Blue Whale Diet: Do Blue Whales Eat Fish?

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The blue whale is the largest mammal that has ever lived on planet earth. So to feed such a huge creature, surely it needs an impressive diet?

In this post, we’re going to take a closer look at the blue whale’s diet, and answer a question we are often asked here, do blue whales eat fish?

Yes, blue whales do sometimes eat small fish. However, their diet is almost strictly krill, which are small shrimp-like crustaceans that the whales consume in the millions each day.

Let’s take a closer look…

Do Blue Whales Really Eat Fish?

The primary food source for the blue whale is krill – a small shrimp-like crustacean that is scooped up by the whale’s large mouth.

However, upon scooping up krill, some small fish may also end up in the whale’s mouth, which the whale will most certainly eat.

Blue whales roam around the ocean in search of swarms of krill. They will then lunge at them with their mouths wide open and scoop up as many as possible.

They take in more food per mouth full than any other animal on earth, and they are even smart enough to calculate which swarms of krill are worth opening their mouths for, and which they should leave.

Opening your mouth when you’re the size of a blue whale can expend a surprising amount of energy, so a few measly krill aren’t worth it sometimes.

Do Blue Whales Eat Big Fish?

Blue whales are filter feeders, which means they use their baleen to filter out krill and other small crustaceans, then separate them from seawater.

Once their prey is trapped in the baleen, they squirt out the seawater and swallow their catch.

Sometimes small fish will end up in their mouths as they get mixed in with the krill, but these fish are so small that they can be swallowed by the whale without chewing.

See, although blue whales are the largest animals to roam the earth, they have very small throats relative to their size.

A blue whale’s throat is no more than a meter wide, meaning the largest fish they could consume would be the size of a grapefruit.

Not only that, but as the blue whale is a baleen whale, it doesn’t have any teeth to chew up any large fish.

It’s rare for blue whales to end up with lots of bycatch in their mouth, their diet is strictly krill and the odd small fish here and there.

What Type Of Fish Do Blue Whales Eat?

Now and again small fish will end up in the mouth of a blue whale, and depending on their size the whales won’t let them go to waste.

However, the fish must be small enough for the whale to swallow.

Blue whales are pretty precise when it comes to which schools of prey they are going to pursue, so won’t waste their time on large fish.

The type of fish that blue whales may eat aside from krill are small schooling fish, small shrimp, and other small crustaceans.

Anything larger than this will need to be left as it won’t be able to be chewed or swallowed by the whale.

Why Do Blue Whales Only Eat Small Fish?

The reason blue whales only eat small fish is that they are unable to eat large ones.

As mentioned earlier, they are filter feeders that have surprisingly small throats.

This means they are not able to swallow fish any bigger than say a Mackrel. Not only that, but they don’t have teeth to chew up fish, so rely solely on krill for the majority of their diet.

Small fish are sometimes able to escape a blue whale’s mouth before they have a chance to close it, whereas krill are a much easier catch for the whales as they are often in swarms of thousands.

Opting for krill means that it’s almost a guaranteed catch, whereas smaller fish may be able to escape and the catch could be a lot smaller.

It’s all about conserving energy as a blue whale. They calculate what prey is worth pursuing and what is not, and krill seems to be the best bang for their buck.

Final Thoughts

Do blue whales eat fish? Yes, they do. However, it’s not their preferred food source as they feed almost exclusively on krill.

Blue whales are filter feeders that have hair like baleen instead of teeth. This baleen works by trapping small crustaceans such as krill and shrimp in it, allowing the whale to separate prey from seawater.

This species of whale does not have teeth, so it is unable to consume large fish. Blue whales will only eat fish that they are able to swallow without chewing.

A blue whale’s throat is only around one meter wide, which is small given the size of this animal.

Even if the whale wanted to catch and eat a larger fish, it wouldn’t be possible.

Hopefully, this post has been helpful and you now have a better idea of what blue whales eat.

Thanks for taking the time to read this post and feel free to stick around to learn more about the blue whale.