Status: Critically Endangered

It is not often that the term ‘hairy’ could be ascribed to a crustacean, but this species of freshwater crayfish does indeed have a hirsute appearance with hair-like bristles over its carapace and other body parts.  It is endemic to the Margaret River in the south-western corner of Australia, where it is restricted to an area of occupancy of less than 10 km², which partly explains its critical status.  Hybridisation with the closely related, but introduced, Smooth marron (Cherax cainii) has been identified as the greatest threat to the species – one of the largest types of freshwater crayfish in the world (attaining weights of up to 2 kg).  The Smooth marron was introduced into the Margaret River in the 1980s, after which population declines in the Hairy marron began to be noticed.  Now, the introduced species occurs at all the sites where the Hairy marron occurs.  Given that the Hairy marron seems to prefer undisturbed habitat and the Smooth marron may have a slight competitive advantage where they co-occur, and the ever-increasing proportion of hybrid individuals that are being captured, the concern is that ultimately the Hairy marron will disappear as a genetically distinct species.  Illegal fishing is another issue threatening the species, but perhaps it is somewhat easier to control through public education than the over-riding issue of hybridisation.  Predation by introduced Redfin Perch, intensifying human-induced habitat degradation and competition with another crayfish species (Cherax albidus) are compounding the multi-faceted threats faced by the Hairy marron.  It is difficult to envisage how the genetic integrity of the Hairy marron can be maintained long-term without a considerable effort to eradicate invasive species from the Margaret River – control measures that could greatly alter the biology of the river given that many such species have become integrated into its food web.  The plight of the Hairy marron highlights the difficulty in dealing with introduced species once they have gained a foothold in a habitat.