Distribution and abundance of herbivorous grazing fishes in the central Great Barrier Reef

A census of herbivorous grazing fishes was undertaken on 9 reefs located across the continental shelf in the central region of the Great Barrier Reef between July 1982 and February 1983. The reefs chosen for surveys were: 3 inshore reefs (Pandora Reef, Phillips Reef and Lorne Reef); 3 mid-shelf reefs (Rib Reef, John Brewer Reef and Lodestone Reef); and 3 outer shelf reefs (Myrmidon Reef, Dip Reef and Bowl Reef). For the mid- and outer shelf reefs, surveys were conducted within each of five reef zones: the windward reef slope, the windward reef crest, the reef flat, the lagoon and the back reef. The inshore reefs lacked distinct patterns of zonation and the perimeters of each reef were censused and treated as a single zone. The census was restricted to a list of 51 species from four families: Acanthuridae (24 species), Zanclidae (1 species), Scaridae (20 species) and Siganidae (6 species). Each species was also assigned to a feeding guild.A visual census technique was used for surveys and abundance was recorded using a log 3 abundance scale from 1 to 7. Each census dive through a zone was 30 minutes long and a distance of between 300 m and 400 m was covered, depending on conditions. Individuals within approximately 5 m either side of the diver were recorded. Juveniles (