Sei whale

Identification and physical features

Sei whales are dark grey to bluish on the back with lighter undersides. Key identifying features include a long, slender body, a pointed rostrum with a single central ridge, a high swept dorsal fin set well aft on the back, and very fine baleen plates adapted to trap small prey. Like other rorquals, they have longitudinal pleats along the throat and chest that expand during feeding.

Distribution, habitat and movements

These whales occupy offshore and continental-shelf waters outside polar regions. Many populations undertake seasonal movements: congregating in higher-latitude feeding areas during the productive months and moving to lower latitudes for breeding and calving. They are generally more common in temperate seas than in equatorial or polar zones.

Feeding behavior and diet

Sei whales feed primarily on small organisms such as copepods, krill and small schooling fish. Their finely spaced baleen is well suited to filtering tiny prey. Feeding often occurs in relatively deep water or at the edges of productive currents and upwellings; animals may feed alone or in small loose groups, and larger aggregations can form where food is abundant.

Social life and reproduction

Social groups are usually small — commonly a few individuals — though larger groups form at good feeding grounds. Reproduction follows the seasonal cycle: mating and calving generally occur outside the main feeding season. Females give birth to a single calf after a gestation period of roughly a year and nurse the young for several months before the calf gradually joins feeding migrations.

Conservation and human interactions

Sei whales were heavily hunted during industrial whaling of the 20th century, and populations declined markedly. Today they are afforded protection in many regions, but they still face threats such as ship strikes, entanglement in fishing gear, ocean noise and habitat changes. Conservation efforts focus on monitoring populations, reducing human-caused mortality, and protecting important feeding and breeding areas.

Notable distinctions

• Member of the rorquals (rorqual).
• Often compared to the Bryde's whale; can be distinguished by the single central ridge on the rostrum (Bryde's whales often show three ridges) (Bryde's whale).
• Characterized by very fine baleen suited to small planktonic prey.