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Available online at http://ajol.info/index.php/ijbcs Int. J. Biol. Chem. Sci. 9(1): 246-258, February 2015 ISSN 1997-342X (Online), ISSN 1991-8631 (Print) Original Paper http://indexmedicus.afro.who.int 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 Giraud David AKELE 1* , Simon AHOUANSOU MONTCHO 1, Antoine CHIKOU 1, Guy Apollinaire MENSAH 2 and Philippe Adédjobi LALEYE 1 1 Laboratoire d’Hydrobiologie et d’Aquaculture, Faculté des Sciences Agronomiques, Université d’Abomey-Calavi, 01 BP 526 Cotonou, Bénin. 2 Institut National des Recherches Agricoles du Bénin (INRAB), CRA-Agonkanmey ; 01 BP. 884 Cotonou, Bénin. *Corresponding author, E-mail:[email protected] 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. © 2015 International Formulae Group. All rights reserved. Keywords: Freshwater mollusk, harvesting activities, human pressure, fisheries management. INTRODUCTION bivalves has critically increased in the last Worldwide, mollusks bivalves group three decades as highlighted by export trends include many edible species of great since the seventies (124 300 tonnes in 1976 commercial interest such as mussels and and 459 300 tonnes in 2005) (Lovatelli et al., oysters (Gosling, 2003).The world market for 2008). Such increase was mainly due to © 2015 International Formulae Group. All rights reserved. DOI : http://dx.doi.org/10.4314/ijbcs.v9i1.22 G. D. AKELE et al. / Int. J. Biol. Chem. Sci. 9(1): 246-258, 2015 mussels with 257 300 tonnes in 2005 small fisheries were assumed to be facing (Lovatelli et al., 2008). However, production unsustainability and overexploitation (poor increase was mainly provided by mussel and growing local population; unregulated aquaculture since natural stocks have faced exploitation, high demands for limited overexploitation. Moreover, freshwater resources) (Narvarte et al., 2007), substantial mussels (Mollusca: Bivalvia: Unionoida) were information on human pressure on freshwater stressed to be threatened worldwide mainly oyster are still lacking. The abundant literature due to overfishing (Anthony and Downing, available on species mainly focused on 2001; Strayer, 2006). systematic and spatial distribution (Graf and In the tropics, oysters are found in Cummings, 2006; Van Bocxlaer and Van rivers and coastal areas and supported many Damme, 2007). Information on bivalve small artisanal fisheries (Haupt et al., 2010; exploitation remains limited to harvesting Van Damme, 2011; Ikpi and Offem, 2012). activities description and harvesters socio- Wild oysters are commonly harvested by local economic traits (Ampofo-Yeboah, 2000; Ikpi residents especially women as main traditional and Offem, 2012). However, understanding activity. Oyster exploitation provides protein how human pressure and harvesting technique and improves income of local communities affect stocks is of great importance not only to (Bogan, 2008; Haupt et al., 2010; Ikpi and settle sustainable management measures but Offem, 2012). However, small artisanal also for sensitization and environmental fisheries, especially in Africa, were education activities targeting residents’ considerably unregulated and were declining dwellers (Hartill et al., 2005). In fine, this also due to overexploitation (de Bruyn et al., 2009; contributes to secure their livelihood. Haupt et al., 2010). For instance, in South The freshwater oyster E. elliptica was Africa, de Bruyn et al. (2009) reported steady harvested by residents in Pendjari River for decrease in biomass of oyster Striostrea livelihoods. The river crosses the Pendjari margaritacea between 1935 and 1955 due to Biosphere Reserve (PBR), a protected area lack of sound regulations. Wild stocks decline (Benin-West Africa) on two-third of its course led to adverse socio-economic consequences (Agbossou and Okounde, 2001). In open for poor people, especially for women, owing access sites, heavy and unregulated to significant decrease of both low-cost exploitation is leading to stocks collapse; protein and income (Narvarte et al., 2007; Ikpi therefore, exploitation pressure is increasing and Offem, 2012). on oysterbed within the Reserve where Etheria elliptica (Lamarck, 1807) collection was under control (Kiansi, 2011). (Mollusca: Bivalvia: Etheriidae) is the only Indeed, within the context of ongoing co- freshwater oyster occurring in many lakes and management between local population and the rivers through Africa (Graf and Cummings, Reserve managers, access was given to 2006; Van Damme, 2011). The oyster was surrounding people to collect some reserve mostly harvested by growing indigenous resources such as medicinal plants, straw and populations along artisanal fisheries in Africa halieutic resources, as they contribute to anti- (Van Damme, 2011; Ikpi and Offem, 2012). poaching activities and biodiversity In West Africa, the traditional exploitation of conservation. Overall, oysters appeared to be freshwater oyster has been described in many the main resource requested by poor and small fisheries mostly in Ghana (Ampofo- growing local residents after fish species Yeboah, 2000) and in Nigeria (Ikpi and (Kiansi, 2011). This leads to increasing Offem, 2012). Besides, species oysterbed pressure on the oyster stocks within the decline was pointed out in Burkina Faso reserve. Therefore, an establishment of (West Africa) resulting from excessive sustainable management strategy for oyster gathering by riverine population of Volta wild stocks is one of the priorities of the PBR Basin (CNRST, 1992). Although African managers. This work aims at analyzing 1) the 247 G. D. AKELE et al. / Int. J. Biol. Chem. Sci. 9(1): 246-258, 2015 socio-economic characteristics of harvesters Porga7, Pouri, Setchendinga) were recorded. (sex, age, ethnic group, profession, income of Distributed in five harvesting groups, they exploitation), 2) the impact of harvesting were active in different sections of the river: pressure on natural stocks and the open access (Borne 0-5) and protected zones implication for co-management success and (Borne 18-28 and Borne 30-40), during 2008 the sustainable use of this resource. and 2009 harvesting seasons. In Tampanga, 60 oyster collectors exclusively active in open MATERIALS AND METHODS access site were registered. As the latter were Study area and species far from the Pendjari Biosphere Reserve, their The study was carried out along the collection activities remained limited to Pendjari River in Northern Benin (West Tampanga accessible sites (Figure 1). Finally, Africa) (10°24 N, 1°21E). The river crosses 150 active harvesters were recorded among the Pendjari Biosphere Reserve for 200 km riverine communities. Respondents were out of 380 km of its course and is a natural chosen for this survey based on their level of border between Burkina Faso and Benin involvement in and dependency on oyster (Agbossou and Okounde, 2001). The Pendjari harvesting (active every year), harvesting sites River has a tropical hydrological regime with location (open access and protected zones), a low water season between December and harvesting activity importance in dry season June and a flood season from September to or time allocated (main activity in dry season) October. The Pendjari River is located in and agreement to take part in the research. Sudanian climatic zone with one rainy season Individual semi-structured interviews were (April/May to October) and one dry season used to collect socio-demographic data (sex, (November to March). Mean rainfall reached age, sociolinguistic group and occupation) of annually 1000 mm with 60% falling between harvesters along the river. Overall, 120 July and September Daily