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The effectiveness of the use of shark dorsal fin photo-identification methods to aid in the conservation of Carcharodon carcharias and Carcharhinus brachyurus
Thesis (MSc)--Stellenbosch University, 2023.
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| Format: | Thesis |
| Language: | English |
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Stellenbosch : Stellenbosch University
2023
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| _version_ | 1867613739104075776 |
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| access_status_str | Open Access |
| author | Maroen, Megan Melissa |
| author2 | Andreotti, Sara |
| author_browse | Andreotti, Sara Maroen, Megan Melissa |
| author_facet | Andreotti, Sara Maroen, Megan Melissa |
| author_sort | Maroen, Megan Melissa |
| collection | Thesis |
| dc_rights_str_mv | Stellenbosch University |
| description | Thesis (MSc)--Stellenbosch University, 2023. |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/128483 |
| institution | Stellenbosch University (South Africa) |
| language | English |
| last_indexed | 2026-06-10T12:40:55.520Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from SUNScholar — Stellenbosch University Repository |
| publishDate | 2023 |
| publishDateRange | 2023 |
| publishDateSort | 2023 |
| publisher | Stellenbosch : Stellenbosch University |
| publisherStr | Stellenbosch : Stellenbosch University |
| record_format | dspace |
| source_str | SUNScholar — Stellenbosch University Repository |
| spelling | oai:scholar.sun.ac.za:10019.1/128483 The effectiveness of the use of shark dorsal fin photo-identification methods to aid in the conservation of Carcharodon carcharias and Carcharhinus brachyurus Maroen, Megan Melissa Andreotti, Sara Matthee, Conrad Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology. White shark (Carcharodon carcharias) -- Conservation Bronze whaler sharks (Carcharhinus brachyurus) -- Conservation Sharks-- Ecology -- Data processing Carcharhinus -- Monitoring Carcharodon -- Monitoring Population biology -- Effect of global warming on Marine biology -- Environmental aspects UCTD Thesis (MSc)--Stellenbosch University, 2023. ENGLISH ABSTRACT: White sharks (Carcharodon carcharias) and bronze whaler sharks (Carcharhinus brachyurus) are regarded as being threatened by human activities. To support the conservation of these species, there is a need for data-driven decision making. Collecting data from marine species is notoriously more challenging than from terrestrial species, because of unpredictable weather conditions and costs associated with the logistical arrangements required. To overcome some of these challenges, shark researchers have resorted to the use of photo-identification (photo-ID) methods using tourist boats to survey areas at a reduced cost. Photo-ID is based on photographing natural markings of a species that enable individual identification and thus differentiation from conspecifics. Traditionally, photo-ID utilised manual searching to match photographs of individuals through a database. However, enhanced digital photography resulted in the availability of a larger number of photographs captured in a shorter period, which led to the development of a novel notches code method, and a semi-automatic software identification tool called Identifin, to ease the search effort and reduce potential errors associated with manual matching. To date, the effectiveness and reliability of these three methods to identify individual sharks have not been independently tested. To address this, the second chapter of this thesis determined which method is the most efficient to correctly identify white shark individuals using the same photographic dataset and 11 novice and 2 trained investigators. Although both manual matching methods could accurately match individuals, they become less efficient (requiring more time and effort) as the size of the photographic database increases. The computer assisted Identifin software, as expected, is the best method (requiring less time and effort), as it outperformed both manual methods by maintaining the highest matching accuracy irrespective of the size of the photographic database. Furthermore, the advantages of using Identifin