Characterization of sandstone reservoirs and hydrocarbon generation potential of selected four wells in the Pletmos basin, offshore South Africa
- Moloi, Busiswa https://orcid.org/0000-0001-6815-4901
- Authors: Moloi, Busiswa https://orcid.org/0000-0001-6815-4901
- Date: 2021-06
- Subjects: Hydrocarbon reservoirs
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10353/22512 , vital:52387
- Description: This study focused on the use of data from four wells (Ga-M1, Ga-S1, Ga-Z1, and Gb-J1) comprises of the Late Jurassic to Early Cretaceous shallow marine clastic sandstones consisting of wildcat wells located in Block 11 of the Pletmos Basin, a sub-basin of the Southern Outeniqua Basin, south offshore South Africa. This research evaluates the hydrocarbon potential in the Pletmos Basin by integrating core and well log data to characterize the source and reservoir rock potential. The methods implemented consist of a mineralogical and petrological analysis of about 300 thin section slides from four wells were studied. Stratigraphic profile computation from core logging, geochemistry analysis focusing on total organic carbon (TOC), geophysical wireline logs, conventional core analysis, geological well reports, and petrophysical analysis (water saturation, porosity, permeability, and volume of clay) were done using Interactive Petrophysics software. The different datasets were used to delineate how the mineralogy, total organic carbon content, poro-perm properties, fluid saturation, and volume of clay impact the hydrocarbon production potential. The evaluated sandstones have depths ranging from 2523.9 m to 3397.2 m with varying thickness depending on the position of the well. The results indicate that the study area consists of shallow marine clastic sandstones with sparse siltstones and mudstone that are fine-grained to silty in texture. The sedimentary sequence is characterized by moderate to intense bioturbation. Depositional environment was in a reducing condition indicated by plenty of glauconites. The tight fine-grained sandstones have low porosity values ranging from 4.5% to 13.8% in the selected intervals. The low porosity values may have been caused by the quartz cement that is observed from the thin sections. Low permeability values ranging from 0 mD to 0.16 mD are present throughout the studied wells caused by calcite cement and clay matrix. Source rock in the studied wells have inferior TOC values ranging from 0.31 wt% to 0.51 wt%. The van Krevelen indicates that the analysed samples have very low hydrogen index (HI) values and are consistent with Type III Kerogen (gas prone). A total of six reservoirs were identified. For well Ga-M1, one reservoir interval (2988.2 m – 30281 m) was selected and is located at BCII formation and was classified as a nonproducing reservoir due to its high water saturation content of 94.2%, even though it has an average porosity of 10.6%. Two reservoirs were selected for well Ga-S1, reservoir one (3026.3 m – 3107.7 m) is located within the 13AT1 formation and was classified as a producing reservoir with an average porosity of 11.9%, water saturation of 38.3%, and volume of clay of 29.5%. Reservoir 2 (3380.7 m – 3397.2 m) and the reservoirs (2970.20 m – 2993.0 m and 3006.80 m – 3049.50 m) from well Ga-Z1 located between the 9AT1 – BCVI formations were classified as non-reservoirs. One selected reservoir from well Gb-J1 had promising gas shows with an average porosity of 19%, water saturation value of 34.8%, and volume of shale of 33.1%. However, well Ga-S1 has a large interval with hydrocarbon potential compared to the well Gb-J1. Results indicate that the absence of hydrocarbon accumulation may result from non-effective seals due to the silty texture of the reservoir sandstones. Also, the presence of calcareous cement, clay minerals, and the argillaceous matrix reduce the porosity and permeability characteristics. To better understand the hydrocarbon potential of the Pletmos Basin, 3D seismic data is recommended to perform seismic well tie analysis for correlation between well log and seismic data to understand the basin‟s potential better. , Thesis (MSc) -- Faculty of Science and Agriculture, 2021
- Full Text:
- Date Issued: 2021-06
- Authors: Moloi, Busiswa https://orcid.org/0000-0001-6815-4901
- Date: 2021-06
- Subjects: Hydrocarbon reservoirs
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10353/22512 , vital:52387
