TURTLE DENSITY AND COMMUNITY COMPOSITION IN SELECTED HABITATS
OF UPPER POOL 20, MISSISSIPPI RIVER.

Michelle L. Gutierrez, Richard V. Anderson, and Michael A. Romano.  Department of
Biological Sciences, Western Illinois University, Macomb, IL  61455

Turtles were collected from 3 sites in the upper reach of Pool 20 from June through
September of 1997.  Habitats sampled included an open river site, a slough, and a
backwater.  Baited turtle traps were used to collect turtles at each site.  Collected turtles
were weighed, shell measurements taken, they were marked and returned to the habitat
from which collected. Two hundred and eighty-three turtles in 7 species were collected
during the study.  Species collected were; smooth softshell (Apalone mutica), spiny
softshell (Apalone spinifera), common snapping turtle (Chelydra serpentina), sliders
(Trachemys scripta), common map turtle (Graptemys geographica), false map turtle
(Graptemys pseudogergraphica) and painted turtles (Chrysemys picta).  Both turtle
density, 81 turtles per 1000 trap hours, and diversity, Simpson's diversity of 0.80, were
significantly higher in the slough habitat than other habitats sampled.  Mark-recapture data
from turtles collected in the slough showed red-eared sliders, painted turtles, and common
snappers to have the highest population sizes in that order.  The open river site had both
the lowest total turtle density and diversity but had the highest density of softshelled
turtles, 23 turtles per 1000 trap hours.  No softshell turtles were collected in the backwater
habitat and only 3 per 1000 trap hours in the slough habitat.  Only 3 species of turtles;
common snapping turtle, painted turtle, and red-eared slider, were collected in the
backwater area.  This community was dominated by the red-eared slider, 31 per 1000 trap
hours, but the common snapping turtle was also abundant, 21 per 1000 trap hours. 
However, mark- recapture data indicated a higher population of common snapping turtles
than sliders in the backwater.  As the water level dropped in the backwater during the
summer the occurrence of turtles rapidly declined.  While turtles were found in all habitat
types in this reach of the river, the slough habitat provided adequate water levels, lower
current velocities, and food sources thus high densities of turtles and a diverse community
occur in this habitat type.

Keywords: turtles, river habitats, Pool 20, turtle communities, turtle density


Michelle L. Gutierrez
Department of Biological Sciences
Western Illinois University
Macomb, IL  61455
309-298-1543, FAX 309-298-2270, e-mail ml-gutierrez@wiu.edu

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