Response of diurnal and nocturnal coral reef fish to protection from fishing: an assessment using baited remote underwater video

Diel variation is known to alter the composition and structure of reef fish assemblages. What is unknown is how nocturnal fish assemblages respond to closed fishery area management. Diurnal and nocturnal reef fish assemblages at the Houtman Abrolhos Islands, Western Australia, were studied using baited remote underwater stereo-video systems (stereo-BRUVs). Surveys were conducted during the day and at night (using blue illumination) from three sites inside and three sites outside a closed fishery area (CFA). The relative abundance of 116 fish species from 41 families was recorded. Significant changes were observed in fish assemblage structure from day to night (driven by high dispersion at night) and in areas open versus closed to fishing (driven by increased abundance within the CFA). The effect of protection from fishing was consistent for both diurnal and nocturnal fish assemblages. Closer examination of six targeted fish species showed that their response to diel changes and the absence of fishing pressure varied from species to species. The targeted fishes Pagrus auratus and Glaucosoma hebraicum were sampled during the day and at night with both species responding positively to protection from fishing. Results suggest that the inclusion of diurnal and nocturnal fish assemblage data will provide an improved ability to assess the effectiveness of closed fishery area management.