Effects of Natural Processes on Sea Level Change along the West African Coastline

Coastal hazards induced by meteo-marine forcing are exacerbated by sea level change along the West African coastline. Changes in sea level are induced by ocean processes such as ocean heat content and river discharge. However, although these processes control largely change in sea level, they remain poorly understood. This study analyzes changes in ocean heat content, river discharge, and sea level and establishes an interconnection between these parameters using several statistical methods over the 1993-2021 period. Results showed a significant correlation between sea level and ocean heat content at 2000 m depth. The yearly minimum value appears in July from Cote d’Ivoire to Benin, whilst this value appears in June in Nigeria. The temporal variability of ocean heat content, river discharge and sea level along the West African coastline exhibits three or four periods interrupted by some breakpoints with unequal duration. The results indicate that the 1993-2000 period was dominated by an increasing ocean heat content along the coastline, while the period after the 2000s exhibits mostly a decreasing trend. Positive and negative trends characterized river discharge and sea level along this coastline. The result of multiple linear regression between sea level, river discharge and ocean heat content is a good approximation of sea level trend along the West African coastline. The results of this study could be used to predict future sea level trends along the coast.

An Empirical Assessment of Marine Debris, Seawater Quality and Littering in Ghana

A baseline survey was carried out at four beaches along Ghana’s Accra-Tema coastline over a period of sixteen weeks to determine beach quality, seawater quality and the perception of beach users towards littering. A total of 18,241 items of marine debris which weighed 297.59 kg were collected. Plastic materials were the dominant debris, accounting for 63.72% of total debris. Land-based marine debris formed the largest proportion of debris collected (93% of items/m2 and 85 kg/m2). Water quality analysis revealed high mean levels of coliforms and E. coli above World Health Organization (WHO) levels on all four beach locations. A social survey that targeted beach users and some stakeholders revealed a habit of littering and beach users as the main source of litter generation on Ghana’s beaches. Intensive education, continuous monitoring and the enforcement of appropriate policy initiatives remain vital to addressing beach and water quality issues along Ghana’s coastline.

Lake-Based Nursery Rearing of Nile Tilapia (Oreochromis niloticus) Fingerlings in Nylon Hapas: Effects of Stocking Density on Growth, Survival and Profitability

The inadequate supply of tilapia fingerling is a major limitation to cage culture development in Ghana. Lake-based hapa systems are very efficient in nursing fingerlings although the process can be tricky due to inherent effects of stocking densities and environmental factors. This study aimed at assessing the growth, survival and profitability of Nile tilapia (Oreochromis niloticus) fingerlings of the Akosombo strain reared in nine 1 m3 Lake-based hapas at different densities. Each hapa was stocked with 2.12 ± 0.14 g sex-reversed tilapia fingerlings at varying stocking densities of 400 fish/m3, 800 fish/m3 and 1200 fish/m3 serving as treatments T1, T2 and T3 respectively. Each treatment was replicated thrice. Bi-weekly samplings were done and water quality parameters were measured. After the experiment, analysis of variance showed significant differences (p

Population structure and reproductive parameters of the Longneck croaker, <i>Pseudotolithus typus</i>(Pisces, Bleeker, 1863) in nearshore waters of Benin (West Africa) and their implications for management

Pseudotolithus typus is one of the two commercially important Sciaenids off Benin nearshore waters mainly fished by beach seining. Unfortunately, since 1994, the production of this species has been decreasing, and increasingly more small-sized fishes are regularly harvested, while little is known about the species’ population structure and its life history. Therefore, population structure, probability of capture and size at first capture were investigated using length-frequency data of 1144 specimens sampled from beach seine hauls over a period of 18 months. A total of 54.3% of this population was immature, confirming the domination of smallsized fishes in the catches. Gonad maturation stages were also examined. Frequency distribution of oocyte size exhibited two cohorts of mature oocytes suggesting two spawning periods per year. Monthly averages of gonado-somatic index confirmed that P. typus spawned twice a year during the major warm season (March - May) and during the transition minor warm to minor cold season in October - November. Length at first capture (L75 = 22.76 cm) was smaller than the length at first sexual maturation (L50% = 23.6 cm) indicating a heavy pressure of the beach seine on this resource. To give each fish the chance of reproducing at least once in its lifetime to recruit into the stock, necessary measures such as the size-limit regulation by gradually increasing beach seine mesh size should be developed. Community-based management of the nearshore fishery could contribute to reducing fishing effort during the reproductive periods from February to May and from October to December each year.

