The world's biggest living amphibian is quite special, they are a relic from the dinosaur era, the males are "den masters" and they can sound like crying babies, but they are now critically endangered

It's not often that you hear an animal being referred to as a "den master". But male Chinese giant salamanders are just that.

They have underwater breeding dens, usually large hollows under rocks or in crevices, where they allow several females to enter to lay large clusters of eggs. A den master will then guard and care for these eggs for over a month after they hatch.

Chinese giant salamanders are the world's largest living amphibians, growing up to 1.8m long - a length many humans don't reach. They can get pretty heavy too, up to 50kg.

In stark contrast, their tadpoles are just 3cm long.

"Imagine a newt in a garden pond growing to this size," says Andrew Cunningham of the Zoological Society of London in the UK. "It is simply awe-inspiring to see a live adult in the flesh."

They have inspired many myths and legends in Chinese culture. The famous yin and yang symbol of opposites is thought to have originally been two Chinese giant salamanders, harmoniously intertwined.

They have remained pretty much unchanged since the days of Tyrannosaurus rex

The salamanders are sometimes called "wa wa yu", meaning "baby fish", because their distress call resembles a baby's cry.

They also belong to an ancient lineage. Their family, Cryptobranchidae, is 170 million years old.

Modern giant salamanders are often called "living fossils", as they are still so similar to their ancient relatives. They have remained pretty much unchanged since the days of Tyrannosaurus rex, says Cunningham.

But these amazing creatures are becoming increasingly rare in the wild. Since the 1950s their population has fallen dramatically. They are currently listed as critically endangered on the Red List of Threatened Species, run by the International Union for Conservation of Nature.

The salamanders are often captured from the wild to stock these farms

The growing salamander farming industry is largely to blame, despite being only a decade old.

The salamanders are considered a delicacy, despite being a protected species. What's more, their sheer size makes them a lucrative food source.

As a result the salamanders are often captured from the wild to stock these farms. Poachers can get a lot of money for them.

But the more that are taken from the wild, the slower the population rebounds, as young salamanders take several years to reach sexual maturity. 

When they were more common, poaching was easy, says Cunningham. But as the species became rarer, more destructive methods were used. That includes dynamite, electrofishing, and pyrethroid insecticides that poison most animals in the river alongside the salamanders.

The species might soon become extinct in the wild

Unfortunately, the penalties for being caught are low, says Cunningham. "There are even reports of the protection agencies actually buying [salamanders] from poachers and then selling them on to farms."

Infectious diseases spread quickly on farms, and can threaten wild salamanders. Also, if the two groups interbreed it is bad news for the wild ones, as farmed ones tend to be more inbred.

A recent investigation into the salamander farming industry, published in the journal Oryx, reports that if wild populations continue to be depleted in this way, the species might soon become extinct in the wild. 

But here's the good news. Having identified these threats, conservationists say they are in a position to protect the species.

Closing down the farms is not a viable option, says Cunningham. "The industry is so huge and the Chinese central, provincial and local governments have invested so much money into it."

Instead, he says the farms need to be better managed. For example, no captive salamanders should be released into the wild.

Wild and captive salamanders should be better kept separate

In the past the government has encouraged the release of captive salamanders, to boost wild populations. But this may have caused more harm than good, says Cunningham.

The animals released weren't screened for disease, so they could have been spreading pathogens. There were no tests of whether their genetic makeup was suitable for the environments where they were re-homed. Furthermore, they were not monitored, and there was no overall evaluation of whether the scheme was a success or a failure.

So Cunningham and his colleagues also suggest that wild and captive salamanders should be better kept separate. For instance, captive ones could be tagged with microchips: that way, non-chipped animals would be easily identified as wild.

"We also propose improved biosecurity and disease control measures on farms, such as quarantining new stock and treating wastewater to prevent the discharge of pathogens from farms into the wild."

If fewer die from disease in the farmed populations, this might in turn reduce the need to top up numbers from the wild.

Still, Cunningham says that for now the outlook for the wild salamanders is bleak, although tens of millions live on the 43 known farms.

Before they can truly rebound, attitudes towards the species will have to change. Conservationists are now working on that.

"It is one of the most incredible species on the planet," says Cunningham. "The Chinese need to learn to cherish this very special species. Only if and when that happens will it have a future."