Whale shark on a white shark’s menu

Abstract

As the world’s largest fish, whale sharks Rhincodon typus could be assumed to be predator-free. Juvenile whale sharks are known to be preyed upon by sharks, marlin and orcas, and, although unconfirmed, bite marks on a sub-adult whale shark were attributed to white sharks Carcharodon carcharias (Department of the Environment and Heritage, DEH 2005). Attacks on large whale sharks by other large sharks are reported, but the predator remains unidentified (Fitzpatrick et al. 2006). Here, we provide confirmation that white sharks feed on adult whale sharks. In the 1960s, a 4.5-m male white shark was caught at Cheynes Beach Whaling Station (near Albany, southwest Australia) by the Department of Fisheries. At that time, white sharks frequented this area and fed on dead whales that were tied up prior to processing for oil. The individual was dissected and two unidentified and damaged shark centra (vertebrae) were recovered from the stomach contents (Fig. 1). These centra have been held in the ichthyology collection of the Western Australian Museum (WAM) for the last 50+ years. The centra were recently re-examined and identified as belonging to a whale shark of at least 8.5 m in length (based on ~12-cm-diameter centra; Wintner 2000). Compared to other orectolobiform sharks, whale shark centra are less calcified, with an open intermedialia. The cartilages of these centra appear etched by stomach acid and distorted due to decalcification, desiccation and shrinkage. Whale sharks are generally tropical, occasionally appearing in more temperate waters, including Albany (DEH 2005). White sharks are most common in temperate Australia; however, they are known from tropical regions, including Ningaloo Reef, where sub-adult whale sharks congregate in the austral Autumn (Fitzpatrick et al. 2006). The diet of white sharks is dominated by smaller sharks, teleosts and mammals (Cortes 1999), and feeding on large cetaceans, either live or dead, is known (e.g. Dudley et al. 2000; Hussey et al. 2012) and regularly reported in the popular media. We cannot confirm whether the white shark preyed on a living whale shark or whether it scavenged on a dead carcass. We also cannot confirm whether the interaction was in tropical or temperate seas.