The Blue whale has a huge long, slim, narrow body. Its skin is hairless and smooth, and is grayish blue, lighter on the underside, with a series of grooves on their throats. Its large tail is straight, splitting at the end into two rubbery flukes. Blue whales are part of the "baleen whales" group, having, instead of teeth, up to 395 hard, bristly baleen plates that descend from the upper jaw. These plates are used to filter seawater for food. They have two blow-holes which expel stale air and sea water out of the top of their heads when they come up to the surface to breathe.
Blue whales are cosmopolitan species being found in every ocean in the world except the Arctic, but absent from some regional seas such as the Mediterranean, Red, Baltic, Okhotsk and Bering seas.
Blue whales are solitary creatures that occasionally come together in casual groups to feed. They communicate with each other using a variety of sounds or songs, including squeaks, hums and rumbles, mainly during the breeding season, which is in winter. The sounds Blue whales make are extremely loud, the loudest of any animal on the planet, and they have been recorded at higher than 180 decibels. They use their tails to perform deep dives, as by lifting their tail above the water's surface, they muster enough power to dive up to 200 meters straight down into the sea.
This whale is carnivorous, with a diet mainly consisting of krill and small crustaceans, although it will occasionally eat a small fish. It can consume as much as six tons of prey daily during summer in Antarctic waters, but will hardly eat anything during migration in winter to warmer waters to breed.
Blue whales are monogamous, mating during winter or early spring in the warmer, tropical waters. Gestation lasts for almost a year, the female giving birth to one calf when she returns to the region the next year. Having spent all summer feeding in the cold, rich waters of Antarctic, the mothers eat almost nothing during the time they are providing their young with milk. Baby blue whales stay with their mother for at least a year and are weaned at about 8 months old. Blue whales can start reproducing between the age of 10-15 years old, producing a calf every 2 or 3 years.
Blue whales have almost no natural predators, due to their enormous size. The calves may be at risk of predation by large sharks and orcas. Humans hunted them so much throughout the 20th century that they almost became extinct. Globally, there appear to be no major threats to Blue whales at present. They can be subject to some ship strikes and entanglements but reported cases are few.
According to IUCN Red List, the estimation of the total world population can be between 10,000 and 25,000 individuals, it is only about 3-11% of the 1911 population size. It is unknown whether the blue whale will fall victim to extinction. Extensive surveys of southern hemisphere populations estimate 400 to 1,400 individuals. In the northern hemisphere, numbers are estimated at about 5,000 but the scientific robustness of these surveys is under question. The Blue whale is classified as Endangered (EN) on the IUCN Red List.
As with other large baleen whales, Blue whales are significant predators of krill.