- Description: This study focused on the use of data from four wells (Ga-M1, Ga-S1, Ga-Z1, and Gb-J1) comprises of the Late Jurassic to Early Cretaceous shallow marine clastic sandstones consisting of wildcat wells located in Block 11 of the Pletmos Basin, a sub-basin of the Southern Outeniqua Basin, south offshore South Africa. This research evaluates the hydrocarbon potential in the Pletmos Basin by integrating core and well log data to characterize the source and reservoir rock potential. The methods implemented consist of a mineralogical and petrological analysis of about 300 thin section slides from four wells were studied. Stratigraphic profile computation from core logging, geochemistry analysis focusing on total organic carbon (TOC), geophysical wireline logs, conventional core analysis, geological well reports, and petrophysical analysis (water saturation, porosity, permeability, and volume of clay) were done using Interactive Petrophysics software. The different datasets were used to delineate how the mineralogy, total organic carbon content, poro-perm properties, fluid saturation, and volume of clay impact the hydrocarbon production potential. The evaluated sandstones have depths ranging from 2523.9 m to 3397.2 m with varying thickness depending on the position of the well. The results indicate that the study area consists of shallow marine clastic sandstones with sparse siltstones and mudstone that are fine-grained to silty in texture. The sedimentary sequence is characterized by moderate to intense bioturbation. Depositional environment was in a reducing condition indicated by plenty of glauconites. The tight fine-grained sandstones have low porosity values ranging from 4.5% to 13.8% in the selected intervals. The low porosity values may have been caused by the quartz cement that is observed from the thin sections. Low permeability values ranging from 0 mD to 0.16 mD are present throughout the studied wells caused by calcite cement and clay matrix. Source rock in the studied wells have inferior TOC values ranging from 0.31 wt% to 0.51 wt%. The van Krevelen indicates that the analysed samples have very low hydrogen index (HI) values and are consistent with Type III Kerogen (gas prone). A total of six reservoirs were identified. For well Ga-M1, one reservoir interval (2988.2 m – 30281 m) was selected and is located at BCII formation and was classified as a nonproducing reservoir due to its high water saturation content of 94.2%, even though it has an average porosity of 10.6%. Two reservoirs were selected for well Ga-S1, reservoir one (3026.3 m – 3107.7 m) is located within the 13AT1 formation and was classified as a producing reservoir with an average porosity of 11.9%, water saturation of 38.3%, and volume of clay of 29.5%. Reservoir 2 (3380.7 m – 3397.2 m) and the reservoirs (2970.20 m – 2993.0 m and 3006.80 m – 3049.50 m) from well Ga-Z1 located between the 9AT1 – BCVI formations were classified as non-reservoirs. One selected reservoir from well Gb-J1 had promising gas shows with an average porosity of 19%, water saturation value of 34.8%, and volume of shale of 33.1%. However, well Ga-S1 has a large interval with hydrocarbon potential compared to the well Gb-J1. Results indicate that the absence of hydrocarbon accumulation may result from non-effective seals due to the silty texture of the reservoir sandstones. Also, the presence of calcareous cement, clay minerals, and the argillaceous matrix reduce the porosity and permeability characteristics. To better understand the hydrocarbon potential of the Pletmos Basin, 3D seismic data is recommended to perform seismic well tie analysis for correlation between well log and seismic data to understand the basin‟s potential better. , Thesis (MSc) -- Faculty of Science and Agriculture, 2021
- Full Text:
- Date Issued: 2021-06
Investigation of the levels of PBDEs and PCNs in the surface water and sediments from selected waterbodies in the Eastern Cape Province, South Africa
- Agunbiade, Idowu Victoria https://orcid.org/0000-0001-5605-0312
- Authors: Agunbiade, Idowu Victoria https://orcid.org/0000-0001-5605-0312
- Date: 2021-06
- Subjects: Persistent pollutants , Water -- Purification -- Organic compounds removal , Organic water pollutants
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10353/22699 , vital:52660
- Description: Studies have revealed that persistent organic pollutants (POPs) are omnipresent in our environment; almost all human beings have definite levels of POPs in their bodies. Even fetus and embryos are not spared; they have been found to bear certain levels of POPs. So far, there are about 28 chemicals listed as POPs among which are polybrominated diphenyl ethers (PBDEs) and polychlorinated naphthalenes (PCNs). PCN and PBDE distributions have been reported from different sources around the world, but studies relating to PCNs occurrence and distribution in Africa, especially South Africa is still minimal. PBDEs have been reported to cause diabetes, cancer, damage to reproductive system, thyroid, liver and other vital organs in the body, while PCNs have been linked to chloracne (severe skin reactions/lesions) and liver disease (yellow atrophy) in humans, chicken oedema and X-disease in cattle. Hence, this study evaluates PCN levels in water and sediment samples from three waterbodies: North End Lake (NEL), Chatty River (CHA) and Makman Canal (MMC), while PBDE levels was reported in NEL and CHA samples. The three sites are located in Port