Stepping stone gene flow in an estuarine‐dwelling sparid from south‐east Australia

Allozyme and mitochondrial DNA variation was surveyed in Acanthopagrus butcheri to examine the pattern of gene flow among estuaries in south‐east Australia. Allozymes distinguished two peripheral estuaries from the remaining six, although the pattern of genetic variation could owe more to selection than reproductive isolation, and overall structure was small (θ = 0·012). In contrast, mitochondrial DNA revealed a high degree of genetic structure (θ = 0·263), and a significant relationship with geographic isolation. Consequently, contemporary gene flow mostly between adjacent estuaries, consistent with a one‐dimensional stepping stone model, is evident in south‐east Australia. The data indicate that management of A. butcheri within the study range should be conducted at the scale of individual or geographically proximate estuaries.