Seasonal variation in the population parameters of kinosternon scorpiodesand trachemys adiutrix, and their association with rainfall in seasonally flooded lakes

Seasonally flooded lakes in the northeast region of Brazil are important areas used for breeding and feeding by two species of turtle, Kinosternon scorpioides, the Scorpion Mud turtle, and Trachemys adiutrix, the Brazilian Slider Turtle. Over 6 y, we captured, marked, measured, and determined the sex of 183 K. scorpioides and 518 T. adiutrix. Over the study period as a whole, the sex ratio of K. scorpioides did not deviate significantly from 1:1, whereas there was a significant male bias in T. adiutrix. There was no significant relationship between relative abundance and mean monthly rainfall in either species, although we captured significantly smaller K. scorpioides females and larger T. adiutrix individuals (males and females) in the drier years. Seasonal residence times ranged from 14–90 d in K. scorpioides and 14–110 d in T. adiutrix. Residence time was not related significantly to mean monthly rainfall in either species. In K. scorpioides, the estimated annual female population size ranged from 14 to 78 individuals, while that of the males varied from 16 to 88 individuals, while in T. adiutrix, estimates of the female population size ranged from 71 to 444 individuals, and those of males, from 80 to 515 individuals. These findings indicate that both turtle species maintain resident populations in the study area, but present distinct patterns of annual variation in body size and the sex ratios, which points to distinct ecological requirements that may require differential conservation strategies.