Spatial variation in size and age structures and reproductive characteristics of the King George whiting (Percoidei : Sillaginidae) in South Australian waters

Adult King George whiting were sampled at 12 localities representing a rang e of habitat types across South Australia. Sampling was undertaken between March and May for a minimum of 2 years between 1995 and 1998. Fish were age d by otolith interpretation, and reproductive maturity was determined by go nad analysis using macroscopic and histological techniques. In total, 6961 fish comprising 3678 females and 3283 males were considered from four local ities in each of three geographic regions. In both Gulf St Vincent and Spen cer Gulf, age structures became more complex from north to south, associate d with a shift in size towards larger fish. In the simplest age structures, >90% of fish were from the 3-year age class, whereas the age range of the most complex was 3-17 years, with the 3-5 age classes most numerous. Males were more abundant in smaller size classes and females in the larger. Altho ugh some fish from each locality showed some gonad development, only at thr ee localities did spawning occur. At these places, populations had the broa dest age and size distributions and were in deep water that experienced med ium to high wave energy. Since spawning grounds and nursery areas are up to several hundred kilometres apart, the processes of larval advection and ad ult movement are implicated as obligate processes of the life history.