Department of Marine and Fisheries Sciences

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    Assessing The Efficiency Of Two Improved Lesser Known Kilns And Their Effect On The Quality And Shelf Life Of Smoked Fish In Ghana
    (University of Ghana, 2019-07) Asamoah, E.K.
    Fish smoking is a traditional fish preservation method which is affordable, and hence employed in most developing countries with logistical challenges in preserving fresh fish for marketing. Smoked fish is a major source of protein in the diets of Ghanaians. Often traditional kilns, that rely on firewood as a source of fuel, are used. These kilns have been shown to be less fuel efficient and the smoked products have high levels of polycyclic aromatic hydrocarbons (PAHs), which are of public health concern. Additionally, poor storage of the products leads to quality losses. This study, which contributes to the search for a more efficient and safe smoking oven, therefore sought to test and compare the efficiency of two improved, but lesser known kilns, the Cabin and Abuesi gas fish smoker (AGFS) to the traditional Chorkor smoker by investigating the physicochemical, microbial and sensory qualities of the smoked products. Finally, the effect of irradiation and different storage conditions on the shelf life of the smoked products was studied. The research was undertaken in Abuesi, in the Western Region, using two marine fish species, the chub mackerel and barracuda. The results showed that the AGFS had 12% lower yield but 86% and 60% higher processing rate than the cabin and Chorkor kilns respectively. Again, the fuel consumption was 68% and 54% better than the Cabin and Chorkor respectively, while the Cabin also saved 29% more fuel than the Chorkor. In terms of the fuel costs, the Cabin was 38% and 54% lower than the Chorkor and AGFS respectively (owing to the lower cost of firewood, compared to LPG). The cost of construction was however extremely high in the AGFS than the Cabin and Chorkor kilns, however, its industrial size (500 kg capacity), faster smoking time and lower fuel consumption make it good alternative to consider. Smoking improved the physical, chemical, microbiological and sensory quality of mackerel and barracuda. These qualities, except for colour and sensory analysis, could not be statistically differentiated between the products from the AGFS and Cabin kiln. The Cabin-smoked products had the more traditional qualities of smoked fish (appearance, odour and flavour), while the gas-smoked products had a pronounced fried appearance and taste. The AGFS produced smoked products with mean benzo(a)pyrene and PAH4 concentrations below the EU MLs (2 and 12 μg/kg respectively). Depending on the type of firewood used, the Cabin also produced benzo(a)pyrene below the MLs when C. mildbraedii (Esa) was used, while the Chorkor had levels 3 to 8 times higher than the MLS. The PAH4 levels in the Cabin and Chorkor products were all above the MLs (4 and 8 times higher respectively). Based on the frequency and quantities of smoked mackerel and barracuda consumed by an average Ghanaian adult (with a life expectancy of 63 years), the potential carcinogenic risks were of least concern in the gas smoked and all barracuda samples (about 1 in 100,000 adults), moderate in the Cabin smoked mackerel (3 and 6 in 100,000 adults) and high in the Chorkor smoked mackerel (7 and 17 in 100,000 adults). Heavy metal (Hg, Pb and Cd) contamination was negligible in fresh and smoked mackerel and barracuda. The effect of irradiation and storage temperature on the quality and shelf life of smoked mackerel showed that irradiation did not affect the nutritional quality (protein, fat, moisture and ash contents) after 65 days of refrigerated storage. The fatty and amino acid compositions were also unaffected by irradiation. Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) respectively constituting about 8% and 18% of the total fatty acids. The essential amino acids also contributed about 59% of the total amino acid concentrations. The non-irradiated and irradiated smoked mackerel, stored at refrigerated temperature, were of good microbial and chemical quality by Day 65 of storage, even though lipid oxidation and hydrolysis were affected. Keeping the non-irradiated and irradiated smoked fish at room temperature were rejected by Day 5 of storage due to insect infestation and visible mouldiness (even though most microbial and chemical qualities were good). The results, therefore, indicates that The AGFS performed better, overall, followed by the Cabin and then the Chorkor. The kilns produced fish with good nutritional qualities. Irradiation did not negatively impact on the quality of the smoked products during the 65 days of storage, but refrigerated storage is key to maintaining quality of irradiated fish
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    Assessing the Efficiency of Two Improved Lesser Known Kilns and Their Effect on the Quality and Shelf Life of Smoked Fish in Ghana
    (University of Ghana, 2019-07) Asamoah, E.K.
