The Eastern stock of Atlantic bluefin tuna (Thunnus thynnus thynnus) has experienced a steep decline, 74.2%, in recent decades, mainly driven by large unreported catches and growth of the capture-based aquaculture of this species in the Mediterranean. This study addresses the potential food-web effects on trophic linkages in the ecosystem through the removal of both small pelagic fish species and wild bluefin tuna (BFT) for capture-based aquaculture operations. An Ecopath model of the Southern Catalan Sea (Western Mediterranean) was modified to include a BFT farm supplied entirely by the area modeled (Coll et al, 2006). Six scenarios were developed to simulate possible changes to the system using Ecosim, including the continued growth of aquaculture operations, as well as changes to the total allowable catch for BFT as set by ICCAT. Species not directly connected with the production of BFT showed large fluctuations in biomass and yield as a result of these simulations. Using these models, increases in biomass of lower trophic level functional groups were observed with reductions in biomass from other top trophic level predators. Jellyfish and benthopelagic fish exhibited an increase in biomass, the largest being 8.76% for jellyfish and 69.76% for benthopelagic fish, while wild BFT biomass decreased 87.26%. Atlantic bonito and swordfish showed similar rates of decline in biomass levels. These outcomes stress that fishing at top trophic levels can have unforeseen outcomes on the structure of the ecosystem, due to the complexity of the food web. Capture-based aquaculture of Atlantic bluefin tuna can be expected to increase along the proposed scenario levels, due to the decision not to place this species on Appendix I of CITES during the CITES meeting of 2010. This study suggests that farming activity has additional impacts on the ecosystems that should be taken into account when evaluating the suitability of this industry and projecting the trends towards the future. Results suggest that, in the case of the Western Mediterranean Sea, increasing BFT farming activities will likely contribute towards further degradation of an already highly exploited marine ecosystem. The development of hatchery technology to close the life cycle and produce juvenile BFT for stocking cages as well as using artificial diets during the grow out stage are required to minimize long-term impacts and support industry expansion.

The Atlantic Bluefin Tuna (Thunnus thynnus) is perhaps the most magnificent and most marvelous nomadic wild animal living in the world. It lives in the deep blue waters of the Atlantic Ocean and is one of the largest of the world’s fin fish and the largest of the 48 other species of tuna (Kuhn, 1996). It is a species that seems to have been designed and sculpted by an artist—sleek, smooth, and beautiful—instead of having been a product of an evolutionary process. Today, the existence and future of the Atlantic Bluefin Tuna is in question because of the constant overexploitation of the stocks for its flesh. The insanely high prices being paid for its flesh have resulted in a modern day gold rush for almost any person who has the ability and equipment to catch it. The movements of the Atlantic Bluefin Tuna take it through multiple jurisdictional, national, and international boundaries, spending part of its life in areas of the world’s commons, also known as the high seas. In each, the species is managed through complex, often cloudy and poorly enforced state, regional, and national laws and international treaties. For decades the terms overfished, under pressure, listing, and extinction have become synonymous with the Atlantic Bluefin Tuna because the scientific facts have, and continue to, indicate that it is in great peril and nearing the tipping point of no return in terms of viability as a species, all because of short-term economics and politics. This dissertation is rooted in complexity theory and public choice theory. The research design for this dissertation is based on the 5-component structure, interactive model, prescribed by Joseph A. Maxwell, Ph.D. (2004), and current policies were evaluated through the policy framework prescribed by Frank Fischer, Ph.D. (1995). Ten public policy steps are suggested to save the Atlantic Bluefin Tuna from collapse.

Commercial capture-based aquaculture of the Atlantic bluefin tuna (ABT), Thunnus thynnus (L.), has been prominent in the Mediterranean for over a decade. Owing to several limitations encountered in working with the species, including its high commercial value, there has been little research carried out relating to this species. The objective of this study was to examine several health parameters of captive ABT. These included an examination of coronary artery lesions, haematology, plasma biochemistry, assessment of immune function and changes in fatty acid (FA) flesh content through the on-growing period. Arteriosclerosis in fish is a pathologic condition of uncertain etiology and involves the main coronary artery in teleosts. Apart from reports of their widespread occurrence in salmonids, they have been described from a restricted number of wild ABT specimens but have not received further attention. This investigation analysed the effect of size and period of net-pen rearing on the prevalence and severity of arteriosclerotic lesions in ABT. Coronary arteries from wild and captive fish were investigated and prevalence was 100 %, but increasing structural degradation was observed with increasing fish size, suggesting that lesions progress throughout the life of the fish. Due to the limited availability of wild specimens, the effect of captivity on arteriosclerosis in ABT could not be adequately quantified, although observations suggest that the farming process has no major effect on arteriosclerotic lesions in ABT. Studies on the haematology, plasma biochemistry and immunology of ABT are limited. Haematological and plasma biochemical indices are useful in animal health assessment but use of these requires the establishment of species-specific ranges. Blood was collected from captive ABT specimens of varying weight (61-361 kg) and the major haematological (n = 45), plasma biochemical (n = 30) and immunological parameters (n = 45) were quantified. Size-based differences were found in haematological indices between experimental sub-groups including increased erythrocyte number and haemoglobin level in smaller ABT. No differences were found in immunological parameters except for total IgM levels, which were higher in the smaller individuals. Preliminary investigations indicated that disease prevalence in captive ABT is very low. Epidermal mucus is an important interface between fish and their environment and comprises immunological components which act as a first barrier against pathogen entry or colonisation. Mucus was collected from captive ABT and analysed for innate immune components. The presence of IgM was detected in the mucus of ABT by an enzyme-linked immunosorbent assay and several different enzymes were detected with an API-ZYM kit assay. Zymography experiments confirmed the presence of protease-like enzymes in the mucus, while enzyme assays quantified alkaline phosphatase, protease, esterase and cathepsin B activities. Lysozyme levels were high. The mucus agglutinated sheep erythrocytes but did not demonstrate complement or bacteriolytic activity. There is restricted information on the fatty acid composition of farmed ABT or how this is influenced when the fish are held under commercial aquaculture conditions. This study investigated the FA composition of farmed ABT, its variation by dorsal muscle region and the correlation between dietary FA composition with that of the fish. Analysis of flesh samples retrieved from farmed ABT did not reveal significant differences in the FA composition of experimental sub-groups irrespective of size, time held in captivity or diet. These results indicate that FA metabolism in ABT is substrate-selective. Gene expression measurements from several organs of ABT showed that expression of Δfad5 and elovl5, genes involved in FA metabolism, were highest in the brain followed by the liver but no expression of these genes was detected in the spleen. The findings of this research address aspects of health evaluation and nutritional status in farmed ABT and are discussed in terms of farming practice. Conclusions from some of these studies suggest that the practice of holding wild-captured stock in cages for periods of up to 18 months does not result in significant impact on ABT.