Using craniometrical predictors to infer body size of Antillean manatees

Body size determines many physiological and ecological variables; however, there are few studies on this parameter for the Antillean manatee (Trichechus manatus manatus). We studied an osteological collection and databases of Antillean manatees in Mexico to infer body measurements and to determine the body mass (BM)/body length (BL) relationship. The studied sample included 165 specimens: skulls (n=60), necropsies (n=51), and individuals captured for health assessment purposes (n=54). Specific regression equations for estimating BM were derived using the following craniometrical parameters: condylobasal length (BSL), occipital condyle width (OCW), and foramen magnum width (FMW). OCW and FMW were not significantly correlated with BL. The equation of the fitted model was BL=-121.644+10.8861×BSL (p<0.05, r2=0.93, SE=14.72). The allometric equation of weight/length relationship was defined as BM=exp (2.7477+0.0110957×BL) (p<0.05, r2=0.99, SE=0.07). The model showed a significant relationship between BL and BSL (>95%). Regression equations proved to be useful in estimating BL when only highly decomposed carcasses or skull dry bones are available, and in estimating weight when it is impossible to do it directly. Studies on biology history and age determination in T. m. manatus are required in order to establish an adequate age classification.