Integrated monitoring of environmental flows (fish component)
This project investigates the responses of fish communities to flow regimes in New South Wales rivers. This investigation is part of the Integrated Monitoring of Environmental Flows program supporting the NSW Government’s Water Reform Program to improve river health.
The relationships between fish communities and river flows have not been clearly established, but river regulation has been implicated in the decline of many freshwater fish species in NSW. The initial IMEF fish study (2000-2003) was based on broadscale surveys and only provided a coarse understanding of the relationships between fish community structure and river flows1. For this study, fish communities were sampled by electrofishing in different functional and morphological zones within 6 regulated inland rivers (Barwon-Darling, Gwydir, Lachlan, Macquarie, Murrumbidgee and Namoi) and 1 regulated coastal river (Hunter). Each site was sampled by standard electrofishing procedures once annually during summer. Detailed habitat assessments were completed with each electrofishing shot to assess changes in habitats as well as fish communities in relation to river flows.
The earlier studied noted that therelationship between flows and fish community structure may be mainly related to recruitment success of individual fish species. Recruitment processes in native freshwater fish are currently poorly understood. For example, to what extent are species reliant on flood events to ensure successful recruitment? Some regulated rivers have Supplementary Environmental Water Allocations (SEWAs) in NSW and these may be used to assist the restoration of native fish communities. SEWAs also provide the opportunity to examine the effects of flow on fish recruitment in a structured experimental framework.
In inland NSW, the Gwydir River system will be used as the experimental system in which SEWA can be used to manipulate river flows. The Namoi River system will act as an inland reference system. In coastal NSW, a similar design will be used to examine fish recruitment in response to manipulated SEWA flow in the Paterson (regulated) and Williams (control) river systems. Larval drift nets will be used to collect monthly samples of planktonic fish larvae and eggs at several sites in each system during the peak breeding times (October to December). Follow up electrofishing sampling will be done in autumn at each site to determine if larval cohort strength is related to larval/juvenile abundances later in the year. The age of a number of larvae will be determined using analysis of daily otolith rings to relate specific flow events with presence of fish larvae in the water column.
1. Growns I. & Gehrke, P. 2005. Integrated Monitoring of Environmental Flows: Assessment of predictive modelling for river flows and fish. Fisheries Final report Series No. 74, 33pp.
The broad objectives of the NSW Government’s IMEF program are to:
1. Measure changes in the hydrology, habitats, biota and ecological processes relevant to fish communities, in the major regulated river systems (and the Barwon-Darling River) following the application of environmental flow rules.
2. As far as practical, to infer relationships between these changes and environmental flows, through statistical analysis and an understanding of ecosystem processes.
3. Provide scientific information needed for the River Flow Objectives review process.
The more specific objectives of the current project are to:
4. Establish the relationship between flows and larval fish abundances in regulated rivers
5. Assess the ability of environmental flows to restore fish larval abundances in regulated rivers
6. Develop recommendations for the release of environmental flows for the benefit of fish communities
7. Assess the relationship between fish larval abundances and juvenile fish densities.
- NSW Department of Primary Industries
- Department of Water & Energy
Dr Bob Creese
with Dr Ivor Growns, Department of Water & Energy