The largest mammal in the world, and indeed the largest animal known to have ever existed, is the blue whale (Balaenoptera musculus), reaching lengths of up to 100 feet (30 meters) and weights of approximately 200 tons (180 metric tonnes) or more. These marine mammals can be found in oceans all over the globe, primarily in deep waters where they hunt their primary food source: tiny shrimp-like creatures called krill. A blue whale eats about 4 tons of krill every day during feeding season.
Blue whales are characterized by their long, streamlined bodies and prominent dorsal fins. Their coloration is typically a bluish-grey with lighter spots, making them unique and easily recognizable. Unlike many other whales, blue whales are known for their ability to produce loud calls, which can reach volumes up to 188 decibels, making them one of the loudest animals on the planet. These vocalizations are thought to be used for communication and navigation in the vast ocean.
Despite their massive size, blue whales face significant threats due to human activities. Historical whaling severely reduced their populations during the 20th century, leading to stringent protections under the Marine Mammal Protection Act and the Endangered Species Act in the United States. Today, while their numbers have been slowly recovering, they are still classified as endangered. Their primary threats now include ship strikes, entanglement in fishing gear, and the impacts of climate change affecting their food supply.
The incredible scale of blue whales extends not just in length and weight but also in their heart size—approximately the size of a small car, weighing around 400 pounds (approximately 180 kilograms). The sheer volume of their lungs is immense as well; a blue whale's lungs can hold around 5,000 liters (about 1,320 gallons) of air. These magnificent creatures continue to captivate researchers and enthusiasts alike, not only for their size but also because of the vital role they play in marine ecosystems, influencing everything from ocean productivity to the health of the krill populations they depend upon.