Declining catches in the Western Zone of Victoria, the Southern Zone of South Australia, and the NW region of Tasmania have been observed over the past 4–5 years. These areas have always been the most productive and most important part of the south-eastern rock lobster fishery, and the declines in observed CPUE do not align with median predictions from each State’s stock assessment models. The lobster fishery in each State is managed primarily with output controls using Total Allowable Catches determined by stock assessment modelling. CPUE is used by the model as a proxy for lobster abundance and the observed trend may be caused by below average recruitment. However, catch rates may also be driven by exogenous changes in catchability influenced for example by environmental effects, fleet dynamics, fisher behaviour, or rock lobster behaviour. Hence, there is a pressing need to determine whether the observed falling CPUE represents an apparent decline in relative abundance caused by reduced catchability or an actual decline caused by reduced recruitment, reduced growth, or increased natural mortality, or a combination of these factors. Importantly, what are the implications for future assessments and what monitoring and management strategies are most robust in the face of these uncertainties.