Coastal Waters Of Ghana Research Articles

Reproductive history of Cynoglossus senegalensis (Kaup, 1858) from coastal waters of Greater Accra, Ghana

Some life history aspects including the reproductive characteristics and population dynamics of Senegalese tongue sole (Cynoglossus Senegalensis, Kaup, 1858), in the coastal waters of Ghana, were studied between August 2018 and July 2019. The length data of 606 specimens from the coastal waters of the Greater Accra region of Ghana was analyzed for size structure, growth pattern, condition factor, sex ratio and length at first maturity. The mean length varied significantly (p -value < 0 .001) with sex (31.3 ± 0.4 cm in males, 34.3 ± 0.4 cm in females). Condition factor (K) did not vary significantly (p -value = 0.054) with sex (i.e. 0.466 ± 0.002 in males, 0.476 ± 0.004 in females). The gonadosomatic index (GSI) varied significantly p -value < 0 .001) with sex (2.29 ± 0.30 in males), (3.94 ± 0.25 in females) and spawning peaks in April and July. Five maturity stages were recorded for both sexes with the size at first maturity for females and males estimated at 44.1 cm and 38.3 cm, respectively. In conclusion, the assessed fish species is likely to experience recruitment failure in the future, if appropriate management measures are not in place. Reduction in fishing efforts ad establishment of closed season is highly recommended.Keywords: Cynoglossus senegalensis; Ghana; Growth; Fisheries management; Life history.

Potential human health risks associated with ingestion of heavy metals through fish consumption in the Gulf of Guinea

Heavy metal pollution of the marine environment has toxic implications for both the aquatic biota and human health. We examined the levels of Zinc (Zn), Lead (Pb), Copper (Cu), Cadmium (Cd), Arsenic (As) and Mercury (Hg) in muscles of Sardinella maderensis, Dentex angolensis, Sphyraena sphyraena and Penaeus notialis caught from the coastal waters of Ghana using inductively coupled plasma mass spectrometry method. Penaeus notialis recorded the highest concentrations of all the metals (Cu:12.08±1.46µg/g, Zn: 19.20±2.27µg/g, As: 8.46±2.42µg/g, and Cd: 0.03±0.01µg/g) except Hg. Mercury was relatively high in D. angolensis (0.14±0.03µg/g). Apart from As, all metals were within globally permissible daily limits for consumption by human per meal. The estimated Target Hazard Quotient due to the intake of Hg through D. angolensis consumption exceeded the threshold value across all age categories. Carcinogenic risks due to As intake through P. notialis consumption far exceeded the 10-6 threshold for all age groups in Ghana. It is recommended that the consumption of these fish species particularly, the shrimp P. notialis be done cautiously to avoid possible future health challenges.

Maturity length, fecundity and spawning season of Atlantic chub mackerel Scomber colias in the coastal waters of Ghana (west-central Gulf of Guinea)

Aspects of the reproductive biology of Atlantic chub mackerel Scomber colias are reported here based on data from random samples of artisanal fish landings from Ghana. The specimens were between 13.7 cm and 40.7 cm total length (TL), and both sexes matured at a mean length (L m50) of approximately 25 cm TL. An overall sex ratio of 1:1 was estimated for the population. Absolute fecundity of the fish ranged between 10 220 and 155 791 eggs (mean 48 238 [SE 2 324] eggs) in individuals measuring between 22.8 and 36.5 cm TL and weighing 104.3 to 525.3 g. Monthly variations in the gonadosomatic index and the proportion of fish with ripe gonads in the samples indicated the occurrence of spawning activities during two periods, March–April and June–August, the latter period of which coincided with the coastal upwelling season in Ghanaian waters. These findings are compared with those for chub mackerel from the northwestern and southwestern coasts of Africa. The results of this study will help inform the management of this small pelagic species in Ghana.

