Journal of Asian Scientific Research, 1(6), pp.299-311 2011 © AESS Publications, 2011 Page 298 Journal of Asian Scientific Research, 1(6), pp.299-311 2011 Fish fauna of Agbokum waterfalls in South Eastern Nigeria Abstract Author Knowledge of ichthyofauna of waterfalls is important in the development and management of conservation measures. In order to establish the fish composition and IKPI Gabriel and OFFEM diversity of a tropical waterfalls monthly fish samples and physic-chemical parameters Benedict were investigated in wet and dry seasons, over a two year period in three regions along Department of Fisheries, Faculty of the length of Agbokum waterfalls. Water turbulence, size of river, flow velocity, water Agriculture and Forestry, Obubra campus, Cross River University of Technology, level, temperature, transparency and food availability explained the observed seasonal Nigeria.*Phone:08055930219 and spatial changes in fish abundance. Five thousand four hundred and eighty four E-mail: [email protected] (5484) fish representing 22 species belonging to 16 genera from 9 families were sampled in both dry and wet seasons, with 10 species being restricted to wet season Key Words: Waterfalls, and only 1 in the dry. Cichlidae, Clariidae and Cyprinidae were the most abundant ichthyofauna, Diversity function, families accounting for 56.7% of the total catch with Tilapia zillii , Clarias gariepinus richness index, Relative and Labeo coubie dominating overall catch constituting 35.5%. Among the three abundance dominant species, two benthic fishes (L. coubie and C. gariepinus) showed inverse distributional pattern with Clariid fish ( C. gariepinus ) most abundant downstream and least represented upstream. Cyprinid (L. coubie ), on the other hand, dominated the upstream reaches and scarce downstream. Five species were site specific because of the association with only the midstream portion of the river (L. senegalensis), upstream (A. gardneri, A. filmentosus and E. sexfasciatus) and downstream reaches (H. fasciatus, A. occidentalis and C. nigrodigitatus). The two benthic species ( C. gariepinus and L. coubie ) produced a bimodal size class distribution in the three sites while T. zilli showed tri-modal size class. Equitability index (E) was generally low ranging from 0.03 (midstream) to 0.14 (downstream). Downstream reaches recorded highest diversity throughout the year with higher values for the wet season samples than dry. Wet season and Downriver region of the waterfalls were therefore critical in maintaining fish stock of the water falls. Introduction quiescent environment. It may also be useful in the aquatic ecology by aerating water bodies that lack Waterfalls is a place where a stream or river falls dissolved oxygen, represents significant barriers to from a high place example over a cliff or rock (Cano upstream movement of fish, serve as natural 2000). It is caused by gravity taking its effect on monuments and source of revenue generation water and pulls it down a cliff (Chernicoff et al.c because of their tourism potentials (Ayodele 1988, ,1997). Large amount of stream energy are expended Krinitskii 1972). Inhabitants of waterfalls use it for at waterfalls. Waterfalls are associated with “tier,” a drinking, irrigation and other domestic purposes. free-fall water drop, beginning when the water leaves the bed of the river or contact with rock and ends The Agbokim waterfall is a product of two rivers, when the water hits rock or the bed of the river again River Ekim and River Bakue. River Ekim is divided (Chester et al , 1999). into three streams, while River Bakue has four streams. These seven streams flow into a floodplain, The water body is important in fisheries and from where they independently cascade over steep aquaculture potentials, hydrology, biodiversity, cliff which provides seven-faced falls into the casket biodiversity conservation, ecotourism and geological or waterfalls. The waterfalls is locally called features (Fischer and Harris 2003). Waterfalls are “Nnabikim”, named after the goddess of the known to form a rich biome for indigenous and waterfalls or “Anigisa” meaning seven denoting the exotic species which are swept upstream and swept number of streams that flow to the casket. Waterfalls over the waterfalls to settle downstream in a more in many local communities are used as places of © AESS Publications, 2011 Page 299 Journal of Asian Scientific Research, 1(6), pp.299-311 2011 traditional and ancestral worship which militate (Brown, 1984). Two environmental factors important against the development of fisheries in these water in influencing aquatic assemblages and habitat bodies. Also the intensity of waterfalls and pressure structure are size and the flow regime (Schlosser, generated from it has given the impression of a 1987). lifeless zone. These reasons could be responsible for The resources of the length of the waterfalls are yet why data of Ichthyofuanal studies of water fall is to be tapped, more so due to the total neglect by scarce in Nigeria and other parts of Africa. stakeholders. This study on