An analysis of Nigerian freshwater fishes: those under threat and conservation options

The study assessed qualitatively the threat status of all nigerian freshwater fishes using such criteria as rarity, size at maturity, mode of reproduction, human population density, habitat degradation, pollution and range of each species among others. The biology of 48% (129n) of nigerian freshwater species is not well known. Of the 266 known freshwater fishes, 47 species represented 17% are critically endangered, 15 (5%) are endangered , 8(3%), are vulnerable while 23(8%) are near threatened. The paper suggests increased basic knowledge of threatened species and conservation policy along three lines public awareness, legislation and creation of national parks, aquaria and reserves as measures needed to ensure the conservation of the fishes

News from Academy Bay

The 25th anniversary of the Galapagos National Park. Fire at the Darwin Research Station. The control of introduced mammals. Good news about the Hood tortoises. The endangered land iguanas. Penguins, cormorants and flamingos in 1984. A workshop on national parks. International conservation award to Secretary Ripley. Visits and events at the Charles Darwin Research Station.

1978 Fisheries statistics - Kariba

Fishery statistics for 1978 are presented for: (1) total production; (2) effort and landings; (3) gill-net fisheries production landings and purchases; (4) monthly percentage composition of catch for Kariba area; (5) African camp effort statistics: (6) sardine fisheries.

An assessment of mussel mortality caused by a drop in the water level of Lake Kariba

The level of Lake Kariba steadily fell during the period 1 June 1979 to 2 Feb 1980, except for a 2-wk period during Dec when it was allowed to rise slightly. Following this the level was again drawn down in anticipation of the Upper Zambezi flood water reaching the lake. At its highest level in June 1979 the lake was 487.42 m above sea level but by Feb 1980 it had dropped to 484.53 m, a total drop of 2.89 m. This left a considerable area of exposed shoreline and a large number of stranded mussels. This report presents the results of an attempt to estimate the mussel mortality, carried out from 28 Jan to 1 Feb 1980. The study area extended from the Charara river mouth to Andora harbour with a total of 24 stations.

Aspects of the ecology of the crustacean zooplankton in the Sanyati Basin, Lake Kariba

Investigations on the zooplankton in Lake Kariba were carried out as part of a broader programme investigating components of the sardine, Limnothrissa miodon, food chain and factors affecting their productivity. This report deals mainly with the crustacean zooplankton, Bosmina longirostris and Mesocyclops leuckarti, which are the most important species in the sardine's diet. Factors which influence the number and distribution of the zooplankton are discussed. The relationship between the zooplankton and Limnothrissa are also briefly discussed.

An evaluation of mark and recapture techniques for estimating tigerfish biomass in Lake Kariba

The effectiveness of 2 mark and recapture techniques was evaluated using tiger fish, Hydrocynus vittatus. The 2 techniques used were: tagging with a plastic tag and fluorescent spray marking. While the tagging method resulted as the logical method to use within the constraints of the tiger fish study, it cannot be considered completely reliable for the estimation of population size in Lake Kariba.

Report on the 1980/81 angling census in the Sanyati Gorge, Lake Kariba

The angling census carried out in the Sanyati Gorge, August 1980 - March 1981, is reported. The results are compared to those obtained in the 1973 census. The objectives of the census were: 1) to determine the extent of angling mortality on tigerfish (Hydrocynus vittatus) thereby quantifying this previously neglected component of total mortality; and 2) to assess the economic importance of tigerfish to the recreational fishery on Lake Kariba.

A re-examination of tigerfish growth rates in Lake Kariba

Growth rates of male and female tigerfish Hydrocynus vittatus were determined from length/frequencies of fish from the Sanyati Basin and Sinamwenda estuary, Lake Kariba. Growth rates were similar in both sexes for the first two years, after which females grew faster and reached a greater length. Fish from the Sanyati Basin appeared to grow slightly faster than those from the Sinamwenda Estuary.

The Gache Gache Fishing Co-operative, July 1984-June 1985

Details are given of development of the Gache Gache Fishing Cooperative and fishing activities in Lake Kariba undertaken during the year June 1984-June 1985. The viability of fishing cooperatives in Lake Kariba is also examined.

Investigation into the factors associated with poor water quality in intensively cultured prawn ponds

Water quality problems are reported to be the factor limiting prawn production in the local prawn farm. This investigation was carried out to monitor water quality and its relationship to physical, chemical and biological conditions in the ponds in order to establish what factors should be monitored in order to predict problems. Pond collapse was found to be associated with high concentrations of ammonium, high pH and blue-green algae dominated phytoplankton populations. There was no easy means of predicting the imminent collapse of ponds as the phenomenon was never associated with the extreme of any of the conditions monitored. Rather it seemed to be related to the stability of the pond's algal population, which was largely unaccounted for. Recommendations toward improving water quality are proposed.

Zonation of submerged vegetation in Lake Kariba, Zimbabwe and its ecological interpretation

The submerged vegetation of Lake Kariba is described in relation to degree of slope (lake morphometry), depth and light transparency. The direct gradient analysis technique - canonical correspondence analysis and the TWINSPAN classification programs were used to analyse the data set. The western end of the lake with low transparency has a low species diversity (with Vallisneria aethiopica dominating). Species diversity increases with increased transparency in the other parts of the lake. The classification revealed monospecific communities for all species as well as mixed communities with Lagarosiphon as the associate species with the broadest distribution. The ordination revealed a first axis strongly related to the depth and transparency gradients and the second axis related to slope.

Macrophyte - mollusc relationship in Lake Kariba

Five species of submerged vegetation Lagarosiphon ilicifolius, Najas pectinata, Vallisneria aethiopica, Ceratophyllum demersum and Potamogeton octandrus; 7 species of gastropods Melanoides tuberculata, Bellamya capillata, Biomphalaria pfeifferi, Bullinus tropicus, Cleopatra sp, and Lymnaea natalensis and 4 species of bivalves Corbicula africana, Caelatura mossambicensis, Mutela dubia and Aspatharia wahlbergii are correlated with environmental variables particularly slope and transparency, in Lake Kariba. A stepwise regression analysis further revealed interdependence between (Cleopatra sp., B. pfeifferi, L. natalensis, B. capillata, and V. aethiopica as well as between as between C. mossambicensis and L. ilicifolius and N. pectinata. The dependence of B. pfeifferi, L. natalensis, B. capillata, Cleopatra sp. on V. aethiopica and C. mossambicensis on L. ilicifolius and N. pectinata implies that a change in the biomass of the vegetation species may affect distribution and biomass of the faunal species.

A comparative study of consumption rates and preference for some species of aquatic plants by Tilapia rendalli

The daily consumption rates and preference of juvenile Tilapia rendalli for some macrophytes, Ceratophyllum demersum, Lagarosiphon major, Najas pectinatas and Valisneria aethiopica were determined. Fish were offered single macrophyte diets to determine daily consumption and a mixture of the 4 macrophytes in equal quantities to determine selection. Consumption rates were 821.50 mg, 829.05 mg, 940.00 mg and 2293.53 mg per fish per day, respectively. The differences in consumption rates were significant. Preference was shown for V.aethiopica, whilst C.demersum was least selected. Fish fed on single species lost weight whereas those fed on a variety of macrophytes gained in weight.