Oral Presentation Australian Society for Limnology Congress 2013

A step too high – understanding natural barriers to fish passage along the upper Murrumbidgee River. (#55)

David Sangston 1 , Fiona Dyer 1 , Evan Harrison 1
  1. Institute for Applied Ecology, Bruce, ACT, Australia
The spatial distribution of fish in unregulated rivers is controlled by natural barriers.  While channel morphological features (such as marked changes in stream gradient or substrate character) define natural barriers, their impacts are both flow and species dependent.  The flow dependence of barrier impacts means that river regulation has the potential to seriously affect the distribution of natural barriers along a river.  Most studies relating to natural barriers in streams are from North America where fish have different characteristics from Australian fish. Few Australian studies have investigated the effects of natural barriers upon riverine fish.  Murray cod Maccullochella peelii peelii are ‘keystone’ native Australian fish that are known to migrate hundreds of kilometres to spawn in lowland rivers.  It is not known if similar behaviour occurs in upland rivers, but it is likely to be affected by the presence of natural barriers.  The aim of this study was to characterise natural barriers to Murray cod migration along the Murrumbidgee River in the ACT, identify how those barriers respond to flow changes and make predictions about their impacts upon Murray cod movement.  Detailed 3D maps of 30 potential barriers were produced from survey data collected during low flow conditions.  Velocity data was also collected for each potential barrier.  Physical characteristics of the barriers were highly variable and it is likely that sequences of barriers may prove insurmountable for Murray cod.  Additional extraction of water from the river may have implications for Murray cod passage along the Murrumbidgee River in the ACT.