• Corresponding Editor: L. B. Crowder


The application of no-take marine-reserve status to an area is expected to increase spawning-stock biomass of species targeted by fisheries, and to help sustain fisheries external to the reserve. However, empirical evidence on rates and patterns of increase of density and biomass of target species following closures to fishing, and of decrease when reserve status is removed, remains rare. We have monitored density and biomass of large predatory coral-reef fish (Serranidae [Epinephelinae], Lutjanidae, Lethrinidae, and Carangidae, as a group) visually in two small no-take marine reserves and at two control (open to fishing) sites in the Philippines from 1983 to 2000. At Sumilon reserve a complex history of management allowed 13 measurements of density and biomass at durations of reserve protection of −3 yr (i.e., fished for 3 years after reserve status removed) to 9 yr. At Apo reserve 13 measurements were taken at durations of protection of 1–18 yr. We recorded 11 significant (P < 0.05) changes in density at the four sites over the 17 years, three declines and eight increases. All three significant declines occurred when reserve protection was removed. Four of the eight significant increases occurred when reserve status was applied. This represents some of the best evidence currently available that application of marine-reserve status causes increases in abundance of target species. Three of the four significant increases in density required 4–6 yr of protection. Significant positive linear correlations of mean density of large predators against years of reserve protection were observed at both reserves. The pattern of increase of mean biomass against years of reserve protection was exponential, with biomass initially increasing more slowly than density. Density and biomass increased by factors of 12.2 and 17.3, respectively, during 18 yr of continuous protection in Apo reserve. At Sumilon Island three bouts of unregulated fishing of 1.5–3 yr duration eliminated density and biomass gains accumulated over 5–9 yr of marine reserve protection.