Reintroduction of the pool frog to the United Kingdom

Summary

The northern clade of the pool frog (Pelophylax lessonae), though globally of Least Concern, was long dismissed in Britain as a non-native introduction until research in the 1990s and 2000s proved it was a genuinely native, genetically distinct population, by which time the last known UK colony had already gone extinct. The Amphibian and Reptile Conservation Trust, working with the University of Kent and a range of government and academic partners, planned a wild-to-wild reintroduction to a confidential Norfolk site within the species' former range, sourcing founders from robust, genetically similar populations in Sweden. Following a 2005 feasibility strategy and full disease risk assessment developed with the Institute of Zoology, frogs (a population-viability-informed mix of adults, juveniles, spawn and larvae) were captured during four annual visits from 2005 to 2008, flown to the UK and released at a specially restored receptor site, with head-starting used alongside hard releases in some years and import mortality kept below five larvae annually. By the end of 2016, ongoing monitoring of individually identified frogs, co-existing species and disease status found an estimated adult population of 67 with regular breeding and colonization of multiple ponds, alongside a substantial increase in common frogs and no evident harm to newts or introduced disease. Difficulties included the many years needed to judge establishment, uncertain causes of mortality, and balancing resources between this site and a second reintroduction begun in 2015. The project rates itself successful, citing thorough planning, a well-chosen and secured receptor site, a strong evidence base, and close collaboration among researchers, land managers and regulators.