Modelling cannibalism and inter-species predation for the Cape hake species Merluccius capensis and M. paradoxus

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dc.contributor.advisorButterworth, Doug S
dc.contributor.authorRoss-Gillespie, Andrea
dc.date.accessioned2016-07-20T11:57:41Z
dc.date.available2016-07-20T11:57:41Z
dc.date.issued2016en_ZA
dc.description.abstractThe hake fishery is South Africa's most valuable and harvests two morphologically similar species, the shallow- water Cape hake Merluccius capensis and the deep-water Cape hake M. paradoxus. Since 1948, annual catches have exceeded 50 000 tons and the current total allowable catch (TAC) is about 150 000 tons, a quantity informed by assessments of the hake resource. Current assessments on which management is based use single-stock models that ignore food-web effects. Usually including such interactions in assessments is problematic because of the complexity of food webs. In the case of Cape hake, however, cannibalism and inter-species predation form a very large component of hake mortality and food consumption, thus making a multi-species model not only more feasible but also likely more reliable. A comprehensive multi-species model incorporating these interactions was last investigated in 1995. Since then, substantially more data have become available, and hake single-species assessments have developed considerably, inter alia now including the ability to take careful account of species differentiation. Additionally, with increased computer processing power, more sophisticated modelling can now be attempted than was possible 20 years ago, rendering an update and refinement of the 1995 analyses timeous. The thesis uses mathematical methods to model hake-on-hake predation and cannibalism in hake populations explicitly by incorporating an additional mortality term to account for these interactions. Information from stomach samples obtained on hake research surveys on predator and prey lengths, as well as on the proportion of hake in the diet of hake predators, is then included when fitting the model to data. Chapter 1 contains a brief introduction to the work. Chapter 2 provides background information on the Cape hake fishery and its management, as well as pertinent information on the biology and diet of the hake (and related fish) from the literature that is relevant to the development of the model constructed in this thesis. Chapter 3 lays out the data available for assessing the Cape hake populations: abundance indices together with catch and catch-at-size data for the standard non-predation model, and hake stomach content data for the years 1999-2013 to inform the predation component of multi-species model developed. Chapter 4 provides the details for the standard hake assessment model used at present to inform management of the stocks. This model forms the basis for the multi-species model developed incorporating predation, which is presented in Chapter 5. The remaining Chapters of the thesis present the results and discussions (Chapter 6), possible future development of this model (Chapter 7) and a brief summary of the main findings of the thesis (Chapter 8).en_ZA
dc.identifier.apacitationRoss-Gillespie, A. (2016). <i>Modelling cannibalism and inter-species predation for the Cape hake species Merluccius capensis and M. paradoxus</i>. (Thesis). University of Cape Town ,Faculty of Science ,Marine Resource Assessment and Management Group. Retrieved from http://hdl.handle.net/11427/20519en_ZA
dc.identifier.chicagocitationRoss-Gillespie, Andrea. <i>"Modelling cannibalism and inter-species predation for the Cape hake species Merluccius capensis and M. paradoxus."</i> Thesis., University of Cape Town ,Faculty of Science ,Marine Resource Assessment and Management Group, 2016. http://hdl.handle.net/11427/20519en_ZA
dc.identifier.citationRoss-Gillespie, A. 2016. Modelling cannibalism and inter-species predation for the Cape hake species Merluccius capensis and M. paradoxus. University of Cape Town.en_ZA
dc.identifier.ris TY - Thesis / Dissertation AU - Ross-Gillespie, Andrea AB - The hake fishery is South Africa's most valuable and harvests two morphologically similar species, the shallow- water Cape hake Merluccius capensis and the deep-water Cape hake M. paradoxus. Since 1948, annual catches have exceeded 50 000 tons and the current total allowable catch (TAC) is about 150 000 tons, a quantity informed by assessments of the hake resource. Current assessments on which management is based use single-stock models that ignore food-web effects. Usually including such interactions in assessments is problematic because of the complexity of food webs. In the case of Cape hake, however, cannibalism and inter-species predation form a very large component of hake mortality and food consumption, thus making a multi-species model not only more feasible but also likely more reliable. A comprehensive multi-species model incorporating these interactions was last investigated in 1995. Since then, substantially more data have become available, and hake single-species assessments have developed considerably, inter alia now including the ability to take careful account of species differentiation. Additionally, with increased computer processing power, more sophisticated modelling can now be attempted than was possible 20 years ago, rendering an update and refinement of the 1995 analyses timeous. The thesis uses mathematical methods to model hake-on-hake predation and cannibalism in hake populations explicitly by incorporating an additional mortality term to account for these interactions. Information from stomach samples obtained on hake research surveys on predator and prey lengths, as well as on the proportion of hake in the diet of hake predators, is then included when fitting the model to data. Chapter 1 contains a brief introduction to the work. Chapter 2 provides background information on the Cape hake fishery and its management, as well as pertinent information on the biology and diet of the hake (and related fish) from the literature that is relevant to the development of the model constructed in this thesis. Chapter 3 lays out the data available for assessing the Cape hake populations: abundance indices together with catch and catch-at-size data for the standard non-predation model, and hake stomach content data for the years 1999-2013 to inform the predation component of multi-species model developed. Chapter 4 provides the details for the standard hake assessment model used at present to inform management of the stocks. This model forms the basis for the multi-species model developed incorporating predation, which is presented in Chapter 5. The remaining Chapters of the thesis present the results and discussions (Chapter 6), possible future development of this model (Chapter 7) and a brief summary of the main findings of the thesis (Chapter 8). DA - 2016 DB - OpenUCT DP - University of Cape Town LK - https://open.uct.ac.za PB - University of Cape Town PY - 2016 T1 - Modelling cannibalism and inter-species predation for the Cape hake species Merluccius capensis and M. paradoxus TI - Modelling cannibalism and inter-species predation for the Cape hake species Merluccius capensis and M. paradoxus UR - http://hdl.handle.net/11427/20519 ER - en_ZA
dc.identifier.urihttp://hdl.handle.net/11427/20519
dc.identifier.vancouvercitationRoss-Gillespie A. Modelling cannibalism and inter-species predation for the Cape hake species Merluccius capensis and M. paradoxus. [Thesis]. University of Cape Town ,Faculty of Science ,Marine Resource Assessment and Management Group, 2016 [cited yyyy month dd]. Available from: http://hdl.handle.net/11427/20519en_ZA
dc.language.isoengen_ZA
dc.publisher.departmentMarine Resource Assessment and Management Groupen_ZA
dc.publisher.facultyFaculty of Scienceen_ZA
dc.publisher.institutionUniversity of Cape Town
dc.subject.otherMathematics and Applied Mathematicsen_ZA
dc.titleModelling cannibalism and inter-species predation for the Cape hake species Merluccius capensis and M. paradoxusen_ZA
dc.typeDoctoral Thesis
dc.type.qualificationlevelDoctoral
dc.type.qualificationnamePhDen_ZA
uct.type.filetypeText
uct.type.filetypeImage
uct.type.publicationResearchen_ZA
uct.type.resourceThesisen_ZA
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