Sea mullet (Mugil cephalus) support one of the largest commercial finfish fisheries on Australia's east coast and are an important shared resource managed jointly by New South Wales and Queensland. The species undertakes annual spawning migrations and uses estuarine, coastal and freshwater habitats that are increasingly exposed to environmental variability and competing human uses.
Recent assessment work highlighted the challenges of evaluating stock status in a changing environment. Recruitment has been variable in recent decades, catch-rate trends differ among regions and fishing sectors, and evidence suggests that migration behaviour and fish availability may vary through time. Regional analyses have also identified declines in catch and abundance indicators in parts of south-east Queensland, along with emerging evidence linking major flood events and habitat change to shifts in productivity and distribution.
To address these challenges, the assessment used an ensemble age-structured modelling framework that evaluated alternative interpretations of fishery and biological data. Rather than relying on a single model structure, the assessment combined multiple hypotheses relating to fish availability, natural mortality and abundance indices. This approach provided a transparent way to quantify uncertainty arising from environmental variability, changing fish behaviour and conflicting signals.
The sea mullet case study demonstrates how stock assessments are adapting to increasing uncertainty associated with climate variability and ecosystem change. It also highlights a growing challenge for harvest strategies: how to distinguish changes caused by fishing from those driven by environmental change. As fisheries management increasingly considers ecosystem resilience and broader social and environmental objectives, assessment frameworks that explicitly evaluate competing hypotheses may become critical tools for decision-making in an increasingly variable world.