Knowledge of Age and Natal Origin is Fundamental to Informing Flow Restoration and Measuring Outcomes for Native Fish

In regulated rivers, restoration of flow regimes to benefit native fish requires an understanding of relationships between hydrology, life history and population dynamics. In Australia’s Murray-Darling Basin, the spawning and recruitment of golden perch (Macquaria ambigua ambigua) constitute common objectives of flow restoration.  Nevertheless, to associate biological response with flow, and adaptively manage flow regimes, an understanding of when and where fish originated is fundamental.

Microstructural and chemical analyses of fish otoliths provide powerful tools for determining the spatio-temporal provenance of fish. We demonstrate how these tools can be used to retrospectively elucidate the spawning date and natal origin of cohorts of golden perch in the lower River Murray in relation to hydrology.

Daily and annual growth increments in otolith microstructure and strontium isotope ratios indicate that golden perch in the lower River Murray are often not spawned locally, but rather, result from spawning that occurs over a broad period (October–January) in regions 100s–1000s kilometres upstream. These data enable the explicit spatio-temporal association of spawning and recruitment with flow, including environmental water allocations. Ultimately, to achieve positive outcomes for native fish, flow restoration must consider recruitment dynamics at appropriate scales.