First observations of dusky sharks (Carcharhinus obscurus) attacking a humpback whale (Megaptera novaeangliae) calf

摘要

Direct observations of sharks attacking mysticetes are rare. The present study provides the first direct observation of dusky sharks (Carcharhinus obscurus) attacking a humpback whale (Megaptera novaeangliae) calf. The event was witnessed on 16 July 2014 within the Pondoland Marine Protected Area, South Africa, during the annual sardine run. The event involved a group of similar to 10 to 20 dusky sharks ranging in length between 2 and 3m. The sharks followed in a loose group behind the whale and attacked it while it was on the surface as well as when diving. Shark bites were concentrated on the left-hand side of the whale's body primarily between the pectoral fin and tail fluke, with almost no bites on the right-hand side. Most of the bites were superficial and resulted in tooth impressions and scrapes with little tissue removed. The condition of the calf deteriorated over the study period and it was presumed to have drowned from exhaustion when it stopped surfacing. These observations provide a new insight into the potential threat that dusky sharks may pose to whale calves.