We have developed fish-based, multimetric indices (Fish Commuity Indices) for quantitatively assessing the ecological health of the Swan-Canning Estuary and its component ecological management zones. These indicators are intended to provide a reliable, simple and affordable method for
(i) quantifying the environmental health of estuaries relative to appropriate reference conditions
(ii) monitoring temporal changes in estuarine health to detect deterioration beyond critical thresholds and
(iii) detecting those regions of individual estuaries at greatest risk of environmental decline.
What are these indices and what can they do?
The Fish Community Indices, which were developed for shallow, nearshore and deeper, offshore waters of the estuary, incorporate information on a range of fish community characteristics, enabling estuary managers to quantify the health of the estuary and to monitor future changes in its condition, and facilitating more informed and preventative management actions. The indices also represent a simple, easily understood method for communicating with the public and stakeholders. These indices have been implemented under an annual monitoring regime since 2012 and it is envisaged that the index will provide a crucial tool for assessing and comparing the health of estuaries across south-western Australia in future years.
How do they work?
A suite of fish community characteristics ('metrics') first were selected, based on their sensitivity to detect inter-annual change in estuarine condition.
Seasonally-adjusted reference conditions for each selected metric were then established for each zone of the estuary using 30 years of historical fish assemblage data, providing a best available standard against which current and future estuarine health may be assessed and scored.
Scores for the health indices were calculated by summing the scores for their component metrics and then adjusting the resultant value by the number of metrics in the index to produce a final, easily interpretable index score ranging from 0-100.
Thresholds for establishing the qualitative health status of the estuary (i.e. A - very good, to E - very poor) were also determined based on quantiles of the observed historical index scores.
The index, which is the first such tool to be developed for Western Australia, provides managers with a reliable and cost-effective, quantitative method for assessing and communicating the health of the Swan Estuary and has now been implemented from 2012 as part of an annual monitoring and reporting regime.
Reports and presentations on the Health Indices
The process of developing the Fish Community Indices has now been fully described in various peer-reviewed papers and reports:
Hallett, C.S. (2014). Quantile-based grading improves the effectiveness of a multimetric index as a tool for communicating estuarine condition. Ecological Indicators 39: 84-87.
Hallett, C.S., Valesini, F.J., Clarke, K.R., Hesp, S.A., Hoeksema, S.D. (2012). Development and validation of a fish-based, multimetric index for assessing the ecological health of Western Australian estuaries. Estuarine, Coastal and Shelf Science 104-105: 102-113.
Hallett, C.S., Hall, N.G. (2012). Equivalence factors for standardising catch data across multiple beach seine nets to account for differences in relative bias. Estuarine, Coastal and Shelf Science 104-105: 114-122.
Hallett, C.S., Valesini, F.J., Clarke, K.R. (2012). A method for selecting health index metrics in the absence of independent measures of ecological condition. Ecological Indicators 19: 240-242.
Dr Chris Hallett gave a presentation on the use of these indices for assessing the health of the Swan-Canning Estuary, at the Swan River Trust Forum. View the slideshow here...
Partners and funding bodies
Our studies have been funded by, and carried out in close cooperation with, the following government agencies, and we would particularly like to thank the Swan River Trust for their ongoing commitment to the implementation of these indices.
Swan River Trust
WA Department of Water
WA Department of Fisheries