Influence of diurnal tides and other physico-chemical factors on the assemblage and diversity of fish species in River Pra Estuary , Ghana (original) (raw)
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Species Composition, Abundance, and Growth of Three Common Fish Species of the Volta Estuary, Ghana
There is growing concern over observed declines in fish catch and therefore catch rate in coastal water bodies in Ghana which have been attributed, in part, to changes in the environment and excessive pressure on exploited fish populations. This research examined biological performance measures (abundance and growth) of estuarine fish under varying physico–chemical factors such as temperature, salinity, dissolved oxygen and pH. Experimental fishing with seine net was done while specified water quality parameters were also collected simultaneously on a monthly basis for eight months in three identified salinity zones of the Volta estuary. The results indicated that temperature and salinity caused most variation in fish abundance. There were a total of 2,333 individual fishes caught in the survey. Most species examined were juveniles of marine migrants; these species ranged from 2.5 to 10 cm. This reinforces the fact that the estuarine environment serves as breeding and nursery ground for a number of fishes. The dominant fish species by number encountered were Caranx hippos, Mugil cephalus and Ethmalosa fimbriata. Fish growth was estimated using length-weight relationships and condition factor. The von Bertalanffy growth function determined for the dominant fishes indicated slow growth. Precautionary management measures should be implemented to regulate their exploitation to help sustain fish populations in the estuary and the adjacent freshwater and marine environments.
The Gambia Estuary, a “normal” estuary with a decreasing salinity gradient from the mouth towards the head, is moderately exploited by small-scale fisheries and does not receive any severe pollution from either agriculture or industrial activities. Neither the Gambia River nor its estuary are artificially impounded. As the last large West African estuary free of major human disturbance, it is of considerable interest for comparative studies on the effect of major environmental perturbations in West African estuarine ecosystems. The aquatic environment and fish communities of the Gambia Estuary (about 250 km long) were studied by purse seine sampling at different periods in the river cycle, covering all hydro-climatic seasons that are characteristic of West African estuaries. Emphasis was placed on the diversity, composition, structure and distribution of fish assemblages in relation to fluctuations in physico-chemical factors such as water temperature, salinity and turbidity. Results on the aquatic environment, mainly the salinity range (from freshwater to 39) and dissolved oxygen (never a limiting factor for fish in the estuary) and on the main characteristics of the fish fauna (high diversity of life cycles, all the ecological categories represented) indicated that the Gambia Estuary was free of major climatic perturbation and reinforced the choice of this system as a reference for the study of the effects of major perturbations on estuarine tropical fish communities.
Abundance, biomass and species composition of nearshore fish assemblages in Ghana, West Africa
Many of the world’s fish populations are overexploited, including Ghana’s fish resources. This study examines spatio-temporal trends in fish species composition in relation to biotic, abiotic and anthropogenic factors, towards achieving better-informed management of the beach-seine fisheries. Fishery-dependent data were collected between November 1999 and October 2001 from 94 beach-seine hauls fished at two stations along the Ghanaian coast. The catch consisted of fish, crustaceans, other invertebrates, and macroalgae. Generally, juveniles of species that are exploited by offshore fisheries were found in the catches. Species abundance and their occurrence generally peaked between November and January. Duration of solar radiation and tide level appeared to be important predictors of fish biomass. It is important to exploit the nearshore fish assemblage sustainably because of its nursery role. A co-managed (fishers and government) three-month ban on beach-seining (between May and July) is recommended as the most appropriate control measure towards the sustainability of Ghanaian fish stocks.
The fisheries of the Black Volta near the Bui dam in Ghana were studied during the pre- and post-impoundment periods between February 2011 and December 2012. The primary objective was to assess the ecological impact of the dam on the fisheries. During the survey, a sampling unit was considered as a fishers’ catch per canoe per day. A three-level stratified random sampling approach was adopted. The first stratum which was defined by four designated hydrological seasons in the study area was as follows: dry season (January to March); pre-wet season (April to June); wet season (July to September); and post-wet season (October to December). The second stratum was defined by the three impoundment periods: pre-impoundment (March to May 2011); immediate post-impoundment (June to December 2011); and late post-impoundment (January to December 2012). The third stratum, on the other hand which was defined to improve sampling for accuracy was: above the dam site or reservoir area with sampling station at Bui (old town currently submerged); and below the dam site area with sampling station at Bamboi. Sixty-three fish species belonging to thirty-eight genera and twenty families were recorded in commercial gill net catches while thirteen species in nine genera and six fish families were recorded in experimental gill nets during the study. 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 Latidae, Clarotidae and Distichodontidae which were very sensitive to oxygen depletion. The trend found in this study was towards the development of a community of herbivore fish species such as Sarotherodon galilaeus, Labeo coubie and Labeo senegalensis. The study revealed that the impoundment altered the fisheries characteristics of the downstream station. Hence, river management strategies should be implemented by fisheries managers and officials of the Bui Power Authority to lessen the impact of the dam on the downstream ecology.
