Snapping Turtle

Turtle Research

This long-term mark-recapture population study is being performed by Gary Breitenbach, Indiana University East.

Two species of aquatic turtles are being studied at MGBS. Beginning in 1985, populations of painted turtles and common snapping turtles were marked individually using non-invasive notching of marginal scales. Each animal was provided a unique identification number. Some animals originally marked in 1985 are still in the populations as of 2009.

This long-term mark-recapture population study is being performed by Gary Breitenbach, Indiana University East (formerly of Earlham College and UCLA). Prior to beginning the MGBS study, he coordinated the largest fresh water turtle population study in the world, an NSF-funded study of three species in southeastern Michigan. These studies focus on life-history evolution and the evolution of longevity in turtles. Several peer-reviewed studies were published using Michigan data, and the MGBS data are being used for geographic comparison.

Important life history data such as age at maturity, clutch size, age-specific mortality rates and longevity have and are being collected. Among the highlights, it has been demonstrated that mortality of eggs in the nest is extraordinarily high, yet unpredictable. In some cases (e.g. common snapping turtle) all eggs are destroyed by predators in a given year, meaning that there is no net recruitment of juveniles into the population. This is likely to be the selective pressure that shaped extreme longevity in that species, estimated to live to be 100 years under natural conditions.

Protected populations, such as the Michigan and MGBS populations, provide natural systems for study. This is important because snapping turtles are marketed world-wide and often appear live, for sale, in Asian countries. Although not many people notice, turtle harvest in the Midwest is a huge business, sometimes operating illegally.

In addition to the research value of this study, other attributes involve using this project for educational purposes. Hundreds of college undergraduates have participated in this study, learning the procedures of mark-recapture population studies. In addition, thousands of primary and secondary school children have seen presentations of this study as part of outdoor education programs. Moreover, educators have participated in professional development courses or activities using turtles and other MGBS species over the years.

To many visiting MGBS who may catch a glimpse of a turtle in one of the ponds, it’s just another turtle. But in fact, these quiet reptiles are furthering scientific knowledge, helping shape future scientists and educators and providing an outdoor experience for the population at large.

Submitted by G. Breitenbach


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