Hopkins Marine Station researchers used a combination of sensors and video to reveal details about the hunting methods and feeding habits of the Blue Whales, the largest predators that have ever lived.
What scientists do know is that a 160-ton blue whale’s method for scooping krill is a tremendous endeavor. Swimming around 4 meters per second, it opens its triple-hinged jaws and takes in a gulp equal to about 140 percent of its mass, slowing back down to filter its snack and prepare for the next one.
Blue whales feed nearly continuously when prey conditions are good during the feeding season, but for biologists, the exact mechanism remains a confounding feat of gigantic proportions.
This type of feeding, called lunge feeding, is unique to rorquals, a family of baleen whales that includes blue whales, humpbacks and minke whales. Having a precise understanding of this process gives us some clues as to how these massive animals survive on such tiny prey, which in turn will help biologists develop more effective conservation efforts.
This feeding process is facilitated by a complex suite of biomechanical and anatomical adaptations that together allow the whales to engulf a volume of water and prey that is larger than their own body. For a large blue whale, this represents a volume of water and prey that is approximately the size of a large swimming pool or a school bus, and this is engulfed in a matter of seconds.
To gulp down a mouthful of krill or fish, rorquals have to time their lunge just right. The enormous intake slows them down rapidly due to the drag caused by opening their mouths and the added burden of the water they take in.
Performing this behavior at deep depths can make it even more energetically costly.
When these animals dive down to 300 meters, holding their breath for 12 minutes or more, they had better be sure it’s worth the cost. To regain the energy lost, the prediction is that they are foraging on a pretty dense, rich resource.
Sensors that record multiple facets of whale life have been around for about 15 years.
To figure out which model of feeding was more accurate, Stanford researchers worked with other whale researchers and engineers to develop a sensor package that housed miniaturized versions of typical movement technology plus new video recording capabilities. They attached these tags to whales in South Africa, Patagonia, and off the west and east coasts of the United States. The resulting video is what you would see if you were riding on the whale’s back.
The researchers found that whales that fed on krill followed a distinct pattern of activity. Humpbacks that fed on fish, however, varied their timing. This is likely in response to the more advanced escape abilities of fish compared to krill; the whales may be performing lunge feeding that is less energetically ideal when the trade-off is eating prey that can supply them with more energy.
The Hopkins researchers hope to dive deeper into whale feeding studies, including figuring out the fluid mechanics of their iconic baleen, which acts as a high-throughput filter to process the vast amounts of small prey.