Global skin fungus threatens to wipe out rare Scots toad

Published on Saturday 21 March 2009 18:34

THEY are one of the most iconic creatures of English literature and a symbol of the health of the countryside.

But already endangered toad colonies in southern Scotland could have been damaged by a fatal disease which is wiping out amphibian populations across the world.

Government scientists have found traces of chytrid fungus in Natterjack Toads along both the northern and southern shores of the Solway Firth, where populations have steeply declined in the past two years.

They are now calling for increased biosecurity measures around amphibian habitats to prevent other populations of frogs, toads and newts in Scotland succumbing to the disease.

Chytrid disease is caused by a fungus (Batrachochytrium dendrobatidis) that infects the skin tissues of amphibians. It has already caused catastrophic declines and extinctions across Australia and the Americas.

It has also been recorded in Europe and the UK, with an outbreak in Kent in 2005 spread by imported American bullfrogs.

But tests have now found the disease to be present among the Natterjack Toad colonies on the Scottish coast at Caerlaverock, Mersehead and Southerness, as well as across the Solway on the Cumbrian coast.

A report by Scottish Natural Heritage scientists says: "Should the disease prove to be malignant in the UK, it is particularly unfortunate that it has been found in the Natterjack, which is already regarded as threatened. It is not clear yet that the disease is causing population declines in the UK, but the death of captive Natterjacks demonstrates that they are susceptible."

It adds that a "considerable reduction in Natterjack numbers has been reported from the North Solway" in the past two breeding seasons and could be due to the disease.

Professor Des Thompson, SNH's policy advice manager, said: "This is a pretty nasty disease that affect the skins of the toads and has wiped out amphibian populations in other countries.

"We have an edge-of-range Natterjack Toad population here which is struggling already and so we want to protect it. Of 60 toads examined, we found two infected, which is a clear sign that the disease is here and could spread. It is likely that it spread to southern Scotland from Cumbria."

SNH is now considering stricter biosecurity measures – such as disinfecting footwear and equipment – for people who come into contact with the toads. "We want to stop it from spreading to other species such as frogs, other toads and newts, which might be affected," Thompson said.

The Natterjack Toad is one of only three amphibians protected under the UK's national Biodiversity Action Plan. Numbers are already in decline through loss of habitat, and the effects of pollution.

Last week, it emerged that the "mountain chicken" frog of Montserrat, a Caribbean island, has become the latest victim of the killer chytrid disease. The mountain chicken (Leptodactylus fallax) – named because its meat tastes like chicken – is one of the world's largest frogs, and UK researchers say only two small pockets of the animals on the island remain disease-free. Conservationists plan to take frogs into captive breeding programmes to save the species.

They suspect the chytrid fungus entered Montserrat on small frogs stowing away in consignments of produce from Dominica.

The risk of chytrid disease comes on top of the threat of global warming to amphibian populations. Scientists said last year that more than half of all frogs, toads – immortalised in Kenneth Grahame's children's classic The Wind In The Willows – and newts living in Europe could be driven to extinction within 40 years as climate change, diseases and habitat destruction take their toll.

The majority of the most threatened species live in Mediterranean regions, which are expected to become warmer and drier. BBC naturalist Sir David Attenborough warned: "Amphibians are the lifeblood of many environments, playing key roles in the function of ecosystems, and it is both extraordinary and terrifying that in just a few decades the world could lose half of all these species."

Some scientists believe chytrid fungus has become more deadly as a result of climate change. In Penalara national park near Madrid, the climate has become more humid and the fungus has caused mass mortality among amphibians.

Toad lowdown

Natterjacks are claimed to be Europe's noisiest amphibian.

&#149 The toads can live for 12-15 years but have many predators, and so few survive to this age.

&#149 Their body length is up to 3in and females are larger than males.

&#149 They have the ability to darken or lighten their skin to camouflage themselves in their environment.