What does the blue whale mainly eat, and roughly how many tons does it eat in a day?
The blue whale is a marine mammal belonging to the suborder Mysticeti. There are four subspecies in total. The blue whale is considered the largest animal known to have ever lived on Earth, reaching up to 33 m in length and weighing up to 181 tons. So what does the blue whale mainly eat? Roughly how many tons does it eat in a day?
What does the blue whale eat?
Like other baleen whales, the blue whale feeds mainly on small crustaceans (such as krill) and small fish, and sometimes also squid. Krill is the most abundant animal in the world, widely distributed in the sea areas of the Arctic and Antarctic. It is precisely because of such abundant food, and because life in the water imposes no limit of supporting body weight, that the blue whale has been able to grow so enormous. The blue whale's stomach is divided into four chambers; the first stomach is formed by the expansion of the esophagus, so its appetite is enormous. It can swallow about 2 million krill at a time, and eats 4000-8000 kg per day. If the food in its belly is less than 2000 kg, it will feel hungry.
The blue whale feeds on plankton, mainly krill. One blue whale consumes 2-5 tons of food per day. When feeding, it swims at 2-6 km/h, during migration at 5-33 km/h, and when chased at a maximum of 20-48 km/h. It generally makes 10-20 shallow dives followed by one deep dive; shallow dives are separated by 12-20 seconds, and a deep dive can last 10-30 minutes. The blow it spouts is narrow and straight, 6-12 m high. Krill is the main food of the blue whale, and the plankton the blue whale eats belongs to different species depending on the ocean region. In the North Atlantic, northern krill is the main food of the blue whale. In the Antarctic, Antarctic krill is the main food of the blue whale. The blue whale usually preys on the densest krill swarms it can find, which means that during the day the blue whale needs to feed in deep water (over 100 m), and only at night can it come to the surface to feed. During feeding, the blue whale's dive time is generally 10 minutes. A 20-minute dive is not unusual, and the longest recorded dive time is 36 minutes (Sears, 1998). In the process of feeding, the blue whale swallows a large swarm of krill at once, along with a large amount of seawater. It then compresses its abdominal cavity and tongue, forcing the seawater out through the baleen plates. After the seawater in its mouth is drained away, the blue whale swallows the remaining krill that cannot pass through the baleen plates.
Living habits of the blue whale
Breathing
Although the blue whale lives in the ocean, it, like other mammals, breathes with its lungs. Its lungs weigh more than 1000 kg and can hold more than 1000 liters of air. Such a large lung capacity greatly reduces the number of times it needs to breathe; it only comes to the surface to breathe about once every 10-15 minutes. When breathing, it first expels waste gases such as carbon dioxide from its lungs through its nostrils, then inhales fresh oxygen. Whenever its head comes to the surface to breathe, it first expels waste gases such as carbon dioxide from its body. When this powerful, scorching air stream shoots out of its nostrils, it can reach a height of about 10 m, and it also sweeps the nearby seawater up out of the sea, creating a spectacular water column on the blue surface of the sea. Seen from afar, it is just like a sea fountain, and at the same time it gives out a sound as loud as a train whistle; people call it a “blow”. People can determine its position based on the sound the blue whale makes when spouting, and the height and shape of the blow. The blue whale lives in all the oceans. It is extremely rarely seen in China's sea areas, and there are records of blue whales having appeared in the Yellow Sea and the South China Sea. It generally dives no deeper than 100 m, but some individuals can dive to 500 m, and a dive can last 10-20 minutes, followed by 8-15 consecutive blows.
Whales in general do not raise their tails before diving, but the blue whale always lifts its tail out of the water before diving, and sometimes even leaps high out of the water, then quickly dives into the water 30-40 m deep to look for food. It also likes to slap the water with its tail flukes; this is a pastime with many uses and many purposes. It may be playing, or it may be trying to attract the attention of its companions, or perhaps it is to get rid of the harassment of parasites on its skin.
Activity
Although some people have seen 50-60 blue whales moving in groups, they generally rarely form groups; most are solitary, or only 2-3 move together. A pair of blue whales is very harmonious with each other, swimming, diving, foraging and breathing together, like mandarin ducks, inseparable, often leaving a wide wake behind them. When 3 blue whales are together, it is mostly a female and a calf staying close together, with the male following behind at a distance of about 3 m.
Despite its enormous size and usually slow movement, often staying motionless, it can rise and sink freely in the water, and its tail swings flexibly, serving both as the driving force for forward movement and as a rudder, reaching a forward speed of up to 28 km per hour.
Vocalization
The blue whale is the loudest animal in the world. When communicating with its companions, the blue whale uses a low-frequency, deafening sound. This sound can sometimes exceed 180 decibels, louder than the sound of a jet taking off that you hear while standing on the runway. A sensitive instrument once detected the sound of a blue whale from 80 km away. Based on measurements at a reference pressure of one millipascal at a distance of 1 m from the blue whale, it is estimated that the blue whale's sound can reach 155-188 decibels at the source. Even taking into account the different impedance of water and air and the different standard reference pressures, the equivalent sound range in air is still 89-122 decibels. For comparison, the sound of a pneumatic drill is about 100 decibels. But humans may not be able to appreciate that the blue whale is the loudest animal. The fundamental frequency of vocalizations in all blue whale populations is 10-40 Hz, while the lowest frequency humans can perceive is 20 Hz. The duration of the blue whale's sound is 10-30 seconds. There is a record of blue whales off the coast of Sri Lanka repeating a “song” of 4 notes, each lasting two minutes, reminiscent of the humpback whale's song. Researchers believe that because this phenomenon has not been seen in other populations, it may be unique to the B.m.brevicauda (pygmy) subspecies.