Biomass and carrageenan yields of Hypnea musciformis in relation to selected environmental variables in the coastal waters of Ghana

Biomass and carrageenan yields of Hypnea musciformis in relation to selected environmental variables in the coastal waters of Ghana

Assessing the stock status of Atlantic bumper, Chloroscombrus chrysurus, Linnaeus 1766, from the coastal waters of Ghana

The main objective of this study was to examine the growth, mortality, and exploitation rate of Chloroscombrus chrysurus from the continental shelf of Ghana, West Africa between July 2018 and June 2019. This study provided results on fishery dynamics parameters to contribute to estimating the stock assessment of these fish species. Monthly length-frequency data were collected from 697 samples and analyzed using fisheries models fitted in TropFish R. The von Bertalanffy growth parameters were utilized to analyze the population dynamics of these species using ELEFAN Simulating Annealing. The estimated asymptotic total length (L ∞ ), coefficient of growth (K), and growth performance index (Φ′) was 24.9 cm, 0.84 year -1, and 2.72, respectively, with a Response surface (Rn) value of 0.79. The total mortality (Z), natural mortality (M), and fishing mortality (F) rates C. chrysurus from the continental shelf of Ghana were 3.27 year -1 , 1.31 year -1 , and 1.96 year -1 , respectively. The exploitation rate (E) estimated was above the optimum level of 0.5 which indicates that the species is overexploited. Based on the Emsy (0.69) value, analyses show that the exploitation rate has exceeded the sustainable limit and hence the need for proper fisheries management measures.

Age and growth of grey triggerfish Balistes capriscus from trans-Atlantic populations.

Anthropogenic factors that negatively impact reef fishes can include changes in life-history patterns of fisheries-targeted species. Understanding these impacts on growth and population age structure is essential in the management of exploited populations of fishes. This is the first study to directly compare age and growth for a major fisheries species between east and west populations of a transatlantic reef fish. The main goal of this study was to document age and growth in grey triggerfish Balistes capriscus from coastal waters of Ghana in the Gulf of Guinea (GOG) and compare those with the previous growth studies from that region and with the western Atlantic population. A secondary objective of this study was to evaluate the use of otoliths to age triggerfish and to provide a preliminary comparison with spine-derived age estimates. The results obtained from this study provided an updated understanding of the growth and age structure of the eastern B. capriscus population in GOG. The authors documented that shifts in population attributes occurred for B. capriscus after its major decline in abundance. The differences in physical and biotic characteristics of the East and West Atlantic regions and the differences in collection methods of samples make direct comparisons of growth parameters difficult. Nonetheless, overall differences in maximum sizes and ages were apparent; the western Atlantic population had a larger maximum size and older maximum age. The authors also documented that sagittal otoliths can be used to provide age estimates for triggerfish species, and otoliths as an ageing structure had better between-reader precision compared to dorsal spines.

Assessment of the fishery, growth and mortality characteristics of the cassava croaker, Pseudotolithus senegalensis (Sciaenidae) from coastal waters of Ghana

This paper reports on the fishery and some population parameters of the cassava croaker (Pseudotolithus senegalensis) at Anlo Beach near Shama (5°01’ N, 1∘37’ W) in the Western Region of Ghana. The study was conducted from July 2012 to June 2013 to contribute to information on the dynamics of demersal stocks in the country. Beach seining was the prime fishing method in the area with the fishing season spanning July to March. Catch per unit effort (CPUE), determined as catch per net haul per day was 9.5 kg in July 2012, 110 kg in January–February 2013 and 47 kg in March 2013. The species was absent from the fishery from April 2013 to June 2013. Monthly catches varied from 2295 kg to 31,500 kg, and specimens of the fish measured 7.5 cm TL to 105.4 cm TL and weighed 2.9 g to 7634 g. The length–weight relationship of the population was described by the equation: BW = 0.005TL3.04 (r=0.99), and grouping the fish at 5 cm class intervals showed modal lengths at 15.0–19.9, 35.0–39.9 and 60.0–64.9 cm TL. Analysis of the length-frequency distribution using the ELEFAN programme indicated an asymptotic length (L∞) of 110.3 cm TL, a growth coefficient (K) of 0.2 yr−1, and total (Z), natural (M) and fishing (F) mortality coefficients of 0.68 yr−1, 0.42 yr−1, and 0.26 yr−1 respectively, for the population. Longevity of the fish was estimated to be 15 years. A low exploitation level of the stock is suggested by the calculated exploitation ratio, E=0.38. These population characteristics are compared with those of other West African P. senegalensis populations.

