Sei Whale

Marine Creature:  Sei Whale (Balaenoptera borealis)

                                                                             Kindly compiled by Planet Whale

General Description

Third largest of the great whales, Sei Whales tend to travel alone or in small groups. Sei Whales are very fast swimmers, but do not appear to be as demonstrative as either Fin or Common Minke Whales and are generally shy of boats. At sea they’re sometimes difficult to tell apart from the Fin whale, although the shape of the dorsal fin can often be key in confirming species identification as it can be strongly sickle-shaped.

© Sarah Jackson at Planet Whale

© Sarah Jackson at Planet Whale


The distribution and movements of the sei whale are not well known and considered erratic – it has a cosmopolitan distribution, generally favouring temperate to sub-polar waters and usually restricted to deep, pelagic waters. In summer it is not thought to reach as far north and as far south as other rorquals.

Interesting Facts

Both whaling data and benign studies in the eastern North Atlantic suggest that numbers of sei whales fluctuate between years, with peak regional numbers referred to as ‘invasion years’.

  • Lifespan: Up to 70 years
  • Size: Up to 21m in length
  • Food: Sei whales are specialist feeders, preying largely upon krill and small crustaceans supplemented by small schooling fish and euphausiids. With such a species-specific diet, variations in prey abundance are likely to be significant factors in the unpredictable annual movements of sei whales. The sei whale is also often associated with large feeding frenzies of seabirds.


Feeding & Hunting

Unlike other rorquals, they often skim-feed just below the surface. When feeding in this manner they can be quite unobtrusive, with only the occasional blow or top of the dorsal fin being visible, although they do sometimes turn on their sides while feeding like the Fin whale.

Conservation Status & International Protection

IUCN categorise the Sei whale as “endangered”. The global mature population is estimated to have declined by about 80% over the last three generations.


© Sarah Jackson at Planet Whale

© Sarah Jackson at Planet Whale

© Sarah Jackson at Planet Whale

© Sarah Jackson at Planet Whale

Best places in the world to see these creatures:

Madeira, the Azores in spring as these whales migrate past these Atlantic islands, Iceland, to name a few.

For plenty more locations plus ethical reviews and rating system for whale watching trips to see Sei Whales visit

Organisation Profile:  Planet Whale

Orca7Description/Background of work

At the heart of Planet Whale is a belief that an encounter with a wild whale or dolphin reconnects us with the natural world in an amazing and powerful way. For one humbling moment we can be moved to tears or celebrating wildly as we stare through the thin veil of water that separates us from these magnificent animals.

Planet Whale understands that we all need such encounters to reawaken our sense of responsibility to the natural world; energising ourselves to act for the greater good. That is our first step – only when we have been inspired will we feel compelled to act. For this reason we promote responsible whale watching and have the largest online searchable database of whale and dolphin watch operators in the world – the public can review trips they’ve been on with regard to their sustainability, educational value and impact on the marine environment, amongst other things.

It is this global community that will change the way we view whales and dolphins forever. By harnessing the passion and ideas of individuals, we will achieve more to protect and defend our oceans than ever before.

Together we will: 

  • Give the people control so they can use it to help whales and dolphins.
  • Inspire change through a new global partnership.
  • Make whale watching more sustainable – and successful – than ever before!
  • Reach out to the world with colossal festivals for whales and dolphins.
  • Create innovative campaigns that harness the power of the web’s global community.


Volunteer/Paid Work Opportunities

We are always looking for passionate and hard-working volunteers to help achieve our Planet Whale mission. In particular we welcome applications for the upcoming Whalefest. You don’t need to be a whale expert but a lot of enthusiasm for marine conservation and a fun attitude are essential. We’re based in Brighton and Hove (UK) but our volunteer network stretches across the globe, so feel free to get in touch wherever you are! Contact us at


Return to Baleen Whales or learn more about the Minke Whale