Ecology and conservation of the agile frog (Rana dalmatina) in Jersey

On the island of Jersey, the agile frog (Rana dalmatina) has declined to a single small population that is displaying erratic breeding success. Survival of eggs from hatching to metamorphosis can vary from 0% to 17% per year. This gives rise to pulses in recruitment, which are reflected in the age structures of adult frogs. Variations in recruitment - and the resulting population fluctuations (the number of males was estimated to vary between 14 and 42 individuals) - were recorded over a three-year study period and seemed to be linked to variations in the level of predation pressures on the tadpole phase by newts and macroinvertebrates, which in turn are related to hydroperiod. Genetic variation in the Jersey population was compared to populations elsewhere in the species’ range using microsatellite DNA analysis. The Jersey population emerged as the least variable population, possibly due to drift and inbreeding. Population Viability Analysis (PVA) models - based on field data - predicted the extinction of the population over 50 years, unless productivity is enhanced (i.e. by protecting the spawn). The Rana dalmatina distribution range should be expanded, to reduce the risk of its disappearance from the wild. Although field observations of Bufo bufo tadpoles indicated a problem with water quality at one potential introduction site (Cannes de Squez), a laboratory bioassay indicated that tadpoles developed normally in water collected from this site the following year. At Ouaisne, enhancing connectivity within the site may facilitate the creation of a metapopulation of frogs. Garden ponds in proximity of the frogs’ breeding habitat represent possible recipients for translocations. PVA models predicted that new Rana dalmatina populations created by translocations of relatively low numbers (20 - 120) of captive-bred individuals could be viable in the medium term providing predation of eggs and larvae are controlled.