Effect of an artisanal fishery on the fish and urchin populations of a Kenyan coral reef

An investigation of the effects of artisanal fishing on coral reef fish assemblage structure was undertaken through a comparison of fish stocks on 2 apparently identical sets of reefs, one (within the Kisite Marine National Park) on w h c h all fishing is prohibited, and one (within the Mpunguti Marine National Reserve) on which artisanal fishing only is allowed. Replicate visual censuses of fish along 250 X 10 m band transects at 6 intensive study sites demonstrated that there were large differences in population density and biomass of the principal families of conunercial reef fish (Lethrinidae, Lutjanidae and Serranidae) between the unfished marine park area and the adjacent intensively fished marine reserve area, with abundances of commercial species within the park (unfished) being up to 10 or more times those in the reserve (fished). In addition, 6 species of butterflyfish (Chaetodontidae) and 2 species of triggerfish (Balistidae) were significantly more abundant on shallow and/or deep transects within the park. For most species of commercial fish, larger individuals were observed in the park than in the reserve, an effect expected from greater fishing pressure within the reserve. In contrast. smaller Cephalopholis spp. (Serranidae), 1 species of butterflyfish, and sea urchins (mostly Echinornetra mathaej) were significantly more abundant on transects in the reserve. It is suggested that these increased abundances may be second order effects (mediated by reduced competition or predation) of increased fishing pressure. In particular, opposing differences in abundance of predatory triggerfishes (Balistidae) and emperors (Lethrinidae) and of sea urchins are compatible with the view that higher populations of sea urchins may sometimes occur where the densities of their predators are reduced. Overall results allow an assessment of the effect of the artisanal fishery on the fish stocks, and provide a measure of the effectiveness of protection afforded by the marine park.