Baseline survey of the fish fauna of a highly eutrophic estuary and evidence for its colonisation by Goldfish (Carassius auratus)

Abstract

This study represents the first quantitative survey of the fish fauna of the highly eutrophic Vasse and Wonnerup estuaries, part of the Ramsar-listed Vasse-Wonnerup Wetland System in south-western Australia. Sampling at five sites in each of these estuaries occurred in January 2012 (austral summer) to provide a species inventory and determine whether the number of species, total density and fish community composition differed between the two water bodies. A total of 18,148 fish were recorded, representing six species across four families. Three species that can complete their life cycle within estuaries, i.e. the atherinids <em>Lepthatherina wallacei</em> and <em>Atherinosoma elongata</em> and the gobiid <em>Pseudogobius olorum,</em> dominated the fish fauna, accounting for >99% of all fish collected. No significant inter-estuary differences were observed in the mean number of species, mean total density or fish community composition. Although the fish community was depauperate in terms of the number of species, total density was high, reflecting the presence of permanent and seasonal barriers to the immigration of marine species into these estuaries and the highly productive nature of this system, respectively. Two introduced freshwater species, i.e. the Eastern Gambusia <em>Gambusia holbrooki</em> and the Goldfish, <em>Carassius auratus</em>, were recorded in the Vasse Estuary. As <em>C. auratus</em> was found in mesohaline conditions, individuals may be able to use the estuary as a ‘saltbridge' to gain access to other tributaries and/or the Wonnerup Estuary, and thus expand their distribution. These findings are of concern given the potential deleterious biological and ecological effects of these alien species.