9 Interesting Sei Whale Facts

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There is no doubt that whales are some of the most breathtaking animals in the world.

Their colossal size combined with their ballet-like swimming and curious, gentle personalities have made them popular for ages and inspired all kinds of stories, myths, and folklore.

Scientists and researchers have been able to learn a lot about these gentle giants in recent years but their pelagic nature makes it quite a challenge to understand the full extent of their behavior. 

This is particularly true when talking about the sei whale as this is arguably one of the least understood whale species largely due to the fact that they prefer to spend most of their time swimming in deep offshore waters. 

However, today you will learn 9 interesting sei whale facts that I’m sure will leave your jaw touching the floor.

Let’s begin!

1. The Sei Whale Is The 3rd Largest Whale

The sei whale weighs 45 tons on average and reaches a length of around 18 m / 59 feet which makes it the third largest whale in the world as well as the third largest animal in the world! 

This length makes it about twice as long as a regular school bus and as heavy as 3 male adult African elephants which are the largest land mammals in the world!

Fun fact: the largest recorded sei whale measured 20 m / 66 feet.

2. The Sei Whale Is Super Fast

Thanks to its slender shape and pointed snout the sei whale has a hydrodynamic body that makes it one of the fastest whale species swimming at speeds of 55 km / 34 miles per hour.

3. The Sei Whale Consumes About 1 Ton Of Food Per Day

When you weigh about 45 tons and must maintain a thick layer of fat and blubber to remain warm I’m sure you can imagine that the food intake must be huge! For these reasons, the sei whale eats an average of 1 ton of food per day.

These whales are filter feeders who prefer to eat mega tiny planktonic crustaceans commonly called copepods and will also eat krill and small fish to a lesser extent. 

Because of the almost microscopic size of their preferred prey items the sei whale spends almost all day swimming close to the surface with its mouth open gorging on large amounts of plankton.

4. The Sei Whale Only Has One Natural Predator

Due to its massive size, the sei whale’s only predator is the killer whale which is capable of killing and eating calves. However, there are reports of killer whale pods killing adult sei whales too. 

In 2021 there was an attack caught on camera close to a salmon farm in Chile where a pod of killer whales cornered a group of 5 sei whales in shallow water that they could not escape from.

The orcas proceeded to kill 2 whales and the remaining 3 later died due to being stranded. 

There is more information regarding this attack as well as footage of it here.

5. Sei Whales Are Endangered

Once abundant throughout the world’s oceans, commercial whaling drastically reduced sei whale populations around the globe.

It is estimated that the whaling industry wiped out around  ⅔ of the entire sei whale population.

Their preference for deeper, offshore waters as well as their unpredictable migration patterns make the sei whale one of the hardest rorqual species to study but their numbers are thought to be slowly increasing.

It is estimated there are around 80,000 sei whales in the world today.

6. Sei Whales Don’t Like The Cold

Unlike their cousins that will spend summers in the polar region feeding off krill, the sei whale prefers to remain in waters that aren’t icy cold.

Likewise, they will also avoid waters that are too warm and will steer away from tropical seas.

While sei whales can be found throughout the world’s oceans they prefer temperate waters that are very far from the shore making them hard to spot and track.

7. Sei Whales Are Not Very Social

Excluding some abundant feeding areas where several thousand sei whales can gather to feed, this species tends to move solo or in small groups of up to 6 individuals.

Little is known about long-term alliances or bonds formed between sei whales. 

8. Sei Whales Have Really Big Babies

The second a sei whale calf is born it is already breaking all kinds of size and weight records.

Measuring a whopping 4.8 m / 16 feet it is already as long as your average pickup truck. And its birth weight of 725 kg / 1,654 lbs. equals that of around 6 baby elephants. 

As you can imagine, creating and birthing such a large baby is no easy feat and the gestation period of a female sei whale lasts around 13 months.

After the calf is born the female sei whale must then produce enough milk to provide for a baby that will grow 2.5 cm / 1 inch PER DAY.

Because of all the time and energy invested in birthing and raising a calf a female will produce a single offspring every 2 to 3 years.

9. Sei Whales Dive Differently

Sei whales are not exceptional divers and rarely go on deep foraging dives. This whale species prefers to remain close to the surface while it skims the ocean gorging on its tiny prey.

This, however, doesn’t mean that they won’t dive if they have to and are known to hold their breath for up to 20 minutes at a time. 

Even after taking breaths, the sei whale has a unique way of diving that is very different from its relatives that are known for arching their backs and showing their flukes while taking a plunge. 

Instead, the sei whale simply sinks below the surface leaving behind “fluke prints” which are glossy circles on the water’s surface formed by the underwater movements of the fluke.