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Ecological Studies on the Freshwater Fishes of the Alligator Rivers Region, Northern Territory
Volume I Outline of the Study, Summary, Conclusions and Recommendations

Research Report 4, Volume I
Bishop KA, Allen SA, Pollard DA & Cook MG
Supervising Scientist 1986
ISSN 0810-9966
ISBN 0 644 01295 1 (Volume 1)
ISBN 0 644 01294 3 (3 Volume Set)

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About this document

The tropical climate of the Alligator Rivers Region of the Northern Territory has a distinctive Wet-Dry cycle resulting in seasonal flows in the creeks and rivers of its catchments. The present study, begun during August 1978, aimed at developing an ecological monitoring system that would detect changes in freshwater fish communities brought about by recent uranium mining and processing in the lowlands of the ARR. The broad objectives were:

  1. to describe fish community structure at sites from a longitudinal array of habitats and show the seasonal changes in structure;
  2. to collect environmental and biological information on the fish species and study sites for use in interpreting changes in community structure; and
  3. to advise on the best practicable approach for detecting, predicting and minimising adverse effects on the Region's fish fauna due to uranium mining and processing operations

A large multi-dimensional matrix of information was generated from sites ´ habitats ´ seasons ´ habitat-structural and physico-chemical variables ´ species ´ lengths ´ weights ´ gonad weights and stages ´ stomach contents and fullness ´ presence of macroparasites.

Distinctive fish communities were present in the upper reaches of the Arnhem Land escarpment and the lower reach floodplain zones. These zones were major Dry season refuge habitats for fish. Distinctiveness was most likely the result of the substrate preferences (including aquatic plants) of some species and allowed recognition of migrations of fish between the escarpment and flood plains as Wet season flows across the lowlands linked the zones. The community structure of lowland habitats in the Wet season showed a flux between the community structures of the two Dry season refuges. In the Wet season the lowlands were very important breeding and feeding areas. Fish movement in the ARR appeared to be a classic response to temporal and spatial patchiness of resources.

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