On the survivorship and historical growth of the South African Cape rock lobster

Abstract

Natural survivorship parameters for male and female Cape rock lobsters Jasus lalandii are estimated using size-structure information from pristine sections of the population, such as animals in sanctuaries. It is assumed that these pristine subpopulations are at steady states, i.e. that annual juvenile settlement is constant, and that migration into and from these populations is negligible. The natural survivorship parameters are calculated in terms of parameters for somatic growth rate, which are obtained by fitting the Ford-Walford growth model to male and female tag data. The results indicate that female natural survivorship is consistently higher than that of males, and that the somatic growth rate of J. lalandii was considerably higher at the beginning of the century than during the past 25 years.