Almost forgotten: Historical abundance of eel-tail catfish populations in south-western Australian estuaries and their decline due to habitat loss and historical overfishing

Abstract

The decline of Estuary Cobbler (Cnidoglanis macrocephalus) stocks in south-western Australia since European settlement of the region in 1829 is described, based on evidence from historical documents, fishery statistics and scientific surveys. Estuary cobbler is a relatively large, long-lived, benthic carnivore that was once abundant in the three largest west coast estuaries, where it was a major component of fishery catches for decades. The breeding stock in each estuary declined dramatically between 1960 and 2000, after which time exploitation effectively ceased. Two stocks appear to have largely disappeared, while the third still persists at a relatively low level. In each estuary historical overfishing coincided with a period of severe habitat degradation including flow modification, eutrophication, benthic habitat loss and hypoxia. Hence there is no obvious, primary driver of decline for these stocks. Exploitation probably acted synergistically with environmental impacts to cause each stock decline. In degraded environments, fisheries management should be highly precautionary to reflect the elevated risk to exploited species posed by multiple simultaneous stressors. A risk-based ‘weight-of-evidence’ approach that can accommodate both quantitative and qualitative lines of evidence, including fishing and non-fishing impacts, is recommended to assess the status of exploited species in such environments.