Relative effects of in-stream habitat and land use on fish distribution and abundance in tributaries of the Grey River, New Zealand

Abstract

The distribution and abundance offish was investigated over 2 years at 78 sites in Redjacks Creek and adjacent tributaries draining native, exotic, and mixed forest catchments within the Grey River system, South Island, New Zealand. The abundance of diadromous fish decreased with altitude and distance from the sea, whereas the abundance of non-diadromous fish species, especially dwarf galaxias (Galaxias divergens), increased with altitude and distance from the sea. Species abundance varied with average stream depth and velocity, generally in accordance with micro-habitat preferences. The relative influences of diadromy, land use, and physical habitat on fish distribution and abundance were difficult to separate. Differences in fish abundance in the three land-use categories were often attributable to differences in physical habitat. Nevertheless, there were indications that land use and its effect on the stream environment was influencing the distribution of some fish species. Ammocoetes (Geotria australis) were least abundant in native forest catchments, whereas dwarf galaxias and bluegilled bullies (Gobiomorphus hubbsi) were abundant in those catchments. Banded kokopu (Galaxias fasciatus) were associated with in-stream cover and only found in the smallest streams sampled. The abundance of torrentfish (Cheimarrichthys fosteri) and bluegilled bullies declined over the study period, and three fish species were found in catchments adjacent to Redjacks Creek, but not in Redjacks Creek or its tributaries. Suspended sediment produced by mining and logging activities may have caused low fish diversity and changes in fish abundance in Redjacks Creek. © 1996, Copyright Taylor & Francis Group, LLC.