Humpback whales have predators

Why do blue whales get so big?

Just krill - nothing else

Of all the furrow whale species still alive today, the blue whales are probably the most specialized. They eat krill and only krill - with very few exceptions. And that is the reason for their extraordinary size.

This specialization has it all. Krill can be found in abundance, but only in certain remote regions of the world's oceans where there is upwelling and where there is a polar climate. In order to find large quantities of krill, blue whales must be extremely mobile and have sufficient energy reserves to fall back on. The animals achieve both thanks to their enormous size, their slim body and their small, hydrodynamic swim fins. Due to their body shape, the blue whales move very energy-efficiently. They also draw energy from their thick layers of fat, the so-called bubble.

If the animals encounter krill, the prey is not an easy catch. A blue whale has to pounce on the swarm quickly and with an element of surprise. Some whales, such as the humpback whale, are able to outmaneuver the krill with their long fins. But blue whales are efficient long-distance swimmers and therefore less maneuverable. In order to grab as much krill as possible, a certain characteristic prevailed in the blue whale: It has a huge mouth, which is the result of a very large body. So it is once again the body size that made the animal successful.

Dozens of species have emerged and become extinct since the furrow whales developed filtering by mouth

But ecological specialization is a double-edged sword. Concentrating on a certain prey animal offers a certain food security, but it also makes the animals vulnerable. As soon as an ecosystem changes, it hits the specialists first and hardest. Because the more a predator settles on prey, the more difficult it becomes for him to adapt. But paradoxically, a predator seems to hunt more successfully if it specializes even more. In this way evolutionary selection goes in circles.

Blue whales are the epitome of this enigmatic specialization loop. To eat krill, they have evolved into long-distance swimmers at the expense of maneuverability. The body of the blue whale is very well suited for this. But if the mammals had to compete with the other furrow whales for other prey, they would lose out. The others swim more agile, so they can catch a lot more different prey and even need less energy to do so. The result: the blue whale is even more dependent on its specialization - and thus on krill.

The vicious circle of height

In addition, the body size determines the diet of the blue whale, but it also increases its energy consumption. A larger body needs more food, which is only found in a few places in the world's oceans. But in order to cover the long distances there, the body has to be big enough and be able to store enough energy. But a large whale needs more krill to survive ... The blue whale's strategy is therefore extremely vulnerable.