Is climate change driving recruitment failure in Australian bass Macquaria novemaculeata in southern latitudes of the species range?

Abstract

Flow regimes have been fundamentally altered in many of the world’s river systems. There is a need to restore components of natural flow variability to protect freshwater biodiversity. The Australian bass is a long-lived, catadromous percichthyid endemic to coastal drainages of south-eastern Australia. Little is known of the timing and magnitude of flows considered important for recruitment and growth of individuals in southern latitudes of the species range. Herein we generate nearly 50 years of otolith-derived recruitment and growth histories for Australian bass and relate these to hydrologic, climatic and demographic variables. We found that younger Australian bass grew fastest in years following a cooler spring, whereas the growth of older fish exhibited little response to temperature. Australian bass year class strength was positively related to high flows in spring and in a negative curvilinear way to spring temperature. A lack of suitable natural flows in spring may be responsible for little to no recruitment of Australian bass in the Genoa River over the past two decades. Based on our findings, the continuing trend of lower rainfall and higher temperatures, coupled with river regulation in some systems in the region, will likely result in depressed juvenile growth and prolonged periods of recruitment failure over the medium to longer term, with significant implications for the viability of populations.