Blue whale-sized mouthfuls make foraging super efficient

December 09, 2010

Diving blue whales can dive for anything up to 15 minutes. However, Bob Shadwick from the University of British Columbia, Canada, explains that blue whales may be able to dive for longer, because of the colossal oxygen supplies they could carry in their blood and muscles, so why don't they? 'The theory was that what they are doing under water must use a lot of energy,' says Shadwick. Explaining that the whales feed by lunging repeatedly through deep shoals of krill, engulfing their own body weight in water before filtering out the nutritious crustaceans, Shadwick says, 'It was thought that the huge drag effect when they feed and reaccelerate this gigantic body must be the cost'. However, measuring the energetics of blue whale lunges at depth seemed almost impossible until Shadwick and his student Jeremy Goldbogen got chatting to John Hildebrand, John Calambokidis, Erin Oleson and Greg Schorr who were skilfully attaching hydrophones, pressure sensors and two-axis accelerometers to the elusive animals. Shadwick and Goldbogen realised that they could use Calambokidis's measurements to calculate the energetic cost of blue whale lunges. They publish their discovery that blue whales swallow almost 2,000,000kJ (almost 480,000kcalories) in a mouthful of krill, and take in 90 times as much energy as they burn during a single dive in The Journal of Experimental Biology at http://jeb.biologists.org.

Analysing the behaviour of each whale, Goldbogen saw that dives lasted between 3.1 and 15.2 minutes and a whale could lunge as many as 6 times during a single dive. Having found previously that he could correlate the acoustic noise of the water swishing past the hydrophone with the speed at which a whale was moving, Goldbogen calculated the blue whales' speeds as they lunged repeatedly during each dive. Next the team had to calculate the forces exerted on the whales as they accelerated their colossal mouthful of water. Noticing that the whales' mouths inflated almost like a parachute as they engulfed the krill, Goldbogen tracked down parachute aerodynamics expert Jean Potvin to help them build a mathematical model to calculate the forces acting on the whales as they lunged. With Potvin on the team, they were able to calculate that the whales used between 3226 kJ of energy during each lunge. But how did this compare with the amount of energy that the whales could extract from each gigantic mouthful of krill?

Goldbogen estimated the volume of the whales' mouths by searching the whaling literature for morphological data and teamed up with paleontologist Nick Pyenson to measure the size of blue whale jaw bones in several natural history museums. He also obtained krill density values from the literature - which are probably on the low side. Then he calculated the volume of water and amount of krill that a whale could engulf and found that the whales could consume anything from 34,776kJ up to an unprecedented 1,912,680kJ from a single mouthful of krill, providing as much as 240 times as much energy as the animals used in a single lunge. And when the team calculated the amount of energy that a whale could take on board during a dive, they found that each foraging dive could provide 90 times as much energy as they used.

Shadwick admits that he was initially surprised that the whales' foraging dives were so efficient. 'We went over the numbers a lot,' he remembers, but then he and Goldbogen realised that the whales' immense efficiency makes sense. 'The key to this is the size factor because they can engulf such a large volume with so much food in it that it really pays off,' says Shadwick.
-end-
IF REPORTING ON THIS STORY, PLEASE MENTION THE JOURNAL OF EXPERIMENTAL BIOLOGY AS THE SOURCE AND, IF REPORTING ONLINE, PLEASE CARRY A LINK TO: http://jeb.biologists.org

REFERENCE: Goldbogen, J. A., Calambokidis, J., Oleson, E., Potvin, J., Pyenson, N. D., Schorr, G. and Shadwick, R. E. (2011). Mechanics, hydrodynamics and energetics of blue whale lunge feeding: efficiency dependence on krill density. J. Exp. Biol. 214, 131-146.

This article is posted on this site to give advance access to other authorised media who may wish to report on this story. Full attribution is required, and if reporting online a link to jeb.biologists.com is also required. The story posted here is COPYRIGHTED. Therefore advance permission is required before any and every reproduction of each article in full. PLEASE CONTACT permissions@biologists.com

THIS ARTICLE IS EMBARGOED UNTIL THURSDAY, 9 DECEMBER 2010, 00.15 HRS EST (05:15 HRS GMT)

The Company of Biologists

Related Whales Articles from Brightsurf:

Blue whales change their tune before migrating
While parsing through years of recorded blue whale songs looking for seasonal patterns, researchers were surprised to observe that during feeding season in the summer, whales sing mainly at night, but as they prepare to migrate to their breeding grounds for the winter, this pattern reverses and the whales sing during the day.

Shhhh, the whales are resting
A Danish-Australian team of researchers recommend new guidelines for noise levels from whale-watching boats after having carried out experiments with humpback whales.

Fishing less could be a win for both lobstermen and endangered whales
A new study by researchers at Woods Hole Oceanographic Institution (WHOI) found that New England's historic lobster fishery may turn a higher profit by operating with less gear in the water and a shorter season.

North Atlantic right whales are in much poorer condition than Southern right whales
New research by an international team of scientists reveals that endangered North Atlantic right whales are in much poorer body condition than their counterparts in the southern hemisphere.

Solar storms could scramble whales' navigational sense
When our sun belches out a hot stream of charged particles in Earth's general direction, it doesn't just mess up communications satellites.

A better pregnancy test for whales
To determine whale pregnancy, researchers have relied on visual cues or hormone tests of blubber collected via darts, but the results were often inconclusive.

Why whales are so big, but not bigger
Whales' large bodies help them consume their prey at high efficiencies, a more than decade-long study of around 300 tagged whales now shows, but their gigantism is limited by prey availability and foraging efficiency.

Whales stop being socialites when boats are about
The noise and presence of boats can harm humpback whales' ability to communicate and socialise, in some cases reducing their communication range by a factor of four.

Endangered whales react to environmental changes
Some 'canaries' are 50 feet long, weigh 70 tons, and are nowhere near a coal mine.

Stranded whales detected from space
A new technique for analysing satellite images may help scientists detect and count stranded whales from space.

Read More: Whales News and Whales Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.