A Survey of the Coral Reef Fish Communities on the Kenyan Coast.
Underwater censuses were used to measure species richness, abundance, and biomass of coral reef fish at nineteen reef slope study sites on the Kenyan coast, in 1987/1988. The survey was designed to examine the structure of the coral reef fish communities in relation to protection, fishing, sediment run-off from rivers, sea urchins, and collecting for the aquarium trade. A further twelve reefs were studied, but no censuses were carried out due to poor visibility or a lack of coral substrate. While species richness was highest in Marine National Parks where no fishing or collecting is allowed, the same was not true for fish abundance, or for biomass of commercially important fish. Some of the highest densities and weights of fish were recorded from the Marine National Reserves where traditional fishing methods are allowed. Standing stocks (biomass) of commercially important fish were negatively correlated with fishing intensity, and localized overfishing was evident near centres of high human populations. On the sparsely populated northern coastline, non-coralline reefs support exceptionally high standing stocks, due to minimal fishing pressure, and possibly a greater input of nutrients. Areas with higher fishing intensities had smaller standing stocks but not comparably smaller abundances. This suggests that more intense fishing is reducing average fish size. In genera] the results indicate that overfishing is not a major problem on Kenya's reef slopes. Two factors, siltation from rivers and dynamite "fishing" have a major impact on the fish communities. Reefs badly damaged from dynamiting in the Shimoni area, including Mako Kokwe in the Kisite Marine National Park, have negligible amounts of living hard coral and are characterised by a low species richness of fish, and exceptionally low densities of fish. For example the biomass of commercially important fish at Mwamba Midjira, which has been severely damaged by dynamiting, was only one tenth of the biomass recorded at Kisite, a neighbouring reef where no dynamiting occurs. Malindi Marine National Park has been subjected to a heavy influx of sediment from the Sabaki river since the early seventies. Coral die-off was evident, and densities and biomass of fish were of a similar magnitude to dynamited reefs, despite the prohibition of all fishing and collecting for the last 20 years. Similarly, coral die-off and sedimentation was apparent at survey sites close to the Tana river mouth, where fish censuses were not possible due to high silt content in the water. No correlation between sea urchin densities and predatory fish (15 species) densities was detected, suggesting that high fishing pressure is not responsible for high densities of sea urchins. High densities of sea urchins were observed on damaged (e.g. from dynamiting) reefs; possibly urchin survival is enhanced in the absence of corals. The total abundance of fish collected for the aquarium trade (48 species) did not differ significantly between a protected site and a site where collecting occurs, suggesting that collecting aquaria fish is not depleting stocks. However, several collectors use methods that are destructive to the reef substrate. In summary, it is clear that the effects of sediment offload from rivers and the use of dynamite far outweigh the effects of protective management and fishing on Kenya's coral reef fish communities. In the face of these impacts, marine park status is no guarantee that a high abundance and biomass of reef fish will be maintained, as exemplified by Malindi and Mako Kokwe Marine National Park sites. Standing stock estimates of commercially important reef fish are high in several reef areas where fishing pressure is low, except where sedimentation and dynamiting occurs. These two major problems have long been recognised (IUCN/UNEP 1985), but no policies have arrested their destructive effects. For the future of Kenya's coral reef fish, conservation action must address these issues.
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| Format: | Report biblioteca |
| Language: | English |
| Published: |
World Wide Fund for Nature (WWF International)
1988
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| Subjects: | Coral reefs, Reef fish, Fishery surveys, Sedimentation, |
| Online Access: | http://hdl.handle.net/1834/7411 |
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