Journal of Applied Sciences and Environmental Management World Bank assisted National Agricultural Research Project (NARP) - University of Port Harcourt ISSN: 1119-8362 Vol. 12, Num. 2, 2008, pp. 55-66

Journal of Applied Sciences and Environmental Management, Vol. 12, No. 2, 2008, pp. 51-60

Aspects of the ecology of Nigeria Fresh Waters: A case study on Physicochemical characteristics Plankton and Finfish from Lower Sombreiro River in Niger Delta

¹ABOWEI, J. F. N; ²TAWARI, C. C; ³HART, A.I; ⁴GARRICK, D. U.

¹Department of biological sciences, Niger Delta University, Wilberforce Island, Amasoma, Nigeria. E-mail: jasper.abowei@shell.com, cebealse@yahoo.com
²Department of Fisheries and Wildlife, Niger Delta University, Wilberforce Island, Amasoma, Nigeria.
³Department of Animal and Environmental Biology, University of Port Harcourt, Port Harcourt, Nigeria.
⁴Department of fisheries and Aquatic Environment, Rivers State University of Sciences and Technology, Port Harcourt, Nigeria
* Corresponding author: Abowei, J. F. N.

Code Number: ja08029

ABSTRACT

This paper is aimed at baseline information on the fisheries status of the fresh water reaches of somberiro river in the Niger Delta; while highlighting the challenges of obtaining fisheries data in the waters of the Niger Delta. Both physico-chemical and plankton were analyzed using standard methods Plankton and fish species were identified using monographs, descriptions, checklists and keys. The mean values temperature, pH, conductivity, turbidity, salinity, dissolved oxygen, total dissolved solids, dept, flow rate and rainfall were: 27.1 ± 0.09 (°C), 6.50 ±0.05, 4515.3±656.67 (μscm^-1), 1.8±.09 (ntu), 3.1±0.45(0/00), 7.10±0.06 (mg/l), 673.27±97.34(mg/l), 6.23±0.22(m), 0.19±0.39(m/s) and 184.1±19.89(mm) respectively. A total of 43 species from 5 taxonomic groups were recorded). The species with the highest number was Melosira granulata (357) with 5.2%, while the least number was for Stephanodiscus asroea (47) with 0.7%. Bacillariophyceae was the highest (50.3%), Chlorophyceae, 24.8%; Cyanophyceae, 15.4%; Xantophyceae, 7.2%; and Chrysophyceae, 2.5%. A total of 17 zooplankton species from 6 taxonomic groups were present. The species with the highest number (248) was Paracyclops fimbriatus, with 12.1%, while Mysis sp. had the lowest number (25) with 1.2%. The family Copepoda had the highest (45.5%), Cladocera, 23.4%; Euphaucea, 10.3%; Protozoa, 11.9%; Rotifera, 7.8%; and Decapod Crustaceae, 1.2% (the least). The family Copepoda had the highest (45.5%), Cladocera, 23.4%; Euphaucea, 10.3%; Protozoa, 11.9%; Rotifera, 7.8%; and Decapod Crustaceae, 1.2% (the least). A total of 72 finfish species from 38 families were present. Brienomyrus branchystius was the species with the highest number (412) accounting for 5.9% of total fish caught. No particular specie was dominant, Breinomyrus branchystius and B. longianalis were aboundant, Erpeptiochthys calabaricus and Chromidotilapia guentheri were common; while the rest were either rare or few. Analysis of variance (ANOVA) was carried out on finfish and plankton collected from the different stations and seasons. The Duncan’s Multiple Range Test was used to determine significance in mean catches and estimates. Correlation analysis of the water parameters and finfish catch was done. Phytoplankton collected had a negative correlation with dissolved oxygen and pH. However, it correlated positively with flow rate. The correlation between zooplankton collected and turbidity was negative. The percentage total catch increased with higher conductivity values, increased total dissolved solids, reduced turbidity and rainfall, and relatively faster flow rates. However, it declined with reduced conductivity, total dissolved solids, relatively slower flow rates, increased turbidity, and rainfall. Finfish catch correlated positively with conductivity and total dissolved solids. The physicochemical characteristics, plankton and finfish species of the lower Sombreiro River in the Niger Delta, correlates the relationship between the biotic and abiotic parameters for the management of similar water bodies for regional, national and international fisheries development.

