Blue whales have a special feeding behavior to support their massive body size and to survive.
Blue Whales are the largest animals ever to have lived on earth. At about 100 feet in length and 180 tons in weight, one might think that this giant marine mammal needs large amounts of food to satisfy its hunger, but surprisingly, it doesn't. All they eat is krill, which is a tiny shrimplike creature.
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"For blue whales, one of our main questions has been: How do they eat efficiently to support that massive body size," said Elliott Hazen, a research ecologist at NOAA Fisheries' Southwest Fisheries Science Center and lead author of the study. "Now we know that optimizing their feeding behavior is another specialization that makes the most of the food available."
Blue whales can eat up to 4 tons of krill throughout the day. Many previous studies suggested that every time when whales are hungry, they simply open their mouth and eat up krill. A new study reveals that blue whales feeding behavior targets the densest, highest quality prey to maximize their energy gain.
Researchers found that when krill are spread out or prey quality is low, blue whales switch to a complex strategy of conserving their oxygen and energy for future dives. When krill density increases, whales began to lunge more frequently, taking in a mouthful of krill along with the water surrounding it and try to obtain as much energy from the krill as possible.
"Blue whales don't live in a world of excess and the decisions these animals make are critical to their survival," said Ari Friedlaender, an investigator with the Marine Mammal Institute at Oregon State University's Hatfield Marine Science Center and co-author on the study. "If you stick your hand into a full bag of pretzels, you're likely to grab more than if you put your hand into a bag that only had a few pretzels."
This kind of lunge-feeding requires huge effort but whales consume more krill and ultimately more energy as a result of it and this feeding pattern supports well their tremendous size.
"Lunge-feeding is a unique form of 'ram-feeding' that involves acceleration to high speed and the engulfment of large volumes of prey-laden water, which they filter," noted Jeremy Goldbogen, co-author of the study. "But we now know they don't take in that water indiscriminately. They have a strategy that aims to focus feeding effort on the densest, highest-quality krill patches."
Up to 100 to 200 krill swarming together in a cubic meter of water are considered dense krill patches, according to the study. Seeing krill around that range, blue whales will dive more often and invest more effort to catch the prey. If krill is below that range, they will conserve oxygen and feed less frequently.
This study can help protect the species from being extinct since blue whales are listed as endangered by International Union for Conservation of Nature.
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“If they are disturbed during the intense, deep feeding, it may not have consequences today or this week, but it could over a period of months,” "said Friedlaender."There can be impacts on their overall health, as well as on their fitness and viability for reproduction.”