Assessment of monitoring and management strategies for local populations of the Mediterranean monk seal Monachus monachus

We constructed age-structured models of the population dynamics of the highly endangered Mediterranean monk seal Monachus monachus which took account of demographic stochasticity and environmental stochasticity caused by episodic catastrophic events. These models were used to identify demographic characteristics which we knew could be measured in monk seal populations and whose occurrence could be used to predict when small seal populations were most at risk of extinction. High-risk predictors had high predictive power (there was a 75-85% probability that a population went extinct within 60 years), but the were not observed at all in 5-15% of computer simulations, and when they did occur there was little time to act (25-35% of populations went extinct withing 10 years). Populations which show such indicators have a poor probability of persistence, even if immediate management action is taken. Lower risk predictors were observed in 95-100% of all computer simulations and provided at least 10 years' warning in 75-95% of cases. However, their predictive power was relatively low (55-70% of simulations went extinct within 60 years). If juvenile or adult survival was increased immediately after a low-risk predictor was observed (for example, by establishing rescue centres for abandoned pups and animals entangled in fishing gear) the probability of extinction could be reduced to one-tenth of its value without intervention.