Visual approach tactics by white sharks (Carcharodon carcharias) under baited conditions and effects of cloud cover

Understanding white shark feeding habits and the influence of environmental factors on feeding is an important step for modelling its behaviour and making decisions about the management of aquatic habitats. To better understand what factors drive variation in shark feeding habits and decisions, we studied feeding and attack behaviour in Dyer Island Nature Reserve (South Africa) in two consecutive years. Specifically, we examined variation in approach patterns and preference using two types of bait (seal decoy and raw tuna) and asked whether these approach patterns and preferences were affected by changes in cloud cover. We found a significant association between approach type and sharks’ length such that large animals mainly performed vertical approaches, while smaller sharks preferred horizontal approaches. Horizontally-oriented approaches were the most often performed approaches. In addition, for the first approach, white sharks significantly preferred the seal-shaped decoy to the bait, but this preference disappeared with subsequent approaches. We observed effects of variation in cloud cover on both approach frequency and approach patterns. Approaches were more frequent as cloud cover increased, and we observed a transition from horizontally oriented approaches to vertically oriented approaches when cloud cover increased. As demonstrated for other environmental factors, cloud cover may affect the white shark’s ability to detect and approach a target, especially during the earliest stages of predation cycle. Keywords: behaviour, Carcharodon carcharias, cloud cover, Dyer Island