Studies on Southern Australian Abalone (Genus Haliotis). XII. Long-term recruitment and mortality dynamics of an unfished population

Abstract

The recruitment strength and natural mortality of an isolated, unfished population of the abalone Haliotis laevigata Donovan at West Island, South Australia, were estimated from 1970 to 1987. Recruitment, as judged by the appearance of 2-year-old abalone, varied widely from year to year, and the frequency of distribution of annual recruitment was found to be best fitted by a log-normal curve. No evidence was found that estimates of spawning stock size were a significant variable contributing to this variability. During the 18-year period, the population size oscillated up and down twice; the increases were due to successive years of strong recruitment, the declines to the dampening effect of density-dependent mortality, which ranged from 0.02 to 0.86 per annum. The changing mortality rates were attributed to the behavioural response of stingrays to abalone densities. Analysis of dead shells collected from the study site for 5 years indicates that stingrays may cause 70-94% of the total mortality of abalone 3 years and older and that octopuses, crabs and unknown causes are responsible for the remainder.