Movement patterns of coastal bottlenose dolphins in the presence of a fast-flowing, prevailing current: shore-based observations at Cape Vidal, South Africa

  • T Photopoulou
  • PB Best
  • PS Hammond
  • KP Findlay

Abstract

The presence and movement of Indo-Pacific bottlenose dolphins Tursiops aduncus were investigated using shore-based observations made during a humpback whale Megaptera novaeangliae migration survey at Cape Vidal, South Africa, undertaken between June and October 1988–1991. Occurrence was analysed as counts of dolphin sightings per hour within a generalised estimating equation framework. Bottlenose dolphin sightings decreased throughout the daily survey period, and there was a small seasonal peak in sightings during August. Data on movement trajectory were collected using a theodolite for 60% of the groups of dolphins sighted. Most groups were  observed travelling in a northerly direction, with few groups recorded moving south. A generalised linear model indicated that northwardtravelling dolphins  were located closer to shore, travelled at higher speeds, and occurred in bigger groups under low-tide conditions, than those seen moving in a southerly direction. The southwardflowing Agulhas Current is close to shore at Cape Vidal, where the continental shelf is particularly narrow. We suggest that bottlenose dolphins in this area have adopted a specific movement regime to cope with the consistent fast-flowing currents that dominate their environment at Cape Vidal.

Keywords: Agulhas Current, generalised estimating equation, generalised linear model, sightings, theodolite, Tursiops aduncus

African Journal of Marine Science 2011, 33(3): 393–401

Author Biographies

T Photopoulou
Sea Mammal Research Unit, Scottish Oceans Institute, University of St Andrews, Fife KY16 8LB, Scotland, UK; Centre for Research into Ecological and Environmental Modelling, The Observatory, University of St Andrews, Fife KY16 9LZ, Scotland, UK
PB Best
Mammal Research Institute, University of Pretoria, c/o Iziko South African Museum, PO Box 61, Cape Town 8000, South Africa
PS Hammond
Sea Mammal Research Unit, Scottish Oceans Institute, University of St Andrews, Fife KY16 8LB, Scotland, UK
KP Findlay
MaRe Institute, Department of Oceanography, University of Cape Town, Private Bag, Rondebosch 7701, South Africa
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Articles

Journal Identifiers


eISSN: 1814-2338
print ISSN: 1814-232X