Sei Whales

Scientific Name: Balaenoptera borealis
Other Names: Japan Finner, Pollack Whale, Rudolphi’s Rorqual, Coalfish Whale, Sardine Whale

The Sei Whale is not as well known as other rorquals, despite the fact that is favours the surface of the water (as opposed to diving deep beneath its surface and concealing itself from onlookers). It is often confused with the Bryde’s Whale and, more occasionally, the Fin, Minke and Blue whales. Interestingly, there are slight differences between the Sei Whales found in the north and those in the south. Therefore, they may actually comprise two similar but distinct subspecies.

Drawings of a Sei Whale.

Put simply, the southern Sei Whale is slightly larger than its northern counterparts, and there are small differences in the numbers of throat grooves and baleen plates. In the Southern Hemisphere, Sei Whales have between 300 and 410 baleen plates. In the Northern Hemisphere, this number is between 318 and 340.

Physical Characteristics

There are white markings along the lips and some individuals have a white chin. The head is rounded and there is no beak.

The elongated head is slightly arched with a single ridge running along the top of it. There are between 32 and 62 grooves that run along the throat from below the mouth to just behind the pectoral flippers.

The top of the body can be black, dark grey or blue-grey in colour, and the bottom is much lighter and mottled. Often, the white belly has been scarred by parasites or Cookie-cutter Sharks.

The slender dorsal fin stands erect with a slightly rounded tip that faces backwards. The pectoral fins have distinctly pointed tips and measure one-tenth of the body length. The tail flippers, also known as flukes, are relatively small with a notable notch in the centre and practically straight trailing edges.

Adult Sei Whales measure, on average, between 12 and 16 metres long, which is equivalent to 39.5 to 52.5 feet.

Sei Whales are consistent about staying at the water’s surface and have a rather regular dive sequence. Usually, the whale will blow once every 40 to 60 seconds for between one and four minutes. Then, it will dive below the water’s surface, where it will stay for between five and 20 minutes. As it dives, its tail leaves a characteristic swirl on the water’s surface.

Sei Whales usually travel in pods of between two and five animals, but some have been observed travelling alone.

Where to Find Them
Sei Whales tend to prefer deep, temperate waters, regardless of where in the world they are. However, their travels tend to go through trends, in which they are sporadically common in certain areas. Northern and Southern Sei Whales do not seem to mix with one another. Sei Whales are very seldom seen close to shore.

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