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Environmental predictors of Carcharodon carcharias presence at two popular beaches in False Bay, South Africa using acoustic telemetry
By understanding when white sharks (Carcharodon carcharias) are likely to be at certain popular beaches, it is possible to predict when the risk of overlap between water users and white sharks is highest, and to convey this information to the public so they can make informed decisions about using th...
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| Format: | Thesis |
| Language: | English |
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Department of Biological Sciences
2019
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| _version_ | 1867613261204029440 |
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| access_status_str | Open Access |
| author | Van Beuningen, Dave |
| author2 | O'riain, Justin |
| author_browse | O'riain, Justin Van Beuningen, Dave |
| author_facet | O'riain, Justin Van Beuningen, Dave |
| author_sort | Van Beuningen, Dave |
| collection | Thesis |
| description | By understanding when white sharks (Carcharodon carcharias) are likely to be at certain popular beaches, it is possible to predict when the risk of overlap between water users and white sharks is highest, and to convey this information to the public so they can make informed decisions about using these areas. Previous studies have shown that white shark presence near popular recreational beaches in False Bay, South Africa, is influenced by a range of environmental variables. These studies have relied on land-based observers (shark observers), whose ability to detect sharks is subject to the depth at which the sharks swim and a suite of environmental conditions that influence water visibility, including cloud cover, wind speed and ambient light levels. In this study, I use passive acoustic telemetry on 56 tagged white sharks to determine whether the same or other environmental variables explain variation in white shark presence at the same beaches. A total of 13 803 and 1 481 white shark detections were recorded between April 2005 and December 2007 at Muizenberg and Fish Hoek beaches, respectively. This represented 32 and 16 individual white sharks with a median number of 32.5 (range 5.5 – 57.8) and 7 (range 4 – 14.8) detections per shark at Muizenberg and Fish Hoek beach, respectively. The low number of detections at Fish Hoek resulted in the data being highly zero-inflated with the result that the subsequent modelling of the data with environmental covariates did not converge, and hence I focused solely on Muizenberg beach. The probability of detecting a white shark at Muizenberg beach was modelled using binomial generalised additive mixed models (GAMMs) with water temperature, wind speed, wind direction, cloud cover, lunar phase, tide height, barometric pressure, year, season and time of day as predictor variables. Water temperature was a significant predictor of white sharks at Muizenberg beach during summer, autumn and winter while wind speed, time of day and barometric pressure were significant predictors of shark presence during the summer and autumn months. There was significant inter-annual variability in white shark detections and a strong seasonal relationship, with presence being highest during spring and lowest during winter. Encouragingly, the findings from this study support some of the key findings of previous studies using observational data, including the significant positive effects of increasing temperature, year, season and time of day. |
| format | Thesis |
| id | oai:open.uct.ac.za:11427/29520 |
| institution | University of Cape Town (South Africa) |
| language | eng |
| last_indexed | 2026-06-10T12:33:19.547Z |
| license_str | Not specified — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from UCTD — University of Cape Town Open Access Repository |
| publishDate | 2019 |
| publishDateRange | 2019 |
| publishDateSort | 2019 |
| publisher | Department of Biological Sciences |
| publisherStr | Department of Biological Sciences |
| record_format | dspace |
| source_str | UCTD — University of Cape Town Open Access Repository |
| spelling | oai:open.uct.ac.za:11427/29520 Environmental predictors of Carcharodon carcharias presence at two popular beaches in False Bay, South Africa using acoustic telemetry Van Beuningen, Dave O'riain, Justin Kock, Alison Irion, Dylan Conservation Biology By understanding when white sharks (Carcharodon carcharias) are likely to be at certain popular beaches, it is possible to predict when the risk of overlap between water users and white sharks is highest, and to convey this information to the public so they can make informed decisions about using these areas. Previous studies have shown that white shark presence near popular recreational beaches in False Bay, South Africa, is influenced by a range of environmental variables. These studies have relied on land-based observers (shark observers), whose ability to detect sharks is subject to the depth at which the sharks swim and a suite of environmental conditions that influence water visibility, including cloud cover, wind speed and ambient light levels. In this study, I use passive acoustic telemetry on 56 tagged white sharks to determine whether the same or other environmental variables explain variation in white shark presence at the same beaches. A total of 13 803 and 1 481 white shark detections were recorded between April 2005 and December 2007 at Muizenberg and Fish Hoek beaches, respectively. This represented 32 and 16 individual white sharks with a median number of 32.5 (range 5.5 – 57.8) and 7 (range 4 – 14.8) detections per shark at Muizenberg and Fish Hoek beach, respectively. The low number of detections at Fish Hoek resulted in the data being highly zero-inflated with the result that the subsequent modelling of the data with environmental covariates did not converge, and hence I focused solely on Muizenberg beach. The probability of detecting a white shark at Muizenberg beach was modelled using binomial generalised additive mixed models (GAMMs) with water temperature, wind speed, wind direction, cloud cover, lunar phase, tide height, barometric pressure, year, season and time of day as predictor variables. Water temperature was a significant predictor of white sharks at Muizenberg beach during summer, autumn and winter while wind speed, time of day and barometric pressure were significant predictors of shark presence during the summer and autumn months. There was significant inter-annual variability in white shark detections and a strong seasonal relationship, with presence being highest during spring and lowest during winter. Encouragingly, the findings from this study support some of the key findings of previous studies using observational data, including the significant positive effects of increasing temperature, year, season and time of day. 2019-02-14T12:41:07Z 2019-02-14T12:41:07Z 2018 2019-02-14T12:20:56Z Master Thesis Masters MSc http://hdl.handle.net/11427/29520 eng application/pdf Department of Biological Sciences Faculty of Science University of Cape Town |
| spellingShingle | Conservation Biology Van Beuningen, Dave Environmental predictors of Carcharodon carcharias presence at two popular beaches in False Bay, South Africa using acoustic telemetry |
| thesis_degree_str | Master's |
| title | Environmental predictors of Carcharodon carcharias presence at two popular beaches in False Bay, South Africa using acoustic telemetry |
| title_full | Environmental predictors of Carcharodon carcharias presence at two popular beaches in False Bay, South Africa using acoustic telemetry |
| title_fullStr | Environmental predictors of Carcharodon carcharias presence at two popular beaches in False Bay, South Africa using acoustic telemetry |
| title_full_unstemmed | Environmental predictors of Carcharodon carcharias presence at two popular beaches in False Bay, South Africa using acoustic telemetry |
| title_short | Environmental predictors of Carcharodon carcharias presence at two popular beaches in False Bay, South Africa using acoustic telemetry |
| title_sort | environmental predictors of carcharodon carcharias presence at two popular beaches in false bay south africa using acoustic telemetry |
| topic | Conservation Biology |
| url | http://hdl.handle.net/11427/29520 |
| work_keys_str_mv | AT vanbeuningendave environmentalpredictorsofcarcharodoncarchariaspresenceattwopopularbeachesinfalsebaysouthafricausingacoustictelemetry |