Intrinsic rebound potentials of 26 species of Pacific sharks

Abstract

A demographic technique is used to compare the intrinsic rates of population increase of 26 shark species hypothetically exposed to fishing mortality. These rates (r_2M) are used as a measure of the relative ability of different sharks to recover from fishing pressure. The method incorporates concepts of density dependence from standard population modelling and uses female age at maturity, maximum reproductive age, and average fecundity. A compensatory response to population reduction is assumed in pre-adult survival to the extent possible given the constraints of the life-history parameters. ‘Rebound’ productivity was strongly affected by age at maturity and little affected by maximum age. Species with lowest values (r_2M < 0.04) tended to be late-maturing medium- to large-sized coastal sharks, whereas those with the highest (> 0.08) were small coastal, early-maturing species. Sharks with mid-range values (r_2M = 0.04–0.07) were mostly large (> 250 cm maximum size) pelagic species, relatively fast growing and early maturing. Possible selection pressures for these three shark groups, management implications, practical applications for the derived parameter r_2M, and recommended areas of research are discussed.