Gilligan, D., 2007. Annual progress report towards achievement of the Lower Murray Darling Catchment Action Plan 2004 – 2015: Fish Community Monitoring 2005/06. NSW Department of Primary Industries – Fisheries Research Report Series No. 16. ISSN 1449-9959. 42pp.

Summary

The Lower Murray-Darling Catchment Action Plan (CAP) identifies Riverine Health as a Catchment Target: “An identifiable nett improvement in riverine health across the Lower Murray-Darling Catchment by 2015”. This annual report presents the freshwater fish data collected in 2006 and compares them with benchmark data collected in 2004, assesses progress towards the CAP fish community targets and discusses any patterns observed in the context of other riverine health targets regarding algal blooms, hydrological condition and salinity.

There was no measurable progress towards the CAP targets between 2004 and 2006. The Native:Alien species and biomass ratios declined slightly at the whole catchment level, although the changes were not statistically significant. The abundance ratio had increased at a whole of catchment level, but again the change was not statistically significant.

There was limited opportunity to asses the CAP algal target alongside the fish community data as the algal bloom frequency was generally poor in all catchment zones. There are few data to suggest negative impacts of algal blooms on fish communities. The observed increase in abundance of fly-specked hardyhead and eastern gambusia could actually lead to higher frequencies of algal blooms as these fish prey on zooplankton that would otherwise feed on planktonic algae.

The relative condition of the fish community across the catchment was highest in zones that had the poorest hydrological condition. However, fish community condition was higher in zones where the seasonality of flows was less impacted by river regulation, suggesting that the seasonality of flows is the most important hydrological parameter impacting on fish communities in the Lower Murray-Darling catchment.

Despite the current consensus that native fishes are generally tolerant of high salinity levels, there was some indication that fish community condition was related to salt levels in rivers as fish assemblage condition is generally best in those catchment zones with the lowest salinity levels and vice versa.

Further fish surveys were done in 2007 and the data will be combined with those in this report to produce a more comprehensive assessment of the fish assemblages in the Lower Murray-Darling catchment.