The first detection of the fungal pathogen batrachochytrium dendrobatidis in Norway with no evidence of population declines for great crested and smooth newts based on modeling on traditional trapping data

The pathogenic fungus Batrachochytrium dendrobatidis (Bd) causes chytridiomycosis in amphibians across the world, often leading to population declines and species extinctions. Here, we present the first detection of Bd in Norway, diagnosed using environmental DNA (eDNA) in water samples. In a genetic screening of 31 ponds in southeastern Norway for Bd, great crested newt (Triturus cristatus) and smooth newt (Lissotriton vulgaris), we detected Bd in five different localities. Resampling in one location revealed that time of sampling seemingly had a strong effect on the concentration of Bd eDNA in the water, which increased from May till June. In contrast, eDNA concentration of great crested newt decreased during the same period. Following a traditional sampling approach with traps, newts in the investigated ponds have been sampled for population estimates since 2012. We imposed a model on the catch data and contrasted the Bd‐positive ponds to the Bd‐negative ponds, finding no signs of population declines in the Bd‐positive ponds. This could suggest either recent infection events, with animals still having low prevalence of Bd and with little time for Bd to affect the present breeding generations of newts, and/or that the two newt species are infection‐tolerant. This study further highlights eDNA as a tool for early detection of invasive species.