A multifaceted approach to modelling growth of the Australian bonito, Sarda australis (Family Scombridae), with some observations on its reproductive biology

Growth of the Australian bonito, Sarda australis, is described for the first time using data from three different sources. Von Bertalanffy growth functions were fitted to: (1) size-at-age data derived from sectioned sagittal otoliths, (2) monthly length-frequency collections from a commercial line fishery, and (3) tag-recapture data from a long-term cooperative tagging study. Age estimates of S. australis were indirectly validated by examining the percentage of otoliths with opaque edges each month. The best-fitting growth functions for each data source yielded similar results, showing strong seasonal variations in growth rate. Maximum growth occurred during summer, with near cessation of growth apparent during winter. Early growth was very fast, with fish attaining similar to 30 cm fork length (FL) after 3-4 months. Growth of males and females was not significantly different. The oldest fish sampled was estimated to be 3+ years old, while the largest fish aged was 63.8 cm FL. Gonadosomatic indices indicated that S. australis has an austral spring/summer spawning period in eastern Australia. A preliminary estimate of the size at first sexual maturity was similar to 36 cm FL for both males and females, corresponding to an age of similar to 1 year.