Student Spotlight - Amy Lee
Analyzing Turtle Census Data
by Amy Lee
Winter 2005
For the past eight years, students have worked with American Museum of Natural History (AMNH) researchers and educators on a census of the Chrysemys picta (eastern painted turtle) population in Black Rock Forest ’s seven ponds. The goal is to obtain demographic data for every individual turtle, using a multiyear mark-recapture process [Ed. Note: See “Research Symposium,” Fall 2003]. Protecting habitats and their resident populations depends on knowing the numbers, types, and status of the individuals making up the communities.
When turtles are initially captured, they are injected with a passive integrated transponder (PIT) tag, a microchip the size of a grain of rice that provides permanent individual identification. Their PIT tag numbers, sex and age, shell measurements, capture method and location, and other information are recorded. The same information is recorded for recaptured turtles.
My part of the project focused on the recatchability of the turtle population, or the frequency with which individuals are recaught after initial capture and processing. I sorted, analyzed, and examined recorded field data for patterns in the turtles’ behavior. Studying recatchability allows researchers to monitor a population over a long enough period to evaluate its status (e.g., stable, increasing, decreasing) and to understand how turtles react to the environment and human activity.
Of the 276 adult turtles (118 males, 157 females, 1 unidentified) that have been tagged, 138 have been recaptured. Females were more likely to be recaptured (53%) than males (46%). Recapture rates vary among the ponds from 8% to 61%, and by original capture method: hoop traps, 47%; basking traps, 53%; and active capture methods, 72%.
More than three-quarters of the recaptured turtles were recaptured three times or less, with the rest recaptured four to twelve times, except for one female that has been recaptured 26 times. Turtles recaptured three times or less were mostly female; those recaptured five times or more were mostly male.
Data analysis can correct misconceptions based on observation alone. What was thought to be one turtle, called “Stumpy” since 1996 because of an amputated rear left foot, turns out to be an amalgam of several turtles, missing different feet!
While field work is an important aspect of this census, data analysis is just as crucial: it is what translates this project into tangible results.
Amy Lee, a senior at Brooklyn Technical High School , has been working with Dave Karrmann, the leader of the AMNH turtle project, since January 2004. She presented her work at the 2004 Northeast Natural History Conference in Albany and has used it for 2005 INTEL and New York City Science & Engineering Fair submissions.
