Balaenoptera borealis

Common Name: Sei Whale*

Sei Whale


A Sei Whale feeding at the surface.

Sei whale size.svg

Size comparison against an average human

Conservation Status
sei Status iucn3.1 EN.svg

Endangered (IUCN 3.1)

Scientific Classification
Kingdom Animalia
Phylum Chordata
Class Mammalia
Subclass Eutheria
Order Cetacea
Suborder Mysticeti
Family Balaenopteridae
Genus Balaenoptera
Species B. borealis
Binomial Name
Balaenoptera borealis
(Lesson, 1828)

sei range map

Sei Whale range.

Source: Wikipedia

General Description: The body of the Sei Whale (pronounced say) is slim and streamlined. The narrow head is slightly arched, with a single prominent ridge from the blowholes to the tip of the snout. A few hairs are present on both jaws and the snout.

This species has 32 to 60 throat grooves, all ending well before the navel. The flippers are relatively small, about one-eleventh the body length, and pointed. The tail flukes are relatively small.

The dorsal fin is 25 to 60 cm tall, hooked and placed slightly less than two-thirds along the back.

The Sei Whale is dark grey on the back and sides, marked with light-coloured scars. These scars may give its body a metallic look. The animal is pale below. A region of the belly is greyish white.


Size: Adults,The maximum length of males is 13.7 m and that of females 15.6 m. The weight is about 16 to 18 tons. Calves at birth, 4.5m long.

Appearance At Sea: Family groups of five or six whales move together, and pair bonds are strong and may last from year to year.

The moderately tall spout (about 3 m high) is shaped like an inverted cone, and the dorsal fin is seen almost simultaneously with it.


The Sei Whale has been named by Norwegians after the seje or pollack, a fish that it does not eat, but whose arrival off the Scandinavian coast coincides with that of the whale. Sei Whales eat a variety of food, especially plankton and smaller fish. Like Fin Whales B. physalus, Seis may approach prey fish on their sides, but for longer periods. They may cruise along with one flipper in the air for half a minute or more.

Found In: Sei Whales are found in the open ocean, usually near the surface, where they feed on plankton, fish and squid.

Records from India:There are several records of the Sei Whale in India. These include dead specimens washed ashore and live animals caught in fishing nets. No records have been found of Sei Whales from neighbouring countries. French tuna-seiners report seeing rorquals of about 15 m length around the Seychelles, which may be either Sei Whales or Bryde’s Whales.

December 1971 One washed ashore at Pullamadam, northwest of Mandapam Camp, Palk Bay. Venkatraman et al., 1973
30 January 1981 Decomposed specimen entangled in drift nets near Mallipatnam, Thanjavur district. James & Soundararajan, 1980
1983 A 13m specimen stranded at Dhanushkodi Island – its skeleton kept at the CMFRI,
Mandapam Camp.
James & Lal Mohan, 1987
26 February 1988 A 12m male stranded at the Tuticorin port area. Mohamad Kasim & Balasubramanian,
18 May 1988 A 10.05m female stranded at Kayalpatnam, Gulf of Mannar. Mohamad Kasim & Balasubramanian,
May 1988 A 7m specimen stranded at Tuticorin. Anonymous, 1988a
14 August 1988 A 9.76m female found dead in a creek at Kalubhas Island, between Salaya and
Sikka ports, Gulf of Kutch.
Anonymous, 1988b
27 January 1990 A 11.4m specimen entangled in a gillnet operated near Katchathievu. Krishna Pillai et al., 1995
21 September 1991 A 9m long specimen stranded near Cochin, landed at Puthuvypu, Vypeen Island. Noble & Nasser, 1992
20 January 1992 One 14m female washed ashore at Theedai, near Mandapam Camp. Nammalwar, Marichamy et al., 1992

World Distribution:The Sei Whale has a cosmopolitan distribution. It is rarely found in polar seas.

Could Be Confused With:The Sei Whale and the similar Bryde’s Whale Balaenoptera edeni have been confused for long. They can be distinguished as follows:

Sei Whale Single ridge on head Large fin, less pointed, more sloping Dives quietly without a roll Uniformly dark appearance
Bryde's Whale Three rostral ridges Small fin, sharply pointed with tattered
trailing edge
Rolls high in water before diving White undersides often visible

Bryde’s Whale makes quicker, more erratic movements while the Sei Whale appears more sedate, allowing ships to get quite close to them before they submerge.

Diagnostic Features:At sea, Large, sloping dorsal fin; narrow head with single prominent ridge.

Stranded Specimens:There are 300 to 410 ash-black baleen plates with fine white fringes. These fringes are silky. Some Sei Whales have several half-white plates near the front of the mouth, like Fin Whales.

* According to the current understanding of distribution, these species are not present in the Northern Indian ocean.