    Fish smoking is a traditional fish preservation method which is affordable, and hence employed in most developing countries with logistical challenges in preserving fresh fish for marketing. Smoked fish is a major source of protein in the diets of Ghanaians. Often traditional kilns, that rely on firewood as a source of fuel, are used. These kilns have been shown to be less fuel efficient and the smoked products have high levels of polycyclic aromatic hydrocarbons (PAHs), which are of public health concern. Additionally, poor storage of the products leads to quality losses. This study, which contributes to the search for a more efficient and safe smoking oven, therefore sought to test and compare the efficiency of two improved, but lesser known kilns, the Cabin and Abuesi gas fish smoker (AGFS) to the traditional Chorkor smoker by investigating the physicochemical, microbial and sensory qualities of the smoked products. Finally, the effect of irradiation and different storage conditions on the shelf life of the smoked products was studied. The research was undertaken in Abuesi, in the Western Region, using two marine fish species, the chub mackerel and barracuda. The results showed that the AGFS had 12% lower yield but 86% and 60% higher processing rate than the cabin and Chorkor kilns respectively. Again, the fuel consumption was 68% and 54% better than the Cabin and Chorkor respectively, while the Cabin also saved 29% more fuel than the Chorkor. In terms of the fuel costs, the Cabin was 38% and 54% lower than the Chorkor and AGFS respectively (owing to the lower cost of firewood, compared to LPG). The cost of construction was however extremely high in the AGFS than the Cabin and Chorkor kilns, however, its industrial size (500 kg capacity), faster smoking time and lower fuel consumption make it good alternative to consider. Smoking improved the physical, chemical, microbiological and sensory quality of mackerel and barracuda. These qualities, except for colour and sensory analysis, could not be statistically differentiated between the products from the AGFS and Cabin kiln. The Cabin-smoked products had the more traditional qualities of smoked fish (appearance, odour and flavour), while the gas-smoked products had a pronounced fried appearance and taste. The AGFS produced smoked products with mean benzo(a)pyrene and PAH4 concentrations below the EU MLs (2 and 12 μg/kg respectively). Depending on the type of firewood used, the Cabin also produced benzo(a)pyrene below the MLs when C. mildbraedii (Esa) was used, while the Chorkor had levels 3 to 8 times higher than the MLS. The PAH4 levels in the Cabin and Chorkor products were all above the MLs (4 and 8 times higher respectively). Based on the frequency and quantities of smoked mackerel and barracuda consumed by an average Ghanaian adult (with a life expectancy of 63 years), the potential carcinogenic risks were of least concern in the gas smoked and all barracuda samples (about 1 in 100,000 adults), moderate in the Cabin smoked mackerel (3 and 6 in 100,000 adults) and high in the Chorkor smoked mackerel (7 and 17 in 100,000 adults). Heavy metal (Hg, Pb and Cd) contamination was negligible in fresh and smoked mackerel and barracuda. The effect of irradiation and storage temperature on the quality and shelf life of smoked mackerel showed that irradiation did not affect the nutritional quality (protein, fat, moisture and ash contents) after 65 days of refrigerated storage. The fatty and amino acid compositions were also unaffected by irradiation. Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) respectively constituting about 8% and 18% of the total fatty acids. The essential amino acids also contributed about 59% of the total amino acid concentrations. The non-irradiated and irradiated smoked mackerel, stored at refrigerated temperature, were of good microbial and chemical quality by Day 65 of storage, even though lipid oxidation and hydrolysis were affected. Keeping the non-irradiated and irradiated smoked fish at room temperature were rejected by Day 5 of storage due to insect infestation and visible mouldiness (even though most microbial and chemical qualities were good). The results, therefore, indicates that The AGFS performed better, overall, followed by the Cabin and then the Chorkor. The kilns produced fish with good nutritional qualities. Irradiation did not negatively impact on the quality of the smoked products during the 65 days of storage, but refrigerated storage is key to maintaining quality of irradiated fish.
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    Measuring and Simulating Shoreline Morphodynamics in the Volta Delta, Ghana
    (University of Ghana, 2019-03) Jayson-Quashigah, P.
