Browsing by Author "Armah, A.K."

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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.
Distribution and Ecology of Nesting Sea Turtles in Ghana
(University of Ghana, 2002-10) Amiteye, B.T.; Armah, A.K.; Darpaah, G.A.; Ofori-Danson, P.K.; University of Ghana,College of Basic and Applied Sciences,School of Biological Sciences,Department of Marine and Fisheries Sciences
Distribution and Ecology of Nesting Sea Turtles in Ghana. Information on the occurrence and reproductive biology of sea turtles in Ghana is very scanty, therefore there is a need for detailed scientific studies on which their conservation and protection could be based. The present study has shown that the Olive ridley, Leatherback and Green turtles are the three main species that continue to nest on the beaches along the coast of Ghana. The Olive ridley having the highest relative abundance of 91% at the intensive study area followed by the Leatherback turtle with 6% and the Green turtle 3%.The nesting season begins in August and extends to March, sometimes early April. It peaks in October for the Olive ridley and between December and January for the Green and Leatherback turtles. The Olive ridley turtles arrive first, followed by the green and Leatherback turtles. The nesting period of the Green and Leatherback turtles overlaps that of the Olive ridley. Sea turtles nest in a wide range of beach sediment type along the coast of Ghana. Beach sand with median grain size between 0.2-0.4 mm (medium to coarse sand) and sorting coefficient between 0.4-0.7 (well-sorted to moderately well sorted) are those preferred by nesting turtles along the coast of Ghana. Based on the above grain characteristics, the potential sea turtle nesting sites in Ghana may include beaches along Princess Town to Busua, Senya Bereku to Accra, Prampram to Old Ningo and Anloga to Denu. Estimated average clutch size for Olive ridley, Green and Leatherback turtles were 86, 83 and 81 respectively. However, those counted for the Olive ridley and Leatherback were 100 (SD=6.64) and 85 (SD=10) respectively. Emergence period for the Olive ridley was 52 days, Green turtle 56 days and Leatherback 63 days. Percentage hatching success was very high among all the three nesting species with Olive ridley recording the highest with 92.40%.The percentage hatching success for the other two, Green turtle and leatherback were respectively 89.38 and 88.32. Destruction of sea turtle eggs by dogs at the intensive study area was very high, but this problem was not widespread along the entire coast of Ghana. Percentage false crawls where found to be higher within zones closer to human habitation.
Early Paleogene climate and productivity of the Eastern Equatorial Atlantic, off the western coast of Ghana
(Quaternary International, 2006-05) Arkaah, A.B.; Kaminski, M.; Ogle, N.; Kalin, R.M.; Atta-Petters, D.; Apaalse, L.; Wiafe, G.; Armah, A.K.
Early Paleogene warmth is consistent with global observation, although temperature reconstructions were characterized by some degree of uncertainty. In spite of applied corrections, the suggested epifaunal benthic foraminifera maximum temperature range (23.65-30.36 °C) was still above the proposed maximum tropical sea surface temperature of ∼27 °C, confirming that foraminiferally derived temperatures are strongly dependent on assumptions. Paleoclimate and paleoproductivity of the Eastern Equatorial Atlantic were poorly correlated (R2 < 0) due to major anomalies. δ13C isotopic signatures have been largely and independently used to resolve discrepancies in eight anomalous depths identified in this study, in view of overlapping δ18O isotopic signatures. The last three anomalies are consistent with the dramatic onset of global cooling which occurred during this interval. The first five still remain anomalous, challenging the conventional view that glacial oceans are more productive than interglacial oceans. Discrepancies in these anomalous depths could have been due to artifacts, preservation biases related to dissolution, and/or shell thickening or encrustation. However, this study suggests extratropical variability and climate dynamics, reflecting regional anomalies due to upwelling or feedback mechanisms of poleward heat transport, which are prevalent in the Eastern Equatorial Atlantic. © 2005 Elsevier Ltd and INQUA. All rights reserved.
Factors affecting macrobenthic fauna in a tropical hypersaline Coastal Lagoon in Ghana, West Africa
(Estuaries and Coasts 5(31): 1006-1019, 2008) Lamptey, E.; Armah, A.K.
