Spatial Distribution of Indo-Pacific Humpback Dolphins (Sousa chinensis) at Richards Bay, South Africa: Environmental Influences and Behavioural Patterns

Abstract: Humpback dolphins (Sousa chinensis) are caught in shark nets at Richards Bay, South Africa, at higher levels than elsewhere along the KwaZulu-Natal coast. As part of an investigation to understand the reasons for humpback dolphin capture in shark nets at Richards Bay, we studied the spatial distribution and behavioral patterns of these dolphins. The study area was divided into five offshore sectors, 13 longshore sectors, and three regions. The geographic positions of humpback dolphins were recorded during boat-based follows, as was the proportion of time focal groups spent feeding, resting, socialising, and traveling. Humpback dolphins used the area within 2 km of the shore extensively. Along the shore, “hot spots” where humpback dolphins were most likely to be found were widely spaced, but sea conditions (water depth, surface, and subsurface temperatures and water visibility) did not appear to influence this spatial distribution. This may be because most measurements were within humpback dolphins’ preferred range. In general, humpback dolphins used the area south of Richards Bay Harbor most often. The inshore area was important for feeding, but humpback dolphins moved further offshore to rest. Feeding was particularly important at the entrance to the harbor, where breakwaters and an estuary mouth are found. The Harbor Mouth region may be considered a feeding area of humpback dolphins, and this is where the shark nets are placed.


Document Type: Research Article

DOI: 10.1578/AM.30.1.2004.84

Page Numbers: 84-93

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