Whales eat up to a third of their body weight every day, which helps the environment more than we give them credit for

Whales are the largest animals on Earth, so it makes sense that they have a big appetite.

But their ability to suck krill and small fish up into their esophagus as they glide through the oceans is far greater than we previously thought, a new study has found.

Every day, baleen whales, which include species such as humpback whales, minke whales and the mighty blue whale, consume between 5 and 30 percent of their body mass.

That’s three times more food each year than we’ve measured in the past, according to research published today in the journal Nature.

By underestimating how much these giants in the ocean eat, scientists say we may have underestimated as well their role in maintaining healthy oceans today, as well as the impact extensive whaling in the early 20th century had on their food sources such as krill.

“Our results say that if we restore whale populations to pre-whaling levels seen in the early 20th century, we will restore a huge amount of lost function to marine ecosystems,” said study co-author Nicolas Pyenson of the Smithsonian National. Natural History Museum.

“It may take a couple of decades to see the benefits, but it’s the clearest reading yet about the enormous role that great whales play on our planet.”

How can whales that eat more help the ocean?

Whale tail with feces on
Whale poo are orange because of the amount of krill they eat.(FlickR: Andrew Purdam)

The more the whales eat, the more they tremble.

Whales act as giant manure in the ocean, said Vanessa Pirotta, a marine ecologist at Macquarie University.

“Whales feed in one area, and heck in another … so they are able to move huge amounts of biomass from one area to another,” said Dr. Pirotta, who was not involved in the research.

Their feces help to suspend important nutrients such as iron on the surface of water, which in turn nourishes the blooms of microscopic organisms at the bottom of the food chain called phytoplankton.

“Some people refer to this as the iron pump,” said Dr. Pirotta.

A krill in the Southern Ocean.
Krill are an important food source for whales.(Delivered: Brett Wilks)

The humpback whales we see in Australia travel primarily to the southern ocean to enjoy small crustaceans known as Antarctic krill (Euphausia superba).

“Antarctic krill are incredibly important to these animals as they provide their main food source,” said Dr. Pirotta.

Between 1910 and 1970, the number of whales in the South Seas decreased as a result of whaling.

It had been thought that krill would explode as a result, but it did not happen – a phenomenon known as the krill paradox.

The fall makes no sense unless you take into account the role of whales as mobile manure, said study lead author Matthew Savoca of Stanford University.

“These whales sowed productivity out in the open Southern Ocean, and there was very little to recycle this manure once the whales were gone,” said Dr. Savoca.

How do we know how much a whale eats?

To get a better estimate of how much whales eat, the team tracked 321 whales spanning seven different species swimming in the Atlantic, Pacific and Southern Oceans.

Using camera and motion sensor systems attached with suction caps, they monitored when the whales were feeding.

suction cap marks used for whales
Several of the suction cup brands are used to obtain high-resolution data from baleen whales around the world.(Delivered to: Goldbogen Laboratory)

They also used drone images of 105 of the whales to calculate the size of each animal.

The length of each animal could then be used to assess its body mass and how much water it sucked up through its mouth.

Once they had determined where the whales were feeding, the researchers used sound waves to assess the size and density of the food swarms the whales were feeding on.

aerial photo of dinghy near whales
Scientists are investigating a humpback whale with a boat and drone in the surface water near the West Antarctic Peninsula.(Delivered: Duke University Marine Robotics and Remote Sensing under NOAA license.)

According to their estimates, for example, an adult blue whale in the eastern North Pacific, which can grow up to 27 meters and weigh more than 45 tons, probably consumes 16 tons of krill a day during its foraging season.

The team also looked back through historical records to calculate how much food whales in the southern ocean would have consumed before whaling.

“We calculate that stocks before whaling on [baleen whales] annually consumed 430 million tons of Antarctic krill, “they wrote.

minke whale with mark on back
A minke whale tagged by the research team off the coast of Antarctica.(Delivered: Ari Friedlaender under NOAA / NMFS permission.)

That is twice the current estimated total biomass of krill in the South Seas and more than double the global catch of deep-sea fishing today.

Such a large diet would have produced as much as 12,000 tons of iron, 10 times the amount whales currently recycle in the southern ocean.

Restoration of whale numbers restores the ecosystem

In the pre-whaling era, observers noted that the oceans were red with krill and the water spouts could be seen from horizon to horizon.

The return of whales would help improve marine ecosystems, said Dr. Pirotta.

“If you have more whales feeding, you will have the return of nutrients and that iron pump in the ocean, so essentially you will have more fertilization happening,” she said.

But the question is whether the number of whales – and krill – can return to pre-whaling levels.

Dr. Pirotta said some species, such as the humpbacks she studies, have returned to Australian waters.

“Fortunately, their numbers have recovered quite well, but there are still other populations of other baleen whales around the world that have not recovered from whaling,” she said.

“There are a number of factors in it, one of which is the availability of food. But also us as humans are limiting their recovery due to man-made impacts such as entanglements, fishing gear and ship attacks.”

Climate change may also play a role in whales’ movement and abundance of their food.

“We know that climate change has the potential to change where the prey is distributed, which will have influencing effects for the animals that depend on the [prey]said Dr. Pirotta.


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