The seasonal variation in species abundance and composition of fish fauna of Lagos Lagoon were studied monthly from January to December, 2013. A total of 11,332 fish specimens made up of juveniles and adults caught were identified. They comprised of forty-nine species belonging to 28 families. Ethmalosa fimbriata (27.4 %) had the highest in terms of number followed by Chrysichthys nigrodigitatus (11.4 %). Twelve species occurred only once during the period of study. The fish reported in this study were group into three; first group were caught during the rainy season, second group were caught during the dry season, and the third group were caught throughout the year. The largest catch was recorded in May (51.05 kg) followed by July (45.34 kg). The least catch was recorded in January; dry season (4.5 kg). The mean value of water temperature (29.8 ℃), salinity (7.49 ‰), pH (7.17), dissolved oxygen (5.49 mg/L) and turbidity (5.68 NTU) were recorded. The results from this work will be a useful contribution to the current knowledge of fisheries needed for proper management and conservation of fisheries resources of Lagos lagoon.
International Journal of Hydrology
The composition and diversity of the fin fish of upper course of Otamiri River was study for the period of three months to evaluate the likely effects of the recent anthropogenic activities around the river on the fish species. Water sample for physcio-chemical parameter were collected and analyses using conventional field and standard laboratory techniques. Likewise, the fish samples were collected bi-weekly using active and passive fishing gear. All the physic-chemical parameters measured fall within the standard recommended limit for aquatic management except the pH, ammonia, total suspended solid, Nitrate and carbon (iv) oxides. Also, sixteen species of fish belong to 9 fish families were recorded with the families, Cichlidae recording the highest percentage abundance and also found to be most diverse. The anthropogenic activities around the river couple with over-exploitation of the fisheries resources were found accounted for the decline in the fishes composition and diversity...
Ghana Journal of Science, Technology and Development
This study assessed the length-weight relationships and the condition factors of nine commercial and abundant fish species namely Liza dumerilli, Mugil curema, Liza falcipinnis, Mugil bananensis, Lutjanus goreensis, Lutjanus fulgens, Sardinella aurita, Caranx hippos, and Eucinostomus melanopterus from the Kakum River Estuary. This study was conducted from November 2016 to April 2017 to provide primary information about the biometrics, the length-weight model parameters, and the state of well-being of fish species inhabiting the Kakum Estuary. Sampling was done monthly using a mini boat of 9 m long with a depth of 1.5 m for both diurnal (06:00, 10:00, 14:00, 18:00, 06:00 h) and nocturnal (22:00, 02:00 h) periods with a medium-mesh cast net of 20 mm stretched. Sampling was done within thirty (30) minutes on all sampling times. The total length of the species from the estuary ranged from 2.2 cm in Liza dumerilli to 29.8 cm in Mugil curema while the total weight ranged from 0.2 g to 251...
The Species Composition and Diversity of the Coastal Waters of Ondo State, Nigeria
A study of the icthyofauna resources of the coastal waters of Ondo State of Nigeria conducted for 18 months (June 2011-December, 2012) revealed the presence of 67 finfish species with the clariids(especially Clarias gariepinus and Heterobranchus bidorsalis) and cichlids(especially Oreochromis niloticus and Coptodon zilli) dominating the stock accounting for 42% and 16% respectively. Other predominant families were A high 'Claroitedae'(Chrysichthys nigrodigitatus) with 9.2% contribution, 'Channidae'(Parachanna africana) with 8.7%, Osteoglossidae (Heterotis niloticus) with 7.1%, Gymnarchidae(Gymnarchus niloticus), Mugilidae (Mugil cephalus) and Clupeidae (Ethmalosa fimbriata). Lausanne Index of Abundance was 89.7% while Margalef.s index(a measure of species richness) was 5.18. The Length-weight relationships of these predominant fishes showed negative allometric growth pattern. A high level of heterogeneity of stock was observed as revealed by Simpson Index and Shannon-Weiner Index of General Diversity (H i) which were 0.13 and 0.35 respectively. A lot of similarity in species composition existed as revealed by Evenness Index(E) of 0.20 and Berger-Perker Index of 0.88. There was comparatively higher catches of fish in the dry season than the wet season probably due to reduced water volume which concentrated the fishes for easier catchability. The author recommends the need to protect the existing stock especially the monospecific families like the Osteoglosidae and Gymnarchidae through regular monitoring of the physicochemical parameters of the coastal waters which are highly susceptible to crude oil pollution, Ondo State being a crude oil-producing area. More funds should be committed by the government to researches on population dynamics and biomass estimate of our coastal waters.