Regional Patterns in the Distribution, Diversity and Relative Abundance of Wetland Fishes of the River Murray, South Australia

This paper documents regional patterns in the distribution, diversity and relative abundance of wetland fishes of the River Murray, South Australia (SA). Patterns are derived from analyses of the combined 'fish' dataset from 74 wetlands surveyed during the 2004-2007 South Australian River Murray wetlands baseline surveys. Sampling occurred once or twice per annum in each survey year. Some 135,000 fish from 28 species were captured, including 18 freshwater native species (five of current conservation significance), five native estuarine species and five alien invasive freshwater species. The river downstream of Blanchetown has (had) a variable hydrology and heterogeneous habitats, and comprised the most diverse assemblage of native fishes. In contrast, the river above Blanchetown has comparatively larger, predominantly stable, permanent, unproductive wetlands, and a community comprised principally of 'generalist' native fishes. In regard to alien fishes, common carp and eastern gambusia were most abundant. Flow control regulators fitted with carp exclusion screens were found to have limited effect on overall patterns in the occurrence and abundance of common carp (or native fish assemblages) but a combination of 'optimised' screens and standard operating protocols promise greater success. The plight of the diverse and unique fish community within and around Lake Alexandrina cannot be overstated. Several fish species in this region are threatened by degrading environmental conditions and proposed management actions, and regional extinctions are likely.