Population Size and Growth in the Turtle Graptemys oculifera

Abstract

Population sizes of Graptemys oculifera were estimated using two mark-recapture proce- dures at five sites on the Pearl River in Mississippi. These were compared with density estimates from basking counts at the same sites to determine if the latter could be used as indices of population size. Density estimates from the mark-recapture studies ranged from 85 to 341 G. oculifera per river km. Jolly- Seber and Schnabel population estimates were similar at three sites, but low numbers of recaptures resulted in inflated Jolly-Seber estimates at the two remaining sites. The Schnabel mark-recapture model appeared to be better suited for estimating population sizes of G. oculifera. Basking surveys provided a rough index to population sizes, but comparisons between sites were potentially complicated by differential wariness of basking turtles. Growth curves were constructed for each sex by fitting data from recaptured turtles to the von Bertalanffy and logistic growth models. The former model provided a better fit to the data than did the latter. Juveniles of both sexes grew at approximately the same rate. Males matured at 3.5 yr of age and females between 10 and 16 yr. Sex ratios were biased toward males at all sites. The ringed map turtle (Graptemys oculifera) is endemic to the Pearl River of Mississippi and Louisiana where it is restricted primarily to the main channel of the river and to the lower