Demography of Australian bass, Macquaria novemaculeata (Perciformes, Percichthyidae), in the Sydney Basin

Abstract

A mark-recapture experiment showed Australian bass to be sparsely distributed through sheltered parts of their habitat, but no significant differences in population density among major habitat categories were detected by catch-per-effort analyses. Total mortality, estimated from the catch curve, was low (Z = 0.28). Tabular and graphical calculations of annual production in a lagoon resulted in similar low estimates (0.84 g m^-2 year^-1), and a strikingly low P/B (annual production/biomass) ratio (0.19) results from the bass' catadromous life history. Populations of bass in the Sydney Basin showed declining recruitment, distribution restricted by impoundments, and increasing mortality attributable to exploitation and habitat damage during the period 1977-82. Estimates of initial cohort abundance indicated that recruitment and subsequent year-class strength are positively related to the level of flooding in the spawning months, but flooding is suppressed by dams. Population declines and continuing environmental degradation give cause for concern over the status of bass populations.