CEES Extra seminar: Linking Demography, Natural Mortality, Life History, and Recovery in Fishes
By Jeffrey Hutchings from Dept. of Biology, Dalhousie University, Canada & CEES
Threat mitigation is clearly a necessary condition for recovery, but it is not always sufficient. Several marine fishes have exhibited little or no substantive recovery (some have declined further) decades after the threat responsible for their depletion – over-fishing – was mitigated. Analyses of binary responses to threat mitigation (recovery, no recovery) provides guidance for the identification of population thresholds below which Allee effects, or depensation, might be manifest. Recovery is also thought to be correlated with specific aspects of organismal life history, including traits such as age at maturity and longevity. However, despite strong theoretical underpinnings, these correlates are based on predicted, rather than realized, population trajectories. Based on data from >50 previously overfished populations (for which overfishing has ceased for ~20 years on average), life-history traits appear to be poor predictors of recovery when considered singly. In combination, however, a subset of traits provides compelling evidence for the hypothesis that rate of natural mortality (M), or a metric thereof, provides an empirically tractable and theoretically defensible predictor of recovery in fishes.
Dept. of Biology, Dalhousie University, Canada
and CEES, University of Oslo