The importance of water, directly or indirectly, to human and animal life is such that obliges proper attention to its quality, consisting of the physical and chemical characteristics that motivated this study in the freshwater reaches of the lower Nun River. For instance, temperature is the single most important factor affecting the survival, growth and reproduction of all fish. It influences water quality and the distribution and abundance of aquatic organisms. Fish and fishery products constitute one of the cheapest sources of good quality animal protein rich in certain amino acids notably methionine, tryptophane and lysine needed for healthy growth. It has been established that the onshore and offshore waters of the West African coast have rich fish resources. They are available in quantities that can support commercial exploitation. Plankton is recognized worldwide as bioindicator organisms in the aquatic environment (Yakubu, et al, 2000). According to Boyd, et.al, (2000) phytoplankton blooms may indicate presence of mineral ions. Populations of planktonic ciliates often develop in organic-rich, oxygen-depleted and polluted waters. Plankton abundance increases productivity of water, as they form the basic food source in any aquatic environment. Phytoplankton constitutes the bedrock or basis of grazing food chains and food webs in surface water systems. According to UNEP, 1998; SPDC, 2001; Chesapeake Bay, 2005 and Herring, 2005, Phytoplankton utilization of organic and/or inorganic elements in the environment, species richness and diversity, density and distribution.

The stretch of the Sombreiro River is one of the most important river systems in the Niger Delta providing nursery and breeding grounds for a large variety of fish species (Ezekiel, et al., 2002). The water body also serves as the only source of water in the area. Due to efforts at speedy industrialization and recreational activities, the Sombreiro River is fast becoming degraded (Ezekiel, 2001). Fishing is carried out indiscriminately with various traditional and modern gears. The objectives of this study paper are: to highlight using the lower Sombreiro river as case study, the physicochemical characteristics, finfish families, planktons species and the correlation between them. This will present baseline information on the fisheries status of the fresh water reaches of the Niger Delta; whil highlighting the challenges of obtaining fisheries data in the waters of the Niger Delta.

MATERIALS AND METHODS

The Study Area

The Niger Delta basin covers all the land between latitude 4⁰ 14¹ N and 5⁰ 35¹ N, and longitude 5⁰ 26¹ E and 7⁰ 37¹ E with a total area of 20,000 km² . It extends along the coast from the river’s basin in the West of Bonny River. The area is characterized by extensive inter-connection of creeks. It is the most important drainage feature of the Niger-Basin rivers system, and covers about 2% of the surface area of Nigeria (Powell et al., 1985 in Abowei 2000). The annual rainfall of the Niger Delta is between 2000–3000mm per year (Powell, 1987 in Sikoki et al 1998). The Sombreiro River is located between latitude 6⁰ 30¹ and 7⁰ 0¹ E, and longitude 4⁰12¹ N and 60 17 N. The river is a distributary of the River Niger, which rises from the northern parts of Ogba/Egbema/Ndoni Local Government Area of Rivers State. It is one of the series of the Niger Delta Rivers that drain into the Atlantic Ocean. It flows southwards from its source to the Atlantic Ocean and is connected to other rivers via creeks in the coastal areas of the Niger Delta (Ezekiel, 1986 in Ezekiel et al 2002). The river is relatively narrow and deep, and as it flows southwards, it widens. The river is lotic throughout the year, with its peak in the dry season. The river is within the tropical rainforest, though the mouth is within the brackish mangrove zone.

Sampling Stations

Some characteristics of the sample stations along the Sombreiro River are as follows:

Sample station 1 (Degema): This is the largest of all the stations. The vegation (mangrove plants) fringing the river consists Rhizophora, Avicennia, and Nypha fruticans (Nypa palm) arising from a characteristic muddy substrate that gives a foul smell. The water is turbid in the rainy months. The site is a brackish and tidal environment.

