INFLUENCE OF SEAWEED FARMING ON THE DIVERSITY AND ABUNDANCE OF WILD FISH IN KIBUYUNI, SOUTH COAST KENYA

Abstract

Several seaweed farms have been established at various fishing villages in the south coast of Kenya. This study was conducted from September 2013 to July 2014 at Kibuyuni where two species of red algae, Eucheuma denticulatum and Kappaphycus alvarezii are farmed. The study hypothesized that seaweed farms might generate ecological benefits by creating habitat and providing a food source for wild fish and hence fish assemblages would exhibit greater diversity and abundance in closer proximity to the seaweed farms. The aim of this study was to determine the influence of seaweed farming on the abundance and composition of wild fish species in Kibuyuni. Fish sampling for biological data on species, size and food habits at a farmed site and an unfarmed site was carried out using traps and Underwater Visual Census (UVC). Fish abundance, species richness, species diversity (H'), Fulton condition factor (K), diet and trophic status were determined and compared between sites. Results from trap sampling showed that the fish species abundance was significantly associated with the unfarmed site compared to the farmed site (p < 0.05) contrary to expectation. UVC results indicated that fish species abundance was significantly associated with the farmed site compared to the unfarmed site (p < 0.05) indicating that seaweed farms enhanced fish abundance. The H' results from trap and UVC sampling methods were not significantly different between study sites, (p = 0.082295) and p = 0.19089) respectively, suggesting that seaweed farms had no influence on species diversity. The K results of four out of the six common fish species were not significantly different between study sites. However, the K value of Scarus ghobban was significantly higher at the unfarmed site compared to the farmed site (p < 0.05) suggesting that it might have benefited more from other food sources at the unfarmed site. Conversely, the K value of Siganus sutor was significantly higher at the farmed site compared to the unfarmed site (p < 0.05) suggesting v that it might have benefited from the farmed seaweeds. The trophic status results indicated non-significant differences in proportions of carnivores (p = 1.000), herbivores (p = 0.651), and omnivores (p = 0.672) between sampling sites, probably due to fish biomass exchange between the study sites. Herbivores were more dominant than carnivores and omnivores in the study area respectively, suggesting that the farmed seaweeds provided readily available food to some of the herbivorous fishes. The frequency of occurrence of K. alvarezii which was only found at the farmed site in the stomach contents of fish at both sites was not significantly different (p = 0.812) thus providing direct evidence of fish biomass transport between the study sites. In this regard, creation of fishing buffer zones around seaweed farms is recommended to limit possible overfishing of targeted species by artisanal fishers owing to possible fish biomass spill-over from seaweed farms to adjacent areas subjected to fishing. There is also need to conduct studies on the grazing impact of wild fish on the growth and yield of the farmed seaweeds.