Department of Marine and Fisheries Sciences

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    Evaluating The Performance Of CMRI For Estimating The Spatial Distribution Of Mangroves At The Keta Lagoon Complex In The Volta Region Of Ghana
    (University of Ghana, 2020-10) Sackey-Addo, S.
    Data obtained from remote sensing is useful for evaluating and mapping infrastructure and natural resources including vegetation. Over the past years, a number of vegetation indices have been developed to detect vegetation with the use of satellite imageries to monitor the distribution and phenology of mangroves. Forest managers and environmental scientists have developed a wide range of indices for delineating and assessing the health of different vegetation and forest cover. This study will evaluate the performance of Combined Mangrove Recognition Index (CMRI) for estimating and distinguishing mangroves in the Keta Lagoon Complex. The CMRI was compared to the Normalized Vegetation Index (NDVI), a widely used vegetation index and supervised classification (maximum likelihood) which were selected based on their classification accuracies of about 80% in the estimation of vegetation. Sentinel-2 imagery was used to generate vegetation maps for the NDVI and CMRI indices and a land cover map generated using the supervised classification (maximum likelihood) technique. The threshold value method was used to extract the values of mangrove areas for each index and used to delineate areas of mangrove and non-mangrove using binary data with the use of UAV imagery for validation. Random points with their coordinates were generated as reference points on the UAV imagery and overlaid on the other maps. Areas of mangroves were denoted “1” and areas with non-mangroves were denoted “0”. The Cochran’s Q test, used for statistical analysis of binary data was used to derive the p-value after which the area coverage of mangroves in the study area was estimated. From the study, the threshold values used to mask out mangroves were observed to be between 0.27 and 0.37, and between 0.51 and 0.70 for NDVI and CMRI respectively. UAV imagery was used to validate the area coverage due to its high resolution. The imagery covered an area of 1.8 km2 and was used as a subset for the mangrove area coverage comparison. Mangrove area coverage was estimated to be 0.32km2, 0.30km2, and 0.25km2 for NDVI, supervised classification and CMRI respectively. All techniques used in classification showed no statistical significance (>0.05) when compared to ground truth data. The CMRI was observed to have performed better and hence confirmed its sensitivity in estimating mangroves and that other satellite missions with optical sensors and multiple bands can be used to generate the index with high accuracy.
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    The Ecological Statusof The Keta Lagoon Using Physicochemical And Biological Indicators Of Water Quality
    (University Of Ghana, 2021-09) Danso, P.
    The Keta Lagoon and its catchment areas are under the influence of intensive agriculture which depend heavily on agrochemical usage. It is necessary that, the quality of water in the lagoon is assessed to broaden our understanding of how the lagoon and its associated biota are responding to agro-related activities in its watershed. This study carried out a comprehensive assessment of the ecological status of the lagoon using physicochemical parameters (temperature, DO, turbidity, pH, nitrate, phosphate, silicate, ammonia), Trophic State Index and diversities of benthic macroinvertebrates and phytoplankton communities. The lagoon was partitioned into five zones (A to E) to depict the intensity of human impact as reflected through farming along the bank of the lagoon. Zone A is the area in close proximity to Anloga, Zone B, covers the mid-section of the lagoon and falls between Anloga and Woe, Zone C is main Woe area, Zone D represents the area between Woe and Afedome and finally Zone E which represents the area beyond Afedome extending towards Keta. The average physicochemical parameters reported during the study showed that Zones A and B recorded the highest levels of pH, 9.6  0.16 which was above the acceptable range levels by Ghana’s EPA and USEPA (6.0 to 9.0). The least pH level was recorded for Zone C at 8.5  0.03 which was within the acceptable range of pH. Dissolved oxygen levels measured was highest in Zone D (8.1  0.26 mg/l) and least in Zone A (6.5  0.13 mg/l), all within Ghana EPA and USEPA as well as the World Health Organization tolerable limits. Zones A recorded the higest nitrate values of 3.4  0.03mg/l and least in Zone E, 1.9  0.02 mg/l. All zones recorded nitrate levels that were above the Ghana and US EPA permissible ranges. Ammonia was highest in Zone A (0.12  0.02 mg/l) and least in Zone E (0.03  0.02 mg/l), and Phosphate levels was highest in Zone A (0.26  0.01mg/l) and least in Zone E (0.13  0.01 mg/l). Both phosphate and ammonia measured were within the permissible limits. The Trophic State Index based on Chlorophyll-a estimation indicated that the lagoon was hypereutrophic (61.3-64.9). However, Zone A recorded the highest TSI value (64.9) and the least TSI was recorded by Zone E (61.3). Zones A, B and C (4.9-6.5) were in poor ecological conditions. D (3.0-3.8) was in fair ecological conditions. Zone E was in good ecological conditions. The mean Plankton Index of Biotic Integrity (P-IBI) for the entire lagoon, however, was 3.96 and that shows a mesotrophic lagoon with diverse populations of phytoplankton.The total number of macrobenthic species counted in the Keta lagoon was 1018 which consisted of 83% mollusks and 17% polychaetes as the major taxa. Generally, Macrobenthic assemblage richness, evenness and diversity were 1.2, 0.8 and 1.7 respectively for the lagoon. The trends of physicochemical parameters (temperature, DO, turbidity, pH, nitrate, phosphate, silicate, ammonia), Trophic State Index, diversities of benthic macroinvertebrates and phytoplankton communities showed that the lagoon is in the state of deterioration with time.
