Transient population dynamics and viable stage or age distributions for effective conservation and recovery

Threshold population sizes are often used to determine the status of depleted populations. The thresholds are typically derived assuming the population is in a steady state. However, although a population may be at the threshold level, the stage or age distribution could be far from the steady state, which may induce transient dynamics. As a result, one may erroneously conclude the status of the population as ‘safe’ when it is not, or vice versa, using such a threshold population size. Here, we describe the metrics called extinction effective population (EEP) and scaled spawning age (SSA). These are used in addition to population sizes for assessing the population status, as they account for the deviations from the stable stage or age distribution. Using these metrics, we demonstrate the importance of incorporating the transient stage or age distributions in population management.