Abstract
Morphometrics and physico-chemical parameters of Oyun reservoir, Offa, Nigeria (a small shallow tropical African Reservoir) were used to estimate the potential fish yield of the reservoir according to the morpho-edaphic index (MEI). Physico-chemical characteristics of the water body were sampled monthly from three stations between January 2002 and December 2003 with standard methods. Estimates of the potential fish yield were obtained using the physico-chemical characteristics of the reservoir and the relationship Y = 23.281 MEI(0.447), where Y is the potential fish yield in kg/ha, MEI is the morpho-edaphic index (given in microS/cm and estimated by dividing the mean conductivity by the mean depth). The reservoir mean depth and conductivity values were 2.6m and 113.10 microS/cm respectively, while its potential fish yield was estimated at 125.72 kg/ha. This estimate was higher than other small shallower and larger African reservoirs. The reservoir high ionic content, high nutrient and dissolved oxygen levels, good pH, low level of pollution and shallow depth were responsible for the high estimate of the fish yield. In order to realize this high potential fish yield and sustainable exploration of the fisheries, effective management of the reservoir to curb eutrophication should be adopted, while other management practices such as stocking and conservation of desirable and indigenous fish species, implementation of fishing regulations and adoption of best management practices should be implemented.
Highlights
Shallow reservoirs are numerous in Tropical Africa, but the study of their limnology and fisheries potentials are scanty despite their high potentials for fish production as compared with large reservoirs
The estimated yield from African shallow tropical reservoir was far more than that of Asia (Lu 1986, Suguna 1995), Latin America and the Caribbean (Jackson 1985, Suguna 1997), North America and Europe (Jenkins 1982, Lelek 1989). Several limnological parameters such as conductivity, total dissolved solids, water quality, phytoplankton and reservoir morphometry have been used in estimating potential fish yields from reservoirs
Study site: Oyun reservoir is a tropical man-made reservoir located in Offa, Kwara State, Nigeria, longitude 8°30’05’’ N and latitude 8°15’55’’ E
Summary
Shallow reservoirs are numerous in Tropical Africa, but the study of their limnology and fisheries potentials are scanty despite their high potentials for fish production as compared with large reservoirs. The estimated yield from African shallow tropical reservoir was far more than that of Asia (Lu 1986, Suguna 1995), Latin America and the Caribbean (Jackson 1985, Suguna 1997), North America and Europe (Jenkins 1982, Lelek 1989) Several limnological parameters such as conductivity, total dissolved solids, water quality, phytoplankton and reservoir morphometry have been used in estimating potential fish yields from reservoirs. The MEI demonstrates that as nutrients in the water increase and depth decreases, fish production increases (Jackson & Marmula 2001) Based on this hypothesis, African tropical shallow reservoirs which are known to be highly productive will have high fish yield. The objective of this paper is to determine the potential fish yield of Oyun reservoir using the morpho-edaphic index (MEI) and the limnological parameters as index of survival, productivity and management of the reservoir and its fisheries
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