Demographic Analysis of the Oceanic Whitetip Shark Carcharhinus longimanus in Southwestern Atlantic Ocean

The oceanic whitetip shark (Carcharhinus longimanus) is an oceanic epipelagic species, with great commercial importance in the southwestern Atlantic. In 1999, C. longimanus represented 29% of the total elasmobranch catch in the southwestern equatorial Atlantic Ocean, within the limits of the Brazilian Exclusive Economic Zone (EEZ), second in abundance only to the blue shark, Prionace glauca and third in shark fins landed by commercial oceanic longliners in the northeastern of Brazil. Signs of declining populations of C. longimanus are already evident, especially in all Atlantic Ocean and this decrease became the species listed as vulnerable in the red list of International Union for the Conservation of Nature. On the Brazilian list of endangered species, C. longimanus was classified Initially as threatened with extinction but was later moved to the category of overexploited, due to the economic interest in species and the absence of more information about the population status. For this reason, the objective of this study is present the status of the C. longimanus population in the southwestern Atlantic ocean, based on demographic analysis conducted by life-history tables (LHT), Leslie matrices (LM) and stage-based model (SBM). Between May 1997 and May 2003, samples of C. longimanus were collected monthly at commercial landings in the city of Natal from pelagic longline fishery activities carried out in the southwestern Atlantic ocean. The annual fecundity of female embryos per pregnant female used was 1.69 and the maximum age and age at first sexual maturity for females) was 13 and 7 years, respectively. The numbers of individuals of C. longimanus sample was 518, with total length range 72.0 to 251.2 cm and ages from 0.4 to >13 years, with 81.3% of sample composed by juveniles. The age at fishery recruitment using for demographic analysis was 2 years-old. The scenario in which fishing mortality from that age, the population decreases about -4.9%/year in LHT and LM, and -8.2%/year for SBM. If there were no fisheries, or if the catches started from the adult stage (7 anos), the population would increase more than 2% per year, indicating that the population is overexploited. Elasticities reveal that the oceanic whitetip shark has low fecundity and low number of juvenile survivors which are not enough to compensate the mortality by fisheries. Those biological features render the species highly vulnerable for exploitation. Besides, the exploitation of juveniles makes C. longimanus one of the most threatened species.