The pool frog became extinct in the UK during the 1990s but a project has commenced in which pool frogs have been reintroduced from Sweden, and we may once again see these ‘marsh nightingales’ inhabiting Norfolk
Amphibians are facing a global extinction crisis, but you may not know that we’re losing species on our very own doorstep. One example is the pool frog, which disappeared from English ponds in the 1990s.
ZSL were asked to take part in a collaborative project with Natural England and Amphibian and Reptile Conservation to reintroduce pool frogs back into England. Reintroducing a frog that used to live here may seem fairly straight-forward, but in fact there are many hoops to go through before you can let them hop off into the sunset. The pool frogs for this project came from Swedish populations, so one of the major risks was the introduction of a foreign disease.
Wildlife disease is one of the main areas of research here at ZSL’s Institute of Zoology, so we were charged with providing Natural England with a rigorous review of all the disease risks associated with reintroducing the frogs, and screening the individual frogs intended for release.
In 2005 permission was granted to commence the reintroduction and so on a warm summer’s day that year we drove to a secret location in the east of England to examine the first frogs for reintroduction.
This is definitely not a job for the fashion-conscious, as strict biosecurity measures mean that we were dressed head-to-toe in white boiler suits, wellington boots and gloves!
Over a 3 year reintroduction period and through subsequent post-release health monitoring we carried out regular health checks on the pool frogs and I am pleased to say that they are thriving in their new home.
This spring we’re revisiting the reintroduction sites to do health checks on all the native amphibians to find out whether they’ve been impacted by their new neighbours.
The disease risk analysis on these animals that screened for the two most dangerous known pathogens, chytrid fungus and ranavirus, as well as protozoa, helminths and bacteria. It established the prevalence of these parasites both within the pool frog populations and in native amphibians.
Post-release health surveillance of the freogs we released in Norfolk is being carried out to monitor the effect of the move from Sweden to the UK on our already-present native amphibians, such as smooth newts and common frogs, and on the released pool frogs themselves.