Biology and conservation of franciscana dolphin in the Buenos Aires Province, Argentina.

NEGRI, M.F.; PANEBIANCO, M.V.; PASO VIOLA, M.N.; CAPPOZZO, H.L

Mérida, México

Congreso; I Reunión Internacional sobre el Estudio de Mamíferos Acuáticos SOMEMMA-SOLAMAC; 2006

SOMEMMA-SOLAMAC

The franciscana, Pontoporia blainvillei, is the most common and vulnerable coastal dolphin in Argentina. Our objective is to present the results obtained between 1999 and 2004 about their biology and conservation. Mortality by fishing nets was estimated along the whole province littoral through surveys and death specimens recovered. Diet was study from stomach contents; we analyzed commercial captures of the coastal fleet. Physical maturity was analyzed through the degree of vertebral epiphysis fusion. Sexual maturity was estimated following standard criteria and histology of gonads. We determined the tissue concentration on 6 heavy metals (Cd, Pb, Cu, Zn, Cr y Ni) from hepatic samples by atomic absorption spectrophotometer. Along the Buenos Aires Province, 500 – 600 dolphins died per year in middle trawl and shrimper nets. The 56% of the recovered individuals are physical as sexually immature (< 2 years old, from GLGs). Their principals preys are stripped weakfish, Cynoscion guatucupa; horse mackerel, Trachurus lathami; argentine anchovy, Engraulis anchoita and raneya, Raneya fluminensis. With a minor proportion cephalopods like Loligo sanpaulensis  and others invertebrates. Except raneya, fishes prey, with the same range of size, are commercially important. Our results suggest that dolphins are exposed to the different heavy metals independently of sex. Cd is accumulated with the age; variations on concentrations of the different heavy metals are related with the maturity of dolphins. High mortality, contaminants, specialized diet and prey consume on commercial sizes could increase vulnerability of franciscana by human activities like fisheries and industrial. Because of this, an impact on the distribution and population dynamic of this species could be induce on the short term, considering the absence of a fishing management plan and taking into account the impossibility of reconvert the fleet into other fishing arts that avoid incidental mortality of dolphins and other non target species, compromise the future of this species.