Joy and Death (2003): Assessing biological integrity using freshwater fish and decapod habitat selection functions.

Joy, M.K. & Death, R.G. (2003) Assessing biological integrity using freshwater fish and decapod habitat selection functions. Environmental Management, 32, 747–759.

To assess human impacts on aquatic systems worldwide the comparison between observed and expected biological communities has been used successfully with predictive models. We developed a methodology based on the comparison between observed and expected freshwater fish and macro-crustacean assemblages to assess the biological quality of stream sites in the Auckland region, New Zealand. Individual discriminant models based on the presence or absence of the 12 most common fish and decapod species were developed. Using the models, predictions were made using environmental measures at new sites to yield the probability of the capture of each of the 12 species and these were combined to predict the assemblage expected at sites. The expected assemblage was compared to that observed using an observed over expected ratio (O/E). The models were evaluated using a number of internal tests including jackknifing, data partitioning and the degree to which O/E values differed between reference sites and a set of sites perceived to be impaired by human impacts.