Conservation efforts fail to halt the decline of the regionally endangered Natterjack toad (Epidalea calamita) in Ireland

Abstract

Amphibian declines are of major conservation concern worldwide. The Natterjack toad (Epidalea calamita) is the rarest amphibian in Ireland, regionally Red-listed as Endangered. The species is at the north-western edge of its European range in Ireland and is subject to substantial conservation efforts, including regular monitoring and surveillance, a pond creation agri-environment scheme, and a head-start and translocation programme to facilitate pond colonisation. We used large-scale intensive monitoring and surveillance data from 2004 to 2018 to quantify temporal trends in egg string production analysing breeding site preferences and occurrence of perceived threats and pressures. Despite substantial conservation efforts, egg string production declined by 23% in Ireland over a 14-year period (−1.6%/year). Twenty-two of 100 artificial ponds had been colonised by 2018, but artificial sites accounted for <10% of eggs laid and had prevented further declines by only 4%. Natterjack toad spawning was associated with ponds with a large surface area, situated in sand dune habitat, with high water conductivity, and a high percentage cover of aquatic vegetation at the substrate with short terrestrial vegetation in the surrounding vicinity. Threats and pressures are related to poor water quality at breeding sites and abandonment of surrounding agricultural land leading to unsuitable terrestrial vegetation. Given the Natterjack toad's population trend in Ireland, continued monitoring and surveillance is vital, while we advocate protection of occupied sand dunes, active engagement with farmers and landowners to ensure compliance with habitat maintenance recommendations and improved habitat connectivity to facilitate colonisation of artificial ponds.