TITLE:
Ecology and Fish Biodiversity of Man-Made Lakes of Southern Benin (West Africa): Implications for Species Conservation and Fisheries Management
AUTHORS:
Houehanou M. A. G. Gbaguidi, Alphonse Adite, Edmond Sossoukpe
KEYWORDS:
Conservation, Diversity, Domestic Wastes, Fisheries, Habitat Degradation, Management, Man-Made Lakes, Sand-Dragging, Sarotherodon galilaeus
JOURNAL NAME:
Journal of Environmental Protection,
Vol.7 No.6,
May
19,
2016
ABSTRACT: Man-made
lakes are alternative and potential habitats for biodiversity conservation,
fisheries and extensive aquaculture. We investigated the ecology and the fish
community structure of two (2) sand-dragged man-made lakes, Lake Ahozon and
Lake Bewacodji of Southern Benin, with implications for species conservation,
fisheries management and aquaculture valorization. From August 2014 to July
2015, habitats conditions were evaluated and fishes were sampled monthly with
seine, cast net, experimental gill net and hooks in the open water and aquatic
vegetation habitats of both lakes. Overall, the water quality of Lake Ahozon was
globally favorable for the growth and the survival of the fish resources
whereas Lake Bewacodji exhibited a poor water quality indicated mainly by an
acid pH (mean: 6.32 ± 0.58) and low dissolved oxygen concentrations (mean: 3.52
± 1.25 mg/l) caused by dense floating plants, Nymphea sp mainly and huge daily
dumping of domestic wastes. The study revealed low species richness, d = 5.89
and d = 3.87, and low species diversity, H’ = 0.76 and H’ = 0.48 for Lakes
Ahozon and Bewacodji, respectively, with Lake Ahozon more diverse than Lake
Bewacodji. The fish community of Lake Ahozon comprised six (6) species, 3
cichlids Sarotherodon galilaeus, Oreochromis niloticus and Tilapia guineensis,
the silver catfish, Chrysichthys nigrodigitatus (Claroteidae), the African
bonytongue, Heterotis niloticus (Osteoglossidae), and the African catfish, Clarias gariepinus (Clariidae). Numerically, S. galilaeus dominated Lake Ahozon
and made 85.21% of the sample. In Lake Bewacodji, the fish composition
comprised four (4) species, Sarotherodon galilaeus multifasciatus, the dominant
species making numerically 91.58% of the total sample, T. guineensis, C.
gariepinus and C. nigrodigitatus. With regard to trophicstructure,
the fish assemblages of both lakes were numerically dominated by
planktinovores/ detritivores, mainly S. galilaeus, O. niloticus, T. guineensis and C. nigrodigitatus making together 99.46% of Lake Ahozon fish community, and S. galilaeus multifasciatus, T. guineensis and C. nigrodigitatusaccounting
together for about 98.59% of Lake Bewacodji. In Lake Ahozon, standard length
(SL) frequencies histograms showed an unimodal size distribution for H.
niloticus, the nile tilapia O. niloticus and C. gariepinus whereas the two
cichlids, S. galilaeus and T. guineensis exhibited a bimodal size distribution.
In Lake Bewacodji, S. galilaeus multifasciatus, C. nigrodigitatus and C.
gariepinus exhibited an unimodal size distribution. A sustainable exploitation
of both man-made lakes requires the implementation of an integrated management
scheme which should include habitat restoration and protection plan,
fisheries/aquacultural valorization, ecological sound agriculture/ecotourism
and environmental monitoring.