STUDIES ON FISH MOVEMENT DYNAMICS IN A TROPICAL FLOODPLAIN RIVER - PREREQUISITES FOR A PROCEDURE TO MONITOR THE IMPACTS OF MINING

Towards the end of the Wet season in the tropical coastlands of northe rn Australia, there are dramatic upstream movements of many fish speci es in some seasonally flowing streams. These movements are considered to be a part of refuge-seeking migrations. Aspects of th, dynamics of the movements in Magela Creek (in the 'Top End' of the Northern Territ ory) downstream from the Ranger Uranium Mine have been examined with a range of techniques (mainly direct observation) to facilitate the dev elopment of a possible procedure for monitoring impacts of the mine on the fish community of the creek system. Data on diel patterns of move ments validated that monitoring, for Ih at midday at a single point ad jacent to the mine, reflects day-to-day changes in total diel movement s. To help identify the location of any impacts arising in the future, information on upstream progress rates, longitudinal changes in movem ents, and movements between the creek and lowland billabongs, were use d to (i) demonstrate the creek-long continuity of movements and (ii) i ndicate the possible sources and destinations of fish approaching the mine. Marked differences in sources were apparent for two groups of sp ecies: terapontids originating from the lowland creek channels, and ch equered rainbowfish and ambassids originating from the floodplain and lowland billabongs. Identification of the relative contributions from these habitats will require additional monitoring effort.