Turtle Ecology Active

Background & Importance

Resource managers are concerned about the declining status of many of the world’s turtle species, especially those that are listed as threatened or endangered under the Endangered Species Act. In addition, many species are data deficient: we simply don’t know enough about their biology or abundance to effectively manage turtle populations. Research conducted by U.S. Geological Survey scientists provides resource managers with information that allows them to make knowledgeable decisions that affect conservation and management of turtles.

General Methods

Field techniques vary according to the objectives of each project. Generally, turtles are captured in the field, and marked with unique and permanent notches on their shell that allow researchers to identify individuals at subsequent captures to measure growth, movements, etc. Individual turtles are measured, weighed and sex is determined by examining shell shape and tail size. In some studies, a small sample of turtles are outfitted with radio transmitters that allow scientists to find them on subsequent visits to the field site. In other studies, adult females are X-rayed to determine clutch size, clutch frequency and egg width to determine reproductive potential. Previous published research by the Principal Investigator determined that this technique poses minimal risk to females and embryos. Small blood samples are occasionally taken to obtain DNA used to compare genetic differences between populations. Detailed measurements and DNA samples are used to determine the taxonomic status of poorly-studied species. To date the Principal Investigator has discovered and described four new species of turtles: one in southern Japan (Ryukyu yellow-margined box turtle) and three in the United States (Escambia map turtle, Pascagoula map turtle, Pearl River map turtle).

Important Results

This research summary does not include projects on desert tortoises or western pond turtles. Those species are covered on separate web pages. The Principal Investigator started turtle research in the eastern United States in 1980. Highlights of the research program are given under regional subheadings below:

Pennsylvania – Dr. Carl Ernst, formerly of George Mason University, started research on the ecology of a community of six species of turtles in Lancaster County, Pennsylvania in 1965. Collaboration with Dr. Ernst lead to the publication of several papers on the growth of wood turtles and bog turtles and a long-term study of overwintering behavior in hatchling turtles. The latter study demonstrated that some turtle species hibernate in their nest after emerging from the egg while others emerge the same year as the nest was constructed. Some species do both depending on seasonal precipitation.

Alabama – The Principal Investigator has long been interested in the diversity of map turtles in the southeastern United States. Fourteen species are currently recognized from the Apalachicola River of Florida to the Guadalupe River of Texas. Early research resulted in the description of two new species in the Escambia and Pascagoula Rivers of Alabama and Mississippi. In 2009 another species was described from the Pearl River of Mississippi and Louisiana. More recently, a hybrid swarm of Barbour’s map turtles and Escambia Map turtles was identified using DNA analysis in the Choctawhatchee and Pea Rivers of Alabama and Florida.

Arizona – USGS scientists are working with Montezuma Castle National Monument to study the Sonora mud turtle population at Montezuma Well, a large natural spring in central Arizona. Sonora mud turtles are found in Arizona, New Mexico and Mexico. They disappeared from California in the 1960s likely from habitat modification due to the effects of river regulation from dams. Montezuma Well was a popular site for releasing unwanted pet red-eared slider turtles. USGS scientists removed all the non-native turtle species as part of an experiment to see if the population of Sonora mud turtles would benefit by removing competitor species. That research is ongoing and has resulted in several publications. It is one of only a few examples where invasive species were completely removed from inside an area administered by the National Park Service.

South Carolina – A great deal of research has been concentrated on the yellow-bellied slider turtle, a common species throughout the southeastern United States. Additional research is focused on the diamond-backed terrapin, the only turtle in the world that spends its entire life in brackish tidal marshes at the interface of freshwater and marine environments. Diamond-backed terrapins are found in the United States, from Cape Cod, Massachusetts, to Corpus Christi, Texas, with an isolated population in Bermuda. The Principal Investigator is a key partner in the longest running study in the world, now in its 35th year at Kiawah Island, South Carolina. Terrapins have decreased throughout their range, and a major cause of the decline is drowning in commercial and recreational crab traps. Terrapins were once the most economically important reptile in the world due to their popularity as gourmet food in the late 1800s and early 1900s. Modern threats to their continued survival also include habitat modification and destruction.

New Mexico – In collaboration with the New Mexico Department of Game and Fish, the Principal Investigator is monitoring the reproductive biology of turtles in the Rio Grande and the Pecos rivers since 2012. That research is providing basic information on poorly-studied species, especially the Rio Grande cooter.

Morocco – In 2008, the Principal Investigator received a Fulbright scholarship to conduct research in Morocco. During that time he trained faculty and students at Cady Ayaad University in Marrakech in basic techniques for turtle research resulting in publications and ongoing collaboration. Students subsequently received advanced degrees as a result of their research.

Japan – In 2014, the Principal Investigator was invited to be the Keynote speaker at the second Japanese Freshwater Turtle Symposium in Kobe, Japan. The invitation was a result of his expertise with the biology of slider turtles that are an invasive species in Japan and a perceived threat to the survival of several native Japanese turtles. Collaboration is ongoing and publications are resulting. After the visit to Japan, his collaborators came to the United States to film a movie that included the Principal Investigator and his research on turtles in Arizona and California that later aired in Japan. The Principal Investigator has a long history of research on Asian turtles.

Galápagos – Because of the Principal Investigator’s expertise with turtles and tortoises, in 2012, he was invited by the Galápagos Conservancy to attend a workshop in the Galápagos to develop a ten year strategy for restoration and repatriation of Galápagos tortoises to all islands in the archipelago.