Elizabeth, Eastern Cape Province (ECP) of South Africa. The lake serves as a recreational resort while the latter two waterbodies are tributaries discharging into the Swartkop Estuary, an important estuary in ECP. Water samples were extracted with C18 cartridges (solid phase), while soxhlet was employed for the extraction of sediments. Water and sediment extricates were purified and quantified with gas chromatography-micro electron capture detector (GC-μECD). Forty-seven (47) water samples and 44 sediment samples were collected in August until December 2020 from six sampling points in NEL, five points in each of CHA and MMC. All the samples were evaluated for physicochemical properties, PBDEs and PCNs using validated standard methods. The sampling period covered three South Africa seasons: August (winter), October (spring) and December (summer). The physicochemical parameters (PP) of NEL water samples for the three seasons generally varied as follows: temperature (15.3–23°C), pH (7.9–10.3), oxidation-reduction potential, ORP (23.4-110 mV), atmospheric pressure, AP (14.52-15.56 PSI), turbidity (15.1–167 NTU), electrical conductivity, EC (114–1291 μS/cm), total dissolved solids, TDS (55-645 mg/L), total suspended solids, TSS (20–107 mg/L) and salinity (0.05–0.65 PSU). All the PPs except for turbidity and TSS are within acceptable limits. NEL sediments had moisture content (MC), organic matter (OM) and organic carbon (OC) in the range of 0.04–8.0percent, 0.08–2.2percent and 0.05–1.8percent, respectively. The sum of eight PCN congeners Σ8PCNs and six PBDE congeners Σ6PBDEs in NEL water samples ranged from 0.164–2.934 μg/L and 0.009-1.025 μg/L individually. The values for Σ8PCNs and Σ6PBDEs in NEL sediment samples varied from 0.991–237 μg/kg and 0.354-28.850 μg/kg, respectively. The calculated hazard quotient (HQ) corresponding to the non-carcinogenic health risk associated with PBDEs in NEL water samples was 2.0×10-3-1.4×10-1, while the TEQ values due to PCNs varied from 6.10×10-7- 3.12×10-3 μg/L in NEL water samples and 3.70×10-5-1.96×10-2 μg/kg dw in sediments. The PP values for CHA water samples include temperature (15.4–22.9°C), pH (7.7–10.5), TDS (991–1771 mg/L), TSS (6–41 mg/L), turbidity (1.0–198 NTU), EC (1981–3542 μS/cm), AP (14.60–14.80 PSI), ORP (-339.1-51.3 mV), and salinity (1.02–1.87 PSU). The EC, TDS and salinity exceeded acceptable values at certain points. The sediments of CHA have MC, OM and OC contents ranging from 0.01-10.2percent, 0.2-1.3percent and 0.1-0.8percent in that order. Sum of Σ8PCNs, Σ6PBDEs in CHA water and sediment samples ranged from 0.026–1.054 μg/L, 0.007-0.079 μg/L and 0.429–1888.468 μg/kg, 0.347-6.468 μg/kg individually. The HQ in CHA water samples was 1.6×10-3-7.7×10-3 and the estimated TEQ was 1.0×10-7-6.62×10-5 μg/L and 1.10×10−5-6.40×10−2 μg/kg in water and sediments, respectively. The temperatures for MMC water samples ranged from 15.6-24.5°C, while other PPs recorded were as follows: pH (8.4-10.2), TDS (943–4002 mg/L), TSS (7-491 mg/L), turbidity (2.9-154.2 NTU), EC (1885-8004 μS/cm), AP (14.53–14.82 PSI), ORP (7.8-130 mV) and salinity (0.96-4.47 PSU). MMC’s sediments recorded MC, OM and OC varying as 0.4- 18.9percent, 0.2-4.5percent and 0.1-2.6percent, respectively across the three seasons. The Σ8PCNs for MMC water and sediment samples were 0.035–0.699 μg/L and 0.260–6744 μg/kg. The TEQ values in MMC water and sediment samples were 1.19×10-7-1.47×10-4 μg/L and 4.43×10−5- 4.19×10−1 μg/kg, respectively. The results are all less than one, and this suggests that the selected water is safe. Results showed that NEL water had highest TEQ, PCN and PBDE concentrations, while MMC sediments recorded maximum TEQ and PCN levels in this study. PBDE concentrations in NEL sediments were above the other site. In conclusion, NEL water was most polluted with both pollutants (PCNs and PBDEs), but MMC sediments contained more PCNs. There is need for the immediate remediation of these selected waterbodies. , Thesis (PhD) -- Faculty of Science and Agriculture, 2021
- Full Text:
- Date Issued: 2021-06
- Authors: Agunbiade, Idowu Victoria https://orcid.org/0000-0001-5605-0312
- Date: 2021-06
- Subjects: Persistent pollutants , Water -- Purification -- Organic compounds removal , Organic water pollutants
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10353/22699 , vital:52660
