Bioecologia e padrões de movimentação de tubarões na costa de Recife, Brasil: aplicações na mitigação do risco de ataque

Tese dout., Ciências do Mar, da Terra e do Ambiente (Ecologia Marinha), Faculdade de Ciências e Tecnologia, Univ. do Algarve, 2013An abnormally high rate of shark attacks on humans off Recife, Brazil prompted the development of a shark monitoring program aiming at mitigating shark peril. Bottom longlines and drumlines were used as fishing gears and optimized for increasing selectivity towards large sharks and reducing fishing mortality. The fishing methodology allowed to reduce the shark attack rate considerably and to generate important bioecological information on tiger and bull sharks, species which seem to be responsible for most of the attacks. Tiger sharks in this region move preferentially to the north through wide home ranges. The presence of a port complex to the south of Recife could be attracting tiger sharks shoreward, which would subsequently visit the littoral of Recife due to their natural movements. Other important, site-specific features such as the presence of an estuary and an alongshore channel close to the beach, together with high pollution and siltation levels, could further promote the high risk of shark attack in the area. Tiger sharks use the continental shelf off northeastern Brazil mostly during early juvenile stages, where they quickly grow between January and September before departing to oceanic waters. Larger tiger sharks use deep oceanic waters more often but they frequently visit nearshore waters, probably in search for prey. The depth distribution of tiger sharks seems to correlate with both diel and lunar cycles, and abundances off Recife were correlated with month, lunar phase, tidal amplitude, pluviosity and wind direction. This information could be useful in determining periods when tiger sharks are more likely to occur in the area of risk. Compared to traditional shark-meshing programs, which produce a considerable amount of bycatch and fishing mortality, the methodology herein reported provides an effective solution to increase user safety at local beaches with minimal ecological consequences