Spawning sources of a coastal fishery species inferred from otolith chemistry and microstructure: implications for management

Spawning sources of King George whiting Sillaginodes punctatus populations in the states of South Australia and Victoria (south-eastern Australia) were analysed using otolith chemistry and microstructure from post-larvae sampled from 3 nursery areas in each state in the spring of 2011 and 2012. Univariate and multivariate analysis of the chemistry of the core region of otoliths showed differences between states, particularly for the 2011 cohort, primarily related to higher Mg in South Australian samples, while differences in Sr and Zn also made a contribution. Even though spawning times overlapped, early larval growth rates were higher for post-larvae from South Australia than Victoria. Differences in microchemistry were most evident for elements influenced by physiological processes and were potentially influenced by the different larval growth rates. Overall, otolith chemical and microstructure analyses for post-larvae in Victoria and South Australia indicated that spawning sources for the 2 states were different, qualified by results from otolith microchemistry that were less clear for the 2012 cohort. Even though genetic analyses do not indicate genetic differentiation across the 2 states, and therefore would support crossjurisdictional management, the results of this study give qualified support to the current arrangement wherein the S. punctatus fishery is managed separately by the individual jurisdictions, subject to further information on stock structure coming to light in the future.