Estimation of Growth, Mortality and Yeild per Recruit of the Australian School Shark, Galeorhinus australis (Macleay), from Tag Recoveries

Abstract

A study of growth, mortality and yield per recruit of G. australis in south-eastern Australia has been undertaken. The species is long-lived, slow growing and has a low natural mortality rate. The fishery in Victoria was recently adversely affected by the imposition in 1972 of an upper size limit of 104 cm, in addition to an existing legal minimum length of 91 cm, to ensure that sharks with flesh mercury levels in excess of 0.5 µg/g were not taken for human consumption. More recent (1976) legislation altered these limits to a minimum length of 71 cm and a maximum length of 112 cm. This paper discusses the possible effects of increased exploitation within the length limitations which are currently operative on the availability of breeding stock of the school shark.