Decline or shifting distribution? A first regional trend assessment for white sharks (Carcharodon carcharias) in South Africa
Unprecedented levels of change in ocean ecosystems bring an ever-increasing need for re-analyses of existing data to explore pressing conservation questions. Substantial declines in white shark (Carcharodon carcharias) presence at two primary aggregation sites have raised concerns about the species’...
| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English |
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Elsevier
2023-10-01
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| Series: | Ecological Indicators |
| Subjects: | |
| Online Access: | http://www.sciencedirect.com/science/article/pii/S1470160X23008622 |
| _version_ | 1827816128492077056 |
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| author | Heather D. Bowlby Matt L. Dicken Alison V. Towner Sarah Waries Toby Rogers Alison Kock |
| author_facet | Heather D. Bowlby Matt L. Dicken Alison V. Towner Sarah Waries Toby Rogers Alison Kock |
| author_sort | Heather D. Bowlby |
| collection | DOAJ |
| description | Unprecedented levels of change in ocean ecosystems bring an ever-increasing need for re-analyses of existing data to explore pressing conservation questions. Substantial declines in white shark (Carcharodon carcharias) presence at two primary aggregation sites have raised concerns about the species’ status throughout South Africa. Using the most comprehensive suite of abundance indices compiled to date, we evaluated temporal trends and the strength of evidence for regional redistribution. Individual indices from all primary aggregation sites in South Africa were highly variable. The overall temporal trend from a log-linear Generalized Additive Model was relatively flat, indicating largely unchanged abundance throughout South Africa since protection in 1991. However, reports of human-shark incidents showed a general shift from the Western to the Eastern Cape. Correlations among individual abundance indices demonstrated that movements were not as simple as animals leaving one site to inhabit another. Further research is needed to explore the effect of movement on monitoring data. Our results reaffirm the need for better standardization in data collection methods to generate abundance indices and to develop long-term monitoring programs on the Eastern Cape. Ideally, environmental or operational factors affecting abundance indices should also be explored in future status assessments at a regional level. Our results provide a baseline for future work, directing research to understand drivers of localized and regional changes and focusing management on reducing anthropogenic sources of mortality within their Southwest Indian Ocean range. |
| first_indexed | 2024-03-12T00:10:32Z |
| format | Article |
| id | doaj.art-cd322eed8d38464680cad8793fa1253a |
| institution | Directory Open Access Journal |
| issn | 1470-160X |
| language | English |
| last_indexed | 2024-03-12T00:10:32Z |
| publishDate | 2023-10-01 |
| publisher | Elsevier |
| record_format | Article |
| series | Ecological Indicators |
| spelling | doaj.art-cd322eed8d38464680cad8793fa1253a2023-09-16T05:29:46ZengElsevierEcological Indicators1470-160X2023-10-01154110720Decline or shifting distribution? A first regional trend assessment for white sharks (Carcharodon carcharias) in South AfricaHeather D. Bowlby0Matt L. Dicken1Alison V. Towner2Sarah Waries3Toby Rogers4Alison Kock5Fisheries and Oceans Canada, Bedford Institute of Oceanography, Dartmouth, Nova Scotia B2Y 4A2, Canada; Corresponding author.KwaZulu-Natal Sharks Board, Umhlanga Rocks, South Africa; Institute for Coastal and Marine Research (CMR), Ocean Sciences Campus, Nelson Mandela University, Gqeberha 6031, South AfricaDepartment of Ichthyology and Fisheries Science, Rhodes University, Makhanda, South Africa; Dyer Island Conservation Trust, Kleinbaai, South Africa; South African International Maritime Institute, Ocean Sciences Campus, Gqeberha 6001Institute for Communities and Wildlife in Africa (iCWild), University of Cape Town, Cape Town 7701, South Africa; Shark Spotters, Cape Town 7945, South AfricaInstitute for Communities and Wildlife in Africa (iCWild), University of Cape Town, Cape Town 7701, South Africa; Shark Spotters, Cape Town 7945, South AfricaSouth African National Parks, Cape Research Centre, Cape Town 7701, South Africa; South African Institute for Aquatic Biodiversity (SAIAB), Private Bag 1015, Makhanda 6140, South AfricaUnprecedented levels of change in ocean ecosystems bring an ever-increasing need for re-analyses of existing data to explore pressing conservation questions. Substantial declines in white shark (Carcharodon carcharias) presence at two primary aggregation sites have raised concerns about the species’ status throughout South Africa. Using the most comprehensive suite of abundance indices compiled to date, we evaluated temporal trends and the strength of evidence for regional redistribution. Individual indices from all primary aggregation sites in South Africa were highly variable. The overall temporal trend from a log-linear Generalized Additive Model was relatively flat, indicating largely unchanged abundance throughout South Africa since protection in 1991. However, reports of human-shark incidents showed a general shift from the Western to the Eastern Cape. Correlations among individual abundance indices demonstrated that movements were not as simple as animals leaving one site to inhabit another. Further research is needed to explore the effect of movement on monitoring data. Our results reaffirm the need for better standardization in data collection methods to generate abundance indices and to develop long-term monitoring programs on the Eastern Cape. Ideally, environmental or operational factors affecting abundance indices should also be explored in future status assessments at a regional level. Our results provide a baseline for future work, directing research to understand drivers of localized and regional changes and focusing management on reducing anthropogenic sources of mortality within their Southwest Indian Ocean range.http://www.sciencedirect.com/science/article/pii/S1470160X23008622Conservation statusAbundance indicesMovement patternsEcological factors |
| spellingShingle | Heather D. Bowlby Matt L. Dicken Alison V. Towner Sarah Waries Toby Rogers Alison Kock Decline or shifting distribution? A first regional trend assessment for white sharks (Carcharodon carcharias) in South Africa Ecological Indicators Conservation status Abundance indices Movement patterns Ecological factors |
| title | Decline or shifting distribution? A first regional trend assessment for white sharks (Carcharodon carcharias) in South Africa |
| title_full | Decline or shifting distribution? A first regional trend assessment for white sharks (Carcharodon carcharias) in South Africa |
| title_fullStr | Decline or shifting distribution? A first regional trend assessment for white sharks (Carcharodon carcharias) in South Africa |
| title_full_unstemmed | Decline or shifting distribution? A first regional trend assessment for white sharks (Carcharodon carcharias) in South Africa |
| title_short | Decline or shifting distribution? A first regional trend assessment for white sharks (Carcharodon carcharias) in South Africa |
| title_sort | decline or shifting distribution a first regional trend assessment for white sharks carcharodon carcharias in south africa |
| topic | Conservation status Abundance indices Movement patterns Ecological factors |
| url | http://www.sciencedirect.com/science/article/pii/S1470160X23008622 |
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