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Body weight/length relationship and mass estimation using morphometric measurements in Amazonian manatees Trichechus inunguis (Mammalia: Sirenia)

  • Rodrigo S. Amaral (a1), Vera M.F. da Silva (a2) and Fernando C.W. Rosas (a2)


This study defined the body weight/length relationship and an equation for body mass estimation using morphometric measurements on Amazonian manatees Trichechus inunguis (Mammalia: Sirenia). Total length (TL), maximum girth (MG) and body mass (M) were obtained from 91 captive Amazonian manatees (46 males and 45 females) of different ages, and TL and M were obtained from eight free-ranging Amazonian manatees (6 males and 2 females). The data were analysed by linear and multiple linear regressions. The maximum length and mass measured were 266.5 cm and 379.5 kg, respectively. The equation for body weight/length relationship was M = 0.00001070 * TL3.122 (r2 = 0.984) (Equation I) and no differences between sexes and between captive and free-ranging animals were found (P > 0.05). We calculated two more equations for mass estimation (Equation II: M = 0.00003284 * TL1.857 * MG1.106, r2 = 0.992; and Equation III: M = 1.506 + 0.00003477 * TL * MG2, r2 = 0.995), and the best equation (high correlation coefficient and low percentage of residues) was Equation III. Equation I provides the body condition of manatees, whereas Equation III is more accurate for estimating body mass. Both equations are important tools for management of captive and free-ranging Amazonian manatees.


Corresponding author

Correspondence should be addressed to: R.S. Amaral, Departamento de Reprodução Animal—LDH/FMVZ/USP, R. Prof. Dr. Orlando Marques de Paiva, 87 Cidade, Universitária São Paulo05508-270—SP/Brazil email:


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