Gem of the Week: Humpback 'Bubble Nets' More Complex
With warming oceans and less prey, humpback whales have to be innovative to catch a full meal these days. Recent research by NOAA's David Wiley shows just how fine-tuned their hunting techniques are. Wiley gets this week's "gem" for revealing a new level of complexity and forethought in the whale's hunting strategy.
Humpbacks feed on densely-packed prey like krill or small fish that travel in schools like herring and mackerel. One of the ways they corral their prey is to create "bubble nets", vertical columns of bubbles that fish see as a barrier. By creating spirals of bubbles, the whales restrict their prey to a smaller sphere of movement, making them easier to scoop into their huge mouths. Wiley was aware of the whale's sophisticated use of bubbles to concentrate prey density and thus more efficient feeding, but in his latest study (published in Behaviour this week), he used sensors attached to the whales which captured the bubble nets in action in 3D.
As Wiley created a computer-generated 3D model of the nets, he found that the nets sometimes consisted of a previously unknown tactic called "double loops". Working in teams of at least two, the double loop consists of "one upward spiral [of bubbles] to corral the prey, a smack of the fluke on the ocean surface (known as a 'lobtail') then a second upward lunge to capture the corralled prey." Wiley also found that despite the humpback's use of teamwork as a species, some individual humpbacks were not immune to "stealing" fish from bubble nets set up by other whales. It seems the best bubble net, even a double looped one, could be foiled by a hungry interloper.