    Coastal erosion is a major challenge facing coastal regions globally. It is projected to increase on regional to global scale as sea levels continue to rise. To manage the situation sustainably, coastal managers require relevant scientific information such as beach sediment and shoreline dynamics. Shoreline change measurement and simulation especially at local scale and at higher resolutions are relevant for decision making and engineering. A review of literature has brought to the fore that the Volta delta is a hotspot for coastal erosion; however, mainly low resolution remotely sensed imagery has been used to assess changes in the Volta delta of Ghana, which compromises the accuracy of the information. In this study, different sets of high-resolution datasets from Unmanned Aerial Vehicles (UAV) surveys and satellite imagery, as well as numerical modelling using Littoral Processes FM (Flexible Mesh) are adapted to estimate historical beach sediment and shoreline dynamics and predict future evolution under sea level rise up to the mid-century. The results show a net loss of beach sediment on the western side of the Volta Delta up to 9,000m3 whilst the eastern side experienced net gain up to 12,100 m3 in the short term. Relatively, short-term erosion rates were higher compared to the medium term shoreline erosion. Simulation of future conditions indicates an increase in shoreline erosion rates by 4 cm/y by mid-century with sea level rise of 13 cm at Old Ningo. Consequently, the shoreline will recede up to 70m inland, which will negatively influence livelihoods and aesthetic value of the area. The study recommends soft engineering approach such as sediment beach nourishment or the Dutch ‘sand motor’ system to protect the shoreline and the community. Regulations should also be enforced to halt nearshore sand and gravel mining.
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    Investigations into Hatchery and Nursery Operations for the Culture of the Freshwater Prawn (Macrobrachium Vollenhovenii, Herklots 1857) in Ghana
    (University of Ghana, 2018-07) Dzidzornu, K.E.A.
    The study was conducted to demonstrate hatching and larval development of the African River Prawn Macrobrachium. vollenhovenii Herklots, 1857) and to establish the spatial and temporal distribution of the prawns and related crustaceans in the Lower Volta River from Torgorme (Akuse) to Ada with focus on the Volta Estuary of Ghana. The ecological survey was undertaken from August 2013 to July 2014 followed with aspects of reproductive biology of the M. vollenhovenii from August 2014 to July 2015 and then the hatching and larval development of the from January to December 2016. Fisheries dependent data was collected together with experimental prawn fishing. The species encountered included Atya gabonensis (Giebel, 1875), Macrobrachium macrobrachion, (Herklots, 1851), Macrobrachium vollenhovenii and Penaeus spp. Comparatively more Penaeus spp. were sampled in the dry months (November to January) in more saline zones while Macrobrachium spp. were more in the rainy months (May to July) in the more freshwater zones. The dominant species in the estuary was the M. vollenhovenii (72.52%) with male to female ratio of 1:1.3 and non-berried to berried females ratio as 1:1.7. The berried females were obtained throughout the year with increased numbers and larger ones in the rainy season. The size and weight of gonad correlated positively with size of berried females and appeared to be a function of the number rather than the size of eggs. Out of four treatment media (Artificial Sea salt, Freshwater, Seawater and Rock salt) used for the larval development, the Freshwater medium could not support the life of the larvae after 48 hours. The 8th Larval stage (ZVIII) was observed from the 23rd day of culture in both Seawater and Artificial Sea Salt media. Survival rate correlated negatively with stocking densities of 50, 100, 150 and 200 larvae/liter, an indication that thinning is necessary as the larvae grow from one stage to another. Survival rates in the 50 larvae/liter were 36.8%, 30.8% and 25% in the Seawater, Artificial Sea salt and Rock salt treatments respectively. From the results, M. Vollenhovenii larvae could be hatched and developed for culture in the grow-out process to boost prawn culture in Ghana.
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    Geochemistry of Estuarine Sediments of Ghana: Provenance, Tracemetal Accumulation Trends and Ecotoxicological Risks
    (University Of Ghana, 2014-07) Mahu, E.
