Studies on southern Australian abalone (Genus Haliotis). II. Reproduction of five species

Abstract

The sizes at sexual maturity, sex ratios and the annual reproductive cycles of five sympatric species of abalone (Haliotis cyclobates Peron, Haliotis laevigata Donovan, Haliotis roei Gray, Haliotis ruber Leach and Haliotis scalaris Leach) were studied at several sites in South Australia. The two species of commercial importance H. laevigata and H. ruber become sexually mature at about 3 years of age and between 75 and 120 mm long, according to growth rate. The other species are sexually mature at smaller sizes. In H. roei and H. cyclobates sex ratios were equal, but in the other species one sex tended to predominate; males were more numerous in younger populations and females in older populations of H. laevigata and H. scalaris, whereas males were more numerous in older populations of H. ruber. Possible explanations are advanced for these disparities. A gonad index and a stage frequency method based on measurement of oocyte diameters were used to determine the occurrence of spawning in each species. H. cyclobates and H. laevigata spawn synchronously during spring and summer at West I. and Tipara Reef; H. ruber spawns during autumn and winter at Tipara Reef and during spring and autumn at West I. ; H. roei and H. scalaris spawn throughout the year. The importance of the supply and availability of food and changes in sea temperatures as factors which can seasonally restrict the spawning periodicity of abalone are discussed.