Age, growth and retrospective stock assessment of an economically extinct sparid fish, Polysteganus undulosus, from South Africa

Age and growth of the endemic, reef-dwelling sparid, Polysteganus undulosus were determined by using archived otoliths collected in 1962 and 1963, before the fishery collapsed. Estimates of age ranged up to 20 years, but reproducibility of the age estimates was low because of stacking on the otolith margins in older fish. Validation of annual deposition of the opaque band indicated that active deposition occurred during late winter and spring. No difference in growth rate between the sexes was observed and the growth rate for the combined sexes was described by the following logistic equation: L_t = 942 mm TL/(1 + exp(-0.277 year^-1 (t - 5.178 years))). The age-at-50% maturity was 8.8 years. A retrospective stock assessment revealed that, although in the early 1960s, the yield-per-recruit was optimal, the spawning biomass of P. undulosus was already at 25% of its unfished level. This study thus suggests that management strategies for slow-growing, long-lived, aggregating reef fishes should go beyond optimising yield alone and pay particular attention to the status of the spawning stock.