Gauntlet Fisheries for Elasmobranchs - the Secret of Sustainable Shark Fisheries

摘要

The longevity and low fecundity of sharks make them particularly vulnerable to over-exploitation. Previous studies have emphasized the range of natural productivities observed across elasmobranch species and have used this to explain the sustainability of some elasmobranch fisheries and the depletion of others. This paper discusses the assessment of the two principal species fished by the Southern Shark Fishery of Australia, school shark (Galeorhimts galeus) and gummy shark (Mustelus antarcticus). The modeled simulations presented here show that shark behaviour patterns and fishing techniques which restrict fishing mortality to a few juvenile age-classes may be equally or more important than the productivity of different species in determining theirrelative robustness under exploitation. Counter-intuitively concentrating a fishery on a few year-classes of pups, juveniles or sub-adults proves to be a robust management strategy for elasmobranch fisheries, as long as the means exist for protecting adults from fishing mortality. Furthermore this management strategy proves to be most effective with the species considered to be least productive, those with greatest longevity. The obverse of this finding is to highlight the damaging impact on elasmobranch fisheries of human activities such as by-catch, finning, sport fishing and beach protection that cause even low levels of adult mortality.