Empirical links between natural mortality and recovery in marine fishes

Probability of species recovery is thought to be correlated with specific aspects of organismal life history, such as age at maturity and longevity, and how these affect rates of natural mortality (M) and maximum per capita population growth (r_max). Despite strong theoretical underpinnings, these correlates have been based on predicted rather than realized population trajectories following threat mitigation. Here, we examine the level of empirical support for postulated links between a suite of life-history traits (related to maturity, age, size and growth) and recovery in marine fishes. Following threat mitigation (medium time since cessation of overfishing = 20 years), 71% of 55 temperate populations had fully recovered, the remainder exhibiting, on average, negligible change (impaired recovery). Singly, life-history traits did not influence recovery status. In combination, however, those that jointly reflect length-based mortality at maturity, M , revealed that recovered populations have higher M , which we hypothesize to reflect local adaptations associated with greater r_max But, within populations, the smaller sizes at maturity generated by overfishing are predicted to increase M , slowing recovery and increasing its uncertainty. We conclude that recovery potential is greater for populations adapted to high M but that temporal increases in M concomitant with smaller size at maturity will have the opposite effect. The recovery metric documented here (M ) has a sound theoretical basis, is significantly correlated with direct estimates of M that directly reflect r_max, is not reliant on data-intensive time series, can be readily estimated, and offers an empirically defensible correlate of recovery, given its clear links to the positive and impaired responses to threat mitigation that have been observed in fish populations over the past three decades.