Determinants of year class strength and growth of estuary perch Macquaria colonorum in a highly regulated system

Abstract

Because fish are sensitive indicators of flow alteration, a detailed knowledge of the response of fish to flows is crucial to the sound management of regulated river systems. Estuary perch are a catadromous, long-lived, estuarine-dependant percichthyid. Here, we relate otolith-derived recruitment and growth histories of individuals of the species in the highly regulated river to hydrologic, climatic and demographic variables. Year class strength was positively related to high flows over the spawning season and in a negative curvilinear way to flows in the austral winter, in addition to cooler annual temperatures in general. Flows benefiting recruitment of estuary perch are best timed to occur in austral winter in addition to the spawning season. Without a substantial increase in the volume of environmental water, large recruitment events will remain dependent on sizable natural catchment-generated inflows. On the basis of our findings, climate change predictions of lower rainfall and higher temperatures in south-east Australia may result in prolonged periods of recruitment failure in the region, and have significant implications for the viability of not only the population of estuary perch in the Snowy River, but also southern populations of the species in general.