    The sedimentary record, as revealed in sediment cores, can be used to reconstruct the past history of contaminant input into the aquatic environment. This is because contaminant inputs equilibrate rapidly with sediment supply, and the sediment column represents a continuous sequence of sediments that are associated with contaminant accumulation. With radiometric techniques, it is possible to date recent sediments over a period corresponding to about five half-lives (approximately 100-200 years using 210Pb). To understand the geochemistry of estuarine sediments in relation to their provenance, trace metal accumulation trends and potential ecotoxicological risks, this study investigated sediment cores and surficial sediments from the Ankobra, Pra, Amisa, Densu, Sakumo II and Volta estuaries of Ghana. Geochemical and petrographical techniques were used to reveal the source of sediment supply into the estuarine environments. In addition, Gamma Spectroscopy and Inductively Coupled Plasma Mass Spectrometric (ICP-MS) techniques were used for deriving geochronologies, sedimentation rates, spatial and temporal accumulation of Mo, Cd, Pb, V, Cr, Cu, Zn, As and Hg in the study sites. The pollution status of the estuarine sediments was investigated using Aluminum-normalized enrichment factors (EFs). Cluster and correlation analysis differentiated natural from anthropogenic sources of trace metal in the estuaries. The excess fluxes of trace metals, estimated using sedimentation rates helped in quantifying the extent of anthropogenic contamination of metals in each estuary. AQUARISK software was used to assess any potential ecotoxicological risks associated with trace metal enrichments. Results showed that sediments from the Ankobra, Pra, Densu and Volta estuaries comprised quartzose sedimentary provenance while those of Amisa and Sakumo II estuaries comprised mafic igneous provenance. The sedimentation rates estimated from the constant rate of supply model were 0.24±0.10 gcm-2y-1, 0.47±0.20 gcm-2y-1, 0.43±0.02 gcm-2y-1, 0.31±0.13 gcm-2y-1, 0.20±0.01gcm-2y-1 and 0.54±03 gcm-2y-1 for the Ankobra, Pra, Amisa, Densu, Sakumo II and Volta estuaries respectively. The sediment core from the Ankobra estuary was significantly enriched with Hg (5.0
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    Evaluation of Farm-Made and Commercial Fish Diets for Hapa Culture of Nile Tilapia (Oreochromis Niloticus L.) in Ghana Francis Assogba Anani
    (University of Ghana, 2015-03) Anani, F.A.; Nunoo, F.K.E.; Steiner-Asiedu, M.; University of Ghana, College of Basic and Applied Sciences, School of Biological Sciences
    One of the major constraints to aquaculture development and expansion in Ghana is affordable nutritionally balanced and cost effective fish diet. Although some fish farmers produce their own farm-made fish diets, these diets do not meet the nutritional requirements of the cultured fish as the farmers do not follow the appropriate feed formulation protocol. This study was carried out to generate information on the commercial fish diets and feed ingredients currently used by small-scale pond fish farmers in five major pond fish farming Regions (Ashanti, Brong-Ahafo, Central, Volta and Western) in Ghana. Six of the commonly used ingredients by the farmers were selected and used to formulate and prepare farm-made tilapia diets which were evaluated against two commonly utilised commercial tilapia diets for Nile tilapia (Oreochromis niloticus). In all, five diets namely A (farm-made diet supplemented with vitamin-mineral premixes, lysine and methionine), B (farm-made diet without supplements), C (commercial tilapia diet, Coppens), D (commercial tilapia diet, Raanan) and E (mixture of B and Raanan in a ratio of 1:1). The first part of the study was conducted in net hapas installed in a 0.2 hectare earthen pond over a 140-day growth period at the Aquaculture Research and Development Centre (ARDEC), Akosombo. O. niloticus with an initial mean weight of 22.8 ± 2.1 g were stocked at a density of 2 fish m-2 and fed at 4-3 % body weight three times a day. The second part of the study involved digestibility of the diets and this was carried out in plastic tanks with 20 L of water each for 20 days. After the culture period, the final mean weights of O. niloticus were 140.3 ± 23.4, 131.0 ± 24.4, 148.3 ± 25.4, 187.6 ± 42.1 and 140.7 ± 28.5 g for A, B, C, D and E respectively. There was no significant difference (p > 0.05) in specific growth rates among all the dietary treatments. Apparent nutrient digestibility coefficients were high (> 60 %) in all the dietary treatments. Crude protein ranged from 77.49 to 87.02 %, crude lipid ranged from 81.46-93.90 % whilst carbohydrate (nitrogen free extract) ranged from 65.28 to 85.94 %. Higher crude protein depositions and lower fat contents were observed in the carcass of fish fed farm-made diet A and Raanan. There were no internal and external abnormalities in O. niloticus fed with the various diets. Both the farm-made and commercial diets did not impact negatively on water quality. In terms of cost-effectiveness, the farm-made diets were more profitable than the commercial ones. The results indicated that nutritionally balanced farm-made fish diet is cost-effective and will boost growth of aquaculture in rural areas where semi-intensive pond aquaculture is mainly practised in Ghana. The current fish production (2 500 kg ha-1 yr-1) by Ghanaian small-scale pond fish farmers could increase up to a fourfold by using appropriately formulated and prepared farm-made fish diets with locally available ingredients. This is likely to increase their profit margin to over four hundred percent of what they are making currently using commercial fish diets. The costs associated with the use of commercial fish diets by small-scale pond fish farmers are high, and in terms of fish growth and economic returns, the use of appropriately formulated and prepared farm-made diets will be a better alternative. Fish farmers should be trained on the formulation and preparation of nutritionally balanced and cost effective farm-made fish diets so as to reduce their production cost and increase their profit margin.
