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Sei Whale


Scientific name: Balaenoptera borealis.
Order: Artiodactyla.
Family: Balaenopteridae. 
Genus: Balaenoptera.

IUCN Status


Other names

Rudolph’s rorqual.
Coalfish whale.


Large whales, with the males growing to 17 meters and females growing 19.5 meters in length. They may appear blackish at sea, but in good lighting, they may appear murky blue to a brown grey. Their blow is distinct, but not as tall or as columnar as a Fin whale. Sei whales have a single ridge that runs from the tip of their nose to their blowhole. The dorsal fin is tall and erect, sickle shaped, and has a hooked back tip. It is set forward at about 2/3 of the way back to the tail.

Habitat and distribution

It is estimated that they are 80,000 sei whales worldwide. They feed in colder waters during the summer and in the winter will migrate to warmer waters. Sei whales have been seen in the Bay of Biscay.


Sei whales are normally seen alone or in pairs. They often surface at a shallow angle so that the blow is visible as the dorsal fin appears. They breath every 20 to 40 seconds for 2 to 4 minutes before diving. Sei whales leave the water at a shallow angle and land with a belly flop.

Confusion with other species

Fin whale: they are much larger with a smaller dorsal fin that is set further back, have a simultaneous blow, and their dorsal fins are smaller and more swept back. 
Minke whale: they are much smaller, their blow is not normally visible, and arch their when diving.


Sei whales were hunted in the 19th and 20th century but received protection in the 1970s. Currently they are vulnerable to pollution from toxic chemicals, ship strikes and entanglement in fishing gear.

Interesting facts

Sei whales leave fluke prints on the water after short and shallow dives, which allows researchers to track their movements.

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