The macrobenthic fauna in the large, hypersaline, shallow Keta Lagoon in Ghana was sampled at 20 stations in the set (September, 2002) and dry seasons (March, 2003) to elucidate the effects of abiotic factors on community patterns. The macrobenthic fauna was low in density and species diversity and numerically dominated by bivalves and capitellid polychaetes. These organisms appear able to withstand physical disturbance (when legoon water levels become extremely low) and osmotic stress (when slinities are extremely high) and tend to redistribute along environmental gradients. Parallel seasonal difference in several environmental variables and the macrobenthic fauna indicate a highly dynamic system. Species richness and diversity were higher in the wet season than the dry season. Salinity, percent clay, pH, and turbidity in that order were the major significant variable structuring the macrobenthic faunal assemblage in Keta Lagoon. The strong effect of seasonal salinity charges on macrobenthic faunal assemblage may have tropic consequences for higher organisms of commercial importance, such as fishes and shorebirds, in the Keta Lagoon.
Fish as Bioindicators of Habitat Degradation in Coastal Lagoons
(University of Ghana, 2012-06) Eugenia, B.B.; Armah, A.K.; Dankwa, H.R.
Lagoons and their wetlands are some of the most biologically and ecologically important ecosystems. The lagoon habitat also forms an integral part of the marine fishing industry and provides important spawning and nursery grounds for many fishes. Aquatic communities including fish and other species act as biological indicators of water quality and alterations by summarizing information about their environment. Two lagoons, Laloi and Oyibi in the and Greater Accra and Central Regions of Ghana were studied from January to May to determine the ecological status using the Estuarine Fish Community Index (EFCI). Metrics assigned were the species diversity, trophic integrity, nursery function and species abundance and composition. At each site, water samples were taken at the riverine, middle and seaward portions during both high and low tides. Fisher folks were hired to fish at each of the sites. Uni-variate analyses (diversity) indices showed no significant differences between sites. Multi-variate analysis (Bray-Curtis similarity) showed a significant similarity between sites in relation to species composition. Eighteen species including both finfish and shellfish were identified. The flat head grey mullet (Mugil cephalus) and the black-chinned tilapia (Sarotherodon melanotheron) were the two most abundant species during the study. Mugil cephalus dominated catches in the Laloi lagoon and Sarotherodon melanotheron dominated catches in the Oyibi Lagoon. S. melanotheron, Lutjanus fulgens and Eucinostomus melanopterus were the most abundant species collected for the Laloi lagoon. Caranx hippos, L. fulgens, and M. cephalus constituted a major part of fishes caught in the Oyibi lagoon. The carangid, Caranx hippos contributed much of the biomass of fishes collected for both lagoons. Total fish abundance was greatest in the rainy season than the dry season. Chloropyll a concentrations and condition factor of S. melanotheron where highest at Oyibi Lagoon than Laloi Lagoon. Total organic carbon was observed to be high in the Oyibi lagoon hence the high numbers of S. melanotheron recorded. Tides were important factor affecting physico-chemical parameters. From the metrics assigned, Oyibi had a moderate site rating, suggesting that it was under moderate stress. The main stress factors identified were garbage dumping, defecation, land use changes and increased human pressure. Laloi Lagoon had a poor site rating, suggesting that it was under severe stress. The main stresses identified were overfishing, mangrove degradation, garbage dumping and increased human settlements along the sides of the lagoon. The multi-metric index described is an effective method that reflects the status of lagoon fish communities and the overall ecosystem conditions.
Meeting socioeconomic objectives in Ghana's sardinella fishery
(Natural Resources in Ghana: Management, Policy and Economics, 2010-01) Bailey, M.; Quaatey, S.; Armah, A.K.; Jacquet, J.; Khan, A.; Alder, J.; Rashid Sumaila, U.