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    Eco-Functional Benthic Biodiversity Assemblage Patterns in the Guinea Current Large Marine Ecosystem
    (University of Ghana, 2015-12) Lamptey, E.; Wiafe, G.; Nyarko, E.; Armah, A. K.; University of Ghana, College of Basic and Applied Sciences, School of Biological Sciences, Department of Marine and Fisheries
    Functional diversity, an important component of biodiversity, has in recent years engaged global attention. This is in great part due to the mechanistic understanding achieved from functional diversity studies in the face of accelerated global biodiversity changes ascribed primarily to anthropogenic drivers. The exigency of the situation has stimulated biodiversity-ecosystem functions (B-EF) studies to elucidate ecosystem processes and services that are at threat notably in the marine ecosystem. The marine benthos is the largest ecosystem on earth and supports the highest phylogenetic diversity but has rather witnessed comparatively low attention in the B-EF studies than the terrestrial counterpart. This thesis is aimed at i) quantifying benthic functional diversity (using biological trait analysis) and assemblages along abiotic gradients in the Guinea Current Large Marine Ecosystem (GCLME); and ii) examining the impact of bottom trawling for demersal fishes on the functional structure of epibenthic fauna along bathymetric gradients. In achieving the above-mentioned objectives, epibenthic fauna of bottom trawl samples were collected from Ghana to western Nigeria‘s continental shelf in 2003. Further, macrobenthic infauna and abiotic samples were collected from coastal waters of Guinea Bissau to Gabon in 2007. Each processed dataset was treated as a stand-alone in the thesis. In decomposing the assemblage patterns, suites of univariate and multivariate statistics were employed. The results indicated 381 macobenthic species comprising polychaetes (61.15% richness and 55.15% abundance), crustaceans (18.64% richness and 28.02% abundance), molluscs (9.19% richness and 2.23% abundance), echinoderms (2.63% richness and 1.84% abundance) and ‗others‘ (8.39% richness and 12.76% abundance). Functional diversity analysis indicated spatial differences in eco-functional traits namely small body size, solitary lifestyle, burrowing and deposit-feeding, and these traits dominated the assemblage especially from Ghana to Benin. The results suggest that these areas are potential surrogates of allochthonous organic material possibly driving pelagic productivity that is translated to the benthos. Significant (p<0.05) relationship was found between functional traits (also species diversity) and sediment parameters (i.e., nitrate, calcium, magnesium, organic carbon, silt & clay). These abiotic variables largely implicate productivity and climate change models as principal community drivers, and are likely to impact ecosystem functions directly by altering B-EF relationship. Inferentially, the results indicated an unstable, dynamic, productive and low biomass-supported ecosystem Guinea Current Large Marine Ecosystem (GCLME), reflecting in the small body size solitary burrow-dwelling deposit-feeding organisms, which potentially exert the strongest influence on ecosystem processes (e.g., nutrient remineralization). These species used multiple adaptative strategies including trophic, lifestyle, anatomical and morphological in the prevailing environment. Bottom trawled epibenthic sample analysis showed significant difference (p=0.002; ANOSIM) of assemblages along bathymetric gradient, notably between shallow-depth (11-30m) and deep-depth (51-70m). Functional analyses showed dominance of carnivores (28% contribution), opportunistic/scavenging (9%) and herbivore (9%) in shallow waters, while filter-feeders (18%) dominated deep waters suggesting gradient in structuring forces. The high abundance of motile epibenthic fauna (64%) is suggestive of an unstable substrate and turbulent system supporting motile carnivores and filter-feeding organisms. The evidence of trophic interactions between demersal fishes and epibenthic fauna occurred ideally in most tolerable and favorable zone (i.e. mid-depth). Abundance-Biomass Comparison (ABC) analyses
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    Causes and Trends in Shoreline Change in the Western Region of Ghana
    (University of Ghana, 2015-03) Boye, C. B.; Wiafe, G.; Appeaning, A. K.; Dzigbodi-Adjimah, K.; University of Ghana, College of Basic and Applied Sciences, School of Biological Sciences, Department of Marine and Fisheries
