Blue Whale: 'Knife Edge' Balance of Energy-Gathering and Breathing, Says Study
To eat or to breathe? That is a question that most of us never want to have to answer, but one the gargantuan blue whale must ponder every day.
Scientists used to think that filter feeders like the blue whale fed on miniscule crustaceans called krill at their leisure, without a thought to how their food source is distributed throughout the ocean. However, new information indicates that the largest animal known to man has developed a complex foraging method aimed at zeroing in on the most condensed groups of krill.
The study, published in Science Advances, demonstrates that blue whales shift their hunting strategy based on the amount of prey and the depth at which they can be found in order to maximize energy efficiency. Blue whales practice lunge-feeding, guzzling up as much ocean water rife with prey as they can and then filtering out the tiny krill for ingestion. The massive size of a blue whale, at weights of up to 150 tons, forces them to consider the amount of energy they consume against the amount of energy they expend.
Researchers from NOAA Fisheries, Oregon State University, and Stanford University compared the data of 41 previously tagged blue whales to 14 recently tagged blue whales off the coast of California. By combining this information with additional data from acoustic surveys that measured the concentration of krill patches, the scientists were able to determine that blue whales ate less frequently when the krill patches were less condensed. This methodology allows the whales to save energy and oxygen for a time when the krill patch is denser, which often occurs at lower depths. When the whales came upon highly compressed krill patches, the researchers observed the whales lunge feeding more often, thus acquiring more energy from the immense amounts of krill consumed.
"The magic number for krill seems to be about 100 to 200 individuals in a cubic meter of water," Elliott Hazen, a research ecologist with NOAA Fisheries' Southwest Fisheries Science Center and lead author of the research, said in a statement. "If it's below that range, blue whales use a strategy to conserve oxygen and feed less frequently. If it's above that, they'll feed at very high rates and invest more effort."
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