Dinâmica populacional de Trachemys dorbigni, (Testudines: Emydidae) em ambiente antrópico em Pelotas, RS

Abstract

Informations about the population dynamic of Trachemys dorbigni were collected from February 2006 to January 2007, in the Santa Barbara stream, Pelotas, Brazil. It was collected 377 individuals in the traps, 160 females, 146 males and 71 juveniles. The sex ratio was not different from 1:1. Males of T. dorbigni reached sexual maturity at 127 mm length. The smallest reproductive female presented 176 mm length. The females were heavier and larger than males in all morphometric measures, except to the CPD. The CPUE of females and juveniles was higher in February and March and in males in February and April. The RELEASE software did not indicated significant violations in premises of equal capture and survival probability. The population size estimated by Jolly-Seber was 3.145 adults and 544 juveniles. The week survival was constant to adults (97%) and to juveniles (94%). The weekly capture probability ranged from 0.3% to 13% to adults and it was constant to juveniles (4%). 122 nests were found. They present the smallest egg average already registered (8.2). Eggs had the smallest average size already reported to the species, 37.3 x 20.2 mm. The smallest reproductive female presented 176 mm in length. Egg width was positively dependent to their length. Clutch size had no relationship with their dimensions. Egg length and egg width also not depended on the female size. However, clutch size increased with female body size. Nesting occurred between October 22 and January 4. Only 35.3% of females in the population nested in evaluated year and 11.9% deposited two nests in the reproductive period. The species nested preferably in soils with more than 88% of sandy and higher frequency of nesting behavior occurred in the morning. Higher abundance of nests were found in areas between 25 m and 50 m away from the water and in flatter areas, between 0 ° and 10 ° of declivity. The incubation temperature ranged from 16.1 °C to 35.5 °C. It was registered 18.1% of predation in the nests. The nests were deposited on an aggregate form and the nests closest of stream, between 20 m and 30 m, had a higher rate of predation (52.4%). Higher survival recorded for the species can be linked to the relatively short period sampled. Besides exposition to human wastes, the turtles of the Santa Barbara stream are subject to high road mortality and to the wild animals trafficking. Only the analyses of the annual fluctuation of the populational parameters will demonstrate if the population is impacted by these effects. Due to the longevity of the turtles, some impacts can be assessed only in long term.