Differential impacts of a wildfire and post-fire sedimentation event on platypus and fish populations in a Victorian upland river

Abstract

Context Wildfire can affect freshwater ecosystems in many ways, notably when post-fire rainfall washes ash and sediment into waterways. Aims We investigated species-specific effects of bushfire and subsequent channel sedimentation on the abundance of platypus and fish populations in the upper Buffalo River, Australia. Methods Pre- and post-fire population surveys were conducted using fyke nets. Key results There was no evidence that fish numbers declined because of direct fire effects. However, native two-spined blackfish and Macquarie perch numbers dropped dramatically following post-fire sedimentation, whereas non-native redfin perch increased, most likely as a result of migration from a nearby lake. Platypus captures were consistently recorded at all survey sites both before and after the fire and sediment inflows occurred, with many juveniles being recorded in the first post-fire breeding season. Conclusions The platypus’s greater resilience to post-fire sediment inflows than that of native fish presumably reflects its reliance on lungs rather than gills and its ability to take refuge in burrows. It also has a broad diet, flexible foraging behaviour, is highly vagile and typically stores enough fat to support fasting for up to 2–3 weeks. Implications Management of fire-affected aquatic ecosystems must consider species-specific responses of freshwater vertebrates to fire.