Conservation implications of distinct genetic structuring in the endangered freshwater fish Nannoperca oxleyana (Percichthyidae).
The Oxleyan pygmy perch Nannoperca oxleyana is a small, freshwater fish native to Australia. This species has a restricted and fragmented distribution within coastal freshwater drainages of northern New South Wales (NSW) and southern Queensland and is listed as ‘endangered’ (in danger of extinction) under the NSW Fisheries Management Act 1994. A recovery plan has been prepared by the NSW Department of Primary Industries to guide conservation and management programs for the species. Integral to recovering this species is knowledge of how closely related the remnant populations of pygmy perch are to each other, and hence whether they are mixing and interbreeding. This study uses genetic techniques to assess the relationships and dispersal patterns of populations distributed across the geographic range of the species.
The results of the study indicated that there was very limited contemporary mixing and interbreeding among the populations sampled in NSW and Queensland. In Queensland, populations are typically isolated from each other by large land distances. In NSW high sand dunes on the coastal river floodplains appear to act as barriers to the dispersal of fish between freshwater drainages in adjacent subcatchments. It was evident, however, that the now fragmented populations were historically connected as recently as 8 000 years ago during the last ice age when sea levels were lower. It was also apparent that some contemporary dispersal and interbreeding may have occurred among water bodies within a small isolated subcatchment located towards the southern limit of its distribution near Evans Head in NSW.
This study highlights the vulnerability of the isolated populations of Oxleyan pygmy perch, and the importance of concentrating efforts to protect and conserve the remaining habitats and dispersal pathways of this species. This may require special attention on the coastal floodplains, where barriers such as roads and levee banks in the catchment can disrupt the movement of water, plants and animals between rivers and streams. The results of the study also emphasise the importance of using genetic research in recovery planning for threatened species.