Sample station 2 (Ogbele): Vegetation is mainly riverine forest, consisting mainly of Raphia, Pandanus sanderiana, Calamas sp. (swamp cane), Khaya sp. (mahogany), Vapaca sp., Ficus vogeliana and Triculia africana. Aquatic macrophytes include Nymphaea sp., Eichhornia crassipes, Sagittaria sp., Pistia stratiotes. The station was flooded in the rainy period when the velocity is slow. The site had little influence from the immediate tidal mangrove zone. The bottom consisted mainly of sand and gravel.

Sample station 3 (Ihuaba): The common vegetation present was a mixture of riverine and terrestrial vegetation. Some common plants noticed included Raphia, and Elaeis guineensis (palm trees). The aquatic macrophytes include Typha lotifolia (cat tail), Eichhornia crassipes, Nymphaea sp., Utricularia sp. and Potamogeton sp. (pond weed).

The site was flooded in the wet season, which receded within November and February. The river bottom consisted of sand and gravel.

Sample station 4 (Odhieke): The vegetation consisted of terrestrial vegetation and riverine vegetation extending into large areas of swamps. These included Raphia, Pandanus sanderiana, Elaeis guineensis (palm trees). Aquatic macrophytes included Ipomea aquatica, Lemna sp. (duck weed), Utricularia sp., Nymphaea sp. and Pistia stratiotes (water lettuce). The water was generally clear, and water velocity increased as flood recedes. River bottom had mainly sand and gravel. Common fishing gears used in the Sombreiro fisheries included seine nets, drift nets, cast nets, lift nets, long lines, fish fences, funnel traps, trigger traps, grass mats, hooks and lines.

Physico-chemical characteristics: Four sampling stations were selected along the shore of the river from Odhieke to Degema. Monthly rainfall values were obtained from the Meteorological Department of the Federal Ministry of Environment, Port Harcourt. Some monthly in situ measurements of parameters were made. Surface water temperature was measured two minutes after dipping an ordinary mercury-in-glass thermometer to a depth of about 5.0cm below water surface. Depth measurements were done using a graduated line. Each month, average depth of pre-determined points were recorded as the water level.

Water velocity/flow rate was measured with a floating object. The time taken for the floating object to move past two fixed points was recorded. The water velocity was calculated and expressed as the time taken (in seconds) to flow through one meter (m/s). The salinity, pH, conductivity, and turbidity were measured using a portable Horiba meter (model U10). Dissolved oxygen was measured using the Winkler method (Stirling, 1999). Total dissolved solids (TDS) were determined by filtering a well-mixed water sample through a fiber filter paper into a weighted dish. The filtrate (in the dish) was evaporated to dryness to a constant weight. TDS was calculated with the following formula.

Where A = weight of dried residue + dish (mg), and B = weight of dish (mg).

Plankton: Both phyto and zooplankton samples were collected at each of the stations. Phytoplankton was randomly collected with 250ml capacity plastic jar at subsurface (10cm) level and emptied into a wide mouthed plastic jar and immediately preserved using 4% formalin solution. Zooplankton was collected in the open water by filtration technique. 25µm mesh size plankton net was towed from a dugout boat at about 5-10m/s for about a minute. The net content was washed out into a wide mouth plastic container and preserved with 10% formalin solution after proper labeling. This was stored in a cool box and taken to the laboratory. In the laboratory, the samples were allowed to stand for at least 24 hours for the plankton to settle before the supernatant was pipette off to concentrate the samples. The concentrated sample was agitated to homogenize before pipetting 1ml sub sample with sample pipette (ibid). The content was placed in a Sedge wick-Rafter plankton-counting chamber, and examined with Leltz-Wetzlar binocular microscope at a magnification of 200X. The plankton was identified and total number per species recorded using keys and checklists. Enumeration of plankton was done on natural unit count and reported as units or organisms per milliliter (ml).

Fish: The four stations were sampled monthly by assessing catches from the fishers. Catches at the different stations were isolated and conveyed in (cool) boxes to the laboratory on each sampling day after preservation with 10% formalin solution. The sampling was done twice every month, for a period of one year. The total number for each species in each station was noted. Fish species were identified using monographs, descriptions, checklists and keys by Schneider (1990); Tuegel, et al., (1992); Idodo-Umeh, (2003); and Olaosebikan and Raji (1998).

