Variable stocking effect and endemic population genetic structure in Murray cod (Maccullochella peelii)
Rourke, M.L., McPartlan, H.C., Ingram, B.A. and Taylor, A.C., 2011. Variable stocking effect and endemic population genetic structure in Murray cod (Maccullochella peelii). Journal of Fish Biology, 79: 155–177.
Murray cod are endemic to the Murray-Darling Basin of eastern Australia and have considerable cultural and recreational value. Over-fishing, habitat change and introduced species have together resulted in a significant decline in population size and distribution. The species is listed under the Environment Protection & Biodiversity Conservation Act (1999) as vulnerable nationally, indicating it faces a high risk of extinction in the future. Substantial restocking efforts since the early 1980s have used hatchery-raised Murray cod to supplement wild populations for recreational and conservation purposes, with largely unknown effects on genetic structure of wild populations.
We used genetic markers to examine the genetic structure of Murray cod throughout its distribution in the Murray-Darling Basin of eastern Australia, and to assess the genetic impacts of over three decades of stocking hatchery-reared fingerlings. Results indicated that the species is one large genetically mixed population throughout much of its extensive range, most likely a result of the high level of river connectivity between catchments. However, three catchments with terminal wetlands (the Lachlan, Macquarie and Gwydir catchments) contained genetically-distinct populations. No stocking impacts were detected in the catchments that were genetically mixed (either because of low genetic power or lack of impacts), but the genetically differentiated Gwydir and Macquarie catchment populations were clearly affected by stocking. In contrast, the only evidence of stocking in the Lachlan catchment was a single stocked fish that was collected upstream of the largest and most heavily stocked dam in the catchment. Therefore, stocking of Murray cod throughout the Murray-Darling Basin has resulted in a range of genetic impacts ranging from minimal detectable impact, to substantial change in wild population genetic structure. Results from this study, will assist the conservation and management of Murray cod in the wild, as well as provide guidelines for genetically sound breeding and stock enhancement programs.