Cross shelf variation in assemblages of Lutjanidae and Lethrinidae in the central Great Barrier Reef

In March 1993, fish traps were deployed on three reefs located across the continental shelf in the central Great Barrier Reef. One reef was nearshore (Pandora Reef), approximately 10 km from the coast; one on the midshelf (Rib Reef), approximately 50 km offshore; and one on the outershelf (Myrmidon), approximately 100 km offshore.Traps were deployed day and night on the protected leeward slopes of the midshelf and outershelf reefs in depths of 15-40 m, and on the leeward slopes of the nearshore reef in depths of 10-15 m (maximum depth of nearshore reefs). Traps were set in a random manner, at a minimum distance of 50 metres apart and ranged up to a few hundred metres apart in order to reduce possible overlap in the capture fields of adjacent traps. A total of 48 trap sets (2 days, 2 nights of sampling with 12 traps) were completed on the outershelf, 24 trap sets (1 day, 1 night of sampling) were completed on the midshelf and 36 trap sets (1 day, 2 nights of sampling) were completed inshore.'Day' set traps were set between 05:30 h and 08:30 h and were hauled from 16:30 h onwards, with sorting and processing usually completed by 18:30 h. Soak times during the day varied from 9 to 11 h. 'Night' set traps were set between 16:30 h and 18:30 h, left overnight and were hauled from 05:30 h onwards, with sorting and processing of trap catches usually completed by 08:30 h. 'Night' soak times varied from 12 to 14 h.The catch of each trap was identified to species, measured to the nearest millimetre, then tagged and released. This study was undertaken to examine and quantify the distribution and abundance of species of the Lutjanidae (snappers) and Lethrinidae (emperors), given the extremely variable physical environmental conditions occurring across the continental shelf in the central Great Barrier Reef region.