Population Parameters of Two Commercially Important Species belonging to the Family Sciaenidae Encountered in the Coast of Ghana

Population parameters for two commercially important fishes of Sciaenidae from the coastal waters of Ghana were assessed using length-frequency data obtained from August 2017 to June 2019. Samples of the assessed fish species were obtained through experimental fish trawl along the coast of Greater Accra, Ghana. Trawling was performed every quarter for an average of one hour at an average speed of 3.0 km/hr. In all, a total of 399 samples were measured and the obtained data were analyzed with FiSAT II. The assessed fish species included Pteroscion peli (165 samples) and Pseudotolithus senegalensis (234 samples). The asymptotic length (L∞) was 19.4 cm and 41.5 cm forPteroscion peli and Pseudotolithus senegalensis. Pteroscion peli and Pseudotolithus senegalensis recorded growth rate (K) of 0.48 and 0.50 per year respectively. Both assessed fish species exhibited continuous recruitment pattern with minor and major recruitment peaks. The total mortality rate (Z) was 1.86 and 1.63 per year for Pteroscion peli and Pseudotolithus senegalensis. The fishing mortality rate (F) was estimated at 0.66 and 0.63 per year for Pteroscion peli and Pseudotolithus senegalensis. The natural mortality rate (M) estimated for Pteroscion peli and Pseudotolithus senegalensis was 1.20 and 1.00 per year respectively. The exploitation rate (E) of Pseudotolithus senegalensis (0.39) and Pteroscion peli (0.36) respectively was far below the maximum exploitation rate (Emax), indicating under-exploitation of its fishery in the coastal waters of Ghana, hence the need to enhance the exploitation of these species.

Hydrodynamic Model for Operational Forecasting in Coastal Waters of Ghana

The provision of economic resources to countries at the shore of Gulf of Guinea is a very important effort that has helped West Africa to develop to some extent. Taking the study area as a system it will be important to know the dynamics that occur in it to help neighouring countries predict its physical and thermodynamics states at all times. Ghana is located in West Africa and it is bordered in the south by the Gulf of Guinea or Atlantic Ocean. The objective of this research is to characterize the hydrodynamic circulation of the Gulf of Guinea areas neighouring Ghana. A 3-Dimensional hydrodynamic model was implemented in the territorial waters of Ghana using the Modelo Hidrodinamico, MOHID model to represent the dynamics and study the complex circulation pattern of the sea. To achieve this in an affordable computational time, nested domain approach was used to implement the hydrodynamic model in both 2 and 3-Dimensional gridded levels. The first level is a barotropic model with only tide. The nested domains of the rest of the levels are baroclinic forced with atmospheric and oceanic elements. To quantify its accuracy, the model was validated and calibrated in three stages; first, the frequency of the water level, followed by the circulation pattern and last, analysing the nature and profiles of the atmospheric and oceanic elements. The implemented model showed good agreement with the measured water surface level in the domain with mean error values not exceeding 14.00% of the measured data and with correlation factors higher than 0.80. Also, the intensity and direction of velocity observed in the current data are well represented by the model at the water surface levels with mean errors lower than 20.00% of the measured data components. The profiles obtained for both the temperature and salinity at shore show completely a straight line for salinity and also a straight line which is slightly curved at the top for the temperature profile. The vertical straight line for the salinity profile shows that at the shore the waters are not stratified vertically or they are well mixed. The slight curve at the top of the temperature graph accounts for the mixing dynamics that occur close to land or the effect of heat flux at the surface. It can be concluded that the hydrodynamic model obtained by this study is the true reflection of the territorial waters of Ghana.

