Investigation of the replacement of Margaret River hairy marron Cherax tenuimanus (Smith) by smooth marron C. cainii Austin

The Margaret River hairy marron, Cherax tenuimanus (Smith, 1912) (Decapoda: Parastacidae) is critically endangered due to the introduction of the widespread marron, C. cainii Austin, 2002. This project investigates the rapid replacement of C. tenuimanus with studies important to its conservation. The ability to identify correctly in the field C. tenuimanuss, C. cainii and hybrids was investigated by linking morphology and marker allozyme loci. C. tenuimanus was readily identified in the field and errors were conservative; no genetically identified hybrids or C. cainii were field identified as C. tenuimauus during tissue samples collection. A prototype field identification guide has been constructed, aiming to provide the general public with an ability to identify correctly in the field C. tenuimanus. This should allow community participation in recovery plans centred on active removal of C. cainii and hybrids and ensure minimal accidental removal of C. tenuimanus. The guide will serve to allow recreational marron fishing within C. tenuimanus habitat, and raise public awareness about C. tenuimanus and its conservation. For the purpose of investigating the role of hybridisation in the replacement, accurate field identification of hybrid marron, based on morphology, was not achievable. Investigation into the relationship between median carina length and orbital carapace length recorded during tissue sample collection provided some distinction, but not at a diagnostic level. The genetically diverse F2 or backcross hybrid marron had the lowest accurate field identification. Further investigation into morphological and morphometric relationships will be necessary if precise accuracy in field identification of marron is deemed possible. The distribution of marron species within Margaret River was mapped with C. tenuimanus found almost exclusively in the forested upper reaches, only in sympatry with C. cainii. An abrupt boundary of occurrence exists for C. tenuimamus between agricultural land use and state forest. A very small population of C. tenuimanus exists in the extreme lower reaches. It is proposed that extrinsic factors associated with the middle and lower reaches (changed water flows, presence of shelter, water pollution, fishing pressure, etc.) might account for the increased replacement of C. tenuimanus. Repeated mark-recapture within a sympatric population aimed to investigate replacement mechanisms based on differences in intrinsic factors. Although not overly powerful, results suggested C. cainii has a greater growth rate and earlier spawning period, both of which are attributes known to influence freshwater crayfish replacement elsewhere in the world. A conceptual flowchart based on interacting intrinsic and extrinsic factors that influence the replacement of C. tenuimanus by C. cainii was constructed. This flowchart provides guidance in future research on replacement mechanisms and recovery actions for C. tenuimanus. C. tenuimanus was nominated as critically endangered to the Western Australian Department of Conservation and Land Management. This was accepted and is currently awaiting final Ministerial approval prior to formal gazettal. An Interim Recovery Team has been established and is led by the Department of Fisheries. Management recommendations are made with an emphasis on prioritising actions providing the most immediate and long-term advantage for C. tenuimanus. The Margaret River community is considered to be an important component in the overall recovery process