It started with a simple question: How much do baleen whales eat?
Because baleen whales – including humpback, northern right and blue whales – usually eat tens of meters below the surface of the water, it is not easy to observe their feeding behavior. Answering the question of keeping megafauna (blue whales grow up to 100 feet in length and are the largest animals on Earth) in captivity is neither possible nor desirable. In addition, some animals eat fat for a few months and then fast for the rest of the year. This makes it more difficult to keep track of how much food they eat.
“This is a basic question that I assumed had already been researched thirty, forty, and fifty years ago. Matthew Savoca of the Hopkins Naval Station at Stanford University in California said:
For Savoca, the question went beyond basic scientific knowledge or curiosity. The amount of food a baleen whale eats is directly related to the amount of feces it produces. These excreta are essential to life in the oceans; They are a source of energy and food for countless marine organisms.
Savoca recently went looking for an answer with researchers from different countries. The team outfitted baleen whales — so named after the comb-like substance in their jaws that “sieves” small prey such as krill and zooplankton from the water — with sophisticated equipment to track them in the Atlantic, Pacific and Southern Oceans. Additionally, the researchers used drones to measure krill concentrations.
The results were recently published in the journal temper nature Surprisingly, whales eat much more than previously thought. For example, a blue whale eats an average of 16 tons of food per day, which is three times what scientists have estimated. (Learn more about the hidden world of whale culture.)
“This research shows that baleen whales play a more important role in our ecosystem than we thought,” said marine researcher Sian Henley of the University of Edinburgh, who was not involved in the study. The reason for this is that the 14 species of baleen whales that we know of are important for distributing essential nutrients, such as carbon, nitrogen and iron, into the ocean, particularly through their feces.
This new knowledge, Henley said, “demonstrates that we need to better protect and manage the oceans as broad as possible, especially the Southern Ocean.” The waters around Antarctica are particularly vulnerable to human influences, particularly due to warming waters due to climate change and overfishing. This disrupts the natural cycle of nutrients and negatively affects krill and other whale food sources. The consequences of this are even more damaging because the whale stock is still recovering from centuries of whaling.
As whale numbers increase, he says, their role in recycling nutrients should help restore the food cycle and increase krill abundance.
‘better than nothing’
To estimate how much food baleen whales ingest, scientists previously analyzed the metabolic needs of baleen whales based on their size and activity level. They used their knowledge of closely related animals or animals of similar size. For example, biologists have tracked what humpback or blue whales ate by measuring the consumption of orcas (or sword whales).
“But blue whales and humpback whales are very different from swordfish in behaviour, ecology and physiology,” Savoca said. He said previous estimates were “better than nothing, but they’re really not good indicators.”
For the study, Savoca’s team fitted trackers to 321 animals from seven different species of baleen whales: humpback whales, blue whales, fin whales, bowhead whales, minke whales, postal whales and northern right whales. (Watch the world’s largest animal eat its meal.)
The researchers attached packages containing accelerometers, magnetometers, GPS, light sensors, gyroscopes and cameras to the whales’ backs with special glue. Savoca describes them as an “iPhone whale”. Just as our phone can tell us how many steps we take in a day, these devices can tell how often and at what depth a whale bites food. Baleen whales often catch their food by rushing: they rush first and then glide straight or sideways through the water, opening their mouths wide.
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