Body Fat Condition in Franciscanas (Pontoporia blainvillei) in Rio Grande do Sul, Southern Brazil

Abstract

In cetaceans almost all the energy reserves in lipid form are allocated to blubber and are related to basal metabolism and thermal insulation. Our study analyzed the blubber of 57 specimens of franciscana (Pontoporia blainvillei) from the state of Rio Grande do Sul, Brazil. Body fat condition was estimated through blubber weight, girth, and thickness of blubber. Blubber weight increased along with growth, from 2.27 kg in calves to 8.86 kg in mature franciscanas. Blubber weight decreased from 33.91% of total weight in calves to 24.32% in mature franciscanas. A significant difference was found when age classes were compared to each other (P , 0.001) for both males and females, indicating that blubber varied according to growth, independent of sex. Girth showed a good correlation with blubber weight at all 6 locations where it was measured, and thickness of blubber presented a low correlation at all 19 locations where it was measured. Calves face the physiologic problems of low surface to volume ratio, whereas adults expend energy in feeding, reproduction, and taking care of calves. In mammals, condition of body fat is commonly considered a general measure of the energy reserves of an individual (Hanks 1981). In cetaceans, most of these reserves are stored in the blubber layer (Yasui and Gaskin 1986), which is the most important energy storage site in this group (Aguilar and Borrell 1990; Pond 1978; Read 1990). The measurement of this layer is a major tool for comparative analysis of how animals of different sexes, ontogenetic stages, and stages of sexual maturity use their energy reserves throughout the year. These reserves may vary interannually, depending on environmental conditions and food supply (Lockyer 1987). Body fat condition may be considered a representation of variation in energy reserves in the form of fat, an index of physiological condition of an individual, and an indicator of the relationship of an individual with the environment (Hanks 1981). Energy reserves in the form of fat are required by cetaceans, not only to maintain their internal temperature, but also as an