Mangrove Degradation and Management Practices along the Coast of Ghana

Mangroves are increasingly being degraded in West Africa. We explored local utilization, threats and assessed existing conservation practices in Ghana through field visits, mapping, laboratory analyses and interviews. The study reports three species of mangroves along Ghana’s coastline;white (Avicennia germinans), red (Rhizophora racemosa), and black (Laguncularia racemosa) mangroves. White mangrove is the most dominant, with black mangroves being the least. The current mangrove cover of Ghana was estimated at 72.4 km2 with over 18 million trees (average = 2284.21 trees per hectare), both naturally occurring and planted mangroves. The Volta Region had the most abundant mangroves, with the Central region recording the least. Notable flora within the mangrove forests included Acrostichum aureum, Sesuvium portulacastrum, Paspalum vaginatum, Sporobolus maritima and Conocarpus erectus. Mangrove wetland in Ghana provides suitable nursery habitats for several important fish species, including Sarotherodon melanotheron, Mugil cephalus, Callinectes amnicola, Cardiosoma armatum, Crassostrea sp, Periophthalmus papilio, Coptodon spp. Ghana’s mangrove forest is declining at a rate of 8.1 km2 per annum due to over-cutting, land conversion, wildfires, pollution, overgrazing and natural death from disease. Over cutting mangrove for fish smoking and housing construction were significant threats to mangroves nationwide. Continuous education, law enforcement, nature-based methods and local control mechanisms effectively protect mangroves.

The Influence of Land-Use on Water Quality in a Tropical Coastal Area: Case Study of the Keta Lagoon Complex, Ghana, West Africa

The Keta Lagoon and its catchment areas in Ghana are influenced by intensive agriculture and the use of agro-chemicals. It has therefore, become necessary to assess the quality of water in the lagoon and the surrounding fresh water aquifers. In this study, a water quality index (WQI), indicating the water quality has been adopted. The WQI was determined on a basis of various physico-chemical parameters like pH, conductivity, turbidity, dissolved oxygen, calcium, magnesium, chloride, nitrates, ammonium and sodium. The index was used both for tracking changes at one site over time, and for comparisons among sites. The WQI was also employed to wells used for irrigation on farms along the Keta Sand Spit as well as that of the Keta Lagoon Complex and its surrounding floodplains, in order to ascertain the quality of water for public and livestock consumption, irrigation, recreation and other purposes. The WQI of the wells, Keta lagoon and its floodplains showed various degrees of poor water quality and therefore considered unsuitable for drinking and recreation. By WHO standards, this calls for intensive physical and chemical treatment of the water for human consumption.

Geochemical Assessment of Heavy Metals in Surface Sediments： A Case Study of the Tema Port, Ghana

Ten trace and heavy metals （Fe, Mn, Ni, Zn, Cu, Cd, As, Co, Cr and V） were analysed in sediments collected from nine stations at the Tema Port of Ghana, during the dry and wet seasons. Analysis of samples was done using INAA （instrumental neutron activation analysis） for Mn, V, Cu, As and Cd, and AAS （atomic absorption spectrophotometry） for Fe, Cr, Zn, Ni and Co. The concentrations of metals in sediments followed the orders Fe 〉 V〉 Mn 〉 Cd 〉 Ni 〉 Zn 〉 Cu 〉As, for the dry season and Fe 〉 V 〉 Ni 〉 Cu 〉 Zn 〉 Mn 〉 Cd 〉As, for the wet season. Concentrations of Co and Cr were below detection limit, whiles Cu, Cd and Ni were found to be above the TELs （threshold effect levels） of NOAA＇s （National Oceanic and Atmospheric Administration＇s） SQuiRTs （screening quick reference tables） at most sites. Estimated enrichment factors for individual metals showed very high contamination of the port＇s sediments, with Cd occurring at all sites, and Cu, As, V and Ni occurring at some sites for both dry and wet seasons. Although sediments from the Tema Port were highly enriched with Cd, Cu, Ni and V above natural background levels, the overall PLI （pollution load index） per sampling station considering background values of the analysed elements indicated that metal pollution in the port＇s sediment is below 1, indicating relatively unpolluted sediment.

