Pectoral herding: an innovative tactic for humpback whale foraging

Abstract

Humpback whales (Megaptera novaeangliae) have exceptionally long pectorals (i.e. flippers) that aid in shallow water navigation, rapid acceleration and increased manoeuvrability. The use of pectorals to herd or manipulate prey has been hypothesized since the 1930s. We combined new technology and a unique viewing platform to document the additional use of pectorals to aggregate prey during foraging events. Here, we provide a description of ‘pectoral herding’ and explore the conditions that may promote this innovative foraging behaviour. Specifically, we analysed aerial videos and photographic sequences to assess the function of pectorals during feeding events near salmon hatchery release sites in Southeast Alaska (2016–2018). We observed the use of solo bubble-nets to initially corral prey, followed by calculated movements to establish a secondary boundary with the pectorals—further condensing prey and increasing foraging efficiency. We found three ways in which humpback whales use pectorals to herd prey: (i) create a physical barrier to prevent evasion, (ii) cause water motion to guide prey towards the mouth, and (iii) position the ventral side to reflect light and alter prey movement. Our findings suggest that behavioural plasticity may aid foraging in changing environments and shifts in prey availability. Further study would clarify if ‘pectoral herding’ is used as a principal foraging tool by the broader humpback whale population and the conditions that promote its use.

Predator-informed looming stimulus experiments reveal how large filter feeding whales capture highly maneuverable forage fish

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Confronting assumptions about prey selection by lunge‐feeding whales using a process‐based model

“…While humpback whales in particular display a variety of coordinated feeding behaviours at the surface (Jurasz & Jurasz, 1979), there remain few studies of coordinated subsurface feeding behaviours despite the development of animal‐borne tags (Wiley et al., 2011). When surface feeding at hatchery release sites, humpback whales sometimes use their flippers to aggregate prey (Kosma et al., 2019), feed inside of individual bubble nets, and feed near shoreline and anthropogenic structures that could act as barriers to prey escape (Chenoweth et al., 2017). Cade et al.…”

Feeding of humpback whales in low latitudes of the Southeast Pacific Ocean

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