Coastal swimming patterns of white sharks (Carcharodon carcharias) at Mossel Bay,South Africa |
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Authors: | Ryan Johnson Marthán N. Bester Sheldon F. J. Dudley W. Herman Oosthuizen Michael Meÿer Lisa Hancke Enrico Gennari |
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Affiliation: | (1) Oceans Research, P.O. Box 1767, Mossel Bay, 6500, South Africa;(2) Mammal Research Institute, Department of Zoology &; Entomology, University of Pretoria, Pretoria, 0002, South Africa;(3) Natal Sharks Board, Private Bag 2, Umhlanga Rocks, 4320, South Africa;(4) Biomedical Resource Unit, University of KwaZulu-Natal, Private Bag X54001, Durban, South Africa;(5) Marine and Coastal Management Branch, Department of Environmental Affairs and Tourism, Private Bag X2, Roggebaai, South Africa;(6) Cape Technical University, Cape Town, South Africa;(7) South African Institute for Aquatic Biodiversity, Private Bag 1015, Grahamstown, 6140, South Africa |
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Abstract: | Between June and December 2005, active and passive acoustic telemetry was used to examine fine scale movements of 13 white sharks (Carcharodon carcharias) (ten passive, three active) at Mossel Bay. A total of 24 active trackings (ranging from 2 h to 103 h in duration) were conducted. Patterns of rate of movement (ROM), swimming linearity (LI), swimming bearing, and instantaneous swimming speed (ISS) were assessed. A conversion quotient (Q) of 1.21 between ISS and ROM (10 min sample interval) was calculated suggesting ROM is a good indicator of white shark activity. The mean ROM for tracked sharks was 0.52 m·s−1, with a greatest sustained ROM of 1.33 m·s−1 (4.8 km·h−1). Sharks displayed greatest LI and ROM during directional travels between the three persistent aggregation sites. The majority of the shark movement was, however, non-linear as the sharks repeat patrolled at the three aggregation sites. Two of these sites were not associated with pinniped presence, and sharks typically patrolled back and forth parallel to the shore line at a comparatively low ROM which suggested resting. The third aggregation site was adjacent to Seal Island, and despite low LI, sharks displayed a high ROM, indicating high activity levels. We propose that the high ROM is related to maximising search area when patrolling to hunt Cape fur seals (Arctocephalus p. pusillus). |
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Keywords: | White shark Rate of movement Activity patterns Habitat use |
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