Statistical analysis: The SAS (statistical analysis system, 1999) was used to analyze the data obtained. Analysis of variance (ANOVA) was carried out on finfish and plankton collected from the different stations and seasons. The Duncan’s Multiple Range Test was used to determine significance in mean catches and estimates. Correlation analysis of the water parameters and finfish catch was done. The same analysis was done for plankton. This was to verify the factors that relate significantly to one another that could influence the abundance of finfish and plankton.

RESULTS AND DISCUSSION

Physico-chemical characteristics: The mean values of these parameters for the various stations are presented Table 1. The lowest water temperature (25.5° C) was recorded in October in sample station 2 and the highest (29.5°C) in March, in sample station 1. The highest mean temperature (28°C) was recorded in sample station 1. Hydrogen ion concentration (pH) values ranged from 5.5 in March (SS4) to 7.50 (SS1). The mean pH was lowest in sample stations 2 and 3 (6.10), and highest in sample station 1 (7.10). Conductivity measurements varied also. The lowest (11.20µscm^-1) was observed in September (SS4), and the highest (21,380µscm^-1) was in May (SS1). Sample station 4 had the least mean conductivity value (17.9µscm^-1). Turbidity values ranged from 0.1 ntu to 4.0 ntu. The lowest was in March (SS3) and the highest, in August (SS1). The mean value was lowest in sample station 3 (1.7ntu). Salinity was highest (13.6%0) in January from sample station 1, and lowest (0.00%) in November and February from sample station 3, and in September and June from sample station 4. Dissolved oxygen levels were from 5.80mg/l to 8.30mg/l. The lowest was recorded in March in sample station 4, and the highest, in August in sample station 1. Sample station 2 had the lowest mean dissolved oxygen concentration (6.80mg/l).

Total dissolved solids measurements showed considerable variability. The highest value of 3,418.7mg/l was observed in January in sample station 1, while the lowest (10.1mg/l) was observed in March in sample station 4. Station 4 also had the lowest mean TDS (total dissolved salts) value (19.10mg/l). Water depth levels ranged from 12.40m in July in sample station 1, to 2.0m in January in sample station 4. The least mean depth was 4.01m in sample station 4. Rainfall values were uniform across the sample stations. The lowest value (28.70mm) was recorded in November, while the highest (397.40mm), was in May. The flow rate (velocity) varied from 0.5m/s in April, in sample station 4, to 0.05m/s in July in sample station 1. The highest mean flow rate (0.3m/s) was recorded in station 4 and the lowest (0.08m/s) in sample station 1.

Phytoplankton: A total of 43 species from 5 taxonomic groups were recorded during the study period (Table 2). The species with the highest number was Melosira granulata (357) with 5.2%, while the least number was for Stephanodiscus asroea (47) with 0.7%. Bacillariophyceae was the highest (50.3%), Chlorophyceae, 24.8%; Cyanophyceae, 15.4%; Xantophyceae, 7.2%; and Chrysophyceae, 2.5%. Station 1 had the highest number of 2257 (32.9%), while station 4 (1349), with 19.7% was the lowest. Most of the species were recorded in all the sample stations. Pinnularia horealis was not recorded in stations 3 and 4, Stephanodiscus asroea was recorded only in station 1. Spirogyra sp. and Volvox globator were not recorded in station 1(Table 2). Analysis of variance for the four sample stations, and seasons, for number of phytoplankton observed showed significant differences (F = 21.75, df = 1467, p = 0.05) between seasons, and (F = 11.91, df. = 1467, p = 0.05) among the stations. The combined effect of seasons and stations was not significantly different (F = 0.70, df. = 1467, P = 0.05) Duncan’s Multiple Range Test showed that the means for the wet and dry seasons differed significantly. Also the means for the stations showed that station 1 differed significantly from all the other stations. Stations 2, 3 and 4 did not show any significant difference. The diversity index measured by the Shannon-Wiener information function (H) ranged from 1.053 to 1.505.

