The effect of habitat fragmentation on New Zealand native fish : a GIS approach.

Abstract

Land use change is likely to have influenced the distributions of adults of the New Zealand galaxiid fishes (family Galaxiidae) with life histories involving a juvenile migratory 'whitebait' stage. The influence of interactions between these diadromous migrations, terrestrial habitat fragmentation, migratory barriers and local habitat conditions on the distribution ofkoaro, inanga, and giant, shortjaw and banded kokopu were investigated using a geographical information system approach. A catchment-scale analysis of Banks Peninsula streams with riparian forest indicated position and extent of forest explained 65.7% of koaro occurrence. When riparian forest was lacking koaro were rare and catchment variables had no influence. A site-scale analysis using logistic regression predicted koaro and banded kokopu presence at > 80% of sites using land use-related variables. Hindcast and forecast models showed that both species likely occupied over 85% of available stream habitat in 1860. Reforestation would have differential effect on koaro and banded kokopu depending on forest position. Banded kokopu, a forest specialist, was affected by edge effects of forest fragmentation, occurring in larger numbers and sizes in forested streams, whereas koaro was affected by catchment forest cover. A large-scale study of migratory galaxiid occurrences on South Island's West Coast indicated maximum slope encountered during upstream migrations was a good predictor of fish occurrence, and species had different slope-thresholds. A hierarchical analysis that differentiated between abiotic barriers, migratory passage, and land use impacts on fish occurrence showed that land use impacts on the migratory passage was the major factor limiting migratory fish distributions. This research shows that migratory galaxiids are sensitive to the configuration of landscape elements and migratory barriers, factors that can be used in predictive models to differentiate and quantify distribution limitations due to migratory passage, catchment land use, and local habitat conditions. The approach is useful for managers because it is robust, feasible, and transferable to other migratory fish species.