Non-lunge feeding behaviour of humpback whales associated with fishing boats in Norway

Abstract

Abstract Top marine predators, such as odontocetes, pinnipeds, and seabirds, are known to forage around fishing boats because fishermen aggregate and/or discard their prey. Recently, there have been reports of humpback whales interacting with fishing boats. However, whether humpback whales utilise discard fish as a food source and how they forage around fishing boats is unknown. This study reports for the first time, the foraging behaviour of a humpback whale around fishing boats. Three whales were tagged using a suction-cup tag containing a video camera, and a behavioural data logger in the coastal area of Tromsø, Norway. Video data from one tagged whale showed that the whale remained in close vicinity of fishing boats for 43 minutes, and revealed the presence of large numbers of dead fish, fish-eating killer whales, fishing boats, and fishing gear. In waters with large numbers of dead fish, the whale raised its upper jaw, a motion associated with engulfing discard fish from fishing boats, and this feeding behaviour differed markedly from lunge-feeding observed in two other whales in the same area. This behaviour was defined as “pick-up feeding”. The behavioural data logger showed that there was no lunge feeding when the whale foraged around fishing boats. This study showed a novel humpback whale foraging strategy: low energy gain from scattered prey but also low energy costs because high-energy lunge feeding was not required.