Blue whales are the biggest animal on earth they are 30 meters long they are also the heaviest with a hart weighing 900kg and blood veins that hold 10 tones of blood their hole body weight is 113 tones !
Blue whales are the biggest animal in the world so they must eat a lot of krill every day.
Blue whales live alone but they do some times swim in groups of around 5.
Sonar is a whale way of finding its way around. It works like this. So the whale makes a loud noise from its head and when it hits some thing it bounces back letting the whale know what it is .
Here's an Octonauts video about blue whales.
I got my facts from my favourite animal book and Wikipedia.