Humpback whales use their flippers to create a barrier that traps gathered prey, which they can then usher towards their mouths by swatting the water. Using aerial photography and filming, researchers were able to capture this foraging strategy for the first time.
“The first time I saw this behaviour, it was from a boat level view and looked chaotic,” says Madison Kosma at the University of Alaska Fairbanks in the US. “But the whale just kept repeating this behaviour over and over again. I watched it for hours!”
Kosma and her colleagues monitored the feeding behaviour of two whales over the course of three years near sites in Southeast Alaska, where salmon are released to boost their population. The researchers photographed and filmed the whales from above during feeding, using digital cameras attached to either a pole or drone.
They saw both whales perform the trapping behaviour called “pectoral herding”, which started after the whales had used their flippers to generate a net of bubbles to confine prey near the water’s surface.
Both whales then performed the technique, using their flippers to create a physical barrier that prevented prey from escaping. This was followed by a rapid lunge towards the prey, which were engulfed into the whales’ open mouths.
One of the whales was also seen using its flippers to guide prey towards its mouth. Over 90 per cent of the pectoral herding was used for targeting juvenile salmon.
The whales performed pectoral herding both when they were moving vertically and horizontally.
Humpback whales have long flippers, called pectorals, which increase their manoeuvrability by helping them navigate in shallow water and accelerate rapidly.
This is the first direct evidence that humpback whales use their flippers to herd prey, says Patrick Miller at the University of St Andrews in the UK, who was not involved in the study.
Miller says many other research groups are now following animals at sea using drones, which will enable further investigation of how humpback whales interact with different types of prey.
Journal reference: Royal Society Open Science, DOI: 10.1098/rsos.191104
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