Differences in the distributions of freshwater fishes and decapod crustaceans in urban and forested streams in Auckland, New Zealand

Using data from existing studies, assemblages of freshwater fishes and decapod crustaceans were examined at 39 sites in urbanised catchments and 57 sites in forested (reference) catchments within the greater Auckland region, New Zealand. Eleven native and I exotic fish species and 2 native decapod crustacean species were recorded. Species richness and fish Index of Biotic Integrity (IBI) scores were lower overall in streams in urbanised catchments. Shortfin eel (Anguilla australis) and mosquitofish (Gambusia affinis) were more dominant in urban streams; all other commonly occurring species were found significantly more often in reference streams. Non-diadromous native species (Cran's bully (Gobiomorphus basalis) and freshwater crayfish (Paranephrops planifrons)) were absent from urban streams, but relatively abundant in reference streams. This absence of non-diadromous species, together with the urban occurrence of five diadromous species suggests that migratory barriers pose less of a threat to freshwater communities than physico-chemical disturbance in streams in the Auckland urban region.