It is frequently stated that there are explicit tradeoffs between biodiversity conservation and poverty reduction. This Chapter examines these tradeoffs through the interaction between Ghana's artisanal canoe fishery and the offshore trawler fishery. Ghana's marine biodiversity is threatened by a sizeable fishing industry partly because poverty is rife, and also because the coastal population has a high dependence on fish for their food security. The artisanal fishing fleet targets small pelagics, predominantly round sardinella (Sardinella aurita), with their catch used mainly for subsistence. By-catch in the trawler fleet, which includes round sardinella, is mainly consumed in urban areas within the country, while their target species are exported. Current artisanal sardinella catch is insufficient to meet subsistence needs, and therefore domestic reliance on trawlcaught sardinella for food security might be in conflict with the conservation of biodiversity. We develop a bioeconomic model, which illustrates that giving priority to the effective management of the artisanal fishery in Ghana could provide food and job security to the fishers of Ghana, without compromising biodiversity conservation, in contrast to the commercial trawl fishery. It appears that the sardinella fishery may be overcapitalized, as optimization results suggest effort could be cut in half while still providing catch levels of about 300,000 tonnes per year, or four times current artisanal catches. Limiting by-catch and spatial conflicts by the trawl fishery could yield economic benefits from the artisanal sector of over US$200 million over 20 years. © 2010 by Nova Science Publishers, Inc. All rights reserved.
Population dynamics of the African river prawn, Macrobrachium vollenhovenii, in Dawhenya Impoundment
(Turkish Journal of Fisheries and Aquatic Sciences, 2011-03) Alhassan, E.H.; Armah, A.K.
Studies were conducted on the growth and mortality parameters, recruitment pattern, probability of capture, yield-per recruit, and present rate of exploitation of the African river prawn, Macrobrachium vollenhovenii from Dawhenya impoundment, Ghana. Estimation of the von Bertalanffy growth parameters gave; L∞ = 14.2 cm, K = 1.0 yr-1, and to = -0.195 yr-1 with the growth performance index, F{cyrillic}' of 2.303. From the linearised length-converted catch curve, total mortality, Z was 5.36 yr-1. Natural mortality, M calculated from Pauly's empirical formula was 2.20 yr-1 and fishing mortality, F calculated from Z - M was 3.16 yr-1. From the mortality estimations, the present rate of exploitation, E calculated from F/Z was 0.59 indicating that, the species is on the verge of being over-exploited in the impoundment. Using the estimated value of the growth coefficient, K, the longevity was found to be about 3 yrs. Estimations from the probability of capture routines gave the length-at-first capture, Lc as 3.07 cm while the size distribution of the catches suggest two recruitment pulses in a year. It is therefore recommended that, the property right-based system for fisheries management should be implemented so that fishermen can cooperate in the management of the Macrobrachium fishery. © Published by Central Fisheries Research Institute (CFRI) Trabzon, Turkey in cooperation with Japan International Cooperation Agency (JICA), Japan.
The Population Parameters, Food Habits and Physicochemical Environment of Three Cichlid Species in The Southwestern Sector Of The Keta Lagoon
(University of Ghana, 2001-12) Ababio, S.D.; Vanderpuye, C. J.; Armah, A.K.; University of Ghana,College of Basic and Applied Sciences,School of Biological Sciences,Department of Marine and Fisheries Sciences.
The study was carried out in the southwestern sector of the Keta lagoon, a closed coastal lagoon located in the southeastern part of Ghana. The study was aimed at studying the population parameters and the feeding habits of the major fish species (in terms of catch) in the lagoon in relation to the prevailing physiochemical parameters and the benthic macro fauna of the area. The water physiochemical parameters studied included the electrochemical and the optical properties of the water as well as the nutrients available for production. Macro benthic fauna studies were also carried out, in relation to sediment grain size distribution and organic matter content, as an index of the ecological state of the area. The findings from the study indicate that the seasonal precipitation pattern of the area was mainly responsible for fluctuations in the lagoon water physiochemical regime during the period of the study. The benthic fauna diversity did not indicate any effect of any external perturbation on the lagoonal environment, except salinity changes. The study on the fishery resource of the lagoon indicated that even though there source is highly exploited, it is able to maintain itself by rapid reproduction at an early age. However, if exploitation is maintained at or above the current rate, its effect, coupled with that of the stressful environment could result in diminishing catches, with catches comprising mainly of small-bodied fishes.