- Description: Studies have revealed that persistent organic pollutants (POPs) are omnipresent in our environment; almost all human beings have definite levels of POPs in their bodies. Even fetus and embryos are not spared; they have been found to bear certain levels of POPs. So far, there are about 28 chemicals listed as POPs among which are polybrominated diphenyl ethers (PBDEs) and polychlorinated naphthalenes (PCNs). PCN and PBDE distributions have been reported from different sources around the world, but studies relating to PCNs occurrence and distribution in Africa, especially South Africa is still minimal. PBDEs have been reported to cause diabetes, cancer, damage to reproductive system, thyroid, liver and other vital organs in the body, while PCNs have been linked to chloracne (severe skin reactions/lesions) and liver disease (yellow atrophy) in humans, chicken oedema and X-disease in cattle. Hence, this study evaluates PCN levels in water and sediment samples from three waterbodies: North End Lake (NEL), Chatty River (CHA) and Makman Canal (MMC), while PBDE levels was reported in NEL and CHA samples. The three sites are located in Port Elizabeth, Eastern Cape Province (ECP) of South Africa. The lake serves as a recreational resort while the latter two waterbodies are tributaries discharging into the Swartkop Estuary, an important estuary in ECP. Water samples were extracted with C18 cartridges (solid phase), while soxhlet was employed for the extraction of sediments. Water and sediment extricates were purified and quantified with gas chromatography-micro electron capture detector (GC-μECD). Forty-seven (47) water samples and 44 sediment samples were collected in August until December 2020 from six sampling points in NEL, five points in each of CHA and MMC. All the samples were evaluated for physicochemical properties, PBDEs and PCNs using validated standard methods. The sampling period covered three South Africa seasons: August (winter), October (spring) and December (summer). The physicochemical parameters (PP) of NEL water samples for the three seasons generally varied as follows: temperature (15.3–23°C), pH (7.9–10.3), oxidation-reduction potential, ORP (23.4-110 mV), atmospheric pressure, AP (14.52-15.56 PSI), turbidity (15.1–167 NTU), electrical conductivity, EC (114–1291 μS/cm), total dissolved solids, TDS (55-645 mg/L), total suspended solids, TSS (20–107 mg/L) and salinity (0.05–0.65 PSU). All the PPs except for turbidity and TSS are within acceptable limits. NEL sediments had moisture content (MC), organic matter (OM) and organic carbon (OC) in the range of 0.04–8.0percent, 0.08–2.2percent and 0.05–1.8percent, respectively. The sum of eight PCN congeners Σ8PCNs and six PBDE congeners Σ6PBDEs in NEL water samples ranged from 0.164–2.934 μg/L and 0.009-1.025 μg/L individually. The values for Σ8PCNs and Σ6PBDEs in NEL sediment samples varied from 0.991–237 μg/kg and 0.354-28.850 μg/kg, respectively. The calculated hazard quotient (HQ) corresponding to the non-carcinogenic health risk associated with PBDEs in NEL water samples was 2.0×10-3-1.4×10-1, while the TEQ values due to PCNs varied from 6.10×10-7- 3.12×10-3 μg/L in NEL water samples and 3.70×10-5-1.96×10-2 μg/kg dw in sediments. The PP values for CHA water samples include temperature (15.4–22.9°C), pH (7.7–10.5), TDS (991–1771 mg/L), TSS (6–41 mg/L), turbidity (1.0–198 NTU), EC (1981–3542 μS/cm), AP (14.60–14.80 PSI), ORP (-339.1-51.3 mV), and salinity (1.02–1.87 PSU). The EC, TDS and salinity exceeded acceptable values at certain points. The sediments of CHA have MC, OM and OC contents ranging from 0.01-10.2percent, 0.2-1.3percent and 0.1-0.8percent in that order. Sum of Σ8PCNs, Σ6PBDEs in CHA water and sediment samples ranged from 0.026–1.054 μg/L, 0.007-0.079 μg/L and 0.429–1888.468 μg/kg, 0.347-6.468 μg/kg individually. The HQ in CHA water samples was 1.6×10-3-7.7×10-3 and the estimated TEQ was 1.0×10-7-6.62×10-5 μg/L and 1.10×10−5-6.40×10−2 μg/kg in water and sediments, respectively. The temperatures for MMC water samples ranged from 15.6-24.5°C, while other PPs recorded were as follows: pH (8.4-10.2), TDS (943–4002 mg/L), TSS (7-491 mg/L), turbidity (2.9-154.2 NTU), EC (1885-8004 μS/cm), AP (14.53–14.82 PSI), ORP (7.8-130 mV) and salinity (0.96-4.47 PSU). MMC’s sediments recorded MC, OM and OC varying as 0.4- 18.9percent, 0.2-4.5percent and 0.1-2.6percent, respectively across the three seasons. The Σ8PCNs for MMC water and sediment samples were 0.035–0.699 μg/L and 0.260–6744 μg/kg. The TEQ values in MMC water and sediment samples were 1.19×10-7-1.47×10-4 μg/L and 4.43×10−5- 4.19×10−1 μg/kg, respectively. The results are all less than one, and this suggests that the selected water is safe. Results showed that NEL water had highest TEQ, PCN and PBDE concentrations, while MMC sediments recorded maximum TEQ and PCN levels in this study. PBDE concentrations in NEL sediments were above the other site. In conclusion, NEL water was most polluted with both pollutants (PCNs and PBDEs), but MMC sediments contained more PCNs. There is need for the immediate remediation of these selected waterbodies. , Thesis (PhD) -- Faculty of Science and Agriculture, 2021
- Full Text:
- Date Issued: 2021-06
Market participation and welfare of smallholder farmers in the Eastern Cape Province South Africa
- Lesala, Mahali Elizabeth https://orcid.org/0000-0001-9921-2190
- Authors: Lesala, Mahali Elizabeth https://orcid.org/0000-0001-9921-2190
- Date: 2021-06
- Subjects: Farms, Small , Economic development -- South Africa , Agriculture -- Economic aspects -- South Africa
