The application of no-take marine reserve status to an area is expected to increase abundance and average size of individuals of species targeted by fisheries. The majority of the evidence supporting such expectations still involves comparisons of abundance at the one time of sites with and without marine reserve protection. Very few studies have data on the abundance and size structure of species targeted by fisheries in an area before reserve status is applied. Quantitative estimates of density and biomass of coral trout, Plectropomus spp., the major target of the hook and line fisheries on the Great Barrier Reef (GBR), Australia, on inshore fringing reefs of the Palm and Whitsunday Island groups, central GBR, are provided for 3–4 years before (1983–1984), and 12–13 years after (1999–2000) the establishment of no-take reserves in 1987. Quantitative estimates of density and biomass of coral trout in areas open to fishing were also collected in 1999–2000 at these two island groups. Density and biomass of coral trout increased significantly (by factors of 5.9 and 6.3 in the Palm Islands, and 4.0 and 6.2 in the Whitsunday Islands) in the reserve sites, but not the fished sites, between 1983–1984 and 1999–2000. In 1999–2000, density and biomass of coral trout and a secondary target of the fisheries, Lutjanus carponotatus, were significantly higher in the protected zones than in the fished zones at both island groups. The density and biomass of non-target fish species (Labridae, Siganidae and Chaetodontidae) did not differ significantly between reserve and fished zones at either island group. This is the most convincing data to date that the management zoning of the world's largest marine park has been effective, at least for coral trout on inshore reefs.