New abbreviated calculation for measuring intrinsic rebound potential in exploited fish populations — example for sharks

Abstract

Intrinsic rebound potential, the demographic measure of a fish population’s productivity that sustains a given mortality, relates to a species’ resiliency and can be useful for understanding and evaluating the status of exploited populations, especially those poorly monitored and of low productivity, like many shark populations. The rebound potential is derived from the Euler–Lotka equation and, with the dynamics kept simple, is easily calculated for a given total mortality, needing only a species’ age at maturity and its natural mortality (M). Its value can be quickly read from an isopleth diagram, whose contour pattern shows the interdependence of these two key parameters among different life histories. How the rebound potentials change as a function of age at maturity and the full range of possible M values also shows a way to estimate a species’ natural mortality bounds. Importance of the age at maturity parameter is stressed.