Upper Midwest Environmental Sciences Center
PSR 99-06 July 1999
Natural History of the Red-Eared Slider Relative to a Variable Hydrologic Regime
by John K. Tucker
The impacts of hydrologic regimes in large river systems on fish, birds, trees, and invertebrates have been the focus of many studies. As a result, we know for instance, that fish reproduction and recruitment benefit from the natural hydrologic pattern of high spring stages and lower summer stages. However, despite numerous studies, essentially nothing is known about the interactions found between hydrologic patterns and reptiles and amphibians.
Studies of the natural history of the red-eared slider (Trachemys scripta elegans) began in 1992 in Pool 26 of the Upper Mississippi River System (UMRS), including the lower Illinois River, as part of the Long Term Resource Monitoring Program (LTRMP). These studies are revealing important information to promote survival of reptiles and amphibians in the floodplains of the UMRS and other regulated rivers.
The red-eared slider (slider), a member of the Emydidae or pond
turtle family, is widely distributed in the Central United States
and occurs in the UMRS south of Pool
13. Turtles in this group commonly bask on logs to thermoregulate.
young, most individuals feed on aquatic invertebrates, but adults,
and particularly sexually mature females, become more herbivorous
with age. Thus, these turtles use two resources whose abundance
is directly related to the health of the UMRS.
I am continuing to examine the influence of flooding and other
abiotic variables on reproduction in sliders from two backwater
lakes of the Illinois River, Swan Lake and Stump Lake. Each
year since 1994, female turtles have been captured on their nesting
migrations that can be as far as 1 km from their aquatic habitats.
They are induced to lay their eggs in the laboratory where the eggs
are counted and weighed. The females are released at the original
collecting areas after oviposition but their hatchlings are overwintered
in captivity. The hatchlings are released after naturally emerging
hatchlings are found. Using these methods, reproductive success
at both sites is being determined. Reproductive output varies from
year to year and from location to location (Figure 2). Generally,
turtles from Swan Lake lay relatively fewer but bigger eggs than
do turtles from Stump Lake.
Although preliminary, the relationship to flooding appears to be
an important one. Sliders produced fewer and smaller eggs in the
year following flood events (e.g., 1993, 1995, 1996) when minimum
monthly stages exceed targeted regulated levels but produce larger
and more eggs following years such as 1994 and 1997 when flooding
was slight (Figure 3). The effect occurs at both study sites and
can change reproductive output by as much at 20%. The causal factors
for the effect on turtle reproductive output is uncertain but may
be related to reduced availability of submersed aquatic vegetation
during larger floods. Mean monthly stage and the three measures
of reproductive output (egg mass, clutch size, and clutch mass)
for both sites (a total of six correlations) tend to be negatively
related during the active season of the turtles (Figure 4). All
six correlations were negative with mean stage in May and July and
five of the correlations were negative with mean stage for June
suggesting that reproductive output decreases with increasing stage.
This is a preliminary result but one that may be strengthened when
sufficient data are accumulated to allow a multivariate study.
This report is a product of the Long Term Resource Monitoring Program for the Upper Mississippi River System.
For further information, contact
U.S. Geological Survey
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