A comparative study on the role of colour and contrast discrimination in the predatory behaviour of oceanic blacktip and bronze whaler sharks

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dc.contributor.advisorCherry, Michaelen_ZA
dc.contributor.advisorAndreotti, Saraen_ZA
dc.contributor.authorNagel, Cicelyen_ZA
dc.contributor.otherStellenbosch University. Faculty of Science. Dept. of Botany and Zoology.en_ZA
dc.date.accessioned2024-02-28T14:04:13Z
dc.date.accessioned2024-04-26T17:34:46Z
dc.date.available2024-02-28T14:04:13Z
dc.date.available2024-04-26T17:34:46Z
dc.date.issued2024-03
dc.descriptionThesis (MSc)--Stellenbosch University, 2024. en_ZA
dc.description.abstractENGLISH ABSTRACT: Despite the low number of yearly fatalities caused by sharks, negative shark-human interactions have been at the centre of national and international debates. Specifically, controversial policies such as shark culling have been adopted in South Africa and Australia to reduce shark populations in the proximity of recreational beaches. This project was designed to determine whether some colours might attract sharks more than others, to help minimize the chances of negative shark-human interactions. Sharks, together with rays, skates and chimaeras are part of the class Chondrichthyans, one of the oldest most prolific vertebrate lineages extant today. Despite their ecological importance and historical longevity, chondrichthyan vision remains poorly studied, especially in regard to their ability to perceive colours. Colour vision in sharks has been debated within the literature for decades, with behavioural experiments providing conflicting results. Recent microspectrophotometry analysis has provided evidence that sharks do not possess multiple cone pigments within their eyes. This suggests that they are colour-blind, and that colour preferences reflect differences in contrast with their background. Utilising a novel in-field behavioural approach, the present study aims to determine whether oceanic blacktip sharks (Carcharhinus limbatus) and bronze whaler sharks (Carcharhinus brachyurus) possess the ability to discriminate between five differently coloured bait tubes (white, yellow, silver, red, and black), in terms of how these colours contrast against a background of sea water. Results show that both C. limbatus and C. brachyurus were able to discriminate between the five coloured tubes, demonstrating a preference for the brighter colours (white, yellow, and silver) over the darker colours (red and black). Shark reactions can be explained in terms of luminance contrast between different coloured bait tubes and sea water. This study is the first behavioural study on C. limbatus and C. brachyurus simulating visual predation and provides empirical evidence on which colours are best avoided when engaging in activities in shark-inhabited areas. Both C. limbatus and C. brachyurus are classified as potentially dangerous to humans, having been involved in 35 and 16 unprovoked attacks, respectively, worldwide since 1540. These findings provide an insight into the visual ecology of sharks, showing that visual cues are important in shark predatory behaviour. Based on the results of this study, to reduce the chances of negative interactions between these two species and humans, dive gear, wetsuits, and bathing suits should avoid high-contrast colours such as white, yellow, and silver.en_ZA
dc.description.abstractAFRIKAANSE OPSOMMING: Ten spyte van die lae aantal jaarlikse sterftes wat deur haaie veroorsaak word, was negatiewe haai- mens-interaksies die middelpunt van nasionale en internasionale debatte. Spesifiek, kontroversiële beleide soos die uitwissing van haaie is in Suid-Afrika en Australië aangeneem om haaibevolkings in die nabyheid van ontspanningsstrande te verminder. Hierdie projek is ontwerp om te bepaal of sommige kleure haaie meer as ander kan aantrek, om te help om die kanse op negatiewe haai-mens- interaksies te verminder. Haaie, tesame met strale, skaatse en chimaeras is deel van die klas Chondrichthyans, een van die oudste mees produktiewe gewerwelde geslagte wat vandag nog bestaan. Ten spyte in hul ekologiese belangrikheid en historiese langlewendheid, bly chondrichthyan- visse swak bestudeer, veral met betrekking tot hul vermoë om kleure waar te neem. Kleurvisie by haaie word al dekades lank in die literatuur gedebatteer, met gedragseksperimente wat teenstrydige resultate lewer. Onlangse mikrospektrofotometrie-analise het bewys gelewer dat haaie nie veelvuldige keëlpigmente in hul oë was nie. Dit dui daarop dat hulle kleurblind is, en dat kleurvoorkeure verskille in kontras met hul agtergrond weerspieël. Deur gebruik te maak van 'n nuwe gedragsbenadering in die veld, poog die huidige studie om te bepaal of oseaniese swartpunthaaie (Carcharhinus limbatus) en bronswalvishaaie (Carcharhinus brachyurus) die vermoë het om te onderskei tussen vyf verskillende gekleurde aasbuise (wit, geel, silwer, rooi, en swart), in terme van hoe hierdie kleure kontrasteer teen 'n agtergrond van seewater. Resultate toon dat beide C. limbatus en C. brachyurus in staat was om te onderskei tussen die vyf gekleurde buise, wat 'n voorkeur toon vir die helderder kleure (wit, geel en silwer) bo die donkerder kleure (rooi en swart). Haai-reaksies kan verduidelik word in terme van net merkbare verskille in kontras tussen verskillende gekleurde aasbuise en seewater. Hierdie studie is die eerste gedragstudie oor C. limbatus en C. brachyurus wat visuele predasie simuleer en verskaf empiriese bewyse oor watter kleure die beste vermy word wanneer aktiwiteite in haai-bewoonde gebiede betrokke is. Beide C. limbatus en C. brachyurus word geklassifiseer as potensieel gevaarlik vir mense, omdat hulle betrokke was by onderskeidelik 35 en 16 onuitgelokte aanvalle wêreldwyd sedert 1540. Hierdie bevindings bied 'n insig in die visuele ekologie van haaie, wat wys dat visuele leidrade belangrik is in roofdiergedrag van haaie. Gebaseer op die resultate van hierdie studie, om die kanse op negatiewe interaksies tussen hierdie twee spesies en mense te verminder, moet duiktoerusting, duikpakke en baaipakke hoë-kontraskleure soos wit, geel en silwer vermy word.af_ZA
dc.description.versionMastersen_ZA
dc.format.extent59 pages : illustrations (some color), mapsen_ZA
dc.identifier.urihttps://scholar.sun.ac.za/handle/10019.1/130437
dc.language.isoen_ZAen_ZA
dc.language.isoen_ZAen_ZA
dc.publisherStellenbosch : Stellenbosch Universityen_ZA
dc.rights.holderStellenbosch Universityen_ZA
dc.subject.lcshSharks -- Behavioren_ZA
dc.subject.lcshSharks -- Effect of human beings on -- Government policyen_ZA
dc.subject.lcshSharks -- Ecology -- Oceaniaen_ZA
dc.subject.lcshRays (Fishes) en_ZA
dc.subject.lcshChondrichthyesen_ZA
dc.subject.lcshSharks -- Predators of -- Control -- Oceaniaen_ZA
dc.subject.lcshColor vision in animalsen_ZA
dc.subject.lcshVisionen_ZA
dc.subject.lcshAnimals -- Coloren_ZA
dc.subject.lcshContrast discriminationen_ZA
dc.subject.nameUCTDen_ZA
dc.titleA comparative study on the role of colour and contrast discrimination in the predatory behaviour of oceanic blacktip and bronze whaler sharksen_ZA
dc.typeThesisen_ZA
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