BIOLOGICAL AND ECOLOGICAL ASPECTS OF THE DISTRIBUTION OF SEPIA-AUSTRALIS (CEPHALOPODA, SEPIIDAE) OFF THE SOUTH COAST OF SOUTHERN AFRICA

During the South Coast Biomass Survey in 1988, 49,4 kg (6336 individua ls) of Sepia australis were caught between Cape Agulhas and Algoa Bay. A biomass index of 803 t of S. australis was calculated for the area at that time. Largest catches were taken between about 20-degrees-E an d 22-degrees-E, in waters of 10-11-degrees-C and 50-150 m depth. The o verall sex ratio was 2M : 3F and mean individual mass was 6,47 g for m ales and 8,67 g for females. The largest animals were a mature male of 58 mm mantle length and a maturing female of 65 mm mantle length. Mos t of the animals trawled off the South Coast were maturing or fully ma ture in early winter and very few immature animals were found. Differe nces in mean mantle length and maturity stage of the animals in differ ent areas were found to be correlated most strongly with water tempera ture but also with depth and longitude. Largest numbers and mean sizes of mature animals caught suggest that the main spawning grounds off t he South Coast may be in deeper water on the western side of the Agulh as Bank. To the east the deeper water is warmer and the animals there may be at a disadvantage, as optimum temperatures and depths for spawn ing do not coincide.