Elasmobranchii (sharks and rays), a potencial resource to protect in the Azores?

Tese de Doutoramento, Biologia, 2 de Outubro de 2017, Universidade dos Açores.[...]. A presente dissertação teve como objectivo aprofundar o nosso conhecimento sobre as populações de elasmobrânquios dos Açores, tendo em conta a sua importância para a região. O estudo abrangeu diversas temáticas como a pesca, a ecotoxicologia e o ecoturismo, visando 4 espécies principais, aparentemente capturadas acidentalmente (bycatch): a raia Raja clavata, o cação Galeorhinus galeus, o tubarão-azul Prionace glauca e o tubarão mako Isurus oxyrinchus. Mais recentemente, as espécies P. glauca e I. oxyrinchus são têm sido igualmente exploradas por uma nova indústria nos Açores – o mergulho com tubarões, uma alternativa económica à pesca, ecologicamente mais sustentável, que carecia de avaliação. [...].ABSTRACT: Elasmobranchs (sharks and rays) evolution, over approximately 450 million years, shaped numerous successful species, developing at the same time specific life-traits (slow growth, late attainment of sexual maturity, long life spans and low fecundity), which made them particularly susceptible to human activities such as fishing, habitat degradation and pollution. In the Azores, in the middle of Northeast Atlantic Ocean, where many species occur or pass by, some constitute an important local, national and/or foreign socio-economic component as a food source and/or ecotourism resource. This thesis aimed to increase our knowledge on elasmobranchs occurring in the Azores, given their importance to the region. The study covered fisheries, ecotoxicology and ecotourism issues, targeting 4 main species usually landed as bycatch: thornback ray Raja clavata, tope shark Galeorhinus galeus, blue shark Prionace glauca and shortfin mako shark Isurus oxyrinchus. Each species presented different management challenges which should be addressed with some care, considering the Northeast Atlantic context and local, national and foreign interests. These high trophic level species are also known to accumulate alarming levels of pollutants such as persistent organic pollutants or heavy metals as arsenic (As), cadmium (Cd), mercury (Hg) or lead (Pb) potentially dangerous for elasmobranch health and especially for human consumption safety. In the overall, all four species shared the same trophic level in a pelagic-based food web and did not present relevant significant differences between genders or metals, except for As. The results also reflected bioaccumulation processes for As and Hg while Cd and Pb were not detected in muscle tissue. Metal content was related to the Azores volcanic nature although generally lower when compared to other less pristine areas from previous studies. Raja clavata was also analysed for Polychlorinated biphenyls (PCBs) for both muscle and liver tissue. This species presented low concentrations of PCBs, especially the dioxin-like congeners, although always higher in liver and not correlated with size. None of these contaminants exceed European Union legislated limits except one individual of I. oxyrinchus, which presented Hg content above regulatory limits. The studied elasmobranch species demonstrated great potential to be used as biological sentinels of metal pollution, each presenting different characteristics regarding the key features that define a good marine bioindicator, allowing long-term monitoring at different temporal and spatial scales. Prionace glauca and I. oxyrinchus are also ocused by the recent shark diving industry in the Azores, an economic alternative to fishing which promotes an ecological and economical sustainable use of these species. The estimated generated income of shark diving in 2014 amounts to 1,983.347€ (around US$2,244.890) which may will easily increase considering the current fast expansion of (eco)tourism in the Azores and the activity infancy. Given the unique features of the Archipelago, socio-economic needs and potential and natural resources availability, this study focusing these charismatic species of the Mid-Northeast Atlantic region provided new important information for decision-makers to develop more efficient monitoring protocols, contributing to a better management and protection of these valuable marine resources