Blue Whale

## Description

The blue whale (Balaenoptera musculus ) is a marine mammal and a baleen whale. Reaching a maximum confirmed length of 29.9 meters (98 ft) and weighing up to 199 metric tons (196 long tons; 219 short tons), it is the largest animal known to have ever existed. The blue whale's long and slender body can be of various shades of greyish-blue dorsally and somewhat lighter underneath. Four subspecies are recognized: B. m. musculus in the North Atlantic and North Pacific, B. m. intermedia in the Southern Ocean, B. m. brevicauda (the pygmy blue whale) in the Indian Ocean and South Pacific Ocean, B. m. indica in the Northern Indian Ocean. There is also a population in the waters off Chile that may constitute a fifth subspecies.

In general, blue whale populations migrate between their summer feeding areas near the poles and their winter breeding grounds near the tropics. There is also evidence of year-round residencies, and partial or age/sex-based migration. Blue whales are filter feeders; their diet consists almost exclusively of krill. They are generally solitary or gather in small groups, and have no well-defined social structure other than mother-calf bonds. The fundamental frequency for blue whale vocalizations ranges from 8 to 25 Hz and the production of vocalizations may vary by region, season, behavior, and time of day. Orcas are their only natural predators.

The blue whale was once abundant in nearly all the Earth's oceans until the end of the 19th century. It was hunted almost to the point of extinction by whalers until the International Whaling Commission banned all blue whale hunting in 1966. The International Union for Conservation of Nature has listed blue whales as *endangered* as of 2018. It continues to face numerous man-made threats such as ship strikes, pollution, ocean noise and climate change.

## Appearance

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 the throat. 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 that expel stale air and seawater out of the top of their heads when they come up to the surface to breathe.

## Distribution

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. They take long migrations, traveling to their summer feeding grounds towards the poles and then heading to their winter breeding grounds in more equatorial waters.

## Behavior

Blue whales are generally solitary creatures that may spend some time in pairs and 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. Blue whales feed through lunge feeding; they swim towards krill at high speeds as they open their mouths up to 80°. While pursuing krill patches, Blue whales maximize their calorie intake by increasing the number of lunges while selecting the thickest patches. This provides them enough energy for everyday activities while storing additional energy necessary for migration and reproduction.

## Diet

Blue whales are carnivorous (piscivorous). Their diet mainly consists of krill and small crustaceans, although they will occasionally eat small fish.

## Reproduction

Blue whales are monogamous, mating during winter or early spring in 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 the 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.

## Population

### Population threats

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.

### Population number

According to IUCN Red List, the global population size of the Blue whale in 2018 is plausibly in the range of 10,000-25,000 individuals or 5,000-15,000 mature individuals. Currently, this species is classified as Endangered (EN) on the IUCN Red List and its numbers today are increasing.

### Ecological niche

As with other large baleen whales, Blue whales are significant predators of krill and control their populations.

## Fun Facts for Kids

The Blue whale is the biggest animal the planet has ever seen. Their tongues are comparable to the weight of an elephant, their hearts to the weight of a car.

Blue whales sleep while they are swimming. While asleep, only half of their brain is in use.

No living thing on Earth grows faster than a Blue whale.

A medium-sized dog would be able to walk with room to spare through the arteries of a Blue whale.

Blue whales prefer to sleep during the middle of the day.

Blue whales appear blue underwater but are gray when above the water's surface.

The spray from the blowhole of a Blue whale blowhole shoots almost as high as a building of three stories (30 feet/9 m). A toddler would be able to fit into its blowhole.

The mouth of a Blue whale has enough space for about 100 people.

These whales have belly buttons.

A Blue whale's milk is said to taste like a mixture of liver, fish, castor oil, and, milk of magnesia.