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About a third of frog, toad and salamander species are facing extinction; threats include fungal disease, pollution and habitat loss.

The extent of amphibian decline was revealed in October 2004, with the publication of a comprehensive worldwide survey, the Global Amphibian Assessment.

Scientists report that almost a third of the 5,743 known species are categorised as Critically Endangered, Endangered or Vulnerable according to criteria established by IUCN, the World Conservation Union.

Thirty-four species are extinct, and more than a hundred other species have not been seen for so long that scientists believe they may be extinct as well.

Establishing the reasons behind this decline has proved more difficult than finding out the numbers. The biggest single threat appears to be a fungus, Batrachochytrium dendrobatidis; first identified just six years ago, it is firmly established in parts of the Americas, Australia and Europe.

The disease which it causes, chytridiomycosis, appears to kill amphibians by damaging their sensitive skins, blocking the passage of air and moisture.

WHAT ARE AMPHIBIANS? Group includes frogs, toads, salamanders and caecilians First true amphibians evolved about 250m years ago Adapted to many different aquatic and terrestrial habitats Present today on every continent except Antarctica Undergo metamorphosis, from larvae to adults Other threats include viral diseases, habitat loss, drought, pollution, and hunting for food.

It is believed that environmental stresses, including drought and pollution, may make the animals more vulnerable to the chytrid fungus, perhaps by weakening their immune system or reducing their birth weight.

The goal is to rescue of some populations at risk from disease, with re-introduction in the wild when the sources of disease or pollution is cleaned up or strategies are found that will allow them to live in the wild with the fungus.

Scientists suggest that specimens of several hundred species of frogs, toads, salamanders and caecilians - legless amphibians - could as a priority be taken from the wild into captive breeding programmes.

More capacity in zoos around the world will be needed to run these captive breeding programs. When further data is gathered on little-known species, about a thousand more could also become candidates.

The price-tag for all this is going to be enormous - tens of millions of dollars per year for at least a decade. Capacity in zoos around the world to run these captive breeding programmes is something that governments might be quite willing to address.

Calls for more protected habitats, for increased testing of agricultural chemicals to discover whether they are toxic to amphibians, and for the establishment of a central laboratory to study the fungus and other pathogens are part of the strategy to support declining amphibian populations.

Because of their sensitivity to environmental factors, amphibians are sometimes referred to as the "canary in the coal mine", an early-warning system for ecological decline which will also impact other species, including humans.

SOURCE: http://news.bbc.co.uk/2/hi/science/nature/4244554.stm