DOES RADIATION AFFECT TURTLES?

by Whit Gibbons

November 5, 2017

“You once conducted research in which you attached metal tags that emitted gamma radiation to shells of living turtles. You also X-rayed turtles. Weren’t these techniques detrimental to the health of the turtle?” John Byrd, an award-winning environmental educator in Tennessee, sent me the question asked by members of an environmental book club he belongs to.

John’s question about X-rays and turtles stemmed from ecological research projects I conducted for many years. Radiation from X-rays has no known positive effects on individual turtles, but no evidence has been forthcoming of any permanent harm. Unquestionably, the technique ultimately has saved many turtle lives. Not unlike a dental X-ray, which can lead to healthier teeth in people, finding out when and where reptiles lay their eggs has led to environmental guidelines and regulations protecting entire populations of turtles as well as other egg-laying reptiles.

Ecologists use X-radiography, a basic medical tool, to study reptile eggs whose shells contain sufficient calcium to be detected by X-ray photography. All crocodilians and turtles and most snakes and lizards lay eggs. Originally, we brought turtles into the laboratory to X-ray them. Today, research ecologists use portable X-ray machines, enabling them to gather pertinent data about numbers and sizes of eggs while in the field. In either case, animals are returned unharmed to their habitat.

One specific set of studies conducted by scientists at the University of Georgia’s Savannah River Ecology Laboratory documented how many turtle eggs were laid outside the periphery of freshwater wetlands. The research reinforced an important principle: “a wetland” extends functionally far beyond the water’s edge. Hence, land around a wetland must be protected as well as the water itself if its inhabitants, such as turtles, are to persist. Quantifying egg numbers laid by each species of turtle could not have been accomplished harmlessly without X-radiography. A notable side note: Before X-ray techniques were developed, scientists would dissect turtles to determine how many eggs they had. Clearly, X-irradiation causes less harm to the turtle.

This nondestructive sampling technique is especially important in ecological studies in which loss of even a single specimen is undesirable. Studies in New Zealand on internationally endangered tuataras, which look like large lizards, relied on X-ray photography to obtain information on when tuataras had eggs and how many. Investigators were able to gather critical information on egg production, which was necessary for understanding population growth patterns in these unusual animals teetering on the threshold of extinction.

John’s reference to attaching radioactive metal tags to turtles was based on studies we conducted many years ago before federal regulations concerning uses of radioactive materials became as stringent as they are today. We used a nonmagnetic metal called tantalum.

One of its isotopes, tantalum-182, emits gamma radiation. After drilling a tiny hole in the shell margin of a turtle, we inserted a half-inch piece of the radioactive metal that was the diameter of a paper clip. A turtle’s outer shell is biologically similar to our fingernails, so the turtle was not physically harmed. We sealed the tiny opening with glue, then each turtle was released where it had been caught.

During the next several days, we used an instrument comparable to a Geiger counter as we drove around the margins of wetlands we were studying. We located turtles buried in dirt or sand hundreds of feet away from water. We had to be within 30 feet of a buried turtle to detect the radioactive signal, but by patrolling in an ever-increasing spiral away from a wetland, we eventually located them. Back then, these aquatic species were only known to come on land to lay eggs. Until our use of tantalum tags, no one knew they also hibernated on land.

Today, researchers attach small transmitters and use radiotelemetry to locate released animals, but the early techniques yielded new information otherwise unobtainable at the time. Meanwhile, should another question be “what were the effects of gamma radiation on the investigators?”

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