October 13, 2012
Researchers Follow Humpback Whales To Study Foraging Lunges
Alan McStravick for redOrbit.com - Your Universe Online
Sure, a whale can lunge underwater, but have you ever seen one do a jumping jack? Ok, so those aren´t the lunges a group of researchers were monitoring.
Simon and her colleagues set off for Greenland to see if they couldn´t gain a little more insight on this discovery. They found and tagged five humpback whales in the hopes they could discover how the animals capture and consume their pray: krill and agile capelin.
On three of the subjects, individual tags were placed behind the dorsal fin to record stroke patterns. In the other two whales the tags were placed closer to the head to help measure head movement during the feeding lunges.
Over 479 dives, the team, comprised of Simon representing the Greenland Institute of Natural Resources, Madsen from Aarhus University in Denmark and Johnsen of the University of St. Andrews, was able to successfully record high resolution depth, acceleration and magnetic orientation data.
The team chose, as their primary focus, analysis of the whales´ acceleration patterns. They noted that as the subject would initiate a lunge they accelerated upward, beating the tail fins, or flukes, twice as fast as normal, eventually reaching speeds of 3 meters per second. That speed is really not much greater than the whales´ top cruising speeds. But it was the next reading that really got the team´s attention. The whales´ speed would, even while the animal was still beating its fluke, drop dramatically. The researchers wanted to determine when in this process the whale would throw open their mouths to collect the over 30 tons of water necessary to consume enough krill to warrant the expense of energy.
Knowing that the top speed attained by the whales during the first stages of the lunge were so close to the animals´ top cruising speed combined with the fact the whales were beating their flukes much harder than what is usually needed to maintain that speed, the team concluded, ““¦the mouth must already be open and the buccal [mouth] pouch inflated enough to create a higher drag when the high stroking rates“¦occur within lunges.”
Additionally, the team suggests the whales continue accelerating after opening their mouths in order to use their peak speed to stretch the elastic ventral groove blubber that inflates as they take in the massive amounts of water. With the buccal pouch completely inflated, the whales continue beating their flukes after closing their mouths so as to accelerate the colossal quantity of water before stopping fluke movement that allows the whale to decelerate to a speed of 1.5 meters per second. It´s during the deceleration that the final step occurs. The whale begins to filter the more than 30 tons of water and then swallows the entrapped fish. This entire process, from beginning to end, takes just 46 seconds. The whales start the process all over again when they begin beating their flukes in preparation for the launch of their next foraging lunge.
It was previously thought humpback whales and other rorquals would simply grind to a halt after they threw their jaws wide open in the foraging process. If that had been true, then equally true would have been the need for these massive creatures to reaccelerate from a stationary start to resume feeding. This process would make lunge feeding extortionately expensive, according to the researchers. They do concede, however, despite the potential reduction in energy expenditure, lunge feeding is still a highly demanding activity. They go on to say how the high-speed tactic is essential for the massive hunters to engulf their nimble prey.
Their findings on the choreography associated with foraging lunges have been published in The Journal of Experimental Biology.