The Use of Bioenergetic Models to Assess Fish Population Carrying Capacity and Restoration Potential in a Regulated Floodplain River System

River regulation and associated loss of channel-floodplain connections has greatly reduced the productivity of large river systems throughout the world. In many regions restoration efforts are now underway to try and reverse these declines. A major focus for these efforts, both in terms of scientific research and management actions, has been directed towards restoring flows associated with habitat restoration and critial life-history events. Much less attention has been given to restoring flows that increase food-resources and carrying capacity. Here we ask whether populations of high-trophic order native fish in a large regulated lowland river in southeastern Australia (the River Murray) are energy limited, either due to altered rates of production or altered energy flows, for example from competition with introduced species. We assemble information on historical and contemporary native fish abundance and historic and present day estimates of basal energy production, and combined these data using simple food-web models to quantify carrying capacity. Our initial results suggest contemporary levels of riverine production are insufficient to support historical biomass estimates, and hence pose constraints on the outcomes achievable from current restoration actions. We discuss the implications of these results in terms of environmental flow management, and future research needs.