Traditional exploitation of edible freshwater oyster Etheria elliptica (Lamarck, 1807) in Pendjari River (Benin-West Africa): assessment of income, human pressure and options for management

Abstract

Freshwater oyster Etheria elliptica (Mollusca: Bivalvia) was harvested in Pendjari River as important source of protein and income. The river crosses the Pendjari Biosphere Reserve, a protected area in Northern Benin. The freshwater oyster is harvested outside and within the protected area with increasing human pressure. The current study aims at assessing fishery production, human impact on wild stocks and suggests sustainable management options. Individual semi-structured interviews and monitoring of oyster collection were used to collect data on harvesters’ socio-economic characteristics, biomass production and seasonal income in 2008 and 2009. Mean shell size and weight as well as size frequency distribution were analyzed in relation to harvesting pressure. Oyster harvesting is the main traditional activity of Berba women in dry season, at low water level period. The oyster collectors used artisanal tools such as chisel-like metal, stone-hammer, rope, metal pan and pot. Biomass production, oysters mean size and weight decreased from protected sites to unprotected zones revealing negative anthropogenic pressure on oyster natural stocks. Size frequency distribution displayed an important proportion of smaller individuals in open access sites whilst larger size oysters were more encountered in protected zones. Therefore, exploitation appeared likely as a potential threat for oyster bed. Moreover, the oyster collectors not only exploited individuals without observing a minimum limit size, but they also targeted each year the same sites regardless rotation planning. Finally, oyster`s shell, a main substrate for larval settlement and bed restoration, were left on riverbanks after exploitation, reducing stocks reconstitution potential. Appropriate measures were suggested to Reserve staff for sustainable management.

Keywords: Freshwater mollusk, harvesting activities, human pressure, fisheries management.