Snot otters. Allegheny alligators. Mud devils. These are three of the quirky nicknames for the hellbender, the largest salamander in North America.

Hellbenders live slow-moving lives in mountain streams of the eastern United States, from Arkansas to New York. They are mostly active at night, feeding on crayfish. Their colors range from mottled olive-gray to chocolate brown with rust-colored splotches. With such camouflage, they can easily be mistaken for large rocks, if they're seen at all. But hellbenders are giants among salamanders. They can reach lengths of .6 meters (two feet) and weigh up to 1.8 kilograms (four pounds).

Big as they are, though, their numbers have been shrinking since the 1980s. Their disappearance concerns biologists, prompting conservation efforts in New York as well as other states where hellbenders are found. These programs aim to study the biology of North America's largest salamander. They also include efforts to reintroduce more hellbenders into the wild.

Murky Future

Salamanders are especially vulnerable to changes in habitat, especially pollution. "They are really closely tied to their environment," said Kim Terrell. She is a conservation biologist with the Smithsonian's National Zoo in Washington, D.C.

Hellbenders breathe through their skin. Because of that, they need clean, cold, oxygen-rich freshwater to live. In other words, they thrive only in areas with good water quality, Terrell said. Unfortunately, the decline in the hellbender population corresponds with the worsening condition of their habitats.

Water quality has been getting worse where hellbenders live. Changing land use, such as an increase in farming, is causing more dirt and silt to end up in streams. This run-off harms water quality, and what's more, human-produced toxins and chemicals are also getting into the water. Both developments are putting hellbenders at risk.

Healthy Hellbenders

Thomas Floyd is a wildlife biologist with the Georgia Department of Natural Resources. Georgia has some of the healthiest populations of hellbenders in the country, Floyd explained. His team regularly monitors the salamanders to make sure they stay that way. Their efforts often involve putting on a mask and snorkel and getting in the cold water of mountain streams. They search under the rocks to find the slippery amphibians.

"[In Georgia], if you look at areas where they're doing really well, they're on public land," Floyd explained. These areas tend to have healthy forests, he said. "There's a direct correlation between forest cover and habitat quality."

That's because forests are natural barriers against erosion. The roots of trees and other plant life help prevent sediment from washing into mountain streams.

Hellbenders In The Empire State

Unfortunately, hellbenders in New York aren't doing as well. They exist in only two river areas in the state — near the Allegheny and Susquehanna Rivers.

"The hellbenders in Susquehanna have nearly disappeared, and we don't know the reasons for the decline," said Ken Roblee, a wildlife biologist with the New York Department of Environmental Conservation.

Roblee and his team are instead concentrating their efforts on the Allegheny. There, the hellbender population is healthier, though their numbers have declined 40 percent since the 1980s.

The overall drop in population could be because not enough young hellbenders are making it to adulthood, Roblee said. "Many of the monitored sites only had large adults."

A Head Start

Roblee and his team of biologists decided to give young hellbenders some help. By hatching and raising hellbenders in captivity, they hoped to give the amphibians a chance to grow to a size that increases their chances of survival. Once the animals get big enough, they're released into streams that lead to the Allegheny River. They are given tags to help researchers identify and study them.

So far, the results have been mixed. Hellbenders tend to stay in one place. However, when researchers went back to check on the tagged amphibians released in 2011, only four percent of them remained where scientists had released them. Of the hellbenders reintroduced into the wild in 2012, only eight percent were found in the original area. Scientists fear these movements increase the chances that the hellbenders get eaten by raccoons, otters, and other predators.

Biologists have since been experimenting with ways to increase the survival chances for the newly released hellbenders. One effort has been to protect them in soft cages set in the water.

Salamander Saviors

Will Miller is chief conservation officer with Seneca Nation Fish and Wildlife. The Seneca Nation is a Native American nation in western New York.

The Seneca Nation originally got interested in hellbenders because of a cultural connection, Miller said. Seneca tribe historians say some of the Nation's stories are connected to the hellbender.

Miller has been encouraged by public fascination with the salamander and its willingness to support conservation efforts. Miller and his teams travel to local schools to help the public understand the salamander's plight.

Their efforts were rewarded when someone sent Miller a cellphone picture of a hellbender. They had accidentally caught the creature while fishing, but then released it once they realized what it was.