Project number: 2002-017
Project Status:
Budget expenditure: $125,374.00
Principal Investigator: Ian Potter
Organisation: Murdoch University
Project start/end date: 29 Jun 2002 - 15 Dec 2006


Environmental and fisheries managers urgently need reliable data to underpin strategies to conserve or improve the ecosystems of normally-closed estuaries in the central region of the south coast of Western Australia. These managers thus need:

1. An understanding of the current status of the fish fauna of the highly-degraded Culham Inlet, and particularly of its population of black bream, and how that status has been influenced by extreme environmental perturbations in the recent past.

2. Reliable information on the extent to which the extreme environmental conditions experienced in certain of the last ten to fifteen years influenced either the spawning success and/or survival of the 0+ age class of black bream in Culham Inlet.

3. An understanding of the current status of the fish fauna of Stokes Inlet, which is less degraded than Culham Inlet but is still the subject of concern for local residents and visitors, and of Hamersley Inlet in whose catchment the vegetation has been the subject of only a relatively low level of clearing.

4. An ability to predict, qualitatively, the extent to which continuing degradation of any normally-closed estuary in the central region of the south coast of Western Australia will affect the fish faunas of those estuaries and, in particular, their recreational and commercial fish species. This information is required by the Department of Fisheries WA for developing its overall plan for managing the recreational and commercial fisheries in these estuaries (R. Lenanton, pers. comm.) and by other governmental authorities for developing strategies for conserving or restoring the quality of the important environments afforded by these estuaries.


1. Determine, on a seasonal basis, the compositions of the fish fauna of the basin and riverine regions of Culham, Stokes and Hamersley inlets and ascertain whether pools upstream act as a refuge for black bream.
2. Relate any differences in the compositions of the fish faunas in the three estuaries to differences in the environmental characteristics within and between these estuaries, and in particular of salinity, dissolved oxygen and water levels.
3. Use age composition data to determine the variations in annual recruitment of black bream in Culham, Stokes and Hamersley inlets in recent years, and relate these to environmental conditions, and particularly to the relative estimated strength of freshwater discharge and whether or not the bar at the estuary mouth had been breached.
4. Compare the growth rates of black bream in the three estuaries and relate any differences that are detected to the environmental conditions that are experienced within each system.
5. Provide to environmental and fisheries managers an assessment of the levels at which salinity and dissolved oxygen influence the abundance of the main fish species and how those critical levels vary amongst those species

Final report

ISBN: 86905-879-7
Author: Ian Potter

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