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Near-shore distribution of Heaviside’s (Cephalorhynchus heavisidii) and dusky dolphins (Lagenorhynchus obscurus) at the southern limit of their range in South Africa

Near-shore distribution of Heaviside’s (Cephalorhynchus heavisidii) and dusky dolphins... Photo-identification surveys over three years along 390 km of coastline north of Cape Town, revealed that Heaviside’s dolphin distribution was consistent between years and higher in areas more exposed to swells and with greater long-term availability of small hake Merluccius capensis (their principal prey). Dusky dolphin sighting rates varied considerably between years, but were generally higher in areas with lower hake availability and sandier shores (mostly straighter coastline). Large groups of 50–200 dusky dolphins were only seen in St Helena Bay, the site of a wind-driven upwelling zone. Heaviside’s dolphins were found in shallower, cooler water than dusky dolphins and were more likely to be seen during brighter phases of the moon (when nocturnal light conditions may influence the vertical migration patterns of prey) and in areas of high hake abundance. Near-shore fishing activity was higher in the northern half of the study area and clustered around harbours. Set netting occurred only at Yzerfontein and St Helena Bay, but due to changes in the industry is currently thought to be a low threat to the population. Interactions between Heaviside’s and dusky dolphins were usually neutral and sympatry appears to be mediated by differences in overall range and the type and size of prey species taken. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png African Zoology Taylor & Francis

Near-shore distribution of Heaviside’s (Cephalorhynchus heavisidii) and dusky dolphins (Lagenorhynchus obscurus) at the southern limit of their range in South Africa

Elwen, S.H.; Thornton, M.; Reeb, D.; Best, P.B.
African Zoology , Volume 45 (1): 14 – Apr 1, 2010
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Near-shore distribution of Heaviside’s (Cephalorhynchus heavisidii) and dusky dolphins (Lagenorhynchus obscurus) at the southern limit of their range in South Africa

Abstract

Photo-identification surveys over three years along 390 km of coastline north of Cape Town, revealed that Heaviside’s dolphin distribution was consistent between years and higher in areas more exposed to swells and with greater long-term availability of small hake Merluccius capensis (their principal prey). Dusky dolphin sighting rates varied considerably between years, but were generally higher in areas with lower hake availability and sandier shores (mostly straighter coastline)....
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Publisher
Taylor & Francis
Copyright
© Zoological Society of Southern Africa
ISSN
2224-073X
eISSN
1562-7020
DOI
10.1080/15627020.2010.11657256
Publisher site
See Article on Publisher Site

Abstract

Photo-identification surveys over three years along 390 km of coastline north of Cape Town, revealed that Heaviside’s dolphin distribution was consistent between years and higher in areas more exposed to swells and with greater long-term availability of small hake Merluccius capensis (their principal prey). Dusky dolphin sighting rates varied considerably between years, but were generally higher in areas with lower hake availability and sandier shores (mostly straighter coastline). Large groups of 50–200 dusky dolphins were only seen in St Helena Bay, the site of a wind-driven upwelling zone. Heaviside’s dolphins were found in shallower, cooler water than dusky dolphins and were more likely to be seen during brighter phases of the moon (when nocturnal light conditions may influence the vertical migration patterns of prey) and in areas of high hake abundance. Near-shore fishing activity was higher in the northern half of the study area and clustered around harbours. Set netting occurred only at Yzerfontein and St Helena Bay, but due to changes in the industry is currently thought to be a low threat to the population. Interactions between Heaviside’s and dusky dolphins were usually neutral and sympatry appears to be mediated by differences in overall range and the type and size of prey species taken.

Journal

African Zoology – Taylor & Francis

Published: Apr 1, 2010

Keywords: Distribution; Dusky dolphin; Fisheries interactions; Heaviside’s dolphin; Predator–prey relationships

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