Fish diversity and fisheries in the Okavango Delta, Botswana

Abstract

During the June 2000 AquaRAP survey of the Okavango Delta, the fish team was responsible for establishing fish biodiversity and abundance in the system, and also for addressing the perceived conflicts between users of the fish resources. A total of 64-66 species out of the 71 species previously recorded from the system were taken in 74 collections in this brief survey, indicating that sampling methods and selected sites effectively covered the diversity of Delta habitats. There were differences between the four focal areas (Upper Panhandle, Lower Panhandle, Moremi Game Reserve, and Chief 's Island) and these indicate real differences in community diversity, although as the focal areas were at different phases in the flood cycle, this may have affected our collection efficiency. The highest diversity was at Shakawe (Upper Panhandle), where the 54+ fish species recorded included predominantly rheophilic species in the main river. The apparent absence of tigerfish, H. vittatus, from the other three sampling areas is a striking example of the difference between the main river fauna and the smaller stream habitats downstream. Other species common at Shakawe and absent from catches in the other areas in the AquaRAP survey were Barbus radiatus Peters, Labeo cylindricus Peters, Nannocharax macropterus and Chiloglanis fasciatus. Guma Lagoon had the lowest diversity, due in large part to the absence of riverine habitats with well-defined banks that could be effectively sampled. The low oxygen levels in the area because of floodwater flushing under the extensive papyrus mats probably also have an impact. At Xakanaxa (Moremi Game Reserve), a broad range of habitats was available for sampling, resulting in high diversity. One undescribed species of Aplocheilichthys was collected at several sites at Xakanaxa. The variety of habitats available for sampling was lower in the Chief 's Island area, resulting in a lower total species count, but the diversity in the individual samples from the well-vegetated riverine and flow-through lagoon habitat was very high. Noteworthy was the presence of five of the six Serranochromis species occurring in the Delta in a single gillnet catch. The addition of several new distribution records for the Delta in the present survey shows that scientific knowledge of finer scale distribution patterns within the Panhandle and Delta is still incomplete. No exotic fish species were found in the system. If there are serious attempts to introduce fish farming into the region, the species used should be indigenous. Exotics such as Oreochromis niloticus (L.) should not be permitted under any circumstances. There are conflicts of interest between commercial fishermen and the recreational/tourist fishery. Tourist lodges and commercial fishing sites are adjacent to one another and the two groups share the same fishing grounds and compete for the same fish resource, particularly the large cichlid species. Options for management include setting and enforcement of regulations to protect stocks and/or segregation of fishing areas to separate commercial fishing and angling tourism. Regulations to be considered for implementation include licensing with strict sets of conditions, prohibition of use of nets blocking lagoon entrances, limitation of effort, closed seasons, limitation of net mesh sizes, limitation on nighttime fishing activities, and segregation of fishing areas. The current conflicts between commercial fishermen and angling tourist lodge operators in the Panhandle area in particular are not a result of overfishing. The issues at stake are economic, social, and environmental, and the impacts of commercial fishing and angling tourism need to be considered. Before management decisions can be taken, a thorough review of all issues is needed, including not just fisheries aspects but other users of the Panhandle resources. Recommendations for further research include the economic viability of the commercial fisheries, the economic status of the angling tourism industry, the scale of the subsistence fisheries sector and its role in the nutritional status of villages in the area, the extent of the fishable area in relation to the overall area in the Panhandle, continuation of the Fisheries Unit's stock assessment research, collection of data on angling catches, further ecological research, environmental impacts of tourism and commercial fisheries operation, commercial fisheries impacts, tourism impacts, fish biodiversity and distribution, impact of fish kills on the fish populations, and fish farming.