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    Evaluating The Performance Of CMIR For Estimating The Spatial Distribution Of Mangroves At The Keta Lagoon Complex In The Volta Region Of Ghana
    (University of Ghana, 2020-10) Samuel, S-A.
    Data obtained from remote sensing is useful for evaluating and mapping infrastructure and natural resources including vegetation. Over the past years, a number of vegetation indices have been developed to detect vegetation with the use of satellite imageries to monitor the distribution and phenology of mangroves. Forest managers and environmental scientists have developed a wide range of indices for delineating and assessing the health of different vegetation and forest cover. This study will evaluate the performance of Combined Mangrove Recognition Index (CMRI) for estimating and distinguishing mangroves in the Keta Lagoon Complex. The CMRI was compared to the Normalized Vegetation Index (NDVI), a widely used vegetation index and supervised classification (maximum likelihood) which were selected based on their classification accuracies of about 80% in the estimation of vegetation. Sentinel 2 imagery was used to generate vegetation maps for the NDVI and CMRI indices and a land cover map generated using the supervised classification (maximum likelihood) technique. The threshold value method was used to extract the values of mangrove areas for each index and used to delineate areas of mangrove and non-mangrove using binary data with the use of UAV imagery for validation. Random points with their coordinates were generated as reference points on the UAV imagery and overlaid on the other maps. Areas of mangroves were denoted “1” and areas with non-mangroves were denoted “0”. The Cochran’s Q test, used for statistical analysis of binary data was used to derive the p-value after which the area coverage of mangroves in the study area was estimated. From the study, the threshold values used to mask out mangroves were observed to be between 0.27 and 0.37, and between 0.51 and 0.70 for NDVI and CMRI respectively. UAV imagery was used to validate the area coverage due to its high resolution. The imagery covered an area of 1.8 km2 and was used as a subset for the mangrove area coverage comparison. Mangrove area coverage was estimated to be 0.32km2 , University of Ghana http://ugspace.ug.edu.gh iv 0.30km2 , and 0.25km2 for NDVI, supervised classification and CMRI respectively. All techniques used in classification showed no statistical significance (>0.05) when compared to ground truth data. The CMRI was observed to have performed better and hence confirmed its sensitivity in estimating mangroves and that other satellite missions with optical sensors and multiple bands can be used to generate the index with high accuracy.
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    Food and Feeding Habits of Three Tuna Species Landed in Ghana
    (2020-08) Tuga, A.
    Food and feeding habits of the three tuna species landed in Ghana were investigated for a period of six (6) months from October 2019 to March 2020. The species are Thunnus albacares, Katsuwonus pelamis, and Thunnus obesus. The study sampled a total of 210 individuals of the three tuna species, out of which 90 individuals were Katsuwonus pelamis, 60 individuals of Thunnus albacares, and 60 individuals of Thunnus obesus. The study sampled 90 specimens for Katsuwonus pelamis because they are of high abundance and very common in Ghanaian waters than Thunnus albacares and Thunnus obesus. These tuna species were sampled for stomach content analysis, to determine which type of prey item is most important and preferred as food for these three tuna species. The samples were transported to the Fisheries Scientific Survey Division (FSSD) laboratory in Tema, under the Ministry of Fisheries and Aquaculture Development for analysis. At the laboratory, some morphometric measurements of the samples were taken. The fish samples were dissected and their guts were removed for examination. Gut content analysis was conducted on each of the fish sampled. The gut fullness was determined on a scale of 0/4 to 4/4 by visual inspection. The commonest prey items discovered in the stomachs during the studies were Engraulis encrasicolus, Exocoetus spp, Penaeus kerathurus, Sepia hierredda, Loligo spp, and Metapenaeus monoceros. Engraulis encrasicolus was found to be the most preferred food item accounting for 58% occurrence by number, with Diplodus spp being the least preferred food item accounting for 2% for Thunnus albacares. For Katsuwonus pelamis, Penaeus kerathurus was found to be the most preferred food item accounting for 57% occurrence by number, with Sepia hierredda being the least preferred food item accounting for 10% of total prey items found. Exocoetus spp was also found to be the most preferred food item accounting for 86% occurrence by number, with Metapenaeus monoceros being the least preferred food item accounting for 12% for Thunnus obesus. Similarly, the most important food items identified using Index of relative importance were Engraulis encrasicolus, Penaeus kerathurus and Exocoetus spp with Diplodus spp, Sepia hierredda and Metapenaeus monoceros recording the least important for Thunnus albacares, Katsuwonus pelamis and Thunnus obesus respectively. There was a significant difference among these three tuna species with respect to Engraulis encrasicolus, Penaeus kerathurus Exocoetus spp, Sardinella aurita, Caranx crysos, Sepia hierredda, Loligo spp, and Brachyuran spp. Continuous research on food and feeding habits of these Tuna species to cover all the yearly seasons was recommended owing to their commercial importance to Ghana and the international community.