McGarvey and Fowler: Seasonal growth of Siltaginodes punctata 



557 



ploited species such as King George whiting where deple- 

 tion of the legal sizes of the cohort is rapid over monthly 

 time scales. In fishery stock assessment models where 

 only legal-size lengths of each yearly cohort are subject to 

 exploitation and where size selection is driven primarily 

 by a legal size limit rather than size-varying gear selec- 

 tivity, model accuracy is improved by dividing the cohort 

 length distribution into legal and sublegal components. 



Growth was variable, reflected in high standard devia- 

 tions in lengths-at-age of King George whiting. This meant 

 a time span of 12-24 months between the crossing into 

 legal size of the first (i.e. fastest growing, at -23 months 

 of age) and last 2'7f of the normal cohort to reach LML. 

 Because fishing mortalities are such that a majority offish 

 are removed within 24 months of reaching legal size, the 

 explicit representation of the distribution of harvestable 

 lengths of cohorts as they cross LML allows substantial 

 improvements in stock assessment, notably in fitting only 



legal sizes to monthly catch totals by weight and sampled 

 numbers at age. Moreover, the seasonal variations in fish- 

 ing effort targeted on South Australian King George whit- 

 ing appear to track the arrival of the bulk of recruits to 

 legal size in autumn and early winter. The growth model 

 presented in our study allowed this feature of seasonal 

 timing in recruitment to be captured in the associated 

 stock assessment population model. 



Acknowledgments 



We thank D. Short for analysis of otoliths and J. M. Mat- 

 thews for bootstrap analysis of weight-length and prepara- 

 tion of figures and tables. We also thank B. D. Smith and an 

 anonymous reviewer for valuable comments. This research 

 was supported by the Australian Fisheries Research and 

 Development Corporation, project no. 95/008. 



