The Sei Whale

Whalecome to our new whale of the month, the sei whale, Balaenoptera borealis! This mysterious baleen whale is the third largest of the rorqual family. It is also an endangered species that was hunted to near extinction and is now slowly recovering. Here are a couple of cool facts about the sei whale.

Sei whale mom and calf
Sei whale mom and calf – Wikimedia Commons/NOAA-Christin Khan

Sonic whale

Despite its large body size and mass, the sei whale is a super-fast swimmer. It can easily swim up to 35-40 mph (55-65 km/h). An American naturalist named Roy Chapman Andrews named it the cheetah whale because of its speed bursts. He also said the whale becomes tired after a couple of hundred meters and needs to calm down, just like a cheetah. Another rorqual species around the same size, the humpback whale, has a maximum speed of 16 mph (27 km/h).

A name associated with fish

Both sei whales and fish feed on plankton (small crustaceans called krill). The Norwegian named the sei whale from “seje” which means pollack. The whales and pollack would appear around the same time in Norwegian waters to feed on plankton. The sei whale has another name in Japan: iwashi kujira, which means sardine whale.

Tall dorsal fin

Sei whales are easily recognizable because of their tall and sharp dorsal fin, which I think looks pretty. The dorsal fin is typically located at the two-third mark on the whale’s body. It can go as high as 35in (90cm).

Whaling history and endangered species

Sei whales were hunted to near extinction in the twentieth century. They did not use to be a prime target for whalers because they inhabit the same waters as other large and commercially interesting whales like the blue whale or the right whale. Quite frankly, they are also quite fast, and their speed bursts discouraged most whalers. Especially since the oil-rich right whale’s top speed reaches 5.5 mph (9 km/h). However, after whalers started to decrease the number of blue and right whales drastically, they turned their attention to sei whales. The hunt for sei whales was intense from 1950 to the late 70s when protection institutions started to establish quotas and protect whale species from whaling.

Commercial whaling ended in 1986, internationally thanks to the International Whaling Commission (IWC). Scientists estimate 300 000 sei whales were killed worldwide. There is some good news, though: sei whales are making a comeback, and scientists believe their current worldwide population is around 40 000 individuals, according to the IUCN Red List document (attached in the sources). These numbers are still quite unclear, so scientists should focus their efforts on population estimates and trends to see how the sei whales are recovering from whaling.

New threats? Japanese commercial whaling

Although the IWC banned commercial whaling in 1986, Japan, Norway, and Iceland did not give up and kept catching whales under so-called “scientific” missions. Japan in particular recently withdrew from the IWC to resume whaling in its own waters. Sei whales are among the whales Japan now targets. However, it is important to note the Japanese set quotas for less than 300 whales. Some experts believe the Japanese decision to leave the IWC and set low catch quotas in its waters is a disguised way to fade out whaling within the next years.

Many other threats impact baleen whales worldwide, including sei whales. You can read our post on them here.

We hope you learned a thing or two about sei whales. Let us know which marine mammal you would like us to feature next month. You can also check our previous whales of the month here.

Sources and further reading:

What are the main threats affecting baleen whales?

Anaïs is the founder of Whale Scientists. She is a PhD student at McGill University working on killer whale ecology and pollution. You can read more about her here.

Leave a Reply

Scroll to Top