Sei whale

© Alan & Trish Henry

Balaenoptera borealis


Size: max 16 m

Key feature: Tall blow, appearing the same time as the dorsal fin

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. In comparison to fin whales the sei whale dorsal fin has more of a hooked shape than that of the fin whale. 


Sei whales usually appear alone, or in pairs. They are fast swimmers but not very lively and rarely breach. When they dive they don’t raise their tail flukes but tend to just sink into the water. They are baleen whales and therefore feed on plankton feeding just below the surface of the water. Sei whales can be very elusive and are often missed unless their blow is seen.


Sei whales have a global distribution but tend to favour temperate and polar waters. They stay in deep pelagic waters and are rarely seen near the coast. They have previously been seen on ORCA surveys through the Bay of Biscay and up into the Arctic, especially in the late summer.


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.

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