Fish communities of Gulungul Creek - a landscape analysis. Phase 2: 'Second-pass' analyses of 1979-2001 Late-wet–Early-dry season data, June 2002
Internal Report 406
Bishop KA & Walden DJ
Supervising Scientist Division
About the report
This report follows closely on from the Phase 1 ‘First-pass’ report of October 2001 (Internal Report 405 – Bishop & Walden 2003). That report investigated changes in fish communities in Gulungul Creek between a baseline period (1978–1990) and a current-condition sample taken in April/May 2001. Of particular interest in that report were any obvious Scenario-1 mine-disturbance signals, and less specifically, any downstream-focused non-specific disturbance signals, which may be a mixed response to a range of disturbances (ie natural processes, Scenario-2 mine disturbances, and a range of other anthropogenic disturbances). To facilitate an interpretation of detected changes, the present investigation further explored baseline-to-current-condition shifts in community structure, and associated variability, through an examination of a diverse array of environmental correlates.
The key elements of the investigation were:
- an assessment of what habitat changes have occurred in the censusing sites since 1989
- an assessment of how the hydrology of the 2000–01 wet season varied from the baseline Wets
- an examination of a diverse array of hydrological and habitat correlates in order to:
- develop an understanding of background flow- and habitat-driven processes, and
- detect the presence of alternate post-1989 disturbances now operating in the creek (evidence of a breakdown in baseline environmental associations was the basis of the detection)
Between 1989 and 2001 a number of within-site habitat changes had occurred. It was considered that only two of the changed habitat variables had the potential to alter a structural feature of the fish communities (the number of species present). It was concluded that the influence on this feature of the particular magnitude of the habitat changes was quite low.
The 2000–01 Wet was a wet-wet, having characteristics (including the length of the prior dry season) different from all of the baseline wets. It was considered reasonable to expect that these unique features could have translated into unique alterations in structural features of the creek’s fish communities.
Understanding of background processes. The structured and detailed approach taken in the correlation analysis revealed major insights into the hydrology- and habitat-driven dynamics of the Late-wet–Early-dry season fish communities in Gulungul Creek. This is vital knowledge for interpreting detected changes, assessing the weakness of existing methods, developing conceptual models and recommending more-attuned detection strategies. In the process of the study it was recognised that the detailed information provided on hydrological correlates with the range of structural features of the fish communities, is likely to have high value for environmental-flow investigations across the wet-dry tropics of northern Australia.
Evidence of alternate post-1989 disturbances?
Conceptually, these disturbances could be natural, anthropogenic (e.g. runoff and discharges from Jabiru township, Scenario-1 and Scenario-2 mining disturbances) and/or semi-anthropogenic (eg vegetation density increases arising from the eradication of water buffalo).