Numbers for North America's largest salamander and the third-largest salamander species in the world are declining in nearly 16 Eastern states in which the hellbender is found, according to the Associated Press.

Scientists believe the disappearance could reflect a decline in the quality of the rivers and streams it is found in.

"If nothing else, if people don't appreciate the animal for itself, that it has value to the world, then it can serve as a messenger," said Trisha Crabill, a biologist with the U.S. Fish and Wildlife Service, according to AP. "It can tell us what's going on in the river."

Hellbenders can be found in a number of locations, including: Alabama, Arkansas, Georgia, Illinois, Indiana, Kentucky, Maryland, Mississippi, Missouri, New York, North Carolina, Ohio, Pennsylvania, Tennessee, Virginia and West Virginia.

The Ozark hellbender, which can only be found in Missouri and Arkansas, was added to the federal endangered species list back in 2011 when its numbers fell to approximately 75 percent between the 1970s and the 1990s, according to AP.

The U.S. Fish and Wildlife Service is currently deciding if the eastern hellbender should also be added to the list. 

"There's nothing else like them in North America," said federal biologist Jeromy Applegate, who's leading the eastern hellbender assessment, according to AP.

Eastern hellbenders are state-endangered in Illinois, Indiana, Maryland, Missouri and Ohio, according to AP.

The nocturnal creatures spend their lives in rivers and streams. They're able to breathe almost entirely through their skin, taking oxygen from the water. They spend most of their time beneath large, flat stones and logs, but leave those spots at night to find some food.

They mainly feed on crayfish, worms, minnows, and snails, according to AP.

They can live 30 or more years in the wild, grow up to two feel long, and weigh up to five pounds. The largest snail ever seen was 2 ½ feet long, according to AP.

"These are animals that live up to 30 years in the wild, so if you have populations declining, that alerts us that there could be a problem with the water quality," said Rod Williams, a Purdue University associate professor of herpetology, in a statement recently, according to AP.

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