Whales - Species | Sei Whale

Sei Whale - Balaenoptera borealis

The Sei Whale has, for many years, been confused with the Bryde’s Whale, and specific identification continues to be best left to the experts. It is usually only when viewers are able to count the ridges on the heads of the whale that an accurate identification can be made – Sei Whales have 1 ridge, where Bryde’s Whales have 3. These are the fastest of the baleen whales, and can swim at speeds of up to 34.5 miles per hour. Interestingly, Sei Whales do not arch their backs when diving below the surface; they simply sink, leaving fluke prints as the only evidence of their surfacing.

The Sei Whale’s body is streamlined and slender to facilitate smooth gliding and optimal entry into and exit from the water’s surface. These magnificent bodies are a blue-grey colour with white bellies. They are of the rorqual genus, which means that they have a dorsal fin and long throat groves that run on the lower side of their bodies. The pectoral fins are short and pointy, while the tall dorsal fins are curved.

Sei Whales reach an average length of 13.7m to 16.8m although some have been found to measure up to 19.8m, with females being the slightly larger of the two. Such impressive bodies weigh between 14 and 17 tons. The Sei Whale has between 32 and 60 throat grooves.

Like the Bryde’s Whale, they have keratin plates in their mouths, in the place of teeth. These +-350 plates are about 480mm each, and fray into finer hairs on the end and next to the tongue. The Sei Whale feeds on plankton, for the most part. However, its firm favourite remains small crustaceans, or copepods.

The Sei Whale is not a ‘pack animal’, and prefers to move around alone. In the rare case of their travelling in groups, these will consist of only 2 or 3 animals. Occasionally, up to 100 Sei Whales will converge in an area where food is particularly abundant. For this reason, Sei Whales have become known as invading an area and exploiting available resources until a more abundant site is discovered.

The Sei Whale displays definite migratory habits. This is reinforced by the fact that, although their feeding spots are well known and identifiable, no researcher has been able to identify where breeding occurs, implying a specific movement according to their patterns and requirements. Sei Whales prefer deep, off-shore, temperate waters, and do not venture into the polar ice regions like most other whales. They are generally found in the oceans between the Antarctic in the south and Iceland in the north, but the exact migratory patterns remain a mystery.

Because the Sei Whale has little body fat, it was not under particular threat from blubber hunters until the late 1950’s. It was at this time that hunters became desperate, based on the fact that they had slayed most of their other resources by that time. From that time until the early 70’s, over 100 000 Sei Whales were slaughtered in the Antarctic. To attempt some sort of recovery, these animals are now under protection and the hunting of them anywhere in the world is prohibited. Japan and Iceland continue to pursue “research programmes” that advocate the killing of whales, but environmental groups are likely to continue to oppose these initiatives in a very active and determined way.