Blue Whale

Blue Whale: Balaenoptera musculus

IUCN status: Endangered

Status and distribution summary:

Occurs in all major oceans of the world, and is strongly migratory between summer feeding areas in higher latitudes (of both hemispheres) and tropical and sub-tropical natal areas. Information on Blue Whale distributions is far from complete, in part due to the scarcity of the animals. In the northern Atlantic, Blue whales are most numerous on the western continental shelf slope, but small populations do survive in eastern waters, and are occasionally seen in Biscay and off SW Ireland. Most summer records are from Iceland and further north.

The world population is estimated at about 5,000 animals with between 600 and 1,500 in the North Atlantic. Only a small  proportion of these are found on the eastern migration route.

Exploitation:

Prior to the 20thC invention of the factory whaling ship, the take of Blue Whales was relatively small, but during the 20thC until commercial hunting was outlawed an astonishing 99.5% of the population was wiped out. Blue Whale populations are recovering only in some of its former range, notably in the north eastern Pacific Ocean where there are thought to be thousands. The reappearance of Blue Whale in the Bay of Biscay in recent years is perhaps a sign that the north eastern Atlantic populations are starting to recover.

Other threats:

Where it is seen:

Over the deeper continental shelf slopes and canyons and over deep waters in southern Bay of Biscay.

Frequency of sightings:

Very rare, usually single animals although two were seen together in 2007. Not recorded every year.

Recognition:

The largest whale, appears massive (20-30m).

In regular surfacing they usually show the following features:

  • Mottled blue grey colouring. Not blackish even in poor light.
  • Prominent splash guard protecting blow hole.
  • Very powerful blow, tall and columnar, lasting for several seconds, can reach 10m.
  • Tiny dorsal fin set far (3/4) back to the tail. Seen seemingly a long time after the blow is finished during slow rolling / breathing sequences

Behaviour:

Usually occurs singly, or as parent and calf.

Blows every 10-20 seconds for only a few minutes before diving, which is for 5 to 20 minutes.

Surfaces at a shallow angle, blows before back is in view, rolls at a gentle angle so back is seemingly endless, with the tiny dorsal fin eventually appearing before the arched tail stock. Flukes sometimes show above the surface on deep diving.

Rarely demonstrative, but is known to breach, and is sometimes seen lunge feeding.

Confusion species:

The combination of size, body colour and tiny dorsal fin set well back should make the Blue Whale unconfusable.  However, distant powerful blows and glimpses of apparently huge bodies should not be assumed to be Blue Whale; Fin Whale can appear very large.