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10353/20916 , vital:46745
- Description: The low market participation of smallholder farmers in markets has received enormous attention from scholars, both in the country and the Eastern Cape Province. However, it is not clear how low their market participation is including its implications on farmer’s welfare. The purpose of the study was to determine the extent to which smallholder farmers in the homelands of the Eastern Cape participate in output markets and assess how their participation in markets has affected wellbeing of their households. This information will have important practical implications for policy regarding appropriate pathways for poverty alleviation and livelihoods improvements in the rural areas of the Eastern Cape Province. Three irrigation schemes; Qamata, Zanyokwe and Tyefu irrigation schemes were selected for this study. A sample of 210 smallholder irrigators were interviewed by means of a close-ended questionnaire. The data were analysed by means of descriptive statistical tools, the multiple-level choice models and the Propensity Score Matching (PSM) technique. SPSS and STATA computer programmes were used to carry out all the estimations. The analysis established that, although agriculture is the primary activity for rural livelihoods, it is not the main contributor to family income. Rather, remittances and social grants were the dominant sources of household income in the Qamata, Zanyokwe and Tyefu areas. From the standpoint of market, maize and potatoes are the most popular crops, but potatoes dominate the market. This result confirms that maize is the staple crop and therefore mostly grown for home consumption while production of potatoes is market-oriented. The Market Participation Index (MPI) revealed that farmers sell at least 55 percent of their farm produce, implying that farmers have made some transition from subsistence to semi-commercial farming. However, farmers’ priority still remains food self-sufficiency and market participation only takes place after satisfying their home food needs. The results revealed that the significant factors influencing the farmers’ decisions and their extent of participation in output markets were the age, gender, marital status of the household head, primary occupation of household head, size of farm cultivated, government financial support, access to extension services and farmer’s membership of cooperatives. Concerning the impact of output market participation on welfare of smallholders, the Average Treatment on the Treated (ATT) as the measure of change revealed that participation in output markets has a positive impact on welfare of the smallholder farmers through increased incomes. Farmers who participated in output market were at least R838.44 better off than those who did not participate in markets although social grants and remittances made significantly higher contribution to household welfare. The study suggests that despite some improvements in income of market participants, the standards of living of the rural households are still far from what would be considered optimal. Crop farming evidently contributes less than desired, hence the persistence of the widespread poverty. It is urgent to focus interventions on improving agricultural productivity while widening strategies for improving rural livelihoods beyond agriculture to diversify the choices open to rural dwellers. , Thesis (PhD) -- Faculty of Science and Agriculture, 2021
- Full Text:
- Date Issued: 2021-06
- Authors: Lesala, Mahali Elizabeth https://orcid.org/0000-0001-9921-2190
- Date: 2021-06
- Subjects: Farms, Small , Economic development -- South Africa , Agriculture -- Economic aspects -- South Africa
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10353/20916 , vital:46745
- Description: The low market participation of smallholder farmers in markets has received enormous attention from scholars, both in the country and the Eastern Cape Province. However, it is not clear how low their market participation is including its implications on farmer’s welfare. The purpose of the study was to determine the extent to which smallholder farmers in the homelands of the Eastern Cape participate in output markets and assess how their participation in markets has affected wellbeing of their households. This information will have important practical implications for policy regarding appropriate pathways for poverty alleviation and livelihoods improvements in the rural areas of the Eastern Cape Province. Three irrigation schemes; Qamata, Zanyokwe and Tyefu irrigation schemes were selected for this study. A sample of 210 smallholder irrigators were interviewed by means of a close-ended questionnaire. The data were analysed by means of descriptive statistical tools, the multiple-level choice models and the Propensity Score Matching (PSM) technique. SPSS and STATA computer