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| “pick-up feeding” in Iwata, Aoki, Miller, Biuw, Williamson & Sato, 2023. DOI: 10.1111/eth.13419 |
Abstract
Top marine predators, such as odontocetes, pinnipeds, and seabirds, are known to forage around fishing boats as fishermen aggregate and/or discard their prey. Recently, incidents of humpback whales interacting with fishing boats have been reported. 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 min, 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”. No lunge feeding was seen on the data logger when the whale foraged around fishing boats. This study highlights a novel humpback whale foraging strategy: low energy gain from scattered prey but also low energy costs as high-energy lunge feeding is not required.
Keywords: biologging, energy cost, feeding behaviour, fisheries interaction, humpback whales
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| Underwater video footage from a whale mn17_026LLa. Images of (a), (b), (c), and (d) were recorded by animal-borne video camera and an image of (e) was taken by an underwater camera of documentary program industry staff (taken by Andreas B. Heide from the sailing vessel Barba). (a) killer whales and fishing ropes. (b) dead cod. (c) dead herring. (d) a tagged whale raised its upper jaw, presumably a motion associated with engulfing the fish. (e) a humpback whale and killer whales feed fish together around fishing boats (photo by Andreas B. Heide). |
Takashi Iwata, Kagari Aoki, Patrick J. O. Miller, Martin Biuw, Michael J. Williamson and Katsufumi Sato. 2023. Non-lunge Feeding Behaviour of Humpback Whales associated with Fishing Boats in Norway. Ethology. DOI: 10.1111/eth.13419
ザトウクジラが漁船周りで拾い食い⁉ －少エネな餌取り方法に潜むクジラと漁船双方へのリスクに警鐘
