The blue whale’s heart weighs about 180 kilograms, and the longest one measured was roughly 30 meters. Studies in 2024 and 2025 corrected inflated weight estimates for the extinct whale Perucetus and the titanosaur Bruhathkayosaurus, leaving the blue whale as the heaviest animal ever. It eats about four tons of krill a day by lunge feeding: accelerating into a swarm, opening its jaws to about 80 degrees, and expanding 60 to 88 throat pleats to engulf up to 220 tons of water before pushing it out through keratin baleen. A lunge into sparse krill costs more energy than it returns, but a dense swarm can pay back up to 240 times the cost. On dives to 315 meters its heart slows to two beats a minute, then races to 37 at the surface.

Scientists age blue whales by counting light and dark layers in earplugs of wax that can exceed half a meter, laid down by yearly cycles of feasting and fasting; the oldest counted was 110. Calves are born six to seven meters long and gain about 90 kilograms a day on milk over 40% fat. A 2024 genomic study found about 3.5% of the North Atlantic blue whale genome comes from fin whales, with genes flowing only one way. Since the 1960s their songs, at 8 to 25 hertz, have dropped steadily in pitch, and in early 2025 researchers found they sang less during California marine heatwaves. Industrial whaling killed over 350,000 in the Antarctic in the first half of the 20th century, cutting about 140,000 animals to 10,000 to 25,000.

• A 50 ton blue whale may have a brain of only about 3.6 kilograms.
• They roll up to 180 degrees during lunges to hit the densest part of a krill swarm.
• One theory says deeper songs signal larger bodies as populations recover, while a 2022 study suggests a spreading cultural fad.
• Protection came in 1966, though Soviet whaling continued illegally into the 1970s.
• Nursing mothers pass stored pollutants from their blubber to calves through milk, and 1800s whalers called them sulfur bottoms for the diatoms on their bellies.