programmes were used to carry out all the estimations. The analysis established that, although agriculture is the primary activity for rural livelihoods, it is not the main contributor to family income. Rather, remittances and social grants were the dominant sources of household income in the Qamata, Zanyokwe and Tyefu areas. From the standpoint of market, maize and potatoes are the most popular crops, but potatoes dominate the market. This result confirms that maize is the staple crop and therefore mostly grown for home consumption while production of potatoes is market-oriented. The Market Participation Index (MPI) revealed that farmers sell at least 55 percent of their farm produce, implying that farmers have made some transition from subsistence to semi-commercial farming. However, farmers’ priority still remains food self-sufficiency and market participation only takes place after satisfying their home food needs. The results revealed that the significant factors influencing the farmers’ decisions and their extent of participation in output markets were the age, gender, marital status of the household head, primary occupation of household head, size of farm cultivated, government financial support, access to extension services and farmer’s membership of cooperatives. Concerning the impact of output market participation on welfare of smallholders, the Average Treatment on the Treated (ATT) as the measure of change revealed that participation in output markets has a positive impact on welfare of the smallholder farmers through increased incomes. Farmers who participated in output market were at least R838.44 better off than those who did not participate in markets although social grants and remittances made significantly higher contribution to household welfare. The study suggests that despite some improvements in income of market participants, the standards of living of the rural households are still far from what would be considered optimal. Crop farming evidently contributes less than desired, hence the persistence of the widespread poverty. It is urgent to focus interventions on improving agricultural productivity while widening strategies for improving rural livelihoods beyond agriculture to diversify the choices open to rural dwellers. , Thesis (PhD) -- Faculty of Science and Agriculture, 2021
- Full Text:
- Date Issued: 2021-06
Movement behaviour and reproductive biology of adult spotted grunter (Pomadasys commersonnii) in the Breede Estuary
- Authors: Ziko, Bantony Alford
- Date: 2021-06
- Subjects: Fishery management , Freshwater fishes , Fishes--Nutrition
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10353/20970 , vital:46870
- Description: Movements of the adult spotted grunter (Pomadasys commersonnii), an overexploited estuary-dependant fishery species, were investigated in relation to its reproduction behaviour and selected environmental influences. The South African P. commersonnii population is known to spawn at sea along the KwaZulu-Natal (KZN) coastline, whereas there no published records on spawning in the Eastern and Western Cape Provinces exist. However, due to the occurrence of ripe running fish that were reported in the Breede Estuary (Western Cape - WC), an investigation into its reproductive behaviour was necessary, as was gaining a greater understanding of its movements between the estuary, the sea, and other connected habitats. Seven adult P. commersonnii (610 – 690 mm fork length, FL) were captured and implanted with long-life acoustic transmitters and their movements were logged on a linear array of 16 acoustic receivers in the Breede Estuary (WC) and six acoustic receivers in the adjacent marine environment. Movements of the tagged fish to other marine and estuary habitats were also determined using data collected by the Acoustic Tracking Array Platform (ATAP) which is an extended network of acoustic receivers along the South African coastline with receivers at sea and in selected estuaries. Furthermore, adult P. commersonnii tagged in the Goukou (n = 6) (WC) and Sundays (n = 8) (Eastern Cape - EC) estuaries, approximately 50 km and 470 km away, respectively, were also monitored to facilitate an improved understanding of inter-habitat connectivity. Fish tagged in Sundays and Goukou estuaries were monitored by the Acoustic Telemetry Array Platform (ATAP). Each individual fish tagged in the Breede Estuary was monitored between 356 and 1166 days and selected environmental parameters, including water temperature, river flow rate and rainfall, were measured during the study period (November 2016 – March 2020) to assess their influence on the movements of the tagged fish. Furthermore, to determine time of spawning and duration, gonads of 112 adult fish (383 – 700 mm FL) were opportunistically collected from recreational anglers in the Breede Estuary to determine the gonadal maturation cycles by using a combination of Gonado-somatic index (GSI) and histology. The