Population dynamics of the natterjack toad (Epidalea calamita) on Balgö and the mainland north of Varberg : A study on the influence of the abiotic factors on distribution patterns between 2012 and 2025

This study investigates the current population status of the natterjack toad (Epidalea calamita) on the island Balgö and nearby mainland sites in Halland, Sweden. The study also includes habitat conditions by surveying abiotic factors such as acidity, salinity, temperature and precipitation. Despite targeted field surveys during favorable weather conditions, no individuals or signs of reproduction were found on Balgö or on the mainland sites, suggesting either a population decline or missed activity during the field operations. Eight water bodies were assessed on Balgö, several of which showed a possible reduced quality for breeding. A significant decrease in salinity compared to 2012 was found in addition with a non-significant trend toward lower acid levels. The lower salinity may negatively affect the natterjack toad as they are inferior when it comes to interspecific competition. Temperature and precipitation data compared to the historical observation data from Artportalen between 2012 and 2024 showed no significant results. Overall, the findings indicate that the population of the natterjack toad on Balgö may be under pressure due to deteriorating habitat quality and changing environmental conditions. Conservation actions such as habitat restoration together with monitoring water quality conditions are recommended to support the long-term persistence of the largest population of the natterjack toad in Halland county.