Fish communities of the Lower Murray-Darling catchment: Status and trends
|Fish communities of the Lower Murray-Darling catchment: Status and trends
Fish are an important part of aquatic ecosystems, with the structure of fish communities providing an indication of the overall health of river systems. The Lower Murray-Darling Catchment Management Authority (CMA) developed three catchment blueprint targets for the status of fish communities in their catchment: 1) A 55% improvement in the ratio of native:alien fish species 2)a 25% improvement in the ratio of native:alien abundance, and 3) a 25% improvement in the ratio of native:alien fish biomass. The CMA funded the Integrated Fish Monitoring project to establish benchmarks for these ratios. Fish were sampled from 27 sites and 3 wetlands across the Murrumbidgee catchment in 2004.
This report represents the most comprehensive assessment of fish species and communities ever undertaken across the whole Lower Murray-Darling CMA catchment area.
The fish community of the Lower Murray-Darling catchment is severely degraded. Only 10 of the 22 native species known to have existed in the Lower Murray-Darling catchment were found. There is a proportionally high number of alien fish species present (23% of the species richness) that dominate the catchment in terms of the proportion of total biomass (56% of the total biomass).
Bony herring, Australian smelt and carp-gudgeons were three of the most abundant species in the catchment. However the fourth most abundant species in the catchment, carp, made up 49% of the total biomass of all fish sampled. The three rarest taxa sampled were the alien redfin perch, the threatened silver perch and freshwater catfish.
Carp-gudgeon were the only species to have increased in abundance consistently throughout the whole catchment area. However Australian smelt had increased significantly in abundance in the Murray River and Murray cod had increased significantly in abundance at Pooncarie on the Darling River. The only significant decline for any species was observed for carp at Carina Bend on the Murray River. The only fish community parameters to change were a significant increase in the species richness at three of the four monitoring sites, and a significant increase in the proportion of fish parasitised by anchor worm.
Data on the commercial fishery and stocking activities the Lower Murray-Darling CMA area, and the February 2004 Murray cod fish-kill in the Darling River are also presented.
Without substantial intervention, the status of fish species and communities in the Lower Murray-Darling catchment will not improve. Rehabilitation of instream and riparian vegetation, rehabilitation of wetlands, improving environmental flow management, reinstating fish passage at a number of key barriers, contributing to the control of alien species and educating the community are all avenues by which the Lower Murray-Darling CMA can rehabilitate fish communities in the Lower Murray-Darling catchment.