    Shoreline change is an issue of concern to most coastal managers because the coastal zone is home to over 60% of the world’s population. In Ghana, shoreline change has been associated with loss of economic lands and properties. Previous researches have shown that the Ghana coastline is eroding at variable rates; the Eastern and Central Zones are receding while the Western zone is thought of as stable. This opinion, however, contrasts field observations and interview with local coastal community members. This research therefore sought to determine the shoreline change trends in the study area through modelling the driving and resistive factors along the shores. The factors investigated are sea-level rise, wave impact, sediment supplied by rivers, resistance of coastal material and human impact. Multi-temporal spatial datasets, hydrodynamic datasets, geological map of the area and systematically sampled field measurements were used. Standard procedures were employed to compute values for the eight variables that were selected as proxies for the driving and resistive variables. Analysis was carried out in short-term (1974-2005) and long-term (1895-2005) change categories in shoreline trends. Average short term change rate of -4.18 ± 0.10 m/year and long term change rate of -7.25 ± 0.11 m/year were obtained for the entire study area. The results revealed that the strength of hard shore outcrops, the shear strength of the soil, the sediment supplied by rivers and human impact contributed significantly to variations in the shoreline change trends along the study area. It was identified that shoreline change trends observed in the study area is mainly caused by physical processes of wave action, which is modified by the characteristic features along the shores, and aggravated by human impact. The shoreline change trends reflect the coastal material resistance at the various sections along the coastline; this is attributed largely to the formation history of the coast. It was, however, found out that the effect of sea level rise on the shoreline trends was minimal. The Western Section of the study area was found to be more vulnerable to erosive forces relative to the Eastern Section. It is recommended that a non-linear model be employed for confirmation of the findings.
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    Comparative Study of the Mangrove Ecosystems of Douala-Edea Reserve (Cameroon) and Songor Ramsar Site (Ghana) Using Parameters of Ecological Value
    (University of Ghana, 2014-06) Ntyam, S.C.O.; Wiafe, G.; Armah, A.K.; Adomako, J.K.
    In most tropical countries including Ghana and Cameroon, knowledge of ecological importance of mangrove ecosystem in terms of litter production, structural characteristics, water and soil properties, has been qualitatively well documented and recognised. However, there is scanty quantitative scientific data to back this up. The purpose of this research dissertation was to study and compare the mangrove ecosystems of Cameroon and Ghana two contrasting coastal zones, using parameters of ecological value and to have a better understanding of their interrelationships within mangrove ecosystem as well as the impact of their values or roles to the global ecosystem (marine and coastal) within the West and Central African ecoregion. The study was conducted within the period of two years for both countries (One year in each country), Two major sites were chosen in Ghana (Songor Ramsar site) and Cameroon (Douala Edea Reserve). In each site, three mangrove stands: 1) Avicennia, 2) Rhizophora and mixed (Rhizophora and Avicennia) were selected and marked out, and parameters like litterfall, structural characteristics, water and soil properties were assessed. This research on mangrove ecosystem addressed four objectives: (1) assessment of the structural parameters; (2) assessmentof litter production; (3) determination of physicochemical and climatic factors affecting mangrove structure and productivity; (4) Show the interrelationships between mangrove resources in both countries. The results in both countries showed that, (1) Leaves, twigs, flowers and fruits were present in litter samples all over the study period with highest peak mainly in the dry season, and leaf production accounted for more than 80% in each country; (2) High values of most of the major nutrients (N, P, K, Mg, Ca) investigated and used in evaluation of mangrove ecosystem importance were recorded between March and October for Cameroon mangroves and in December for Ghana mangroves. (3) The mean highest species density was observed in Rhizophora for Cameroon and Avicennia and mixed in Ghana. The mangrove of Cameroon showed greater heights than their Ghanaian counterparts. (4) The values of Physical parameters (DO, BOD, EC, TDS, TSS), and nutrients were most often high in Cameroon, compared to Ghana. Mangrove waters were also found more alkaline in Cameroon than in Ghana. (5) It was observed that in both countries, Avicennia had the highest percentage of silt. In addition to that nitrogen ,phosphorus, leaves (Litterfall), nitrate, Biochemical Oxygen Demand, pH, Phosphate, salinity, Conductivity (Mangrove Water ), percentage organic nitrogen, electrical conductivity, acidity, Exchangeable magnesium, ECEC Effective Cation Exchange Capacity, and available phosphorus Av P (Mangrove Soil), height, basal area and density (Structural characteristics) were the major discriminatory ecological features of the mangroves of Ghana and Cameroon. Correlations with litterfall, structural, water and soil variables indicated that mangrove ecosystem within and across the countries respond differently to environmental conditions. The combination of rainfall, temperature and salinity was a good predictor of variability in the production of litterfall in both countries. This study contributes to a better understanding of how mangrove ecosystems function. Additional work in other geographic areas within the West and Central African ecoregion is needed to provide a broader perspective on the ecological importance of mangrove ecosystem and their impact on the nearby marine and coastal areas.