tagged adult P. commersonnii spent significantly more time in the estuary (83.5 percent) than the marine (16.5 percent) environment, with all of the tagged P. commersonnii making sea trips of varying frequency and duration. While in the estuary, fish showed a strong preference for the lower reaches of the estuary compared to the middle and upper reaches. Area use varied seasonally, with the mouth area being heavily utilized during winter, then followed by summer. Sea trips in all three tagging estuaries also fluctuated seasonally, with more frequent movements during summer which lasted for longer periods. This coincided with the peak of the spawning period inferred from the gonad developmental cycle of fish captured in the Breede Estuary. Results from a generalized linear mixed model showed that the presence of Breede tagged P. commersonnii in the sea, where the species is known to spawn, was significantly influenced by water temperatures in the estuary and river flow rate with fish more likely to occur at sea during warmer months (summer) and periods of high river flow (winter). Furthermore, circular analysis showed that season (month) had a significant influence on the departure from and arrival in the Breede Estuary, with most departures and arrivals occurring during January. Moreover, P. commersonnii tagged in the Sundays Estuary also showed similar results where both departures and arrivals were influenced by season, mostly taking place in December and January, respectively. The increased frequency of sea trips by adult P. commersonnii in summer suggests regional spawning occurring in the WC. Based on the similar movement behaviour displayed by tagged fish in the Sundays Estuary, it is possible that spawning also occurs in the EC. Most of the P. commersonnii tagged in all the three estuaries never left their tagging estuaries (57 percent Breede, 66 percent Goukou, 38 percent Sundays), only making short sea trips, while others displayed use of multiple habitats. On average, the tagged P. commersonnii that left their tagging estuaries travelled a maximum distance of 377 km (Breede), 63 km (Goukou) and 300 km (Sundays). Tagged fish were more likely to visit nearby estuaries and offshore marine habitats (< 130 km) compared to distant ones (> 130 km). These results suggest that there are high levels of localised connectivity between P. commersonnii populations in different habitats although connectivity between distant habitats appears to be rare. Connectivity will likely occur on habitats located close to the boundaries of the WC, EC and KZN. The findings from this long-term monitoring study have shown that adult P. commersonnii rely heavily on the estuarine environment, undertaking short sea trips, thus demonstrating the importance of estuaries to the adult population. Due to various threats faced by estuaries such as habitat degradation and overexploitation, management of these systems is paramount to conserve such fishery resources. Due to the resident behaviour of the P. commersonnii within estuaries, Marine Protected Areas (MPAs) and area closures, in conjunction with Estuarine Protected Areas (EPAs) will be significant in the recovery and management of P. commersonnii populations. Since P. commersonnii appears to reach peak spawning activity during summer when fishing pressure is usually highest, improved enforcement during this period is necessary to conserve the spawning stock. As connectivity is an important aspect in the life of the P. commersonnii, ensuring such connectivity is maintained by protecting all these habitats is important. , Thesis (MSc) (Zoology) -- University of Fort Hare, 2021
- Full Text:
- Date Issued: 2021-06
- Authors: Ziko, Bantony Alford
- Date: 2021-06
- Subjects: Fishery management , Freshwater fishes , Fishes--Nutrition
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10353/20970 , vital:46870
- Description: Movements of the adult spotted grunter (Pomadasys commersonnii), an overexploited estuary-dependant fishery species, were investigated in relation to its reproduction behaviour and selected environmental influences. The South African P. commersonnii population is known to spawn at sea along the KwaZulu-Natal (KZN) coastline, whereas there no published records on spawning in the Eastern and Western Cape Provinces exist. However, due to the occurrence of ripe running fish that were reported in the Breede Estuary (Western Cape - WC), an investigation into its reproductive behaviour was necessary, as was gaining a greater understanding of its movements between the estuary, the sea, and other connected habitats. Seven adult P. commersonnii (610 – 690 mm fork length, FL) were captured and implanted with long-life acoustic transmitters and their movements were logged on a linear array of 16 acoustic receivers in the Breede Estuary (WC) and six acoustic receivers in the adjacent marine environment. Movements of the tagged fish to other marine and