01. Annual spawn clump losses in a population of the agile frog Rana dalmatina in western France

Abstract

The agile frog Rana dalmatina is a common and frequently studied species in Europe including long-term studies of population change. Several have employed spawn clump counts to give estimates of annual presence of reproductive females. Spawn clumps are also subject to predation but little is known of the extent of losses but it could impact population densities significantly. The objective of the present study was to assess the extent of spawn clump losses due to predation in a population of R. dalmatina in western France using data from numbers of spawn clumps recorded over a four-year period (2019–2022). Spawn counts were greatest during 2019 but numbers declined with a zero count in 2022. Predation was greatest in 2021, the year total counts were lowest, but there were no statistical difference between annual losses, which varied from 22.9–41.6 %. Most spawn was deposited in a series of ditches rather than in the two available ponds but statistically predation levels were in agreement, with ditches ranging from 26.1–40 % versus ponds 28.6–40 %. Observed predators were ducks and alien crayfish Procambarus clarkii. The latter consumes all stages of frog development and hence likely represents the greater threat, especially since it has the capacity for population increase to very high numbers.