Super Efficient Feeding Habits of Blue Whales
As most people will know, the blue whale is the largest animal alive and probably the largest animal that has ever lived. When a blue whale calf is born it is as big as a fully-grown hippopotamus and during its first seven months it will drink about 400 litres of its mother's milk every day.
It is known that a blue whale's mouth is big enough to accommodate 100 adults, but what Bob Shadwick and his colleagues from the University of British Columbia wanted to know was how much a blue whale could eat in a single mouthful and how much energy it would burn while foraging.
Typically a blue whale will dive to about 100 metres or more for food, with the longest recorded dive being 36 minutes. This length of time is most unusual because although with the colossal supplies of oxygen that these huge creatures carry in their blood and muscles, dives are not usually any longer than 15 minutes.
Bob Shadwick's theory was that the act of feeding must use up a great deal of energy. He explained how whales lunge repeatedly through deep shoals of krill, engulfing their own body weight in water before filtering out the nutritious crustaceans. It was thought that the huge drag effect of slowing down to feed and then accelerating again simply took its toll.
Proving this seemed impossible until Shadwick and his student Jeremy Goldbogen discovered that by the skilful use of hydrophones, pressure sensors and two-axis accelerometers, it would be possible to use the resulting measurements to calculate the energetic cost of blue whale lunges.
A number of whales were studied and Goldbogen discovered that dives lasted for between 3.1 and 15.2 minutes, with a whale lunging for up to six times in a single dive. Goldbogen had previously established that he could calculate the speed of a whale by correlating the acoustic noise of the water swishing past a hydrophone. In this way he was able to establish the speed of the whales as they lunged repeatedly during each dive.
The team wanted to calculate the forces exerted on the whales as they accelerated with their colossal mouthful of water. Noting that their mouths seemed to inflate like parachutes as the whales engulfed the krill, Goldbogen tracked down a parachute expert who was able to help him with building a mathematical model to calculate the forces involved.
In this way researchers were able to determine that the whales used about 3,226 kilojoules of energy on each dive, but they still needed to know how much energy could be extracted from one mouthful of krill.
Goldbogen precisely estimated the size of a blue whale's mouth and then calculated the volume of water and the amount of krill it could hold. He found that resulting energy could be anything from 34,776 kilojoules to an amazing 1,912,680 kilojoules. This led the team to the conclusion that on a foraging dive a blue whale could provide itself with 90 times as much energy as it used up.