Sei whale

Balaenoptera borealis
Sei whale


Size: max 12-16m

Key features:
- Upright fin two thirds of the way down its body
- Both sides if the jaw is the same colour
- Appears to sink when dives

Sei whales are dark grey with a long thin body. Their colouration and shape make them easy to confuse with fin whales, but there are a few notable differences. Sei whales are shorter than fin whales and also have a shorter blow. When the whale surfaces their blow hole can be seen at the same time as their dorsal fin. The dorsal fin of a sei whale is more upright than that of a fin whale.


Sei whales tend to travel alone or in pairs. They are one of the fastest rorqual whales but rarely breach. When they dive they don’t raise their tail flukes but tend to just sink into the water. They skim-feed just below the surface.


Sei whales have a cosmopolitan distribution but appear to favour temperate to sub-polar waters. Typically they are restricted to deep pelagic waters and are rarely found near the coasts. They feed in cool temperate waters in the summer and are believed to migrate into warmer lower latitudes in the subtropics for winter.


Although not a traditional whaling target, sei whales were heavily exploited through the 1960’s and 70’s until they were made a protected species in 1976 and the international whaling ban came into force in 1986. Currently they are vulnerable to human impact through chemical and noise pollution, ship strikes and entanglement in fishing gear.

Sightings Map

  • Zoom in by using the scroll on your mouse or using the + and - buttons on the map.
  • Click and drag the map to move it around and see different areas.
  • Click on each icon on the map to find out the date, time, latitude, longitude, route, vessel, species, and group size seen for that species at that point.

Whale watching


Join in on a Sea Safari Whale Watching trip
Train with us


Become an Ocean Conservationist
Volunteer with ORCA


Become a Marine Mammal Surveyor & volunteer in offshore surveys

Support ORCA

There are many ways you can help ORCA to continue its vital work

Get involved

Become a surveyor

All you need is a passion for whales and dolphins and to take an ORCA Marine Mammal Surveyor course, which will teach you everything you need to know to become a citizen scientist.

Book a sea safari

ORCA partner with Brittany Ferries to offer our unforgettable Sea Safari trips each summer, where you can see some of the wonders of the ocean right on our doorstep.