AN EXPLORATION IN GROWTH OF THE RED-EARED SLIDER, TRACHEMYS SCRIPTA ELEGANS, IN 
THE UPPER MISSISSIPPI  RIVER POOLS 19 & 20 AND SELECTED SITES ON THE DES MOINES 
AND FOX RIVERS.

Kelly J. Larson, Michael A. Romano, Richard V. Anderson, and Sean E. Jenkins
Western Illinois University, Department of Biological Sciences, 1 University 
Circle, Macomb, IL 61455.

Growth rates of emydid turtles is well-documented for populations in lentic 
habitats.  Few studies examine the growth rate of these species in lotic 
riverine systems.  Red-eared sliders (Trachemys scripta elegans) were trapped 
during consecutive summers from 1997 through 2003 at sites in the Mississippi 
River Pools 19 and 20, Des Moines River, and  Fox River.  Sites in the 
Mississippi River included three in Pool 20:  open river, slough, and backwater; 
and one in Pool 19: just above Lock and Dam 19.  In addition, one site was 
located in the Des Moines River and one site in the Fox River.  The latter two 
sites were located just upstream form their confluence with the Mississippi 
River, Pool 20.

Specimens were measured for carapace length, plastron length, weight, and 
gender.  Morphometric values were log-transformed and those for carapace length 
and weight were analyzed by simple linear regression as an estimate of growth 
rate.  Analysis of Covariance (ANCOVA) was utilized to compare growth rates 
between sexes, among sampling years, and among sites.

Data revealed significant differences in slopes for females versus males 
(p<0.0001) and thus, the data from different genders were not pooled.  No 
significant differences were found among slopes of females and among slopes of 
males for sample years (females:  p=0.65; males:  p=0.115) or sites (females:  
p=0.91; males:  p=0.23).  Data from all sample years and sites were pooled for 
each sex.  For females, significant differences were found among elevations of 
slopes of the year 2003 and all other years (p<0.0001).  For males, significant 
differences were found among elevations of slopes of the year 2003 and all other 
years (p<0.0001) and also between the years 1999 and 2002 (p<0.01).  For both 
sexes, significant differences existed among the elevations of slopes of the 
Mississippi River sites and, concordantly, the Des Moines River and Fox River 
sites (females:  p<0.0001; males:  p<0.0001).  Linear regression produced two 
lines: one for each gender:  females, r2=0.97 and y=2.83x-1.58, males, r2=0.94 
and y=2.49x-0.69.

The growth rates for sexes were different, with female growth rate greater than 
male growth rate.  From these data, and based on the resulting slopes, it was 
determined females in this study have a faster growth rate than males.  Growth 
rate (slope) was the same for all sample sites and years for females or males.  
Thus, sample site and year had no effect on growth rate for the study 
populations.  Elevations of slopes among certain sites and years differed due to 
different starting points in weight for the regression lines.

Keywords:  red-eared sliders, Trachemys scripta elegans, growth rates, linear 
regression, ANCOVA