Bayesian hierarchical modelling of maturity-at-length for rock lobsters, Jasus edwardsii, off Victoria, Australia

Maturity-at-length is a key input to stock assessments when the management objectives are expressed in terms of the size of the spawning output relative to some reference level. Data for rock lobsters, Jasus edwardsii (Hutton, 1875), off Victoria, Australia, are used to estimate logistic relationships between carapace length and the probability of being mature. The analyses are based primarily on mixed-effects models in which the parameters governing maturity-at-length depend on year and region, fitted using a Bayesian hierarchical approach. Maturity-at-length differs among years and regions, and the length-at-50%-maturity increases from west to east and then remains relatively constant. However, the estimates for all years and regions are not equally precise, so there is value in using a mixed-effects approach to allow the years for which the dataset is large to 'provide support' for the years for which the data are sparse. The results provide the input needed to conduct assessments of rock lobster populations off Victoria and to form the basis for conducting population projections.