Using mark-recapture methods to estimate population size and survival of pyjama sharks (Poroderma africanum) in Mossel Bay, South Africa

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dc.contributor.advisorGennari, Enricoen_ZA
dc.contributor.advisorMoloney, Coleen Len_ZA
dc.contributor.advisorDistiller, Greg Ben_ZA
dc.contributor.authorGrusd, Samanthaen_ZA
dc.date.accessioned2017-09-01T14:21:02Z
dc.date.available2017-09-01T14:21:02Z
dc.date.issued2017en_ZA
dc.description.abstractSharks are vulnerable to exploitation as a result of their biological characteristics. Markrecapture models were applied to conventional tag recapture data and acoustic telemetry data to estimate abundance, apparent survival, recapture probability and temporary emigration for the pyjama shark, Poroderma africanum in Mossel Bay, South Africa over a five-year period. This study applied Pollock's robust design (with the conventional tag data) and Cormack-Jolly-Seber (CJS) models (with the acoustic tag data) to analyze the mark-recapture data. In addition, a von Bertalanffy model was fit to the data to estimate individual growth. The best-fit robust design model showed the population as having no temporary emigration, survival probability that is dependent on the length at first capture, and time-constant capture probabilities. The best-fit CJS model showed the population also having time-constant survival, but sex dependent capture probabilities. Robust design abundance estimates (with 95% C.I.) in Mossel Bay varied from 279 (102-787) sharks to 733 (320-1777) sharks, although confidence intervals were quite large. CJS apparent annual survival (95% C.I.; CJS) was estimated to be 0.271 year⁻¹ (0.04 to 0.56) and annual recapture probability (95% C.I.) was estimated to be 0.008 year⁻¹ (0.003-0.20), indicating that survival and recaptures for this endemic species are relatively low. Annual somatic growth rate (k) was estimated to be 0.213 year⁻¹, indicating that this population is slow growing, a characteristic common in most shark species. Overall, the results in this study provide baseline knowledge on this population in Mossel Bay and can be used to implement proper management techniques. This knowledge can be further expanded upon to give a more in-depth understanding of all size and age classes in the population and the role that the environment and anthropogenic activities play in the population structure.en_ZA
dc.identifier.apacitationGrusd, S. (2017). <i>Using mark-recapture methods to estimate population size and survival of pyjama sharks (Poroderma africanum) in Mossel Bay, South Africa</i>. (Thesis). University of Cape Town ,Faculty of Science ,Department of Oceanography. Retrieved from http://hdl.handle.net/11427/25026en_ZA
dc.identifier.chicagocitationGrusd, Samantha. <i>"Using mark-recapture methods to estimate population size and survival of pyjama sharks (Poroderma africanum) in Mossel Bay, South Africa."</i> Thesis., University of Cape Town ,Faculty of Science ,Department of Oceanography, 2017. http://hdl.handle.net/11427/25026en_ZA
dc.identifier.citationGrusd, S. 2017. Using mark-recapture methods to estimate population size and survival of pyjama sharks (Poroderma africanum) in Mossel Bay, South Africa. University of Cape Town.en_ZA
dc.identifier.ris TY - Thesis / Dissertation AU - Grusd, Samantha AB - Sharks are vulnerable to exploitation as a result of their biological characteristics. Markrecapture models were applied to conventional tag recapture data and acoustic telemetry data to estimate abundance, apparent survival, recapture probability and temporary emigration for the pyjama shark, Poroderma africanum in Mossel Bay, South Africa over a five-year period. This study applied Pollock's robust design (with the conventional tag data) and Cormack-Jolly-Seber (CJS) models (with the acoustic tag data) to analyze the mark-recapture data. In addition, a von Bertalanffy model was fit to the data to estimate individual growth. The best-fit robust design model showed the population as having no temporary emigration, survival probability that is dependent on the length at first capture, and time-constant capture probabilities. The best-fit CJS model showed the population also having time-constant survival, but sex dependent capture probabilities. Robust design abundance estimates (with 95% C.I.) in Mossel Bay varied from 279 (102-787) sharks to 733 (320-1777) sharks, although confidence intervals were quite large. CJS apparent annual survival (95% C.I.; CJS) was estimated to be 0.271 year⁻¹ (0.04 to 0.56) and annual recapture probability (95% C.I.) was estimated to be 0.008 year⁻¹ (0.003-0.20), indicating that survival and recaptures for this endemic species are relatively low. Annual somatic growth rate (k) was estimated to be 0.213 year⁻¹, indicating that this population is slow growing, a characteristic common in most shark species. Overall, the results in this study provide baseline knowledge on this population in Mossel Bay and can be used to implement proper management techniques. This knowledge can be further expanded upon to give a more in-depth understanding of all size and age classes in the population and the role that the environment and anthropogenic activities play in the population structure. DA - 2017 DB - OpenUCT DP - University of Cape Town LK - https://open.uct.ac.za PB - University of Cape Town PY - 2017 T1 - Using mark-recapture methods to estimate population size and survival of pyjama sharks (Poroderma africanum) in Mossel Bay, South Africa TI - Using mark-recapture methods to estimate population size and survival of pyjama sharks (Poroderma africanum) in Mossel Bay, South Africa UR - http://hdl.handle.net/11427/25026 ER - en_ZA
dc.identifier.urihttp://hdl.handle.net/11427/25026
dc.identifier.vancouvercitationGrusd S. Using mark-recapture methods to estimate population size and survival of pyjama sharks (Poroderma africanum) in Mossel Bay, South Africa. [Thesis]. University of Cape Town ,Faculty of Science ,Department of Oceanography, 2017 [cited yyyy month dd]. Available from: http://hdl.handle.net/11427/25026en_ZA
dc.language.isoengen_ZA
dc.publisher.departmentDepartment of Oceanographyen_ZA
dc.publisher.facultyFaculty of Scienceen_ZA
dc.publisher.institutionUniversity of Cape Town
dc.subject.otherApplied Marine Scienceen_ZA
dc.titleUsing mark-recapture methods to estimate population size and survival of pyjama sharks (Poroderma africanum) in Mossel Bay, South Africaen_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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