A protected flow breaks the drought for golden perch (Macquaria ambigua) spawning along an extensive semi-arid river system

Abstract

Freshwater ecosystems are under extreme stress due to anthropogenic influences including changing climate, river regulation and water abstraction. Improving our understanding of the hydrological determinants of key life-history processes of fish, as well as the spatial scales over which these processes occur, is fundamental to inform effective recovery actions. We monitored the spawning response of native fish to a drought-breaking long-distance flow pulse that was protected from extraction by a legal intervention order in Australia's northern Murray–Darling Basin. Sampling sites were distributed across >1600 km of the Barwon–Darling River and three of its major tributaries. Larvae of the pelagophilic golden perch (Macquaria ambigua) were captured at all sites, with the size and age distribution indicative of both mainstem and tributary spawning. A mismatch between estimated hatch dates and river discharge at some locations suggested substantial flow-assisted dispersal from upstream spawning sites, although this was site-specific and more prevalent at downstream locations. Early life growth rates were the highest at tributary sites compared with mainstem sites, and within mainstem sites, golden perch grew faster in upper reaches compared with lower reaches. The present study provides insight into the environmental benefit of a post-drought protected flow event whereby connected lotic habitats promoted fish spawning and dispersal over a large spatial scale. Protection of future flow events should occur to support the conservation of golden perch and other pelagophil species, particularly following future drought periods which are forecast to become more intense and frequent.