Production of Biodiesel from Marine Macroalgae occurring in the Gulf of Guinea, off the Coast of Ghana

The purpose of this study was to determine the suitability of marine macroalgae (also known as seaweeds), from the Gulf of Guinea, off the coast of Ghana, for the production of biodiesel as an alternative to liquid fuels like gasoil and gasoline. Five green marine macroalgae species: Caulerpa taxifolia, Chaetomorpha antennina, Chaetomorpha linum, Ulva fasciata, and Ulva flexuosa, were collected from the coastal waters of Ghana at West Tema Rocks during low tide. Algal lipids were extracted from dried algae biomass with hexane and diethyl ether. Biodiesel was produced from algal lipids by base-catalysed transesterification, with alcohol. The lipid content of samples was highest in C. linum (1.13 g; 5.65% dry wt.) and lowest in C. antennina (0.54 g; 2.70% dry wt.). Similarly, the quantity of biodiesel produced from the lipids was highest in C. linum (0.97 g; 4.85% dry wt.) and lowest in C. antennina (0.48 g; 2.40% dry wt.). The quantity of biodiesel produced from samples of the five species fell well within the range obtained for such species worldwide. The implications of the yield of biodiesel for commercial production and future work on marine macroalgae from Ghana as source of biofuel are discussed.

Stomach Content Analysis and Concentrations of Chemical Pollutants in the Clymene Dolphin (Stenella Clymene, Gray 1846) from the Coastal Waters of Ghana

Stomach content analysis constitutes an important component of fisheries management, providing insight into fish feeding patterns and quantitative assessment of food habits. Thus, a study aimed at obtaining dietary information from stomach contents analysis of the most common by-caught dolphin species, Stenella clymene, beached from the coastal waters of Ghana, along the Gulf of Guinea was undertaken. The stomachs of 39 by-caught clymene dolphins landed at three fisheries landing beaches along the Ghanaian coast, were analyzed. A further study correlating the chemical contaminant load in tissues of Clymene dolphins to that of their preferred prey was undertaken. The stomach contents were generally composed of digested items. Fish, cephalopods and crustaceans were identified and represented a diversity of 12 species. On taxa level, fish was the most frequent (69%) and numerically the most important prey (46.57) followed by cephalopods (3.05) with crustaceans being present in trace amounts (1.55). However, both cephalopods and fish represented a more balanced share of the diet in biomass (45% and 51%) respectively. Thus, clymene dolphins off the coastal waters of Ghana appear to rely principally on both fish and cephalopods for food. Parasites also dominated the gut contents in relative abundance (48.83%). Prey items accumulated chemical contaminants at relatively the same concentrations (50%) as the blubber, liver and muscle of the clymene dolphins, confirming that food is the main source of exposure to contaminant load for marine mammals. With regards to quantitative analysis of prey species of cetaceans, this study of diet in clymene dolphins is the first recorded in this area.

Risk of heavy metal ingestion from the consumption of two commercially valuable species of fish from the fresh and coastal waters of Ghana.