The wet season recorded more phytoplankton presence (3928) with 57.3%, than the dry season (2932) with 42.7% (Table 3). All the species were recorded for both seasons. Cosinodiscus lacustris was the most recorded (308) for the wet season, while Amphora ovalis (24) was the least. The dry season had the highest occurrence in Melosira granulata (189), while Stephanosdiscus asroea (18) was the least.

Zooplankton: A total of 17 zooplankton species from 6 taxonomic groups were recorded during the study period (Table 4). The species with the highest number (248) was Paracyclops fimbriatus, with 12.1%, while Mysis sp. had the lowest number (25) with 1.2%. The family Copepoda had the highest (45.5%), Cladocera, 23.4%; Euphaucea, 10.3%; Protozoa, 11.9%; Rotifera, 7.8%; and Decapod Crustaceae, 1.2% (the least). The family Copepoda had the highest (45.5%), Cladocera, 23.4%; Euphaucea, 10.3%; Protozoa, 11.9%; Rotifera, 7.8%; and Decapod Crustaceae, 1.2% (the least). Station 1 had the highest record (631), with 30.7%, while station 4 had the lowest (376), with 18.3%. All the species were observed in all the stations, with the exception of Mysis sp. that was absent in station 4. The analysis of variance for the seasons and stations for number of zooplankton recorded showed that there was significant difference (F = 14.10, d.f = 604, p = 0.05) between the stations. There was, however, no significant difference between seasons, and also none for the combined effects of seasons/stations. Using the Duncan’s Multiple Range Test, a further analysis showed the significant differences between means for the stations. The distribution showed that station 1 differed significantly from the rest. Station 3 also differed significantly from others. Stations 2 and 4 did not differ significantly. More zooplankton was recorded in the wet season (1267), with 61.6%, than the dry season (790), with 38.4% (Table 5). All species were observed in both seasons. In the wet season, Meganicliphanes norvegica had the highest record (159), while Paracyclops fimbriatus was the highest in number (95) for the dry season. Mysis sp. was the least recorded for both seasons, as 9 individuals were recorded for the wet season, and 16 for the dry season.

Finfish: A total of 72 species from 38 families was caught during the study period (Table 6). Brienomyrus branchystius was the species with the highest number (412) accounting for 5.9% of total fish caught. No particular specie was dominant, Breinomyrus branchystius and B. longianalis were aboundant, Erpeptiochthys calabaricus and Chromidotilapia guentheri were common; while the rest were either rare or few. The species with the least percentage composition was Tilapia zilli (14), with 0.2% of the total number of fish caught; 4,309 (62.1%) was caught in the wet season and 2,625 (37.9%) in the dry season; The species was with Brienomyrus branchystius as highest catch in both seasons and Phractolaemus ansorgei and Clarias gariepinus in the wet and the dry season respectively. Heterotis niloticus did not occur in the dry season (Table 7). Analysis of variance for seasonality in number of fish caught showed significant difference between the two seasons (F = 17.33, d.f. = 1644, p = 0.05). A further analysis using the Duncan’s Multiple Range Test showed the variability in means for both seasons.

Zooplankton increased with higher conductivity, lower dissolved oxygen; relatively faster flow rates and more rainfall. The abundance seemed to decline with lower conductivity, higher turbidity, higher dissolved oxygen, and slower flow rates. The correlation between zooplankton collected and turbidity was negative (Table 8). The percentage total collection increased with increased temperature, increased conductivity, increased flow rate. However, it reduced with reduced temperature, conductivity, increased turbidity, and rainfall. The correlation coefficients of phytoplankton abundance and physico-chemical parameters measured during the study. The phytoplankton collected had a negative correlation with dissolved oxygen and pH. However, it correlated positively with flow rate (Table 9). The percentage total catch increased with higher conductivity values, increased total dissolved solids, reduced turbidity and rainfall, and relatively faster flow rates. However, it declined with reduced conductivity, total dissolved solids, relatively slower flow rates, increased turbidity, and rainfall. Table 10 shows the correlation coefficients of number of fish caught and physico-chemical characteristics measured in the lower Sombreiro river. The fish catch correlated positively with conductivity and total dissolved solids.

