Estudo de modelos não lineares de crescimento em peixe-boi marinho Trichechus manatus manatus e peixe-boi amazônico Trichechus inunguis (Mammalia: Sirenia) em cativeiro

Abstract

Knowledge of the parameters that affect the growth of manatees in captivity is important in terms of conservation. This information is vital in making predictions using non-linear models of growth. During this work data on biometrics (length, wingspas, thorax maximum circumference, fluke peduncle and fluke width) and weight of marine manatee (n=23) and Amazonian manatee (n=15), with different ages and sexes from many regions of north and north-eastern Brazil were analysed. For the Amazonian manatee analysis of variance presented differences due to the effect of year and sex on the weight at different ages. For the other characteristics measured until the age 70 weeks, there was no effect of sex. Over all effects: sex and year of measurement were observed in marine manatee, in different ages. For the other characteristics differences due to yer of measurement were observe at different ages, and sex related differences occurred only in older animals. Correlation among the studied characteristics were calculated for males and females on Amazonian manatees, and varied between 0.78 to 1.0. For the marine manatees, the females' age presented low correlation to the other characteristics, with a magnitude between 0,40 and 0,6, for the other characteristics and for the males, the correlation varied between 0.77 and 1.00. Due to high correlation between the characteristics, the data of: weight/age, wingspan/age and thorax maximum circumference/age were adjusted. The data were modeled using, Richards', Brodys's, Logistic, Gompertz's and Von Bertalanffy's functions. Only Brody's and Gompertz's functions reached the convergence and generated the A, B, k, SQR, Nºiter, R² parameters, observed and estimated means and MRE. Using the parameter values the data had the bes-fit using the Gompertz function for: weight/age and wingspan/age in the Amazonian manatee. According to the function: the weight at maturity was estimated as 172.28 + 6.13 kg for females and 169.13 + 3.13 kg for males; the wingspan was estimated as 214.93 + 2.42 cm for females and 216.53 + 1.52 cm for males; for thorax maximum circumference/age Brody function was more appropriate and estimated this characteristics as 154.00 + 1.6 cm for females and 154.10 + 1.60 cm for males. For the marine manatee the Brody function was more appropriate: the weight at maturity was estimated as 280.60 + 8.62 kg for females and 219.66 + 12.02 kg for males; the wingspan was estimated as 283.28 + 2.18 cm for females and 294.69 + 6.10 cm for males; and the thorax maximum circumference was estimated as 216.68 + 2.77 cm for females and 190.06 + 2.67 cm for males.