Prior to 1980, cobbler (Cnidoglanis macrocephalus) was an important commercial fishery species in southern estuaries in WA, with a combined annual catch of several hundred tonnes. Fishing pressure and habitat degradation led to stock declines in several estuaries. The biological characteristics (e.g. low fecundity, high parental care/nest guarding, specific habitat requirements, small discrete populations in each estuary) make cobbler inherently vulnerable to these threats. Today only one WA estuary, Wilson Inlet, continues to host a significant cobbler fishery.
In Wilson Inlet, a relatively large amount of fishery-dependent and -independent information has been collected since the 1980s (catch sampling, juvenile surveys, tagging, etc). Key indicators now strongly suggest the current stock status is unacceptable: i) declining recruitment; ii) very high mortality with increasing trend; iii) highly truncated age and length structure with increasing trend. Retrospective SPR estimates suggest the spawning stock level has been below 20% for at least a decade. However, despite the apparently dire state of the stock, the catch and commercial CPUE has remained stable for 3 decades. Why?
We discuss the lines of evidence and analyses used in the latest assessment, including sources of uncertainty that are common to many fishery assessments.