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Spatial and temporal variability of multimetric health index scores: implications for management

Hallett, C.ORCID: 0000-0002-8844-3388 and Valesini, F. (2011) Spatial and temporal variability of multimetric health index scores: implications for management. In: 48th Annual Conference of the Australian Marine Science Association, 3 - 7 July, Fremantle, Western Australia.

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Assessments of estuarine health status using multimetric biotic indices should consider the variability of index scores. Index variability not only affects the precision and reliability of health status assessments, but may also provide a signal of impaired health. We examine aspects of the variability associated with scores for a fish-based, multimetric health index for the Swan Estuary, Western Australia. The reliability of the nearshore (waters <1.5 m deep) and offshore (>1.5 m deep) indices developed for this system was evaluated by quantifying the variability of index scores among replicate sites, between seasons and between consecutive years. Bootstrap resampling techniques were also used to determine the effects of random sampling variation on the precision of index scores. The far greater inter-seasonal and inter-annual variability observed among offshore than nearshore index scores may provide evidence that the deeper waters of the estuary are in poorer health than the shallower waters, most notably in the upper reaches of this system. Although the inter-annual variability of index scores was relatively high, health status classifications were fairly robust to these changes and can thus be considered reliable. Overall, validation of the indices developed during this study demonstrated that their spatial and temporal variability was comparable to that of existing multimetric indices employed in the USA and Europe, and that classification of the health status of the estuary was fairly robust, despite the effects of both natural spatio-temporal variability and sampling error on index scores. The consistently lower spatial variability of both nearshore and offshore index scores recorded in summer and autumn indicates that, dependent upon an appropriate examination of intra-seasonal index variability, these seasons represent a suitable index period for future monitoring of the ecological health of the Swan Estuary.

Item Type: Conference Item
Murdoch Affiliation(s): Centre for Fish and Fisheries Research
School of Biological Sciences and Biotechnology
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