are unable to provide suitable alternative remedies. However, the interaction and political leveraging effect of these multilateral instruments has now established an enabling environment for an effective management regime, with a revitalised ICCAT now universally recognised as the most appropriate forum to address the threats to bluefin tuna. It is advised that ICCAT parties continue to work collaboratively, as has begun in recent years. The body should seek to maintain not only a scientifically derived sustainable fishing quota but also to address high levels of illegal, unreported and unregulated fishing, which threaten to undermine progress in restricting quota allocations. This could be supported by inclusion of a formal dispute resolution mechanism with the Convention or by developing linkages to related UNCLOS articles. However, ultimately, this complex issue is probably best dealt within the international body most well positioned to convene a consensus amongst stakeholders, namely ICCAT.

The spectre of uncertainty in management of exploited fish stocks: The illustrative case of Atlantic bluefin tuna

The recent overexploitation of East Atlantic and Mediterranean bluefin tuna stock has been well documented in the media where it has become the archetype of overfishing and general mis-management. Beyond the public debate, the crisis also highlighted how the interactions between science and management can change through time according to the awareness of the public opinion. To reflect these issues, the history of Atlantic bluefin tuna overfishing is first described. Then, the major uncertainties that undermine the current scientific advice are summarized and the importance of reducing their impacts by improving knowledge and developing robust scientific framework is considered. The study also discusses how uncertainty was used by different lobbies to discredit science-based management. The recent improvement in bluefin tuna stock status following the implementation of the rebuilding plan shows that, despite uncertainty in the scientific advice, the management of a heavily exploited fish stock can be positive when there is a political will. However, optimizing long-term yields of modern fisheries implies good science. The study concludes by advocating for the implementation of a scientific quota that should be part of the management framework to support the scientific advice.

Age structure and growth of bluefin tuna (Thunnus thynnus, L.) in the capture-based aquaculture in the Mediterranean Sea

Abstract The principal objective of this study was to estimate the age and growth, length–weight relationships and condition factors of the Mediterranean bluefin tuna ( Thunnus thynnus ) in a capture-based aquaculture farm and to reveal possible differences among farmed (reared in sea cages for 18 months), fattened (reared in sea cages for 6–7 months) and wild specimens. Moreover, to determine the age composition of the fish destined for fattening and farming operations with the current lack of demographic information makes the bluefin tuna stock assessment extremely difficult. For this purpose, a total number of 2096 specimens (ranging from 102 to 295 cm in fork length and from 33 to 540 kg in round weight) were sampled, from the Greek Bluefin Tuna Farm (GR 01/2004), in the Ionian Sea (38 ° 26′ 0.07ʺ N, 21 ° 1′ 48.85ʺ E), during the five year period 2007–2011. In addition, length and weight literature data from wild specimens captured in the central Mediterranean Sea were analyzed. The results revealed high percentage difference in weight between wild and reared in sea cages bluefin tuna of the same fork length, which reached a maximum of 43.9% in large specimens. The condition factor of the reared in sea cages bluefin tuna ranged from 1.24 to 3.16 with a mean value of 2.04 ± 0.19. The mean condition factor of the farmed specimens (1.92 ± 0.17) was lower than that of the fattened specimens (2.08 ± 0.15). This difference was consistent both in younger and older specimens in the sample. Estimated ages that were obtained using the caudal vertebrae of 619 reared in sea cages specimens ranged from 5 to 18 years. It was observed that the age of fish has a significant impact on the condition factor. The comparison among the mean condition factor values of each age class revealed that older fish (10–20 years old) present higher values than younger ones (5–9 years old). With a view to estimating the precision of the aging method, the Average Percent Error (APE) and the Coefficient of Variation (CV) were calculated (APE = 1.89% and CV = 2.46%). The von Bertalanffy growth model was fitted to mean lengths at estimated ages and the growth parameters were determined (L ∞ = 360.3 cm, k = 0.083 yr − 1 , t 0 = − 0.942 yr).

The efficiency of using remote sensing for fisheries enforcement: Application to the Mediterranean bluefin tuna fishery

This paper analyzes the impact of applying vessel detection technology using satellite images (vessel detection system, VDS) to complement air patrols for fisheries enforcement and control. Due to limited fisheries enforcement budgets there is the need to allocate costs efficiently among competing control tools. This paper focuses on assessing the benefits of using VDS jointly with VMS (vessel monitoring system) and air patrol surveillance to improve effectiveness of controls. A statistical model to estimate the number of inspections was developed and was used with enforcement costs data as reported by a number of EU countries. The result of applying VDS in fisheries enforcement is presented in one of the most demanding fisheries enforcement contexts: the Mediterranean bluefin tuna (BFT) fishery.

A mediterranean agreement for tuna conservation: The political benefit of an international ITQ scheme

Mediterranean bluefin tuna have been increasingly overfished since the early 1990s, but the countries involved have so far been unable to reach an agreement on an ecologically and economically more efficient use of this shared resource. A system of individual transferable quotas could foster international agreement on reducing the total allowable catches. One condition for this, however, would be that fisheries be adequately compensated for the opportunity costs of decommissioning vessels.

The Tragedy of the Commodity

This article develops a critique of the tragedy of the commons theory that is frequently applied to explain fisheries decline. In its place the authors offer the tragedy of the commodity as an alternative framework that better explains resource overexploitation and environmental degradation. They use a political economic analysis to discuss the social and ecological transformations that have occurred in the Mediterranean bluefin tuna fishery, with an emphasis on the Sicilian traditional trap fishery. Examining this case, the authors argue that Marx’s explanation of capitalist private property, commodity production, and the general formula for capital provide powerful theoretical guides for clarifying the social relations of production that have driven the overexploitation of fisheries in the recent past. Relying on historical and qualitative data, the case study illustrates the ways in which the social imperative of capitalist commodity production toward accumulating surplus-value directs production, reorganizes social relations, and transforms nature into an instrumental input that can more easily serve the needs of capital. The resulting ecological problems demonstrate the tragedy of the commodity.

Updated estimate of the growth curve of Western Atlantic bluefin tuna

The curve used until recently by the International Commission for the Conservation of Atlantic Tunas (ICCAT) to represent the growth of western Atlantic bluefin tuna, Thunnus thynnus, was estimated using tagging information and modal sizes that corresponded primarily to very young fish (ages 1–3, primarily). The estimated maximum average size from this curve is very large (382 cm), which could be a result of the scarcity of large bluefin in the data used. Recently, scientists have developed techniques for reading ages from bluefin ear bones (otoliths); the accuracy of the age readings has been validated with bomb radiocarbon dating. These age readings are primarily for large bluefin (ages 5 and older), and indicate slower growth and older ages than was previously assumed. However, an analysis of these data resulted in growth curves that predicted very small mean sizes for the youngest age group, which could be a result of the lack of small fish in the data used. In this study, we combine the otolith-based age readings with the size frequency distributions of small (ages 1–3) bluefin caught by purse seiners in the 1970s where the age groups are distinctly statistically as well as visible to the eye. We analyzed the two datasets jointly using a maximum likelihood approach and assumed that variability in length-at-age increases with age. The resulting growth curve predicts sizes at young and old ages that are very consistent with observed data such as the maximum sizes observed in the catch and the modal sizes for very young bluefin. The resulting curve is also very similar to the curve used by ICCAT for eastern Atlantic and Mediterranean bluefin.