is that it automatically generates a binomial history of captures matrix from the images metadata, further reducing the risk of human error. The history of captures matrix can then be analysed in MARK to estimate the population size using capture-mark-recapture (CMR) models. As such, the third chapter analysed the binomial history of captures matrix across 2016–2018 to generate an updated population estimate for white sharks in Gansbaai. The outcome of this part of the study was directly compared to previous estimates of the same study region, to provide the first empirical population trend for Gansbaai. We found that, despite an increase in sampling efforts in the recent years, less white sharks frequented the bay across 2016–2018 in comparison to 2009–2011 and, as a result, the population estimate generated in this chapter is substantially lower than any previous study (N < 126 individuals). Given the potential for generating up to date shark population information based on photo-ID, the last chapter of this thesis investigated the use of Identifin on bronze whaler sharks. Identifin proved to accurately match bronze whaler shark photo-ID data, but due to their less pronounced notches patterns, identification was limited to the use of only high-quality images. Similar to that of white sharks, our dataset also showed potential to use photo-ID data and Identifin to provide population estimates for this species. The outputs of this thesis indicate that Identifin has the potential to serve as a standardised platform for shark data cataloguing and the generation of comparative outputs across multiple regions globally. The use of this software can ultimately facilitate collaborative research and the implementation of globally recognised conservation strategies for both white sharks and bronze whaler sharks. AFRIKAANSE OPSOMMING: Witdoodshaaie (Carcharodon carcharias) en brons walvishaaie (Carcharhinus brachyurus) word bedreig deur menslike aktiwiteite. Daar is ‘n behoefte aan data-gedrewe besluitneming om die bewaring van hierdie spesies te ondersteun. Om data van mariene spesies te versamel is baie meer uitdagend in vergelyking met terrestriële spesies, as gevolg van onvoorspelbare weerstoestande en die koste verbonde aan die logistieke reëlings wat vereis word. Om van hierdie uitdagings te oorkom maak navorsers van foto-identifikasie (Foto-ID) metodes gebruik. Navorsers vergesel toeriste wat uitgaan op bote waar opnames dan in sekere areas teen laer koste gemaak kan word. Foto–ID is gebaseer op fotografie van natuurlike merke van ‘n spesie wat individuele identifikasie moontlik maak. Foto-ID was traditioneel met die hand uitgevoer waar fotos van individue met behulp van ‘n databasis, by hul ooreenstemmendes gepas kon word. Verbeterde digitale fotografie het egter gelei tot die beskikbaarheid van ‘n groter aantal foto's wat in 'n korter tydperk geneem kan word en nou beskikbaar is. Die groot data stelle het dit moeilik gemaak om met die hand te verwerk en dit het gelei tot die ontwikkeling van 'n nuwe kerfkodemetode asook semi-outomatiese sagteware-identifikasie genaamd Identifin. Hierdie metodes vergemaklik die soektog om individue met mekaar te vergelyk en verminder potensiële foute geassosieer met handmatige passing. Tot op hede is die doeltreffendheid en betroubaarheid van hierdie drie metodes, om individuele haaie te identifiseer, nie onafhanklik getoets nie. Om dit aan te spreek, het die eerste hoofstuk van hierdie tesis bepaal watter metode die doeltreffendste is om witdoodshaai individue korrek te identifiseer. Dit is uitgevoer en bepaal deur gebruik te maak van dieselfde fotografiese datastelle en meestal beginners wat die metodes nie geken het nie. Alhoewel beide handmatige passing metodes akkuraat individue met hulle soortgenote kon pas, word hulle minder doeltreffend (langer tyd en meer moeite vereis) soos die grootte van die fotografiese databasis toeneem. Die rekenaar geassisteerde Identifin-sagteware, soos verwag, is die beste metode (benodig minder tyd en moeite). Die resultate bewys dat Identifin beter as beide handmetodes gevaar het deur die hoogste bypassende akkuraatheid te handhaaf, ongeag die grootte van die fotografiese databasis. Verdere voordele van die gebruik van Identifin is dat dit