Comparative age and growth of juvenile dusky kob (Argyrosomus japonicus) in three South African estuaries, with notes on diet and temperature effects

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dc.contributor.advisorGovender, Aneshen_ZA
dc.contributor.advisorGriffiths, M Hen_ZA
dc.contributor.authorMafwila, Samuel Kakambi.en_ZA
dc.date.accessioned2014-09-08T09:57:03Z
dc.date.available2014-09-08T09:57:03Z
dc.date.issued2003en_ZA
dc.descriptionBibliography: leaves 36-43.en_ZA
dc.description.abstractThe dusky kob Argyrosomus japonicus is an important commercial and recreational linefish species in South Africa. It has a wide distribution range from Cape Agulhas to the Mozambique border. Juveniles A. japonicus <1070 mm) occur inshore and in estuaries where surf-zone and estuarine anglers target them. Adult A. japonicus (> 1070 mm) are caught beyond the surf zone by line fishermen. In this study, 380 juvenile dusky kob were caught by hook and line from the Breede River, Fish River, and Keiskamma River estuaries. Age of juvenile A. japonicus in these three South African estuaries was estimated by counting growth rings in sectioned sagittal otoliths read under a dissecting microscope using reflected light. The reproducibility of otoliths readings was described by the average percentage error (APE) index and was found to be 0.44% (Breede), 2.78% (Fish), 0.25% (Keiskamma) for an experienced reader and 0.5% (Breede), 4.37% (Fish), 0.53% (Keiskamma) for an inexperienced reader. Comparisons of A. japonicus otoliths by an experienced and an inexperienced reader indicated a reasonable between-reader consistency, however, the otoliths from the Fish River estuary were more difficult to read than from the other two estuaries. The Schnute growth model was used to determine which sub-model would best describe the growth of juvenile A. japonicus. Linear regression lines were fitted to the age-at-length growth curves of juvenile A. japonicus for each estuary to determine whether there were significant differences in growth rate. It was found that growth was the highest in the Breede River estuary (113.7 mm/yr), followed by the Keiskamma River estuary (92.1 mm/yr) and the Fish River estuary (83.9 mm/yr). Variable growth rates of juvenile A. japonicus in the three estuaries may be related to food availability and prey item types and to a lesser extent to water temperature in the estuaries. The comparisons of estuarine diets of A. japonicus indicate that juvenile dusky kob in different estuaries have different dominant prey species. There were one or two taxa dominant in each estuary with Galeichthys feliceps (61.9%), and the mysids (71.8%) being the most important prey items in the Breede River and the Great Fish River estuaries respectively, while teleost Pomadasys commersonnii (73.8%) were the most important prey species in the Keiskamma River estuary.en_ZA
dc.identifier.apacitationMafwila, Samuel Kakambi. (2003). <i>Comparative age and growth of juvenile dusky kob (Argyrosomus japonicus) in three South African estuaries, with notes on diet and temperature effects</i>. (Thesis). University of Cape Town ,Faculty of Science ,Department of Biological Sciences. Retrieved from http://hdl.handle.net/11427/6972en_ZA
dc.identifier.chicagocitationMafwila, Samuel Kakambi.. <i>"Comparative age and growth of juvenile dusky kob (Argyrosomus japonicus) in three South African estuaries, with notes on diet and temperature effects."</i> Thesis., University of Cape Town ,Faculty of Science ,Department of Biological Sciences, 2003. http://hdl.handle.net/11427/6972en_ZA
dc.identifier.citationMafwila, Samuel Kakambi. 2003. Comparative age and growth of juvenile dusky kob (Argyrosomus japonicus) in three South African estuaries, with notes on diet and temperature effects. Thesis. University of Cape Town ,Faculty of Science ,Department of Biological Sciences. http://hdl.handle.net/11427/6972en_ZA
dc.identifier.ris TY - Thesis / Dissertation AU - Mafwila, Samuel Kakambi. AB - The dusky kob Argyrosomus japonicus is an important commercial and recreational linefish species in South Africa. It has a wide distribution range from Cape Agulhas to the Mozambique border. Juveniles A. japonicus <1070 mm) occur inshore and in estuaries where surf-zone and estuarine anglers target them. Adult A. japonicus (> 1070 mm) are caught beyond the surf zone by line fishermen. In this study, 380 juvenile dusky kob were caught by hook and line from the Breede River, Fish River, and Keiskamma River estuaries. Age of juvenile A. japonicus in these three South African estuaries was estimated by counting growth rings in sectioned sagittal otoliths read under a dissecting microscope using reflected light. The reproducibility of otoliths readings was described by the average percentage error (APE) index and was found to be 0.44% (Breede), 2.78% (Fish), 0.25% (Keiskamma) for an experienced reader and 0.5% (Breede), 4.37% (Fish), 0.53% (Keiskamma) for an inexperienced reader. Comparisons of A. japonicus otoliths by an experienced and an inexperienced reader indicated a reasonable between-reader consistency, however, the otoliths from the Fish River estuary were more difficult to read than from the other two estuaries. The Schnute growth model was used to determine which sub-model would best describe the growth of juvenile A. japonicus. Linear regression lines were fitted to the age-at-length growth curves of juvenile A. japonicus for each estuary to determine whether there were significant differences in growth rate. It was found that growth was the highest in the Breede River estuary (113.7 mm/yr), followed by the Keiskamma River estuary (92.1 mm/yr) and the Fish River estuary (83.9 mm/yr). Variable growth rates of juvenile A. japonicus in the three estuaries may be related to food availability and prey item types and to a lesser extent to water temperature in the estuaries. The comparisons of estuarine diets of A. japonicus indicate that juvenile dusky kob in different estuaries have different dominant prey species. There were one or two taxa dominant in each estuary with Galeichthys feliceps (61.9%), and the mysids (71.8%) being the most important prey items in the Breede River and the Great Fish River estuaries respectively, while teleost Pomadasys commersonnii (73.8%) were the most important prey species in the Keiskamma River estuary. DA - 2003 DB - OpenUCT DP - University of Cape Town LK - https://open.uct.ac.za PB - University of Cape Town PY - 2003 T1 - Comparative age and growth of juvenile dusky kob (Argyrosomus japonicus) in three South African estuaries, with notes on diet and temperature effects TI - Comparative age and growth of juvenile dusky kob (Argyrosomus japonicus) in three South African estuaries, with notes on diet and temperature effects UR - http://hdl.handle.net/11427/6972 ER - en_ZA
dc.identifier.urihttp://hdl.handle.net/11427/6972
dc.identifier.vancouvercitationMafwila Samuel Kakambi. Comparative age and growth of juvenile dusky kob (Argyrosomus japonicus) in three South African estuaries, with notes on diet and temperature effects. [Thesis]. University of Cape Town ,Faculty of Science ,Department of Biological Sciences, 2003 [cited yyyy month dd]. Available from: http://hdl.handle.net/11427/6972en_ZA
dc.language.isoengen_ZA
dc.publisher.departmentDepartment of Biological Sciencesen_ZA
dc.publisher.facultyFaculty of Scienceen_ZA
dc.publisher.institutionUniversity of Cape Town
dc.subject.otherApplied Marine Scienceen_ZA
dc.titleComparative age and growth of juvenile dusky kob (Argyrosomus japonicus) in three South African estuaries, with notes on diet and temperature effectsen_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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