Purdue University graduate research assistant Emily McCallen, left, holds a hellbender collected during a survey for the rare salamander in southern Indiana's Blue River near Corydon, Ind., while associate professor of herpetology Rod Williams uses a scanner to determine if the big amphibian has an identifying microchip implanted beneath its skin. The Associated Press

A group of Purdue University graduate and Ph.D. students fan out along southern Indiana's Blue River during an annual survey of populations of hellbenders, an aquatic species that lives only in swift-flowing, rocky rivers and streams. The Associated Press

An adult hellbender, measuring 21 inches in length, rests in a measuring device after being caught by a Purdue University team. The big salamander was later released back into the river. The Associated Press

Rod Williams, a Purdue University associate professor of herpetology, holds a hellbender that he and a team of students collected in southern Indiana's Blue River. The Associated Press