estuary habitats were also determined using data collected by the Acoustic Tracking Array Platform (ATAP) which is an extended network of acoustic receivers along the South African coastline with receivers at sea and in selected estuaries. Furthermore, adult P. commersonnii tagged in the Goukou (n = 6) (WC) and Sundays (n = 8) (Eastern Cape - EC) estuaries, approximately 50 km and 470 km away, respectively, were also monitored to facilitate an improved understanding of inter-habitat connectivity. Fish tagged in Sundays and Goukou estuaries were monitored by the Acoustic Telemetry Array Platform (ATAP). Each individual fish tagged in the Breede Estuary was monitored between 356 and 1166 days and selected environmental parameters, including water temperature, river flow rate and rainfall, were measured during the study period (November 2016 – March 2020) to assess their influence on the movements of the tagged fish. Furthermore, to determine time of spawning and duration, gonads of 112 adult fish (383 – 700 mm FL) were opportunistically collected from recreational anglers in the Breede Estuary to determine the gonadal maturation cycles by using a combination of Gonado-somatic index (GSI) and histology. The tagged adult P. commersonnii spent significantly more time in the estuary (83.5 percent) than the marine (16.5 percent) environment, with all of the tagged P. commersonnii making sea trips of varying frequency and duration. While in the estuary, fish showed a strong preference for the lower reaches of the estuary compared to the middle and upper reaches. Area use varied seasonally, with the mouth area being heavily utilized during winter, then followed by summer. Sea trips in all three tagging estuaries also fluctuated seasonally, with more frequent movements during summer which lasted for longer periods. This coincided with the peak of the spawning period inferred from the gonad developmental cycle of fish captured in the Breede Estuary. Results from a generalized linear mixed model showed that the presence of Breede tagged P. commersonnii in the sea, where the species is known to spawn, was significantly influenced by water temperatures in the estuary and river flow rate with fish more likely to occur at sea during warmer months (summer) and periods of high river flow (winter). Furthermore, circular analysis showed that season (month) had a significant influence on the departure from and arrival in the Breede Estuary, with most departures and arrivals occurring during January. Moreover, P. commersonnii tagged in the Sundays Estuary also showed similar results where both departures and arrivals were influenced by season, mostly taking place in December and January, respectively. The increased frequency of sea trips by adult P. commersonnii in summer suggests regional spawning occurring in the WC. Based on the similar movement behaviour displayed by tagged fish in the Sundays Estuary, it is possible that spawning also occurs in the EC. Most of the P. commersonnii tagged in all the three estuaries never left their tagging estuaries (57 percent Breede, 66 percent Goukou, 38 percent Sundays), only making short sea trips, while others displayed use of multiple habitats. On average, the tagged P. commersonnii that left their tagging estuaries travelled a maximum distance of 377 km (Breede), 63 km (Goukou) and 300 km (Sundays). Tagged fish were more likely to visit nearby estuaries and offshore marine habitats (< 130 km) compared to distant ones (> 130 km). These results suggest that there are high levels of localised connectivity between P. commersonnii populations in different habitats although connectivity between distant habitats appears to be rare. Connectivity will likely occur on habitats located close to the boundaries of the WC, EC and KZN. The findings from this long-term monitoring study have shown that adult P. commersonnii rely heavily on the estuarine environment, undertaking short sea trips, thus demonstrating the importance of estuaries to the adult population. Due to various threats faced by estuaries such as habitat degradation and overexploitation, management of these systems is paramount to conserve such fishery resources. Due to the resident behaviour of the P. commersonnii within estuaries, Marine Protected Areas (MPAs) and area closures, in conjunction with Estuarine Protected Areas (EPAs) will be significant in the recovery and management of P. commersonnii populations. Since P. commersonnii appears to reach peak spawning activity during summer when fishing pressure is usually highest, improved enforcement during this period is necessary to conserve the spawning stock. As connectivity is an important aspect in the life of the P. commersonnii, ensuring such connectivity is maintained by protecting all these habitats is important. , Thesis (MSc) (Zoology) -- University of Fort Hare, 2021
- Full Text:
- Date Issued: 2021-06
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