outomaties 'n binomiale geskiedenis opstel wat die opnamematriks van die beelde in metadata uitbeeld, wat die risiko van menslike foute verder verminder. Die geskiedenis van vangmatriks kan dan in die sagteware MARK ontleed word om die bevolkingsgrootte te skat deur gebruik te maak van vang-merk-hervang (CMR) modelle. Die tweede hoofstuk bevat die ontleding van die binomiale geskiedenis van vangmatriks vanaf 2016–2018, om 'n op datum bevolkingsskatting vir witdoodshaaie in Gansbaai te genereer. Die uitkoms van hierdie deel van die studie is direk vergelyk met vorige skattings van dieselfde studiestreek was die eerste empiriese bevolkingstendens vir Gansbaai verskaf het. Ons het gevind dat, ten spyte van 'n toename in monsternemingspogings in die afgelope jare, minder witdoodshaaie die baai oor 2016–2018 besoek het in vergelyking met 2009–2011. Gevolglik is die bevolkingsskatting wat in hierdie hoofstuk gegenereer word aansienlik laer (N < 126 individue). Met die potensiaal om haaibevolking inligting gebaseer op foto-ID te genereer, het die laaste hoofstuk van hierdie tesis die gebruik van Identifin op brons walvishaaie ook getoets. Identifin het bewys dat dit akkuraat brons walvishaai foto-ID data kan verwerk, maar as gevolg van hul minder prominente kerfpatrone, was identifikasie beperk tot die gebruik van slegs hoë resolusie en kwaliteit foto's. Soortgelyk aan dié van witdoodshaaie, het ons datastel ook potensiaal getoon om foto-ID-data en Identifin te gebruik om bevolkingskattings vir hierdie spesie te verskaf. Die uitsette van hierdie tesis dui daarop dat Identifin die potensiaal het om as 'n gestandaardiseerde platform vir haaidata-katalogisering gebruik te kan word en kan dus vergelykende uitsette oor verskeie streke wêreldwyd ondersteun. Die gebruik van hierdie sagteware kan uiteindelik samewerkende navorsing en die implementering van wêreldwye erkende bewaringstrategieë vir beide witdoodshaaie en bronswalvishaaie vergemaklik. Masters 2023-03-01T10:53:15Z 2023-08-30T13:10:29Z 2023-03-01 2023-03-01T10:53:15Z 2023-08-31T09:18:50Z 2023-03-01T10:53:15Z 2023-08-31T09:18:50Z 2023-03 Thesis https://scholar.sun.ac.za/handle/10019.1/128483 en Stellenbosch University application/pdf xii, 104 pages : illustrations, maps application/pdf Stellenbosch : Stellenbosch University |
| spellingShingle | White shark (Carcharodon carcharias) -- Conservation Bronze whaler sharks (Carcharhinus brachyurus) -- Conservation Sharks-- Ecology -- Data processing Carcharhinus -- Monitoring Carcharodon -- Monitoring Population biology -- Effect of global warming on Marine biology -- Environmental aspects UCTD Maroen, Megan Melissa The effectiveness of the use of shark dorsal fin photo-identification methods to aid in the conservation of Carcharodon carcharias and Carcharhinus brachyurus |
| title | The effectiveness of the use of shark dorsal fin photo-identification methods to aid in the conservation of Carcharodon carcharias and Carcharhinus brachyurus |
| title_full | The effectiveness of the use of shark dorsal fin photo-identification methods to aid in the conservation of Carcharodon carcharias and Carcharhinus brachyurus |
| title_fullStr | The effectiveness of the use of shark dorsal fin photo-identification methods to aid in the conservation of Carcharodon carcharias and Carcharhinus brachyurus |
| title_full_unstemmed | The effectiveness of the use of shark dorsal fin photo-identification methods to aid in the conservation of Carcharodon carcharias and Carcharhinus brachyurus |
| title_short | The effectiveness of the use of shark dorsal fin photo-identification methods to aid in the conservation of Carcharodon carcharias and Carcharhinus brachyurus |
| title_sort | effectiveness of the use of shark dorsal fin photo identification methods to aid in the conservation of carcharodon carcharias and carcharhinus brachyurus |
| topic | White shark (Carcharodon carcharias) -- Conservation Bronze whaler sharks (Carcharhinus brachyurus) -- Conservation Sharks-- Ecology -- Data processing Carcharhinus -- Monitoring Carcharodon -- Monitoring Population biology -- Effect of global warming on Marine biology -- Environmental aspects UCTD |
| url | https://scholar.sun.ac.za/handle/10019.1/128483 |
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