IMPACTS OF PREDATOR DEPLETION BY FISHING ON THE BIOMASS AND DIVERSITYOF NONTARGET REEF FISH COMMUNITIES

An understanding of the indirect effects of fishing on predator-prey r elationships is required for the development of valid multispecies yie ld models for reef fisheries and for determining the factors governing fish community structure at larger scales. We used an underwater visu al census technique to examine the indirect effects of fishing on the biomass and diversity (species richness) of reef fishes in a series of ten traditional Fijian fishing grounds (qoliqoli) subject to a range of fishing intensities. All members of the families Chaetodontidae (bu tterflyfishes), Labridae (wrasses), Lutjanidae (snappers), Mullidae (g oatfishes), Scaridae (parrotfishes) and the sub-family Epinephelinae ( groupers and coral trout) which could be reliably identified were cens used. Each species censused was assigned to one of three trophic group s: herbivore, invertebrate feeder or piscivore. The biomass of all pis civorous fishes and of large (> 30 cm) piscivorous fishes differed sig nificantly between qoliqoli and was significantly correlated with fish ing intensity. However, the biomass of piscivorous fishes was not corr elated with the biomass or diversity of their potential prey (which we re not targeted by the fishery). This suggested that the indirect effe cts of fishing did not have an important bearing on fish diversity or biomass and that predation by the target species did not play an impor tant role in structuring these Fijian reef fish communities. The resul ts contrast with those from a number of studies at smaller scales and provided further indications that the structure of reef fish communiti es is not governed by a single dominant process, but by a range of pro cesses which operate on different scales in different circumstances.