DISCUSSION

This study recorded 72 species of finfish from 38 families. Dokubo (1982) in Abowei and Ezekiel 2003 identified 45 species belonging to 34 families, from 6 sample stations in this water body. The stations were Okansu, Akpabo, Ahoada, Agba-Ndele, Degema, and Harris Town. Dokubo found that Chrysicthys nigrodigitatus, Hepsetus odoe, Chromidotilapia guentheri, and Hemichromis bimaculatus were distributed along the entire course of the Sombreiro river. This study made the same observation, (except for H. bimaculatus). Dokubo’s study was done in the dry season. He also considered salinity as the major restrictive factor in fish distribution in the river, and reported that pH, turbidity and basic food types we secondary factors. Between August and February, Eziekel (1986) in Ezekiel et al 2002; recorded 78 species from 39 families in the Sombreiro River, from five sample stations. This study maintained three of those stations, while the forth (Odhieke) was about 4km from Odhiemudhie (used by Ezekiel). Ekpe-Mbede (Ezekiel’s station 5) was over 50km from sample station 4.

His finding that Xenomystus nigri, Papyrocranus afer, and Hemichromis elongatus (fasciatus) were distributed through the length of the river compared favourably with this study. However, some of the species he identified but were not recorded in this study include Petrocephalus bovei, Pollimyrus isidori, Alestes chaperi, Nanocharanx ansorgei, Nannaethops unitaeniatus and Amphilidae sp. Other similar studies include Abowei (2000), where 36 species from 22 families were observed in Nun River. Also, Alfred-Ockiya (1998) observed 41 species in Kolo Creek, Okereke (1990) recorded 46 species from 20 families in her study of Otamiri River, Imo State. Sikoki, et al., (1998) recorded 34 species in Nun River, Bayelsa State. The number of species recorded in this study compared favorably with some and varied from other studies. Differences in number of species inhabiting various river systems are largely influenced by the size of the river as represented by its basin area, or some correlate of it, such as length of main channel or stream order (Welcomme, 1985 in Abowei, 2000.) Of the 72 species recorded in this study, Brienomyrus branchystius was the most abundant. Ezekiel (1986 in Ezekiel et al 2002) also recorded Brienomyrussp., however, it was not the most abundant. Fish catch landings, amongst others, may be influenced by gear efficiency, fishing effort/skills and habitat diversity (King, 1995).

Comparatively, the mean catch in the dry season was lower than that for the wet period. This is in agreement with the findings of Abowei (2000). During the rains, most communities abandon farming and take up fishing, which may result in higher catches. The effect of season on catch composition was tested using the analysis of variance. There was significant difference between seasons. According to Abowei, 2000; fish community diversity is correlated with habitat diversity in some rivers. This study recorded 43 species of phytoplankton from 5 taxonomic groups. This result compared favorably with records from some other Nigerian waters (Kemdirim, 2001). Yakubu, et al., (2000) observed 34 species in Nkisa river, and 20 species in Orashi river. Also, Kosa (2007) recorded 39 phytoplankton species in the upper Luubara Creek. Nwadiaro and Ezefili (1986) in Abowei 2000 recorded a total of 56 species in New Calabar river. However, this result varies considerably from some other studies in Nigeria. Edogbotu (1998) identified 143 species in Elechi Creek, while Chinda and Pudo (1991) had 148 species from Oginigba Creek, all in Port Harcourt. Also, Adeniyi (1978) in Ezekiel et al 2002; recorded 305 species in Kainji lake, while Chinda and Keremah (2001) reported 89 species from the Bonny estuary. The major factors influencing phytoplankton abundance are temperature, velocity of current, nutrient availability, and light. The highest percentage catch in this study was recorded when the temperature was high with low water depth, low. However, the periods of high percentage collection coincided with relatively high water flow rates, contrary to reports by Prowse and Talling (1958) and Egborge (1972) in Abowei 2000. Generally, both studies reported that phytoplankton abundance inversely related to both water level, and current velocity.

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