the ichthyofauna resources of Agbokim waterfalls serve to determine Knowledge of status of the ichthyofauna of waterfalls the rich resources of this biome and also reduce our is important in the development and management of over- dependence on estuarine and open water body conservation measures. The fundamental attributes of systems. an aquatic ecosystem are the number of species present and their abundance. Both attribute are Materials and methods dynamic and related (Tokeshi and Schmid, 2002). In aquatic ecosystems interaction between the Study area environment and population processes affects the distribution and abundance patterns of species The study area is Agbokim Waterfalls in South Eastern part of Nigeria (Figure 1). the tropical hinter-land type, with wet (May- November) and dry (December-April) seasons. Mean Figure 1:Map of Cross River State showing annual temperature ranged between 20 0C and 32 0C Agbokim Waterfalls. and annual total average rainfall, from 1450mm to 3015mm. The vegetation is the rainforest type with Agbokim Waterfalls is located in latitude 5 059’ North 0 Soil consisting of deep laterite and dark fertile, and longitude 8 45’ East. It is bounded in the West clayey and loamy soils. Agbokim Waterfalls is by the Cross River and in the North by the Cameroon drained by two small rivers, Ekue and Bakue, which high forests. The climate of Agbokim Waterfalls is are tributaries of the Cross River system. Of © AESS Publications, 2011 Page 300 Journal of Asian Scientific Research, 1(6), pp.299-311 2011 ecological importance are numerous small pools and Genus and species identifications was carried out swamps which are found along the length of the following Elvira (1987) for the Cyprinids; Erkakan et waterfalls. The high annual discharge and rainfall of al (2007) for the Bagrids, Teugels (1982) for the the Agbokim Waterfalls provide excellent buffers Clariidae; Fisher et al (1987) for the Clupeidae and against natural ecological stresses such as drought Mugilidae. Length distribution was analysed for three (Teugels et al 1992) which can lead to the loss of of the most abundant species: Tilapia zilli, African important fish taxa. The total length of the waterfalls catfish; Clarias gariepinus and Labeo coubie is 6817.73m. For the purpose of this study the waterfalls is divided into upstream, midstream and Species abundance and diversity downstream reaches. Upstream is close to cocoa farms with high forest cover along its shoreline and Species abundance of each reach was presented as a moderately fast water currents during the dry season numerical contribution by each species. This was and very fast water current during the wet season. determined by calculating the ratio each species Midstream has heavy water turbulence during the wet represented of the total catch for each reach based on season and moderate water turbulence during the dry the number of species and relative abundance. season with shoreline sparsely shaded with vegetation while downstream water current is low with an extensive wide area. The length upstream is Data treatment and analysis 2003.13m, midstream 807.42m and downstream 4007.18m. Mean width upstream, midstream and The mean and standard deviation of each of the downstream are 26.34±2.2m, 32.84m and physico-chemical parameters were calculated. 40.52±10.9m, respectively. Upstream mean height is Analysis of variance (ANOVA) was used to test for 31.87+3.4m while the depths upstream and statistical differences between the means of the downstream are dependent on variation of the volume physical and chemical parameters of the sampling of water from rainfall and water discharge. sites. To calculate mean abundance, numbers in different samples were summed for each species and Physico- chemical sampling averaged across all sampling sites. Physico-chemical parameters were correlated with the abundances of Physico-chemical parameters were determined once fish species using Pearson product moment every month for two years (August, 2007 to July, correlation coefficient analysis. Shannon-Wiener 2009). Standard methods for the examination of diversity function (H) was used to calculate water and waste water (APHA, 1987) were used for heterogeneity for each site. Richness index was all measurements. Monthly rainfall data for the study expressed using Margalef’s richness index. area was obtained from weather meteorological d = (S – 1) / logN (Clarke and Warwick 1994) stations, located in each of the three reaches. Habitat S variables; water level and river width were measured ∑ Pi Ln Pi on site. Water velocity (flow velocity) was H´ = - i = 1 (Krebs 1978) determined with Wagtech current flow meter, model E = d / S (Zar 1996). WFM001 with 125mm diameter impella. Water discharge was determined as in Fischer and Harris E = Equitability (2003) using the formula: WTD = CSA x WD x WV. 3 -1 d = Margalef’s richness index and H´ = Shannon- Where WTD = Water discharge (m s ), CSA = Cross Wiener Diversity Function Sectional Area (m); WD = Water dept (m) and WV = S = total species number Water velocity (ms -1).