Blue whales are the largest animal on the planet. One blue whale can consume about 16 tonnes of krill in a single day.
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The Tons that Whales Eat...and Poop
How much do whales eat? As you'd imagine, it's a lot. Smithsonian scientist Nick Pyenson took part in new research that indicates that in one day a blue whale can eat about 16 tonnes (or metric tons) of krill. That’s about the same as 8,800 quarter-pound burgers! When considering all the blue whales that live today, it means blue whales eat over half a million tonnes of krill every year.
Information about how much food whales consume provides more than just a fun fact for parties with friends, it can give us insight into why certain changes and issues arise in an ecosystem. Twentieth century whaling reduced global whale populations by about two-thirds, but blue whales were hit especially hard. When considering just blue whales, whaling reduced their krill consumption by 99.6 percent. Today, krill populations in the Southern Ocean are down by over 80 percent since the end of whaling, a fact that left scientists scratching their heads for quite a while. Initially it seemed counterintuitive—less whales eating krill should mean krill are able to explode in numbers. The answer became clear when scientists factored in one particularly important factor—poop. Krill rely on the reintroduction of nutrients, especially iron, back into the ecosystem and a large supply of those nutrients comes from whale poop. When whaling decimated the whale populations it also wreaked havoc on the balance of the ecosystem. No whales meant no iron recycling which meant less krill.
Helping whales rebound may help ecosystems already struggling with the impacts of climate change. When whales thrive, so do the ecosystems they live in, meaning more growth in all parts of the food chain. Perhaps, a future exists where whales return to their historical numbers once again, and both the planet and humanity will reap the rewards.
Big Animals
Credit: Stanford University
A Feast of Krill
Credit: WikipediaSwarms of krill feed the largest animals on earth. A single Antarctic krill measures about 2 to 3 inches (5 to 8 cm), while a blue whale can measure over 100 feet (30 m) long.
Feeding Blue
Credit: Slater Moore PhotographyTo understand how much krill a whale consumes scientists combined information about the rate at which the whales dive for food, the volume of water they can filter in their mouth, and the density of their prey (i.e.) how many krill are there in a cubic meter of seawater.
Tagged
Credit: Ari Friedlaender under NOAA/NMFS permit 23095Scientists estimate krill consumption by using data collected from suction tags. The tags monitor the whales movement, measuring speed and depth. Scientists are then able to use this information to determine when a whale makes a feeding dive. Here, a minke whale, one of the smallest of the baleen whales, breaches the surface with a tag suctioned to its head.
Tagging a Whale
Credit: Elliott HazenScientists attach a suction tag on a blue whale. The tag sits at the end of a pole which the scientist then gently taps onto the back of the whale. This job requires immense skill on both the scientist’s part and the boat driver’s part.
The Humpback
Credit: John DurbanSmaller than blue whales, humpback whales are another baleen whale that consume about 9 tonnes of krill in a single day.
A Big Gulp
Credit: Elliott HazenLike all baleen whales, humpback whales are filter feeders. They engulf their prey in gigantic gulps and then once their mouths fill they slowly sift the water back out through their baleen. Scientists refer to this as “lunge-feeding.” Annually, an individual humpback-sized whale (10 to 15 m) filters approximately one 131 million cubic meters of water, or the same amount as 52,400 Olympic sized swimming pools.
A Bigger Gulp
Credit: John DurbanRight whales (pictured here) and bow head whales feed slightly differently. Still filter feeders, they practice continuous filtration, or a method called “ram feeding.” In this method the whale swims through a cloud of prey and simultaneously filters the water out as it comes in. Through this method, a right whale can filter about 4 times the amount of water that a blue whale filters.
A Pink Cloud
Credit: Elliott Hazen under NOAA/NMFS permit 16111A whale poops a pink cloud, a remnant of all the pink krill it eats! Large baleen whales excrete massive amounts of iron, a portion of which is then consumed by growing phytoplankton. Oceans are naturally very limited in iron content, so the boost in nutrition is vital for food chains out at sea.
Prior to 20th century whaling, all of the baleen whales on the planet potentially recycled an amount of carbon equal to that stored in the Amazon river basin!
The Toll of Whaling
Credit: Scott Polar Institute, University of Cambridge/Getty ImagesIn total, 1.5 million of the 2 million baleen whales killed in the 20th century were removed from the Southern Ocean, with the largest species facing the greatest exploitation. At the beginning of the 20th century, prior to industrial whaling, Southern Hemisphere populations of Antarctic minke, humpback, fin and blue whales consumed twice as much Antarctic krill as the total amount of Antarctic krill in existence 100 years later (215 million tonnes per year).
The Future
Credit: Matthew SavocaWhile some whale populations are rebounding, climate change and other human activities continue to hamper their progress. We now know that baleen whales have a massive impact on their environment through their ability to recycle nutrients back into the ecosystem. Encouraging whale populations to recover may help restore ecosystems damaged during the 20th century and lead to overall population growth in the ocean. That, in turn, can lead to increased human wellbeing and overall planetary health.