1. Implement an age-structured stock assessment model. Stock assessment models that incorporate catch-at-age data and annual fishery-independent estimates of spawning biomass are powerful tools for optimising management strategies for fisheries resources that undergo large inter-annual fluctuations in abundance (Cochrane 1999). The need to implement the WA age-structured stock assessment model in SA is pressing (Fletcher 2000) as there is considerable pressure to further expand the rapidly growing fishery and a clear responsibility to ensure the resource is managed sustainably.
2. Develop a reliable and accurate age-determination method. Knowledge of patterns of age and growth is central to the development of strategies for the sustainable management of clupeoid populations (Cochrane 1999). The major factor limiting current understanding of the age and growth of SA pilchards is the absence of a reliable and accurate age-determination method (Fletcher 2000). The development of a valid ageing protocol has been impeded by lack of data from juveniles (Ward et al 1998). A reliable and accurate method for determining the age of SA pilchards is needed to implement the WA model.
3. Estimate the age structure of the commercial catch. Age-structured stock assessment models require reliable estimates of the age structure of the commercial catch and/or population (Cochrane 1999). Otoliths collected from the SA fishery since 1995 and by the fishery-independent means since 1998 provide an opportunity to assess (1) the validity of the age-determination method developed in objective 2 and (2) the degree to which catch-at-age data reflects the age structure of the population. Reliable estimates of the age structure of the commercial catch and/or the population are needed to implement the WA model.