Effects of fishing effort and catch rate upon the structure and biomass of Fijian reef fish communities

1. An improved understanding of fishing effects is required to assess the sustainability of existing fishing practices and to determine the ecological implications of offering fishing concessions in marine reserves. 2. The effects of fishing were investigated in six Fijian fishing grounds (qoliqoli) subject to different fishing intensities. 3. A visual census technique was used to determine the structure and biomass of the shallow-water reef fish communities targeted by the fishers. 4. A supervised voluntary logbook scheme was used to assess the size and composition of yield from the qoliqoli. 5. The fish communities in the least intensively fished qoliqoli were significantly different from fish communities elsewhere. The significance of these differences was attributable to the greater biomass of invertebrate feeding and piscivorous fishes in the least intensively fished qoliqoli. 6. Annual yields of herbivorous fishes ranged from 0.3 to 5.2% of the biomass estimated by visual census. There were no significant differences in herbivore biomass among qoliqoli subject to different fishing intensities. 7. The biomass of invertebrate feeding fishes was significantly higher in the least intensively fished qoliqoli. The biomass of invertebrate feeding/piscivorous fishes was significantly higher in the two least intensively fished qoliqoli. 8. In the two least intensively fished qoliqoli the estimated annual yields of invertebrate feeding and invertebrate feeding/piscivorous fishes did not exceed 4% of the biomass estimated by visual census. However, yields of these trophic groups approached 20% of biomass in the intensively fished qoliqoli where biomass was significantly lower. 9. The fishing effects observed were primarily attributed to significant differences between the fish communities in the least intensively fished qoliqoli and all others. Thus, at higher fishing intensities, the biomass of target species provided a poor index of relative fishing pressure. 10. The results suggest that the annual removal of 5% of fish biomass may cause significant structural changes in reef fish communities. Thus, it is important to ensure that fishing concessions and poaching activities are carefully regulated in marine reserves.