Environmental variables influencing spatial and temporal patterns of fish spawning and recruitment

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dc.contributor.advisorMoloney, Coleen Len_ZA
dc.contributor.advisorOstrowski, Mareken_ZA
dc.contributor.advisorLipinski, Mareken_ZA
dc.contributor.authorMbatha, Fisokuhle Lungileen_ZA
dc.date.accessioned2017-09-26T14:55:19Z
dc.date.available2017-09-26T14:55:19Z
dc.date.issued2017en_ZA
dc.description.abstractABSTRACT Spawning times and spawning intensity during the life cycles of some fish species found off South Africa and Norway were synthesized using data collected from the literature. The comparison of temporal patterns in spawning of South African fish species showed variable spawning times and intensity depending on the environmental conditions within that spawning habitat. Their spawning migration durations were suggested to be short since they inhabit a dynamic coastal upwelling ecosystem with intra-seasonal differences caused by changes in upwelling strength enhanced by south-easterly winds, nutrient-limited waters on the spawning grounds and stable thermal conditions. This contrasts with Norwegian fish species, which showed patterns of spawning times and durations that are restricted and confined to spring (February – May), probably due to strong, consistent seasonality, depending on primary production. This explains the inter-annual differences observed in their spawning periods, where strong south-westerly winds (downwelling), light intensity and salinity stratification could influence long spawning migrations. For Cape hakes, environmental variability influencing recruitment was further investigated on the west coast nursery grounds of the southern Benguela, particularly for deep-water Cape hake (Merluccius paradoxus). Biophysical characteristics of the west coast nursery grounds were assessed in relation to distribution of deep-water Cape hake juveniles (< 15 cm) using physical data (CTD, alongshore wind speed anomalies) and biological data (abundance/density of hake juveniles, recruitment estimates). Distinct spatial patterns of hake distribution were evident in relation to near-bottom environmental factors (temperature, salinity and oxygen). Nansen surveys conducted from 2003 – 2013 during summer (January – February) showed greater abundance of hake juveniles over the Orange Banks than in other nursery areas. The hake juveniles occurred in mid-shelf waters with oxygen depletion (2 – 3 mL O₂.L⁻¹) and hypoxic conditions (< 2 mL O₂.L⁻¹) and temperature ranges of 7 – 11 ⁰C. Salinity appeared to have less influence on hake juveniles' distribution. During spring surveys, hake catches were reduced on all nursery grounds except near Cape Columbine. There was a strong positive correlation between deep-water Cape hake recruitment indices and summer wind speed anomalies for the same year (Lag = 0 year) and with autumn wind speed anomalies of the previous year (Lag = 1 year). The relationship between winds and near-bottom oxygen concentrations on the Orange Banks is unclear and needs to be investigated.en_ZA
dc.identifier.apacitationMbatha, F. L. (2017). <i>Environmental variables influencing spatial and temporal patterns of fish spawning and recruitment</i>. (Thesis). University of Cape Town ,Faculty of Science ,Marine Research (MA-RE) Institute. Retrieved from http://hdl.handle.net/11427/25402en_ZA
dc.identifier.chicagocitationMbatha, Fisokuhle Lungile. <i>"Environmental variables influencing spatial and temporal patterns of fish spawning and recruitment."</i> Thesis., University of Cape Town ,Faculty of Science ,Marine Research (MA-RE) Institute, 2017. http://hdl.handle.net/11427/25402en_ZA
dc.identifier.citationMbatha, F. 2017. Environmental variables influencing spatial and temporal patterns of fish spawning and recruitment. University of Cape Town.en_ZA
dc.identifier.ris TY - Thesis / Dissertation AU - Mbatha, Fisokuhle Lungile AB - ABSTRACT Spawning times and spawning intensity during the life cycles of some fish species found off South Africa and Norway were synthesized using data collected from the literature. The comparison of temporal patterns in spawning of South African fish species showed variable spawning times and intensity depending on the environmental conditions within that spawning habitat. Their spawning migration durations were suggested to be short since they inhabit a dynamic coastal upwelling ecosystem with intra-seasonal differences caused by changes in upwelling strength enhanced by south-easterly winds, nutrient-limited waters on the spawning grounds and stable thermal conditions. This contrasts with Norwegian fish species, which showed patterns of spawning times and durations that are restricted and confined to spring (February – May), probably due to strong, consistent seasonality, depending on primary production. This explains the inter-annual differences observed in their spawning periods, where strong south-westerly winds (downwelling), light intensity and salinity stratification could influence long spawning migrations. For Cape hakes, environmental variability influencing recruitment was further investigated on the west coast nursery grounds of the southern Benguela, particularly for deep-water Cape hake (Merluccius paradoxus). Biophysical characteristics of the west coast nursery grounds were assessed in relation to distribution of deep-water Cape hake juveniles (< 15 cm) using physical data (CTD, alongshore wind speed anomalies) and biological data (abundance/density of hake juveniles, recruitment estimates). Distinct spatial patterns of hake distribution were evident in relation to near-bottom environmental factors (temperature, salinity and oxygen). Nansen surveys conducted from 2003 – 2013 during summer (January – February) showed greater abundance of hake juveniles over the Orange Banks than in other nursery areas. The hake juveniles occurred in mid-shelf waters with oxygen depletion (2 – 3 mL O₂.L⁻¹) and hypoxic conditions (< 2 mL O₂.L⁻¹) and temperature ranges of 7 – 11 ⁰C. Salinity appeared to have less influence on hake juveniles' distribution. During spring surveys, hake catches were reduced on all nursery grounds except near Cape Columbine. There was a strong positive correlation between deep-water Cape hake recruitment indices and summer wind speed anomalies for the same year (Lag = 0 year) and with autumn wind speed anomalies of the previous year (Lag = 1 year). The relationship between winds and near-bottom oxygen concentrations on the Orange Banks is unclear and needs to be investigated. DA - 2017 DB - OpenUCT DP - University of Cape Town LK - https://open.uct.ac.za PB - University of Cape Town PY - 2017 T1 - Environmental variables influencing spatial and temporal patterns of fish spawning and recruitment TI - Environmental variables influencing spatial and temporal patterns of fish spawning and recruitment UR - http://hdl.handle.net/11427/25402 ER - en_ZA
dc.identifier.urihttp://hdl.handle.net/11427/25402
dc.identifier.vancouvercitationMbatha FL. Environmental variables influencing spatial and temporal patterns of fish spawning and recruitment. [Thesis]. University of Cape Town ,Faculty of Science ,Marine Research (MA-RE) Institute, 2017 [cited yyyy month dd]. Available from: http://hdl.handle.net/11427/25402en_ZA
dc.language.isoengen_ZA
dc.publisher.departmentMarine Research (MA-RE) Instituteen_ZA
dc.publisher.facultyFaculty of Scienceen_ZA
dc.publisher.institutionUniversity of Cape Town
dc.subject.otherApplied Marine Scienceen_ZA
dc.titleEnvironmental variables influencing spatial and temporal patterns of fish spawning and recruitmenten_ZA
dc.typeMaster Thesis
dc.type.qualificationlevelMasters
dc.type.qualificationnameMScen_ZA
uct.type.filetypeText
uct.type.filetypeImage
uct.type.publicationResearchen_ZA
uct.type.resourceThesisen_ZA
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