Annotated checklist and fisheries interactions of cetaceans in Togo, with evidence of Antarctic minke whale in the Gulf of Guinea

Based on strandings and captures,9 cetacean species,including 6 odontocetes and 3 mysticetes,are document-ed(photos and specimens)in Togo’s coastal waters(newly-recorded species marked with an asterisk):Antarc-tic minke whale(Balaenoptera bonaerensis*),Bryde’s whale(Balaenoptera brydei or B.edeni),humpback whale(Megaptera novaeangliae),sperm whale(Physeter macrocephalus),pygmy sperm whale(Kogia brevi-ceps*),short-finned pilot whale(Globicephala macrorhynchus*),pantropical spotted dolphin(Stenella attenu-ata*),common bottlenose dolphin(Tursiops truncatus)and common dolphin Delphinus sp.An anecdotal sight-ing record for killer whale(Orcinus orca)is considered reliable.The lack of Sousa teuszii records in Togo is consistent with its apparent contemporaneous absence in Ghana.The B.bonaerensis specimen,entangled in a purse seine set on small pelagics,is a first record for the Gulf of Guinea.The occurrence of this Southern Ocean species north of the equator underscores the severe gaps in our understanding of cetacean distribution off west-ern Africa.The majority of artisanal fishermen operating in Togolese coastal waters are of Ghanaian origin and are thought to promote trade and consumption of cetacean bushmeat.Because captures are illegal,enforced with some success in the main fishing centers,covert landings of cetaceans are exceedingly difficult to moni-tor,quantify or sample.Concern is expressed about pollution of Togo’s coastal waters with heavy metals due to phosphorite mining and export from the coastal basin near Hahotoéand Kpogamé.

Acute hyperthermia and hypoxia tolerance of two improved strains of nile tilapia(Oreochromis niloticus)

Tilapia production in Ghana has been hit with episodes of stress and pathogen-induced mass fish kills which have anecdotally been linked to the culture of illegally imported Genetically Improved Farmed Tilapia(GIFT)strains of Nile tilapia,Oreochromis niloticus.This study was thus set up to comprehensively assess the stress tolerance of the GIFT strain and a native strain of Nile tilapia(the Akosombo strain)following exposures to hyperthermic and hypoxic stressors.In a series of experiments,oxygen consumption(MO_(2)),aquatic surface respiration(ASR),thermal limits and hypoxia tolerance were assessed.The effects of these stressors on haematological parameters were also assessed.The GIFT strain was less tolerant of hypoxia and performed ASR at higher O_(2) levels than the Akosombo strain.Under progressive hypoxia,the GIFT strain exhibited higher gill ventilations frequencies(fV)than the Akosombo strain.The thermal tolerance trial indicated that the Akosombo strain of O.niloticus has higher thermotolerance than the GIFT strain and this was reflective in the higher LT_(50)(45.1℃)and LT_(max)(48℃),compared to LT_(50) and LTmax of 41.5℃ and 46℃ respectively.These results imply that it is crucial to consider how the GIFT strain performs under various environmental conditions and changes during culture.Particularly,raising the GIFT strain of Nile tilapia in earthen ponds rich in phytoplankton and subject to protracted episodes of extreme hypoxia may have a detrimental physiological impact on its growth and welfare.

Effect of an amalgamated antibiotic and its connection to cytogenotoxicity and histo-architectural malformations in stinging catfish

Intensive fish farming has an excessive prevalence of infection and is typically controlled by the administration of antibiotics.Although amalgamated antibiotics are a relatively novel therapeutic idea and more effective than traditional antibiotic monotherapy,they can also have a toxic effect on the fish body when it is administered abruptly.This study investigated the cyto-genotoxic effects on erythrocytes and histo-architectural malformations in the liver and kidneys of stinging catfish(Heteropneustes fossilis)in relation to Enrocip plus use as an amalgamated antibiotic agent.The experimental fish with an initial average weight of 17.38±1.94 g were divided into four treatment groups with antibiotic doses:according to the recommendation of the manufacturer 0.167 mg/ml Enrocip plus was used as a standard dose(x)and it was treated as T3,while 0%of the standard dose(0×mg/ml),1/2×(0.083 mg/ml),and 2×(0.333 mg/ml)were treated as T1,T2 and T4,respectively for a period of 30 days.The observed erythrocyte cellular deformities(ECD)were twin,tear-drop,serrated,tail budded and de-membranated cells,whereas the erythrocyte nuclear deformities(END)were a nuclear bridge,bi-nucleus,nuclear termination,karyopyknosis,and micronucleus at different concentrations of Enrocip plus.Both ECD and END percentages experienced the interaction of antibiotic dose and exposure time,and were significantly different(P<0.01).Significant changes in hepatocytes,mild to severe necrosis,vacuole formation,and hepatopancreas damage were also observed in the liver of the treated fish whereas highly degraded renal tubules and hematopoietic tissue,glomerular occlusion,and vacuolation were evident in the kidneys.The current investigation fully emphasizes the adverse effects of amalgamated antibiotics on the cytogenotoxicity and the histomorphology of the kidneys and liver of fish.Thus,the use of an amalgamated antibiotic in aquaculture must be carefully evaluated.