Sea-level rise and coastal biodiversity in West Africa: A case study from Ghana
(Climate Change and Africa, 2005-01) Armah, A.K.; Wiafe, G.; Kpelle, D.G.
Available evidence points to an eventual rise of sea level for coastal areas as a result of global warming. Sea-level rise would introduce or aggravate existing threats to the continued survival of the biodiversity of low-lying coastal areas. In Ghana and the coastal states of West Africa, vulnerable habitats include the strand zone, lagoons, wetlands, and intertidal sandy and rocky areas. Physical and biological parameters of several of these habitats would change substantially as a result of submersion and increased salinity regimes. This would adversely affect, for example, the habitats of water birds, nesting beaches of sea turtles, and the brackish-water dependent fauna and flora of the estuaries and lagoons. Species extirpation leading to local loss of genetic diversity is envisaged to affect fauna like ghost crabs (Ocypoda spp.) and the fiddler crab (Uca tangeri). Plants in this category include five species of true mangroves (Rhizophora racemosa, R. harrisonii, R. mangle, Avicennia germinans and Laguncularia racemosa) and their associates (Conocarpus erectus, Acrostichum aureum and the uncommon creeper, Phylloxerus vermicularis). Strategies that would mitigate or protect biodiversity of the coastal zone from the anticipated effects of rising sea level are advanced. The potential role of coastal infrastructures in biodiversity conservation is addressed. © Cambridge University Press 2005.
Seasonal Dynamics of Benthic Macrofauna in the Keta Lagoon
(University of Ghana, 2003-05) Lamptey, E.; Armah, A.K.; Wiafe, G.; University of Ghana, College of Basic and Applied Sciences, School of Biological Sciences, Department of Marine and Fisheries Sciences
This study was therefore, undertaken to investigate the seasonal dynamics of benthic macrofauna distribution and abundance in relation to environmental variables of the Keta lagoon. The studyl provides an understanding into benthic ecology in the Keta lagoon. The study also will provide an important baseline information on the likely long-term impacts of constructional activities of Keta Sea Defence Work Project and anthropogenic impacts of the settlements around the lagoon especially from the growing populations on the coastal belt.
Some Aspects of The Biology and Dynamics of the Blue- Spotted Sea Bream, Sparus Caeruleostictus in Ghanaian Waters
(University of Ghana, 1994-05) Owusu-Boateng, K.; Vanderpuye, C.J.; Koranteng, K.A.; Armah, A.K.; University of Ghana, College of Basic and Applied Sciences, School of Biological Sciences, Department of Marine and Fisheries Sciences
This study, undertaken during the period March, 1992 - March, 1993, investigated the distribution, growth, population parameters, dynamics, food habits and reproduction of Sparus caeruleostictus in Ghanaian coastal waters - S.caeruleostictus show a distinctive size distribution by depth; bigger fish are found in deeper waters - There are two spawning periods in a year and new recruits come into the exploited population in their first year of life. S.caeruleostictus mature in their second year of life. Crustaceans are the main diet for the species. Growth and mortality parameters, as estimated with the Electronic Length Frequency Analysis (ELEFAN) methods are: LCTO = 44.3 cm (fork length), K = 0.48/yr., Z = 2.480/yr., M= 0.856 and F= 1.621/yr. The mean length at first capture, LC50 was estimated to be 10.75 cm (fork length) and the rate of exploitation E, 0.65. The lengths at first maturity for the males and females, were 18.4cm and 17.2cm (fork length) respective1y. Fecundity ranged from 4 0,000 — 400,000 (size range: 17.5 - 24.8cm fork length). Length and fecundity relationship was exponential and described by the equation: Log F = 1.3671 + 2.9479 Log L. Analysis of the relative yield per recruit (Y/R)’ showed that to achieve the maximum sustainable yield (MSY) it will be necessary to reduce the level of the present fishing effort.
“Species diversity and extinction”. In: Geraloine H. Tepper (ed.) Spatial assemblages of tropical intertidal rocky shore communities in Ghana, West Africa
(Nova Science Publishers, Inc., pp. 239-264, 2010) Lamptey, E.; Armah, A.K.; Allotey, L.C.