BackgroundThe need to evaluate the human health safety of fishery resources remain urgent in the mist of the ever-increasing fear of heavy metal toxicity from the consumption of Ghana’s fisheries resource, as a consequence of pollution from several anthropogenic activities including artisanal gold mining. Nevertheless, the bigeye grunt (Brachydeuterus auritus) and Bagrid catfish (Chrysichthys nigrodigitatus) remain commercially valuable fish species in West Africa and continue to attract high patronage.MethodForty-five specimens each of C. nigrodigitatus and B. auritus collected from the Weija Dam and the Tema Fishing Habour in Ghana, between June and September 2016, were analysed for seven heavy metals using Atomic Absorption Spectrometry.ResultLead and Cadmium were below detection in all samples while Cu was not detected in B. auritus. Levels of the remaining metals (mg kg-1) were below FAO/WHO maximum permissible limits in fish and occurred in the rank order Se (3.5) > Zn (2.34) > Cu (0.59) > As (0.37) > Hg (0.19) in C. nigrodigitatus and Se (2.97) > Zn (2.28) > Hg (0.31) > As (0.21) in B. auritus. Only As in C. nigrodigitatus recorded Estimated Weekly Intake (EWI) greater than FAO/WHO Provisional Tolerable Weekly Intake (PTWI). Also, As in C. nigrodigitatus and Hg in B. auritus had Targeted Hazard Quotient (THQ) greater than 1 for individuals consuming the fishes on daily basis and therefore, raising concerns. However, for both species of fish, cancer risk of As was 1 in 10,000,000,000 and modified Health Benefits values of Se (HBVSe) were positive indicating the health risks that might accompany Hg exposure would be negated. Since toxicity depends on the concentration and quantity of a pollutant consumed, safe maximum consumption rate of C. nigrodigitatus based on As concentrations was 0.21 mg per day and that of B. auritus was 0.058 mg per day for Hg. With an average of 0.227 kg fish per meal of an adult human, these translated into not more than 24 C. nigrodigitatus and nine (9) B. auritus meals in a month but because fish is consumed at 0.0685 kg per person per day in Ghana, these values respectively translates to 93 and 30 safe days of consumption per month.ConclusionAt the rate of 0.0685 kg fish per person per day that fish is consumed in Ghana, the consumption of the two species of fish in Ghana would essentially be of little or no consequence to consumers.

Population dynamics of Sardinella aurita (Val., 1847) within Ghana’s coastal waters

Following the declining stocks of Sardinella aurita within the coastal waters of Ghana, this study aimed at examining some population parameters of Sardinella aurita as a guide for managing this important stock sustainably. Length-frequency data of 717 samples were obtained from June, 2014 to January 2015 and measured for total length with the resultant data analyzed using FiSAT II. The asymptotic length (L∞) and growth rate (K) were 21.53 cm SL and 0.25yr-1 respectively. The theoretical age at birth (t0), longevity (tmax) and growth performance index (ϕ) were -0.74yr-1, 12 years and 1.849 respectively. Total mortality rate (Z), natural mortality rate (M) and fishing mortality rate (F) were 3.17, 0.76 and 2.41yr-1 respectively. The ages at first recruitment and first capture signaled future collapse of the stock, in the absence of proper management interventions. VPA outcome showed that mid- lengths of 11 cm and 12 cm SL experienced the highest harvesting rate with MSY estimated at 7733 tons. The recruitment pattern was continuous with two major recruitment pulses. Exploitation rate (Ecurr=0.76) was higher than the maximum exploitation rate (Emax=0.56), indicating unsustainable exploitation. Further, the fishing regime fell within the overfished stage based on the Quadrant Rule. For sustainable exploitation of this commercial fish species, implementation of relevant biological reference points through reduction in fishing efforts, creation of marine protected areas and mesh size regulation are urgently advocated.Res. Agric. Livest. Fish.4(3): 237-248, December 2017

Aspects of population dynamics of Red Pandora, Pagellus bellottii (Steindachner, 1882) from the coastal waters of Ghana

Population parameters for Red Pandora, Pagellus bellottii (Steindachner, 1882) from the eastern coastline of Ghana, using length-frequency data from June 2014 to January 2015 were assessed. A total of 440 samples of Pagellus bellottii were measured for standard length and analyzed with FiSAT II. The asymptotic length (L∞) and growth rate (K) were 19.43 cm and 0.42 per year. Theoretical age at birth (t0 ) and growth performance index (ϕ) were -0.44 per year and 2.20. The age at first maturity (tm50) and longevity (tmax) were 2.2 years and 7 years. The Bhattacharya’s method revealed three modal lengths groups: 9.3 cm, 12.1 cm, and 14.6 cm. Total mortality rate (Z), natural mortality rate (M) and fishing mortality rate (F) were 2.58 per year, 1.10 per year, and 1.48 per year. Exploitation rate (Ecurrent) and maximum exploitation rate (Emax) were estimated as 0.57 and 0.93 respectively. The recruitment pattern was continuous with two major recruitment pulses. VPA outcome showed that midlengths of 11.5 cm and 12.5 cm experienced the highest harvesting rate. The fishing regime of Pagellus bellottii fell in the developed stage based on the quadrant rule. Maximum Sustainable Yield (MSY) was 7864.18 tons. Results from the study indicated the existence of growth overfishing with the present state of exploitation as a forewarning to the collapse of the fishery in future. With resilience of Red pandora within the medium category, incidence of overfishing will produce economic consequences. The developed stage of fishing suggested that maximization of yield per recruits will lead to low stock biomass of Red pandora.