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    Hydro-Biology and Fish Production of the Black Volta Near the Bui Dam During the Pre and Post Impoundment Periods
    (University of Ghana, 2013-06) Alhassan, E.H.; Ofori-Danson, P.K.; Nunoo, F.K.E.; Samman, J.
    The hydro-biology of the Black Volta near the Bui dam were studied in relation to fish production as measured by catch per unit effort (CPUE) during the pre- and post-impoundment periods between February 2011 and December 2012. The primary objective was to assess the ecological impacts of the dam on the hydro-biological factors and fish production and provide data for monitoring the hydro-biology and fisheries of the Bui reservoir. Two sampling stations at Bui and Bamboi were selected to represent the upstream and downstream stations respectively. Physico-chemical parameters such as electrical conductivity, total dissolved solids, colour, dissolved oxygen and sulphates differed significantly (p < 0.05) during the pre-impoundment (March – May 2011), immediate post-impoundment (June – December 2011) and late post- impoundment (January – December 2012) periods. Hence, indicating the impact of the impoundment on these parameters. The Canonical Correspondence Analysis was used to trace temporal phytoplankton and zooplankton community changes, and to examine the relationships between species composition and physico-chemical variables. These variables were subjected to analysis, pair-wise, to identify correlations. The relative abundance of some phytoplankton species such as Anabaena sp, Planktothrix sp and Scenedesmus sp were directly correlated to nitrates. The phytoplankton groups, namely Bacillariophyceae, Chlorophyceae, Euglenophyceae and total phytoplankton differed significantly (p < 0.05) between the pre- and post-impoundment periods. The phytoplankton and zooplankton groups were also significantly (p < 0.05) higher in the upstream station than the downstream station indicating the impact of the impoundment on the downstream ecology. The change from riverine to lacustrine conditions during the formation of the reservoir, led to the immediate reduction in the numbers of a variety of fish families, including Centropomidae, Clarotidae and Distichodontidae which were very sensitive to oxygen depletion. The basic trend in this study was towards the development of a community of fish species which had vegetarian food habits such as Sarotherodon galilaeus, Labeo coubie and Labeo senegalensis. The mean estimated CPUE for the 2 years (2011 and 2012) was lower (6.23 kg/canoe/day) in the post-wet season than in the dry season (10.86 kg/canoe/day) with a mean of 7.95 kg/canoe/day. Hence, the dry season was the most important season for fish catches, while the post-wet season was the lean season in the study area. The CPUE also differed significantly (p < 0.05) between the pre- and post-impoundment periods indicating that the dam had impact on fish production as measured by CPUE. These findings suggest that the impoundment altered not only the river hydro-biology but also its fish production. A multi-linear regression analysis of both water level and chlorophyll a content on the CPUE indicated that both partial coefficients were significant (p < 0.05) and the best, most prudent model to predict fish production as measured by CPUE was derived as: CPUE = - (0.456 x water level) + (0.062 x chlorophyll a) + 3.363 The coefficient of determination, R 2 of 0.906 of the model explained about 91 % of CPUE variability. This study has provided a checklist of organisms present in the water for subsequent exploitation, conservation and sustainable management of the resources of the Bui reservoir. The study also revealed that the impoundment altered the hydro-biology and fisheries characteristics of the downstream station. Hence, river management strategies should be implemented by fisheries managers to lessen the impact of the dam on the downstream ecology.