Gunbower Forest Fish Monitoring Surveys 2008/2009

"June 2009".

Project Number: Gunbower Forest Fish Monitoring Surveys - M/BUS/294.

MDFRC item.

In November 2008, the North-Central Catchment Management Authority (CMA) engaged The Murray-Darling Freshwater Research Centre (MDFRC) to undertake two surveys of the Gunbower Island fish community during December 2008 and March 2009. The objective of these surveys was to assess the spatial distribution, relative abundance, age structure, evidence of recent recruitment, detection of disease/abnormalities and degree of nativeness (i.e. the native to exotic ration) of fish assemblages at 23 sites across Gunbower Island. Survey sites included specific wetlands within Gunbower Forest (7 sites), lagoons (9 sites) and channel reaches of the Gunbower Creek (7 sites). This report presents results from these surveys and forms a deliverable for Contract No. 2008_054 between the North Central CMA and the MDFRC. In addition to the objectives listed in the project brief, this study took the opportunity to report against the objectives set for fish in The Living Murray Outcomes and Evaluation Framework (LTM OEF) (MDBC 2007) for sites upstream of the Murray Mouth, Coorong and Lower Lakes, within which the Gunbower Island Icon Site is included (MDBC 2007). The TLM OEF provides a framework to measure condition of functional groupings of fish (below) relative to other TLM Icon Sites. Reporting against the listed objectives of the OEF will provide the North Central CMA with a measure of condition relative the objectives of TLM. In line with the project brief and while considering the objectives of the TLM OEF, the current study endeavours to interpret observed fish population demographics (population size structure, spatial distribution and abundance) across the study area in view of populations shifting from or to ecologically sustainable levels.

A total of 62,870 individuals from 17 species of fish (12 native and 5 exotic species) were recorded across the two sampling events presented here. The native carp gudgeon (Hypseleotris spp.) was ubiquitous and the most abundant species overall, followed by the exotic mosquito fish and native flathead gudgeon which were present at most survey areas. Common carp dominated the biomass of fish assemblages in most water bodies. Murray cod were collected in greater numbers than in previous years, while the relative abundance and spatial distribution of golden perch declined as compared to previous survey findings. Freshwater catfish, bony herring and trout cod were collected in the current study, as compared to previous studies when these species were not reported on Gunbower Island. Progress toward the TLM OEF objective '…sustainable populations of Murray cod, golden perch and catfish and restrict population of common carp…' has been achieved, with higher numbers of Murray cod collected as compared to previous surveys and the first confirmed record of freshwater catfish on Gunbower Island. Golden perch however have declined in abundance (but have declined at other Icon Sites also), as did common carp as compared to previous studies. The relative decline of common carp was accompanied by the restriction of carp colonisation of particular wetlands, potentially due to the use of screens on inlet watering point: a strategy which is recommended to be investigated further in future environmental water events on Gunbower Island.