Morphology of the franciscana (Pontoporia blainvillei) off southeastern Brazil: sexual dimorphism, growth and geographic variation

Variations in body and skull morphology may exhibit geographic differences evidencing distinct population stocks. The objectives of the present study were to analyze such variation to test the hypothesis of a disjunct distribution of the franciscana (Pontoporia blainvillei) off the southeastern coast of Brazil. Body length and 39 cranial variables were measured from bycaught animals to considere sexual, ontogenetic and geographic variations. The areas studied were Espírito Santo (ES) (18°30'S-19°40'S), northern Rio de Janeiro (NRJ) (21°35'S-22°25'S) and São Paulo (SP) (23°30'S-25°30'S). Franciscanas from NRJ and SP presented significant sexual dimorphism, with the means for the metric characters larger for females than for males. Sexual dimorphism for franciscanas from ES was not examined due to limited sample size. The growth pattern for body and skull did not indicate clinal variation. The asymptotic values obtained for franciscanas from SP were smaller than the values obtained for franciscanas from NRJ and ES. Canonical discriminant analysis of the cranial metric characters indicated significant differences among the three geographic areas. Differences between areas ES and NRJ accounted for 85%; of the variation (axis 1). The remaining 15%; (axis 2) was due to difference between the area SP from the others. The geographic variation supports the hypothesis stock division in southeast Brazil; allopatry might be present. Therefore, three franciscana stocks from the southeastern coast of Brazil should be considered distinct for conservation and management actions