Many coastal riverine fish species migrate from freshwater into the sea to complete their life cycles. During the marine phase, these fish disperse among river basins along the coast, leading to a ‘metapopulation’ structure, where spatially discrete populations are connected by dispersal and may act as ‘sources’ or ‘sinks’ of new recruits. Demographic dependencies among connected local populations have profound implications for population viability. For example, cumulative increases in the number of local populations functioning as recruitment sinks due to disturbance (e.g., river regulation, fire) may drive species extinctions via ‘recruitment dilution’, as the loss of recruits to sinks becomes greater than the supply from remaining sources.
A shortcoming of most water management regimes is that river basins are implicitly considered as non-interacting entities, with a focus on reach-scale targets for key ecological assets and processes. This fails to recognise the critical demographic dependencies among local populations and the cumulative, broad-scale impacts that may drive vulnerable species towards extinction. In this presentation, we describe early results of a project that aims to develop a conceptual management framework that incorporates the principles of metapopulation theory to account for the spatial structure, connectedness, and temporal dynamics of fish metapopulations.