Whales are amongst the most enigmatic creatures on the planet. Cruising the world's deepest oceans in search of food, some of these massive predators filter and consume as much as one tonne of krill a day. While many species feed by filtering the oceans as they swim along, others take enormous gaping lunges, filling their vast mouths with krill-laden water before filtering out the nutritious morsels within. But `our knowledge of the lunge feeding process was limited to aerial or ship observations near the sea surface' explains Jeremy Goldbogen and colleagues, making them wonder what happens when the mammals plumb the depths? The team tagged diving fin whales with an accelerometer, hydrophone and depth gauge to monitor the animal's aquatic acrobatics while dining at depth(p. 1231).
Successfully tagging 7 whales over 7 days off the southern California coast, the team recorded 28 foraging dives as the animals routinely descended to over 200 m. Goldbogen reports that the whales only beat their flukes during the first 20 m of descent, before `taking advantage of their negative buoyancy to accelerate and glide to great depths' he explains. Reaching the end of their descent, the animals decelerated rapidly before gliding along the bottom. But when the whales spied a shoal of tasty seafood, they beat their flukes to accelerate horizontally and lunge forwards before throwing their jaws wide, decelerating and rolling backwards with a mouthful of water. Having made between 1 and 7 lunges per dive, the whales swam slowly back to the surface.
Given the whale's size and oxygen carrying capacity, each of the dives was relatively short, with an average duration of 7 min. The team suspects that the exertion required to overcome drag during a feeding lunge is extremely costly, limiting the time spent foraging and forcing the whales to take a lengthy rest after returning to the surface.