Population dynamics of freshwater oysterEtheria elliptica(Bivalvia: Etheriidae) in the Pendjari River (Benin-Western Africa)

Abstract

Etheria elliptica (Bivalvia: Etheriidae) is the only freshwater oyster occurring in Africa. The current study provides the first data on the population structure, growth, age, mortality and exploitation status of this species in the Pendjari River. E. elliptica length-frequency data were collected monthly from January to December 2009 and analyzed with FiSAT software. Population parameters including the asymptotic length (L ∞ ) and growth coefficient (K ) were assessed to evaluate the stock status. The recruitment pattern was modeled with a FiSAT routine. The asymptotic length (L ∞ ) was 14.75 cm, while the growth coefficient (K ) was 0.38 year-1 . The growth performance index (o′) reached 1.92. Specimens of Etheria elliptica reached a mean size of 4.66 cm and 6.41 cm at the end of one year and 1.5 years, respectively. We estimated total mortality (Z ), natural mortality (M ) and fishing mortality (F ) to be 2.90 year-1 , 1.16 year-1 and 1.74 year-1 , respectively. The recruitment pattern was continuous over the year with one major peak event during the rainy season (July). The exploitation rate (E = 0.60) revealed that the freshwater oyster was probably facing overexploitation due to lack of a minimum limit size and also due to an increase in the harvesting effort. Therefore, efficient management methods were urgently required to conserve the species. The return of empty shells into the water to increase the recruitment surface, rotation planning among harvesting sites and the imposition of a minimum limit size were recommendations made in order to ensure the sustainable exploitation of wild stocks.