Phil Hickley

The status and future of the Lake Naivasha fishery, Kenya

Lake Naivasha is a freshwater lake situated in the eastern rift valley of Kenya. Only five species of fish are present, all of which have been introduced. They are Oreochromis leucostictus, Tilapia zillii, Micropterus salmoides (largemouth bass), Barbus amphigramma and Poecilia reticulata (guppy). The first three of these form the basis of an important gill net fishery and bass are also taken by rod and line for sport. Barbus are occasionally caught by dip net. Actual and potential yields for the Lake Naivasha fishery are discussed and the fishery is shown to be under-performing. The feeding regimes of the commercially exploited fish were examined in the context of available food supply, in particular the benthic fauna. Small bass depend heavily on Micronecta and large bass mostly take crayfish. Detritus predominates in the diet of Oreochromis leucostictus and Tilapia zillii but the former also eats algae and the latter, Micronecta and macrophyte. Various food resources, especially the benthos, appear to be under-utilized and so it is possible that further species could be introduced to enhance the commercial fishery.

The use of PHABSIM in the management of water resources and fisheries in England and Wales

Abstract The PHABSIM technique enables the quantitative prediction of suitable physical habitat in a river reach for chosen species and lifestages under different river flow scenarios, based on field measurements, hydraulic calibration, and species physical habitat preferences (depth, velocity, and substrate). The technique was recently transferred to the UK from America, and is now being tentatively used by the Environment Agency to support water resources decision making in England and Wales. Applications to date have concentrated mainly on fish habitats, investigating the potential relative impacts of changing reservoir or borehole releases, abstractions, and water transfers. Although the application is both expensive and time consuming, it is nonetheless proving to be a valuable tool, and is the subject of ongoing research to further develop its applicability and transferability. Although taking no account of water quality, sediment transport, or other constraints on habitat suitability and population, the technique appears to have significant potential when used in combination with other habitat protection aids.

The dynamics and ecology of exotic tropical species in floating plant mats: Lake Naivasha, Kenya

The floating water fern Salvinia molesta has occurred in Lake Naivasha since the early 1960s and during this period has obstructed fishing activities and navigation. In recent years the extent of Salvinia has declined markedly. Since 1988, a second floating weed, Eichhornia crassipes (water hyacinth), has colonised the lake. Salvinia formed large mats around the edges, bays and lagoons and had very few plant or invertebrate species associated with it. Mats of E. crassipes, however, support a greater abundance and variety of animal and plant species, which shows a relationship with mat size. This seems to have facilitated plant succession but without a zonation typical of the classic hydroseral sequence for the lake.

Economic Gain versus Ecological Damage from the Introduction of Non-native Freshwater Fish: Case Studies from Kenya~!2008-10-24~!2008-11-03~!2008-12-04~!

Non-native freshwater fish species that have been introduced to the inland waters of Kenya are listed and the consequences of stocking such fish are reviewed. Original species composition and lake ecosystem function can be detri- mentally affected but, also, the introduction of non-native species can result in significant economic benefit. In the context of impact on recipient fish communities and the performance of exploited fisheries, the merits or otherwise of alien fish species introductions are discussed with the aid of two case histories; lungfish (Protopterus aethiopicus) in Lake Baringo and a number of species, particularly carp (Cyprinus carpio), in Lake Naivasha.

Bathymetry of Lake Bogoria, Kenya

ABSTRACT This paper presents the first bathymetric map for the approximately 17 km by 2 km alkaline Lake Bogoria situated in the eastern Rift Valley of Kenya. Longitudinal and transverse cross sections of the lake are also provided. Northern, central and southern basins of the lake had maximum depths of 5.9 m, 10.2 m and 8.4 m respectively. Average depth was 5.68 m and volume was calculated to be 164 × 106 m3.