Population viability analysis of the current and potential management strategies for populations of the agile frog (Rana dalmatina) in Jersey, Channel Islands
The “Anthropocene” era has seen accelerated extinction rates across all taxa that threaten global communities, justifying a high priority for studies into the causes and extent of the crisis. Amphibians are globally the most at risk taxa, and face a number of threats, the highest being habitat loss and degradation. Although widespread throughout Europe, the agile frog (Rana dalmatina) populations are declining due to the same threats. The two populations in Jersey, Channel Islands, R. dalmatina survive in fragmented habitat islands and are critically endangered locally due to their rate of decline. Islands contain a higher proportion of keystone species, and face a greater risk if functional groups such as amphibians are lost. This study presents the results of a stage-structured PVA of the Jersey R. dalmatina populations, based on data collected since 1987. It is suggested that Ouaisné can enter a monitoring phase, as showed a <5% probability of extinction. Noirmont showed a moderately higher than 5% risk, with declining population trends for both. Headstarting increased the egg to adult survival rate to 0.11, and was essential in restoring the populations, so should continue at Noirmont for two years. An almost certain extinction probability in a short time period is projected at both sites by the drought model, urging continuation of habitat management. A relocation of 20 spawn clumps could establish a new Jersey population. However, the impact on the donor population would be reduced by instead introducing 120 one-year olds, headstarted from only four spawn clumps. Sensitivity analysis highlighted juvenile survival as the most important, improvements to which would benefit the populations, and should be a focus for future studies.