Variable Growth in South-Eastern Australian Fish Species: Evidence and Implications for Stock Assessment

Length-at-age data for several southern and eastern Australian fish species reveal marked temporal changes to mean size-at-age (variable growth). Despite this, current stock assessment practices assume growth and other life history traits remain constant through time. Here we demonstrate simple methods for discerning degrees of temporal change to mean-size-at-age from fisheries data and present novel stock assessment methods that account for this variability. We illustrate how the stock assessment of blue grenadier Macruronus novaezelandiea in Australia’s Southern and Eastern Scalefish and Shark Fishery can be conducted to take account of cohort specific variability in growth.  Model outputs suggest that accounting for variable growth allows for better description of historical time-series data related to the fishery. Furthermore, models that account for variable growth provide different population estimates to those models that assume constant growth, with implications for the estimation of quantities important to management and thus to recommended future catch levels.