Seasonal Variations in Temperature and Salinity in the Gulf of Guinea

A simple linear regression model was used to determine variations in temperature and salinity profile in the coastal waters of Ghana in Gulf of Guinea (GOG) from four surveys, two from each hydrographic season conducted between 2000 and 2002. The model estimated an average sea surface temperature (SST) of 27.13°C for thermocline season and 22.52°C for upwelling season. The average sea surface salinity (SSS) estimated by the model for the thermocline season was 35.24‰ and the upwelling season was 35.56‰. A seasonal sea surface temperature (SST) variability of 4.61°C was observed in the GOG. This revealed that that seasonal SST variability in the Gulf of Guinea (GOG) has reduced. The changes in temperature and salinity with unit change in depth did not show any clear pattern between thermocline and upwelling seasons. Temperatures showed higher level of correlation with changes in depth than salinity. The range of temperature within the 80-metre water column was higher in the upwelling season than the thermocline season. The range of salinity however did not show any clear pattern between the thermocline and upwelling seasons. There were no significant differences in temperature and salinity between the two upwelling seasons. There were however significant differences in temperature and salinity between the two thermocline seasons. The reduction in seasonal variability of SST in the GOG has implications for marine life in the region.

The effect of physico-chemical parameters on speciation of trace metals insediments from inland and coastal waters of Ghana

The speciation of cadmium, lead, copper, zinc, manganese and iron into exchangeable, carbonate, reducible and organic bound fractions was studied in sediments from coastal and freshwater environments in Ghana. This was relevant as the species in which metals are stored within specific sediment components is important in determining their impact on the environment. For both coastal and inland sediments, a higher percentage of cadmium was associated with the more available exchangeable and carbonate fractions, while iron, zinc and manganese were mainly associated with the reducible and organic fractions. Lead and copper were found to have the greatest ability to form different species in the samples examined and were more evenly associated with all the fractions. The metals generally showed more ability to form different species in inland freshwaters than in coastal relatively saline waters. However, differences between inland and coastal waters were based more on whether the environments were oxidising or reducing than on whether they were fresh or saline. The metals may be divided into three groups of high mobility consisting of lead and copper; moderate mobility made up of cadmium, manganese and zinc; and low mobility, represented by iron.

The seasonal cycle of the phytoplankton in the coastal waters of Ghana

Seasonal changes in the phytoplankton at four depths off Tema, Ghana were investigated between September 1973 and November 1974. The physico-chemical factors show that there are two marine seasons, the season of major upwelling (July–October), characterized by low water temperatures ( 35‰) and high nutrient levels, and a non-upwelling period (November–June) when water temperatures are higher and salinity and nutrients are lower. The latter marine season is broken by a small, unpredictable upwelling (December-January). Phytoplankton cell counts are high (> 1000 × 103 cells/1) during the major upwelling period and can be very low (< 2 × 103 cells/1) during the non-upwelling period. Dinoflagellates form the main components of the phytoplankton population during the nonupwelling period and diatoms form the dominant components at other times. There is a close relationship between the physicochemical factors and the phytoplankton population especially during the major upwelling period. For example there is a good correspondence between the peaks in phytoplankton numbers and low levels of nutrients such as silicate, nitrate and phosphate with the reverse taking place at other times.