The Influence of Sampling Methods on the Estimation of Population Structure in Painted Turtles

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Abstract
A natural population of painted turtles [Chrysemys picta (Schneider)] was studied in University Bay of Lake Mendota, Dane County, Wisconsin, from September 1960 to October 1962. Five methods were used to capture turtles for marking, measurement, and release. Each of the methods yielded a different size-class distribution and a sex ratio which, in four out of five cases, was significantly different from that of the total population estimate. Baited hoop nets yielded predominantly males and relatively few juveniles; basking traps tended to yield higher percentages of females than did nets, and large turtles were an important component of the sample. Hand capture resulted in a sample heavily weighted by juveniles and a 1:1 sex ratio for adults. The influence of trapping method in the estimation of population structure in turtles must not be overlooked. This study indicates that even within a species, trapping method introduces considerable bias in the estimation of sex ratio and size-class distribution.

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