Barmah-Millewa Fish Condition Monitoring 2006-2017
Raymond, S., Duncan, M., Tonkin, Z. and Robinson, W., 2017. Barmah-Millewa Fish Condition Monitoring 2006-2017. Report to the Murray Darling Basin Authority, 55p.
The Barmah-Millewa Forest (B-MF) is a wetland complex adjoining the mid-Murray River that provides important habitat for both terrestrial and aquatic fauna. Fish condition monitoring has been designed to assess the health and status of the fish community across 21 sampling sites distributed across two strata; permanent flowing (riverine) and semi-permanent flowing (creeks, lakes and wetlands) habitats. Fish condition is reported using a range of community and population indices. The fish community indices are combined to give an overall score for the fish condition ranging from A-E (best to worst condition). A change in grade from the previous survey is reflected as increasing (+) or decreasing (-). This report presents the results from the tenth year of monitoring. We also present data from a trial of an updated sampling protocol for Murray crayfish that was designed to improve our reporting on the condition of this species.
In 2017, B-MF fish scored a B- for overall community indices and a D for the population indices, with variability across indices since the last round of sampling. In general, native fish recruitment was high (100%) and stable across strata and years, native species expected to be sampled (based on historical species richness) was low (<50%) within and between strata, and the number of large-bodied native fish at maturity was stable across years in permanently flowing strata. Population indices (proportions of abundance, species and biomass that are native) were higher in permanent flowing habitats than semipermanent habitats.
Monitoring of riverine spawning indicated that Murray cod, trout cod, golden perch and silver perch all spawned during the spring/summer of 2016. Good numbers (relative to past years) of golden perch (103) and moderate numbers of silver perch (160) eggs were sampled in 2016 compared with the previous nine sample years, and in the case of golden perch, likely reflect an increase in flow related spawning cues (e.g. in-channel pulse and flow variability) during peak spawning periods for this species. Murray cod larvae were detected at all sites in 2016, including the most downstream site, Morning Glory, which was subject to blackwater early in the season.
The 2017 crayfish catch data was modelled to establish a new sampling protocol (with sufficient precision and power) to enable researchers to generate an index of abundance for Murray crayfish as well as baseline data on population size structure and sex ratios. The new sampling protocol allows for direct comparison of population parameters between sample events and may be used to assess the impact of specific events (eg blackwater, flows) as well as long-term population trends.