Within-channel flows promote spawning and recruitment of golden perch, Macquaria ambigua ambigua – implications for environmental flow management in the River Murray, Australia

Abstract

Restoring fish populations in regulated rivers requires an understanding of relationships between hydrology and population dynamics. In the present study, spawning and recruitment of golden perch, Macquaria ambigua ambigua, were investigated in relation to flow in the regulated lower River Murray. All life stages were sampled in three successive years, with peak flows of 8500 (2004–05), 15 000 (2005–06) and 7000 ML day–1 (2006–07). Larvae occurred only in November/December 2005, and young-of-year fish only in early 2006. Counts of daily increments in otolith microstructure indicated spawning in late October/early November 2005. Back-calculated birth years for adults, derived from otoliths and compared with the hydrograph for the preceding 25 years, revealed the dominance of three year classes spawned in association with increased discharge in 2000, 1998 and 1996. In 2007, an additional year class of 1-year-old fish appeared, following spawning in 2005. In each case, strong recruitment followed spring–summer spawning, when peak flows were >14 000 ML day–1 and water temperatures would have exceeded 20°C. Restoration of within-channel flows of 15–25 000 ML day–1 from late spring through summer would promote spawning and recruitment and improve the resilience of golden perch populations in the lower Murray.